UTS site search

Professor Matt Phillips

Biography

Matthew Phillips is Professor of Applied Physics at UTS. He was appointed as Director of the Microstructural Analysis Unit in 1996 and was Associate Head (Research) of the Department of Physics and Advanced Materials since 2006 - 2011. Professor Phillips was awarded a PhD degree from UTS in experimental solid state physics in 1991 for his work on the optical properties of native point defects and transition metals in single crystal sapphire. In 1992 he received the Cowley-Moodie award from the Australian Microscopy and Microanalysis Society.

Dr Phillips has served as Deputy Director of the UTS Centre of Materials Technology (1998 to 2000) and as Research Program Leader in the Institute for Nanoscale Technology (2002 to 2008). Professor Phillips was the Foundation Director of the UTS core research strength, Materials and Technology for Energy Efficiency (2010-2012). He was a Visiting Research Fellow at the University of Sydney in 1996, a Visiting Professor at the Université de Sherbrooke, Quebec in 2005 and a Visiting Professor at the Institute of Solid State Physics at the Technical University of Berlin in 2013. Professor Phillips is currently a member of the International Advisory Board for the Thai National Nanotechnology Center (NANOTEC).

Professor Phillips' research expertise is in materials physics, particularly in the use of novel microscopy based experimental techniques to investigate the opto-electronic properties of technologically important light-emitting materials and nanostructures. ARC Field of Research: Materials Engineering, Nanotechnology and Condensed Matter Physics. Professor Phillips has presented over 30 invited conference papers at international conferences as well as over 35 seminars in overseas laboratories and has co-authored over 260 peer reviewed publications as well as over 220 conference papers.

Professional

Invited Speaker at International Conferences (since 2005)

34   The Sixteenth RGJ-Ph.D. Congress (RGJ-Ph.D. Congress XVI), RGJ-Ph.D. Congress XVI "ASEAN: Emerging Research Opportunities", Pattaya, Thailand, 11-13 June 2015
33   Photonics West, Oxide-based Materials and Devices Conference OE108, San Francisco, 8 - 12 February 2015
32   The 10th National Science and Technology Development Agency (NSTDA), April 1-3 2014, Bangkok
31   Photonics West, Oxide-based Materials and Devices Conference OE108, San Francisco, 1 - 6 February 2014
30   Fall European Materials Research Society, Warsaw, Symposium F, Novel materials for electronic, optoelectronic, photovoltaic and energy saving applications, 16 - 20 September, 2013
29   International Conference on Defects – Recognition, Imaging and Physics in Semiconductors (DRIP XV), 15 - 19 September, 2013
28   Fall Materials Research Society, Boston, 25-30 Nov 2012, Symposium FF: Semiconductor Nanowires
27   New Frontiers in Advanced Functional Nanomaterials, Bangkok, October 2012
26   Beam Induced Assessment of Microstructures in Semiconductors, 25-28 June Anabas Algeria, 2012
25   2nd International Congress in Advances in Applied Physics and Materials Science, 26 - 29 April 2012 Antalya, Turkey
24   Fall Materials Research Society, Boston, 25-30 Nov. 2012, Symposium Z: Oxide Semiconductors
23   ACEM22/ICONN, 5-9 February Perth, 2012
22   International Conference on Materials for Renewable Energy and Efficiency, Shanghai, China, 20-22 May, 2011
21   European Materials Research Society, Fall Meeting, Warsaw, 2011
20   Conference of the International Union of Microbeam Analysis Societies, Seoul, Korea, 2011
19   European Materials Research Society, Fall Meeting, Warsaw, 2009
18   Microscopy & Microanalysis, Annual Conference of the Microscopy Society, Richmond, USA, 2009
17   9th Asia-Pacific Microscopy Conference, ICC, Jeju Island, Korea, 2008
16   Microscopy & Microanalysis, Annual Conference of the Microscopy Society, Chicago, USA, 2006
15   Microscopy & Microanalysis, Annual Conference of the Microscopy Society, Honolulu, USA, 2005
13   Conference of the International Union of Microbeam Analysis Societies, Florence, Italy 2005

Professional Seminars (since 2009)

37   University of Technology Sydney, Materials Physics & Nanophotonics Seminar Series, 22 August 2014
36   University of Magdeburg, Das Institut für Experimentelle Physik, July, 2013
35   National Nanotechnology Center (NANOTEC), Pathumthani 20 February 2013
34   MINATEC, Grenoble, France, 17 September 2012
33   Mahidol University Bangkok, Thailand, 21 March 2012
32   King Mongkut’s University of Technology Thonburi (KMUTT), Thailand, 20 June 2011
31   Mahidol University Bangkok, Thailand, 21 June 2011
30   National Nanotechnology Center (NANOTEC), Pathumthani, Thailand,  21 June 2011
29   Rajabhat University (PSRU), Pibulsongkram, Thailand, 22 June 2011
28   Naresuan University, Pibulsongkram, Thailand, 22 June 2011
27   Thammasat University, Patumtani, Thailand, 23 June 2011
26   Public Seminar for the Thailand Environment Institute (TEI), Bangkok, Thailand, 24 June 2011
25   Chulalongkorn University, Bangkok, Thailand, 24 June 2011
24   Nanjing University, China, October, 2011
23   UTS Speaks, Public Lecture, UTS, November 2010
22   German Centre of Excellence for Semiconductor Nanophotonics, Berlin, Germany, June, 2009
21   FEI Company, Portland Oregon, USA, July, 2009
20   BluGlass Pty Ltd, Silverwater, 10th February, 2009
19   UTS Science Research Day, 29th September, 2009

Conference and Symposium Organiser (since 2010)

34   International Scientific Committee, Beam Induced Assessment in Microstructures in Semiconductors, 5-9 June 2016, Versailles France
33   Program Committee, SPIE Photonics West 2016, Oxide-based Materials and Devices VII Symposium, San Francisco, 14 - 17 February 2016
32   ICONN 2016, Program Committee – Nanocharacterisation Symposium, 1 -5 February, Canberra
31   Member of the International Advisory Board (IAB) for the Thai National Nanotechnology Center (NANOTEC) 2014 – 2016
30   International Advisory Committee, The 4th Thailand International Nanotechnology Conference (NanoThailand 2014) November 26-28, 2014 in Pathumthani, Thailand
29   International Program Committee, International Conference on Defects in Semiconductors, Espoo, Finland 27th - 31st July 2015
28   6th Forum on New Materials, Symposium Co-Chair, Materials and Technologies for Solid State Lighting, , Montecantini Terme, Italy, 8-20 June 2014
27   European Materials Research Society, Symposium Co-Chair, Nitride Semiconductors, Strasbourg, France, 27 – 31 May, 2013
26   Conference Chair, Australian Microbeam Analysis Society Symposium and Workshops, XII, Sydney, 4 - 8, February 2013
25   Scientific Committee, 11th International Workshop on Beam Injection Assessment of Microstructures in Semiconductors, 23-28th June, Annaba, Algeria, 2012
24   ACMM23 & ICONN2012 , Program Committee – Nanocharacterisation Symposium, 2-6 February, Adelaide
23   Symposium Chair, Advances in Cathodoluminescence, International Union of Microbeam Analysis Societies, Seoul, Korea, 2011
22   Scientific Committee, 10th International Workshop on Beam Injection Assessment of Microstructures in Semiconductors, 4th – 8th July, Halle, Germany, 2010
21   Symposium Chair: "Scanning Cathodoluminescence Spectroscopy and Microanalysis, Microscopy and Microanalysis 2010, Portland, Oregon, August, 2010
20   ACMM22 & ICONN2010 Program Committee – Nanocharacterisation Symposium, 5-9 February, Adelaide

Professional Societies

  • Materials Research Society
  • Australian Microscopy and Microanalysis Society
  • Microbeam Analysis Society
  • ARC Nanotechnology Network
  • ARC Australian Network for the Fluorescence Applications in Biotechnology and the Life Sciences
Image of Matt Phillips
Professor, School of Mathematical and Physical Sciences
Member, Research Centre for Clean Energy Technology
Core Member, Research Strength Materials and Technology for Energy Efficiency Member
BSc (UNSW), PhD (UTS)
 
Phone
+61 2 9514 1620

Research Interests

Professor Phillips and his group conduct research on the light emitting properties of bulk and nano-structured technologically important materials, in particular group III-nitrides and binary oxide semiconductors. Experimental methods include; scanning cathodoluminescence microscopy and spectroscopy, in-situ variable pressure SEM, scanning tunnelling microscopy and spectroscopy, UV laser photoluminescence spectroscopy, deep level transient spectroscopy and a broad range of associated materials microcharacterisation and fabrication techniques. ( www.sydneynano.com )

Specific research interests involve:

  1. optical and electrical properties of point defects in semiconducting nitrides and oxides.
  2. luminescence mechanisms in nanowires and nano-particles.
  3. light emitting low dimensional semiconductor structures, quantum wells, wires and dots.
  4. physics and chemistry of super-luminescence ceramic and semiconductor phosphors.
  5. transport dynamics of polarons, excitons and polaritons in semiconductors.
  6. in-situ studies of nano-wires during growth using variable pressure electron microscopy.
  7. light-matter interactions in spatially confined systems.
  8. light extraction using photon - surface plasmon coupling.
  9. direct-write resist-free nano-lithography using focussed electron beam induced deposition and etching.
  10. application of this work to the development of high performance solid state lighting devices, advanced light and electron detectors as well as innovative bio-imaging platform technologies.
Can supervise: Yes

Current Postgraduate Students

  1. Saskia Fiedler, PhD, principal supervisor, 2015
  2. Md Azizar Rahman, PhD, co-supervisor, 2015
  3. Sajid Ali, PhD, co-supervisor, 2015
  4. Sumin Choi, PhD, co-supervisor, 2013
  5. Toby Shanley, PhD, co-supervisor, 2012
  6. Christian Nenstiel, PhD, principal supervisor, co-tutelle TU Berlin, 2010

Completed PhD and MSc

  1. PhD (2016) Mark Lockrey, principal supervisor
  2. MSc (2016) Joel Davis, principal supervisor
  3. PhD (2016) Suranan Anantachaisilip, PhD, principal supervisor
  4. PhD (2016) Liangchen Zhu, PhD, co- supervisor
  5. PhD (2015) Gordon Callsen, PhD, principal supervisor, co-tutelle TU Berlin
  6. PhD (2015) Aiden Martin, co-supervisor
  7. PhD (2013) Marcus Straw principal supervisor
  8. PhD (2013) Olivier Lee (2013), co-supervisor
  9. MSc (2012) James Bishop, MSc, principal supervisor
  10. PhD (2010) Matthew Foley, PhD, 2007, co-supervisor
  11. PhD (2008) Enno Malguth, IPRS, principal supervisor
  12. PhD (2007) Rachel White, APA, principal supervisor
  13. PhD (2007) Sudha Mokkapati, supervisory committee ANU
  14. PhD (2006) Scott Morgan, APA, principal supervisor
  15. PhD (2006) Victoria Coleman, supervisory committee ANU
  16. PhD (2005) Stephan Schelm, co-supervisor
  17. PhD (2005) Carl Masens, co-supervisor
  18. PhD (2004) Olaf Gelhausen, IPRS, principal supervisor
  19. PhD (2001) Richard Wuhrer, co-supervisor
  20. PhD (2000) Milos Toth, APA, principal supervisor
  21. PhD (1999) Svetlana Dglitach, co-supervisor
  22. MSc (1998) Lisa Emerson, principal supervisor

Exchange StudentsTechnische Universitäet Berlin Exchange Students:

Karsten Fleischer (1999), Olaf Gelhausen (2000), Hagen Telg (2001), Holger Klein (2002), Nicolas Pomplum (2003), Enno Malguth (2003), Markus Wagner (2004), Christian Rauch (2005), Gordon Callsen (2007), Jurgen Probst (2007), Daniela Neuman (2008), Bruno Riemenschneider (2008), Dorian Alden (2009), Nadja Jankowski (2012), Sarah Schlichting (2012)

Other Exchange Students:

Zuzana Majlinova, Slovak University of Technology, Bratislava (2003); Moritz Merklein, University of Konstanz (2010) and May Patropon, Mahidol University, Thailand (2011)

Current Subjects:

  • Solid State and Nano-device Physics 68606
  • Scanning Probe and Electron Microscopy 68320
  • Physics & Nanotechnology Honours Course Work 68861

Past Subjects:

  • Techniques of Materials Analysis 68516
  • Electron Microscopy and Microanalysis 60502
  • Scanning Probe Microscopy 60503
  • X-ray Diffraction Techniques 60501
  • Forensic Imaging 65341
  • Nanoscience 1 60103
  • Nanoscience 2 60104

Chapters

Ton-That, C. & Phillips, M.R. 2015, 'Cathodoluminescence microanalysis of ZnO nanowires' in Semiconductor Nanowires: Materials, Synthesis, Characterization and Applications, pp. 393-407.
View/Download from: UTS OPUS or Publisher's site
© 2015 Elsevier Ltd. All rights reserved. Cathodoluminescence (CL) is an enabling quantitative technique for the characterisation of luminescent materials. In this chapter, following a brief review of the basic principles and recent advances in CL imaging and spectroscopy, a number of examples are chosen to demonstrate the utility of CL for the microcharacterisation of semiconductor nanowires, with a focus on ZnO material. Various analytical methods such as monochromatic CL imaging, depth-resolved analysis, and excitation density-resolved analysis are presented, which can provide information on the local optical and electronic properties of nanowires at the nanometre spatial resolution.
Remond, G., Phillips, M. & Roques-Carmes, C. 2000, 'Importance of Instrumental Factors on the Reliability of Cathodoluminescence Data' in Pagel, M., Barbin, V., Blanc, P. & Ohnenstetter, D. (eds), Cathodoluminescence in Geosciences, Springer-Verlag, Berlin, Germany, pp. 59-126.
Kalceff, M.A.S., Phillips, M.R., Moon, A.R. & Kalceff, W. 2000, 'Cathodoluminescence microcharacterisation of silicon dioxide polymorphs', SPRINGER-VERLAG BERLIN, pp. 193-224.

Conferences

Phillips, M., Manning, T.J., Nenstiel, C., Lockrey, M.N., Ton-That, C. & Hoffmann, A.V. 2011, 'High Temperature In-Situ Cathodoluminescence Studies of the Thermal Stability of Hydrogen in p-type Magnesium Doped Gallium Nitride', Microscopy and Microanalysis, Vol 17, Supplement 2, High Temperature In-Situ Cathodoluminescence Studies of the Thermal Stability of Hydrogen in p-type, Nashville, pp. 1-2.
Manning, T.J., Hardy, T., Merklein, M., Wintrebert-Fouquet, M. & Phillips, M.R. 2010, 'A Mechanism for Mg acceptor activation in GaN by Low Energy Electron Beam Irradiation', Conference on Optoelectronic and Microelectronic Materials and Devices, Proceedings, COMMAD, pp. 139-140.
View/Download from: UTS OPUS or Publisher's site
Low Energy Electron Beam Irradiation (LEEBI) was found to quench the donor-acceptor pair (DAP) attributed to carbon (CN at 3.28 eV at 80 K) and enhances the emission of the 3.27 eV peak, which has been attributed to a free-to-bound (e,Mg0) transition at 300 K. This results in increased cathodoluminescence (CL) emission at room temperature and a decrease in CL emission at liquid nitrogen temperatures (~77 K). © 2010 IEEE.
Nenstiel, C., Switaisky, T., Alic, M., Suski, T., Albecht, M., Phillips, M.R. & Hoffmann, A. 2010, 'Luminescence of InGaN MQWs grown on misorientated GaN substrates', Conference on Optoelectronic and Microelectronic Materials and Devices, Proceedings, COMMAD, pp. 135-136.
View/Download from: UTS OPUS or Publisher's site
Optoelectronic devices based on InGaN have already been commercialised, however, the Indium content is limited to around 5%. With higher Indium concentration the quantum efficiency decreases, which is thought to be due to increasing inhomogeneity. In this work it is shown that the growth of InGaN on misorientated GaN substrates forces these Indium fluctuations on a nanometre scale. Temperature dependent luminescence measurements provide information about the homogeneity of the band structure. Energy selective excitation confirms the existence of localisation centres and indicates their energetic depth. Time-resolved measurements define the lifetime of localized excitons, which provides information about radiative and nonradiative processes as well as tunnelling mechanisms between the localization centres. Indium fluctuations at the nm and ?m scale are measured using cathodoluminescence (CL) and Micro Photoluminescence (?PL) respectively. © 2010 IEEE.
Foley, M., Ton-That, C. & Phillips, M.R. 2010, 'Cathodoluminescence characterisation of vapour transport grown ZnO structures', ICONN 2010 - Proceedings of the 2010 International Conference on Nanoscience and Nanotechnology, pp. 207-209.
View/Download from: UTS OPUS or Publisher's site
ZnO structures grown under controlled vapour-phase transport growth conditions were characterised by electron microscopy and high-resolution cathodoluminescence techniques. Variations in the defect related emission and morphology were observed to be dependent on the distance from the source material. Annealing of grown structures under oxygen eliminated the defect emission. These experimental observations suggest that oxygen deficiency in ZnO is linked to the defect related emission, and that defect emission is strongly influenced by the oxygen gas content during vapour transport growth. © 2010 IEEE.
Dowd, A.R., Armstrong, N.G., Ton-That, C., Johansson, B. & Phillips, M. 2008, 'Cathodoluminescence for High Resolution Non-Destructive Luminescence Depth Profiling.', IUMRS-ICEM 2008 | COMMAD 2008, A-MRS, Sydney, Australia.
Coleman, V.A., Bradby, J.E., Jagadish, C. & Phillips, M.R. 2007, 'A comparison of the mechanical properties and the impact of contact induced damage in a- and c- axis ZnO single crystals', Materials Research Society Symposium Proceedings, pp. 213-218.
Nanoindentation studies were conducted on a-axis oriented ZnO single crystals. The mechanical properties and deformation mechanisms were monitored and compared to previously determined data from c-axis material. Hardness and modulus values reveal that a-axis ZnO is significantly softer than c-axis material (hardness of 2 ± 0.2 GPa), and behaves more plastically. Additionally, the influence of contact induced damage on the defect structure of a-axis material was examined using cathodoluminescence spectroscopy and monochromatic imaging to monitor the luminescence from indent sites. Deformation directly under the indent site enhanced the occurrence of red luminescence, and was attributed to a native defect in ZnO that has a higher formation energy than the defects responsible for the green and yellow visible defect bands, which were present in ZnO during growth and clustered to the indent site during annealing. © 2007 Materials Research Society.
Mnlguth, E., Hoffmann, A., Phillips, M. & Gehlhoff, W. 2006, 'Fe-centers in GaN as candidates for spintronics applications', Materials Research Society Symposium Proceedings, pp. 131-136.
View/Download from: UTS OPUS
The potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a sel of 400 ?m thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 51017 cm-3 to 21020 cm -3 was studied by means of photoluminescence. photoluminescence excitation (PLE) and Fourier transform infrared (FTIR) transmission experiments. The Fe3+/2+ charge transfer (CT) level was determined to be at 2.80 ± 0.01 eV above the valence band maximum considerably lower than the previously reported value of 3.17 ± 0.10 eV. A bound state of the form (Fe2+, l1VB) with a binding energy of 50 ± 10 meV has been established as an excited state of Fe3+, FTIR transmission measurements revealed an internal (5E - 5T2) transition of Fe2+ around 400 eV which, until now, was believed to be degenerate with the conduction band. Consequently, a second CT band was detected in PLE spectra. © 2006 Materials Research Society.
Zareie, H., Sarikaya, M., McDonagh, A.M., Barber, J., Cortie, M. & Phillips, M. 2006, 'Self-organized materials: From organic molecules to genetically engineered gold-binding proteins', Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology, ICONN, pp. 517-519.
View/Download from: UTS OPUS or Publisher's site
We present examples of ordered assemblies of organic and biological molecules on gold(111) surfaces. The first example shows how control over mono- or multilayer assemblies of 1,4-phenylenedimethanthiol can be achieved and monitored. The second example shows how monolayers on gold can be prepared using amine groups to anchor aromatic molecules to the surface. A third example shows how ordered assemblies of genetically-engineered inorganic-binding polypeptides can be formed on gold surfaces using a 3-repeat, 14 amino acid gold-binding protein (GBP1). © 2006 IEEE.
Phillips, M.R. & Morgan, S.W. 2006, 'Enhanced high speed SE imaging in a VPSEM using a Frisch grid', Microscopy and Microanalysis, pp. 1480-1481.
View/Download from: UTS OPUS or Publisher's site
Wuhrer, R., Moran, K., Phillips, M.R. & Davey, P. 2006, 'X-ray mapping using a multiple-EDS (DUAL) detectors', Microscopy and Microanalysis, pp. 1406-1407.
View/Download from: UTS OPUS or Publisher's site
Phillips, M.R. & Drouin, D. 2006, 'Comparison of low voltage cathodoluminescent phosphors', Microscopy and Microanalysis, pp. 1526-1527.
View/Download from: UTS OPUS or Publisher's site
McBean, K.E., Phillips, M.R. & Drouin, D. 2006, 'Effects of lithium doping and post-processing on the cathodoluminescence of zinc oxide nanoparticles', Microscopy and Microanalysis, pp. 1510-1511.
View/Download from: UTS OPUS or Publisher's site
Mokkapati, S., Tan, H.H., Jagadish, C., McBean, K.E. & Phillips, M.R. 2006, 'Integration of quantum dot devices by selective area epitaxy', Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology, ICONN, pp. 442-445.
View/Download from: UTS OPUS or Publisher's site
The results of nucleation of InGaAs and InAs quantum dots by selective area epitaxy are presented. By pre-patterning the substrates with different (SiO2) mask dimensions, the bandgap of the quantum dots can be tuned over a large range. This technique is used to demonstrate a quantum dot laser integrated with a quantum well waveguide. © 2006 IEEE.
Drouin, D., Pauc, N., Phillips, M., Poissant, P., Delample, V., Souifi, A., Aimez, V. & Beauvais, J. 2006, 'SEM characterization of nanodevices and nanomaterials', Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology, ICONN, pp. 596-599.
View/Download from: UTS OPUS or Publisher's site
The scanning electron microscope (SEM) can be used to study and characterize a wide variety of materials used in nanoelectronic and photonic applications. Several different techniques make use of this versatile tool. These include voltage contrast in secondary electron imaging, charge collection for semiconductor samples and cathodoluminescence. These techniques are important in device nanofabrication process development and nanomaterials characterization. © 2006 IEEE.
Phillips, M.R., Drouin, D. & Pauc, N. 2006, 'Probing Carrier Behavior at the Nanoscale in Gallium Nitride using Low Voltage Cathodoluminescence', Microscopy and Microanalysis, pp. 156-157.
View/Download from: UTS OPUS or Publisher's site
Wuhrer, R., Moran, K. & Phillips, M.R. 2006, 'X-ray mapping and post processing', Microscopy and Microanalysis, pp. 1404-1405.
View/Download from: UTS OPUS or Publisher's site
Phillips, M.R., Drouin, D. & Pauc, N. 2006, 'Probing carrier behavior at the nanoscale in gallium nitride using low voltage cathodoluminescence', Microscopy and Microanalysis, pp. 156-157.
View/Download from: Publisher's site
Dowd, A., Johansson, B., Armstrong, N., Ton-That, C. & Phillips, M. 2006, 'Cathodoluminescence as a method of extracting detailed information from nanophotonics systems: A study of silicon nanocrystals', Proceedings of SPIE - The International Society for Optical Engineering.
View/Download from: Publisher's site
We investigated Si nanocrystal samples produced by high dose 600 keV Si+ implantation of fused silica and annealing using cathodoluminescence (CL). CL spectra collected under 5-25 keV electron irradiation show similar features to reported photoluminescence spectra, including the strong near IR peak. The CL intensity distribution is formulated as a linear inverse problem and two methods namely the régularisation method and maximum entropy method can be applied to determine the depth profile without making any assumptions concerning the profile function, i.e. a free form solution. We show using simulated CL data that the maximum entropy method is the most appropriate as it preserves the positivity and additivity of the depth profile. This method is applied to experimental CL data and we have localised the spatial origin of the near IR emission to the near-surface region of the implant, 400 nm from the surface, containing the smallest Si nanocrystals.
Pauc, N., Phillips, M., Aimez, V. & Drouin, D. 2006, 'Cathodoluminescence study of GaN and GaN:Si on sapphire', Proceedings of SPIE - The International Society for Optical Engineering.
View/Download from: Publisher's site
We present a luminescence study of as-grown GaN and GaN:Si samples by means of low voltage cathodoluminescence (CL) at low temperature. It is shown that high spatial resolution CL microscopy allows direct luminescence mapping of threading dislocations in the doped and undoped samples. Comparison of monochromatic CL images acquired near the band gap energy (free and bound excitons) and at lower energies (recombination on defects) reveal the dopant segregation around dislocations.
Malguth, E., Hoffmann, A., Phillips, M. & Gehlhoff, W. 2006, 'Fe-centers in GaN as candidates for spintronics applications', Materials Research Society Symposium Proceedings, pp. 219-224.
The potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a set of 400 ?m thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 51017 cm-3 to 21020 cm -3 was studied by means of photoluminescence, photoluminescence excitation (PLE) and Fourier transform infrared (FTIR) transmission experiments. The Fe3+/2+ charge transfer (CT) level was determined to be at 2.86 ± 0.01 eV above the valence band maximum considerably lower than the previously reported value of 3.17 ± 0.10 eV. A bound state of the form (Fe2+, hVB) with a binding energy of 50 ± 10 meV has been established as an excited state of Fe3+. FTIR transmission measurements revealed an internal (5E - 5T2) transition of Fe2+ around 400 eV which, until now, was believed to be degenerate with the conduction band. Consequently, a second CT band was detected in PLE spectra. © 2006 Materials Research Society.
Butcher, K.S.A., Ferris, J.M., Phillips, M.R., Wintrebert-Fouquet, M., Jong Wah, J.W., Jovanovic, N., Vyverman, W. & Chepurnov, V.A. 2005, 'A luminescence study of porous diatoms', Materials Science and Engineering C, pp. 658-663.
View/Download from: UTS OPUS or Publisher's site
The cathodoluminescent and photoluminescent properties of the nanoporous silica frustules of various diatom strains and of natural diatom samples are presented. The spectra are observed to be similar to that of pure silica glass and the phenology is therefore believed to also be somewhat similar. A strong UV-blue luminescence peak is commonly observed as well as a yellow peak at 2.15 eV. For the more heavily silicified field-collected freshwater benthic samples, a strong red peak at 1.95 eV is also observed. The 2.15 eV peak is also more strongly evident for the field-collected samples. The UV-blue peak is related to common silica defect structure but cathodoluminescent microanalysis shows that this emission is highly localized in the diatom samples. © 2005 Elsevier B.V. All rights reserved.
Wuhrer, R., Moran, K., Phillips, M.R. & Davey, P. 2005, 'X-Ray Mapping Using Multiple-EDS and WDS Detectors', Microscopy and Microanalysis.
View/Download from: UTS OPUS or Publisher's site
Wuhrer, R., Huggett, P., Moran, K., Phillips, M.R. & Ben-Nissan, B. 2005, 'EBSD and XRM of Phases in Vacuum Cast Composite Alloys', Microscopy and Microanalysis.
View/Download from: UTS OPUS or Publisher's site
Phillips, M.R. & Morgan, S.W. 2005, 'Direct Comparison of Various Gaseous Secondary Electron Detectors in the Variable Pressure Scanning Electron Microscope', Microscopy and Microanalysis.
View/Download from: UTS OPUS or Publisher's site
Coleman, V.A., Tan, H.H., Jagadish, C., Kucheyev, S.O., Zou, J. & Phillips, M.R. 2005, 'Towards p-type doping of ZnO by ion implantation', Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, pp. 847-848.
View/Download from: Publisher's site
The thermal stability of ion implanted ZnO was investigated. Heavily damaged ZnO decomposes with thermal treatment. This result has significant implications for ion implants into ZnO for p-type doping, and subsequent thermal treatments for activation. © 2005 IEEE.
Coleman, V.A., Tan, H.H., Jagadish, C., Kucheyev, S.O., Phillips, M.R. & Zou, J. 2005, 'Towards p-type doping of ZnO by ion implantation', Materials Research Society Symposium Proceedings, pp. 361-366.
Zinc oxide is a very attractive material for a range of optoelectronic devices including blue light-emitting diodes and laser diodes. Though n-type doping has been successfully achieved, p-type doing of ZnO is still a challenge that must be overcome before p-n junction devices can be realized. Ion implantation is widely used in the microelectronics industry for selective area doping and device isolation. Understanding damage accumulation and recrystallization processes is important for achieving selective area doping. In this study, As (potential p-type dopant) ion implantation and annealing studies were carried out. ZnO samples were implanted with high dose (1.4 1017 ions/cm2) 300 keV As ions at room temperature. Furnace annealing of samples in the range of 900°C to 1200°C was employed to achieve recrystallization of amorphous layers and electrical activation of the dopant. Rutherford backscattering/channeling spectrometry, transmission electron microscopy and cathodolumiescence spectroscopy were used to monitor damage accumulation and annihilation behavior in ZnO. Results of this study have significant implications for p-type doing of ZnO by ion implantation. © 2005 Materials Research Society.
Wójcik, A., Kopalko, K., Godlewski, M., ?usakowska, E., Guziewicz, E., Minikayev, R., Paszkowicz, W., ?wia?tek, K., Klepka, M., Jakie?a, R., Kiecana, M., Sawicki, M., Dybko, K. & Phillips, M.R. 2005, 'Thin films of ZnO and ZnMnO by atomic layer epitaxy', Optica Applicata, pp. 413-418.
We discuss properties of thin films of ZnO and ZnMnO grown with atomic layer epitaxy using new, organic zinc and manganese precursors. Several characterization techniques, including X-ray diffraction, atomic force microscopy, scanning electron microscopy, cathodoluminescence, superconducting quantum interfernece device (SQUID) and electron spin resonance, show good topography of the films and their advantageous optical and magnetic properties.
Mokkapati, S., Lever, P., Tan, H.H., Jagadish, C., McBean, K.E. & Phillips, M.R. 2005, 'Selective area epitaxy of InGaAs quantum dots for optoelectronic device integration', Conference on Optoelectronic and Microelectronic Materials and Devices, Proceedings, COMMAD, pp. 273-275.
View/Download from: Publisher's site
We demonstrate that selective-area-epitaxy can be used to selectively tune the properties of InGaAs quantum-dots in different regions of the same wafer. We report single step, MOCVD growth of different sized dots, luminescing at wavelengths spread over a range of 100nm. © 2005 IEEE.
Godlewski, M., Phillips, M.R., Czernecki, R., Targowski, G., Perlin, P., Leszczy?ski, M., Figge, S. & Hommel, D. 2005, 'Light emission properties of GaN-based laser diode structures', Acta Physica Polonica A, pp. 675-680.
Cathodoluminescence is applied for evaluation of in-depth and in-plane variations of light emission from two types of GaN-based laser diode structures. We evaluate in-depth properties of the laser diode emission and demonstrate that potential fluctuations still affect emission of laser diodes for e-beam currents above thresholds for a stimulated emission.
Tomaszewska-Grz?da, A., Lojkowski, W., Godlewski, M., Yatsunenko, S., Drozdowicz-Tomsia, K., Goldys, E.M. & Phillips, M.R. 2005, 'Growth and characterization of ZnO nanoparticles', Acta Physica Polonica A, pp. 897-902.
In this work we evaluate structural and optical properties of ZnO nanoparticles grown by wet chemistry method. Light emission properties of these nanoparticles are studied with cathodoluminescence and micro-photoluminescence. Even at the room temperature excitonic emission is well resolved, due to high exciton binding energy of ZnO. Decay kinetics of photoluminescence emissions and efficiency of inter-nanoparticles energy migration is evaluated from maps of in-plane variations of photoluminescence decay times measured in microphotoluminescence setup.
Godlewski, M., Yatsunenko, S., Drozdowicz-Tomsia, K., Goldys, E.M., Phillips, M.R., Klar, P.J. & Heimbrodt, W. 2005, 'Dynamics of light emission in CdMnS nanoparticles', Acta Physica Polonica A, pp. 681-688.
We demonstrate coexistence of slow and fast components of photoluminescence decay of the Mn2+ intra-shell emission in nanoparticles of CdMnS. We explain the observed decrease in PL lifetime of the Mn2+ intra-shell transition by high efficiency of spin dependent magnetic interactions between localized spins of Mn2+ ions and free carriers. This mechanism is enhanced in nanostructures, but it is also present in bulk samples.
Mokkapati, S., Wong-Leung, J., Tan, H.H., Jagadish, C., McBean, K.E. & Phillips, M.R. 2005, 'Controlled nucleation of InAs/GaAs and InGaAs/GaAs quantum dots for optoelectronic device integration', 2005 5th IEEE Conference on Nanotechnology, pp. 593-595.
View/Download from: Publisher's site
We demonstrate that InAs and InGaAs quantum dots can be grown selectively in specific regions of GaAs substrates using selective-area MOCVD. Growth parameters can be controlled to obtain high density (?1010/ cm2) of defect free quantum dots. Emission spectra from these selectively grown dots are presented and are comparable in linewidth to that from dots grown on unpatterned substrates. We propose that this growth scheme can be used for fabrication of quantum dot lasers integrated with waveguides. ©2005 IEEE.
Wuhrer, R., Moran, K., Huggett, P., Phillips, M.R. & Ben-Nissan, B. 2004, 'X-ray mapping and electron back scattered diffraction of phases in welded materials', Microscopy and Microanalysis, pp. 916-917.
View/Download from: Publisher's site
Wuhrer, R., Phillips, M.R., Mason, K., Roux, C., Maniago, J.R. & Hales, S. 2004, 'GSR analysis in the environmental scanning electron microscope', Microscopy and Microanalysis, pp. 1362-1363.
View/Download from: Publisher's site
White, R., Phillips, M., Thomas, P., Wuhrer, R. & Dredge, P. 2004, 'Interactions between pigments in 19th and early 20th century oil paintings - In situ studies using the environmental scanning electron microscope', Microscopy and Microanalysis, pp. 132-133.
View/Download from: Publisher's site
Gelhausen, O., Malguth, E., Phillips, M., Goldys, E.M., Strassburg, M., Hoffmann, A.V., Graf, T., Gjukic, M. & Stutzmann, M. 2003, 'Optical Properties of Mn -doped GaN', Proceedings MRS Fall Meeting, Materials Research Society, Materials Research Society, Materials Research Society, Boston, MA, USA, pp. 569-574.
Phillips, M.R. & McBean, K.E. 2004, 'In-situ evaluation of post growth treatments on the cathodoluminescence properties of fluorescent nano-particles in the environmental scanning electron microscope', Microscopy and Microanalysis, pp. 1064-1065.
View/Download from: Publisher's site
Phillips, M.R., Gelhausen, O. & Goldys, E.M. 2004, 'Cathodoluminescence properties of zinc oxide nanoparticles', Physica Status Solidi C: Conferences, pp. 229-234.
View/Download from: Publisher's site
Zinc oxide nano-particles (25 nm) have been investigated by cathodoluminescence spectroscopy (300 nm-1700 nm) at 80 K and 300 K following thermal annealing in high purity H2/N2, N2, O2 and Ar gaseous atmospheres. The intensity of the ZnO near band edge peak was significantly increased after heat treatment in hydrogen. Conversely, thermal annealing in the other gas types decreased this emission. This effect is attributed to hydrogen passivation of competitive non-radiative defect centers, most likely bulk zinc vacancy centers. The appearance of a strong green emission centered at 2.4 eV following thermal annealing in all gas atmospheres is ascribed to the formation of bulk oxygen vacancy defects. A strong red shift of the near band edge emission with increasing beam current at 300 K is accredited to electron beam heating rather than to an increase in the carrier density. Electron beam heating is evidenced by the occurrence of a strong black body emission in the near infrared spectral region. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Godlewski, M., Wojtowicz, T., Goldys, E.M., Phillips, M.R., Czernecki, R., Prystawko, P., Leszczynski, M., Perlin, P., Grzegory, I., Porowski, S., Böttcher, T., Figge, S. & Hommel, D. 2004, 'In-depth and in-plane profiling of light emission properties from semiconductor-based heterostructures', Opto-electronics Review, pp. 353-359.
Cathodoluminescence (CL) technique is applied for evaluation of in-depth and in-plane variations of light emission from semiconductor heterostructures, including laser diode structures. Light emission properties of heteroepitaxial and homoepitaxial structures are studied. We demonstrate possibility of in-depth profiling of complicated multi quantum well structures, which allows us to evaluate light emission characteristics from different regions of, e.g., laser structures. Due to this property of the CL, we can evaluate interconnections between structural quality of the samples and light emission characteristics. Stimulated emission under electron beam pumping is achieved in a conventional CL set up for selected heterostructures. Threshold currents for stimulated emission are evaluated from the CL investigations. We demonstrate that potential fluctuations are not fully screened in the active regions of laser structures, even at large excitation densities.
Gelhausen, O., Malguth, E., Phillips, M.R., Goldys, E.M., Strassburg, M., Hoffmann, A., Graf, T., Gjukic, M. & Stutzmann, M. 2003, 'Optical properties of Mn-doped GaN', Materials Research Society Symposium - Proceedings, pp. 569-574.
View/Download from: UTS OPUS
Molecular beam epitaxy-grown GaN with different Mn concentrations (5-231019 cm-3) and codoped with Si were investigated by cathodoluminescence (CL) spectroscopy and optical transmission measurements. In the GaN:Mn, an intense absorption peak at 1.414 +/- 0.002 eV was observed. This peak was attributed to an internal 5T 2? 5E transition of the deep neutral Mn3+ state since its intensity scaled with the Mn3+ concentration. The CL measurements showed that Mn-doping concentrations around 1020 cm -3 had three effects on the emission spectrum: (i) the donor bound exciton at 3.460 eV was reduced by more than one order of magnitude, (ii) the donor-acceptor-pair band at 3.27 eV was completely quenched and (iii) the yellow luminescence centered at 2.2 eV was the strongly decreased. The latter two effects were attributed to a reduced concentration of VGa. In the infrared spectral range, three broad, Mn-doping related CL emission bands centered at 1.01 ± 0.02 eV, 1.09 ± 0.02 eV and 1.25 ± 0.03 eV were observed. These bands might be related to deep donor complexes, which are generated as a result of the heavy Mn-doping, rather than internal transitions at the Mn atom.
Gelhausen, O., Phillips, M.R., Goldys, E.M., Paskova, T., Monemar, B., Strassburg, M. & Hoffmann, A. 2003, 'Formation and dissociation of hydrogen-related defect centers in Mg-doped GaN', Materials Research Society Symposium - Proceedings, pp. 497-502.
View/Download from: UTS OPUS
Moderately and heavily Mg-doped GaN were studied by a combination of post-growth annealing processes and electron beam irradiation techniques during cathodoluminescence (CL) to elucidate the chemical origin of the recombination centers responsible for the main optical emission lines. The shallow donor at 20-30 meV below the conduction band, which is involved in the donor-acceptor-pair (DAP) emission at 3.27 eV, was attributed to a hydrogen-related center, presumably a (VN-H) complex. Due to the small dissociation energy (<2 eV) of the (VNH) complex, this emission line was strongly reduced by low-energy electron irradiation. CL investigations of the DAP at a similar energetic position in Si-doped (n-type) GaN indicated that this emission line is of different chemical origin than the 3.27 eV DAP in Mg-doped GaN. A slightly deeper DAP emission centered at 3.14 eV was observed following low-energy electron irradiation, indicating the appearance of an additional donor level with a binding energy of 100-200 meV, which was tentatively attributed to a VN-related center. The blue band (2.8-3.0 eV) in heavily Mg-doped GaN was found to consist of at least two different deep donor levels at 350&plusmn;30 meV and 440&plusmn;40 meV. The donor level at 350&plusmn;30 meV was strongly affected by electron irradiation and attributed to a H-related defect.
Griffin, B., Suvorova, A. & Phillips, M. 2002, 'A review of gas-electron interactions imaging and X-ray analysis in variable pressure SEM', Proceedings of the 15th International Congress on Electron Microscopy, 15th International Congress on Electron Microscopy, Microscopy Society of Southern Africa, Durban, South Africa, pp. 215-216.
View/Download from: UTS OPUS
Phillips, M. & Morgan, S.W. 2002, 'Time dependent behaviour of positive ions in the variable pressure scanning electron microscope', Proceedings of the 15th International Congress on Electron Microscopy, 15th International Congress on Electron Microscopy, Microscopy Society of Southern Africa, Durban, South Africa, pp. 219-220.
View/Download from: UTS OPUS
Toth, M., Craven, J.P., Phillips, M.R., Thiel, B.L. & Donald, A.M. 2002, 'X-ray microanalysis of insulators in a variable pressure environment', Microscopy and Microanalysis, pp. 1478-1479.
View/Download from: UTS OPUS
Phillips, M.R. & Morgan, S.W. 2002, 'Time resolved analysis of the positive ion dynamics in the variable pressure scanning electron microscope', Microscopy and Microanalysis, pp. 446-447.
View/Download from: UTS OPUS
Gelhausen, O., Phillips, M.R., Klein, H.N. & Goldys, E.M. 2002, 'Influence of low-energy electron beam irradiation on defects in activated Mg-doped GaN', Materials Research Society Symposium - Proceedings, pp. 653-658.
CL spectroscopy studies at varying temperatures and excitation power densities as well as depth-resolved CL imaging were conducted to investigate the impact of low energy electron beam irradiation (LEEBI) on native defects and residual impurities in metal-organic vapor phase epitaxy (MOVPE) grown Mg-doped p-type GaN. Due to the dissociation of (Mg-H)0 complexes, LEEBI significantly increases the (e,Mg0) emission (3.26 eV) at 300 K and substantially decreases the H-Mg donor-acceptor-pair (DAP) emission (3.27 eV) at 80 K. In-plane and depth-resolved CL imaging indicates that hydrogen dissociation results from electron-hole recombination at H-defect complexes rather than heating by the electron beam. The dissociated hydrogen atoms associate with nitrogen vacancies, forming a deeper donor, i.e. a (H-VN) complex. The corresponding deeper DAP emission with Mg centered at 3.1 eV is clearly observed between 160 and 220 K. Moreover, a broad yellow luminescence (YL) band centered at 2.2 eV is observed in MOVPE-grown Mg-doped GaN after LEEBI-treatment. It is suggested that a combination of LEEBI-induced Fermi-level downshift due to Mg-acceptor activation and simultaneous dissociation of gallium vacancy-impurity complexes, i.e. (VGa-H), is responsible for the observed YL.
Aubin, A.S., Drouin, D. & Phillips, M.R. 2002, 'ESEM beam current measuring device based on a planar Schottky Diode', Microscopy and Microanalysis, pp. 1538-1539.
Rémond, G., Fialin, M., Nockolds, C.E., Phillips, M.R. & Roques-Carmes, C. 2002, 'Absorption correction of Fe La,? emission from iron oxides', Microscopy and Microanalysis, pp. 1496-1497.
Godlewski, M., Ivanov, V., Khachapuridze, A., Narkowicz, R. & Phillips, M. 2001, 'Effects of Localisations in CdTe-Based Quantum Well Structures in optical Organic and Inorganic Materials', Proceedings of the SPIE, SPIE, SPIE, Lithuania, pp. 86-91.
Phillips, M., Griffin, B., Drouin, D., Nockolds, C. & Remond, G. 2001, 'X-Ray Micronalaysis in the Environmentl SEM Using Mapping and Fourier Deconvolution Techniques', Microscopy & Microanalysis 2001 Proceedings Volume 7 Supplement 2, Microscopy & Microanalysis 2001, Springer Verlag, California, pp. 708-709.
View/Download from: UTS OPUS
Gross, K.A., Phillips, M.R. & Suetsugu, Y. 2001, 'Cathodoluminescence emission for differentiating the degree of carbonation in apatites', Key Engineering Materials, pp. 179-182.
View/Download from: UTS OPUS
Cathodoluminescence has recently been used successfully in detecting and determining the spatial location of the amorphous phase in plasma sprayed calcium phosphate coatings. The aim of this study is to determine whether this same technique can be used to detect different carbonate substitutions in apatites. Single crystals were analysed with cathodoluminscence spectroscopy and the results indicated a change in peak shape. The substitution of carbonate into the hydroxyapatite structure creates a more well defined peak with a narrower width at half the peak height.
Morgan, S.W. & Phillips, M. 2001, 'Time Dependent Study of the Positive Ion Current in the Environmental Scanning Electron Microscope (ESEM)', Microscopy & Microanalysis 2001 Proceedings Volume 7 Supplement 2, Microscopy & Microanalysis 2001, Springer Verlag, California, pp. 788-789.
View/Download from: UTS OPUS
Goldys, E.M., Godlewski, M., Phillips, M.R. & Toropov, A.A. 2001, 'Photo- and cathodoluminescence investigations of piezoelectric GaN/AlGaN quantum wells', Materials Research Society Symposium - Proceedings, pp. G6.12.1-G6.12.5.
We have examined multiple quantum well AlGaN/GaN structures with several quantum wells of varying widths. The structures had strain-free quantum wells and strained barriers. Strong piezoelectric fields in these structures led to a large red shift of the PL emission energies and long decay times were also observed. While the peak energies could be modelled using the effective mass approximation, the calculated free exciton radiative lifetimes were much shorter than those observed in experiments, indicating an alternative recombination mechanism, tentatively attributed to localised excitons. Cathodoluminescence depth profiling revealed an unusually small penetration range of electrons suggesting that electron-hole pairs preferentially remain within the multiple quantum well region due to the existing electric fields. Spatial fluctuations of the cathodoluminescence intensity were also observed.
Kucheyev, S.O., Bradby, J.E., Williams, J.S., Swain, M.V., Toth, M., Phillips, M.R. & Jagadish, C. 2001, 'Mechanical properties of As-grown and ion-beam-modified GaN films', Materials Research Society Symposium - Proceedings, pp. Q5.5.1-Q5.5.6.
The deformation behavior of as-grown and ion-beam-modified wurtzite GaN films is studied by nanoindentation with a spherical indenter. Atomic force microscopy (AFM) and cathodoluminescence are used to characterize the deformation mode. No systematic dependence of the mechanical properties on the film thickness (at least for thicknesses from 1.8 to 4 ?m) as well as on doping type is observed. Results strongly suggest that (i) slips is the major contributor to the plastic deformation of crystalline GaN and (ii) slip nucleation (rather than a phase transformation) is responsible for "pop-in" events observed during loading. Indentation with an ? 4.2 ?m radius spherical indenter at maximum loads up to 900 mN does not produce any cracking visible by AFM in crystalline GaN. Instead, under such loads, indentation results in a pronounced elevation of the material around the impression. Implantation disorder dramatically changes the deformation behavior of GaN. In particular, implantation-produced defects in crystalline GaN suppress (i) "pop-in" events during loading, (ii) slip bands observed by AFM, and (iii) the plastic component of deformation. GaN amorphized by ion bombardment exhibits plastic flow even for very low loads. The values of hardness and elastic modulus of amorphous GaN are dramatically reduced compared to those of as-grown GaN.
Godlewski, M., Ivanov, V.Y., Khachapuridze, A., Narkowicz, R. & Phillips, M.R. 2001, 'Effects of localisation in CdTe-based quantum well structures', Proceedings of SPIE - The International Society for Optical Engineering, pp. 86-91.
View/Download from: Publisher's site
The properties of strongly localised excitons in quantum well structure of CdTe/CdMnTe were observed at low temperature. Strong localisation effects on exciton dynamics and on strength of exciton-phonon coupling were also demonstrated. A link was determined between the microstructure of the sample and the observed strong potential fluctuations in quantum well (QW) planes. It was shown that at low temperatures excitons in the structure with 68% Mn fraction in the CdMnTe barriers were quasi-zero-dimensional.
Remond, G., Nockolds, C.E., Phillips, M.R. & Cazaux, J. 2000, 'Charging phenomena of wide bandgap materials in a VP-SEM.', MICROBEAM ANALYSIS 2000, PROCEEDINGS, 2nd Conference of the International-Union-of-Microbeam-Analysis-Societies, IOP PUBLISHING LTD, KAILUA KONA, HAWAII, pp. 269-270.
Phillips, M.R. & Toth, M. 2000, 'Charge neutralization of insulators in an ESEM', MICROBEAM ANALYSIS 2000, PROCEEDINGS, 2nd Conference of the International-Union-of-Microbeam-Analysis-Societies, IOP PUBLISHING LTD, KAILUA KONA, HAWAII, pp. 273-274.
Toth, M., Phillips, M.R., Kucheyev, S.O., Williams, J.S., Jagadish, C. & Li, G. 2000, 'Charge contrast in SE images obtained using the ESEM', MICROBEAM ANALYSIS 2000, PROCEEDINGS, 2nd Conference of the International-Union-of-Microbeam-Analysis-Societies, IOP PUBLISHING LTD, KAILUA KONA, HAWAII, pp. 275-276.
Griffin, B.J., Nockolds, C.E., Phillips, M.R. & Remond, G. 2000, 'New needs for imaging and x-ray microanalysis standards: ESEM, CHIME and low voltage microanalysis', MICROBEAM ANALYSIS 2000, PROCEEDINGS, 2nd Conference of the International-Union-of-Microbeam-Analysis-Societies, IOP PUBLISHING LTD, KAILUA KONA, HAWAII, pp. 395-396.
Wuhrer, R., Yeung, W. & Phillips, M.R. 2000, 'SEM/EDS, AFM and XRD analysis of ternary nitride coatings produced by magnetron co-sputtering at different nitrogen pressures', MICROBEAM ANALYSIS 2000, PROCEEDINGS, 2nd Conference of the International-Union-of-Microbeam-Analysis-Societies, IOP PUBLISHING LTD, KAILUA KONA, HAWAII, pp. 449-450.
Kucheyev, S.O., Williams, J.S., Jagadish, C., Zou, J., Toth, M., Phillips, M.R., Tan, H.H., Li, G. & Pearton, S.J. 2000, 'Surface disordering and nitrogen loss in GaN under ion bombardment', Materials Research Society Symposium - Proceedings, pp. T791-T796.
The damage build-up and amorphization behavior in wurtzite GaN films under a wide range of implant conditions are studied by Rutherford backscattering / channeling spectrometry, transmission electron microscopy, and cathodoluminescence spectroscopy. A strong surface peak of lattice disorder, in addition to the expected damage peak in the region of the maximum of nuclear energy loss, has been observed for all implant conditions of this study. Capping of GaN with SiOx and SixNy layers prior to implantation does not eliminate surface disordering. This may suggest that nitrogen loss is not the main reason for the observed enhanced surface disorder, but, rather, the GaN surface acts as a strong sink for migrating point defects. However, pronounced loss of N during ion bombardment is observed for high dose implantation when the near-surface region is amorphized. Moreover, after amorphization, annealing at temperatures above about 400 &deg;C leads to complete decomposition of the near-surface layer.
Toth, M., Fleischer, K. & Phillips, M.R. 1999, 'Electron beam induced impurity electro-migration in unintentionally doped GaN', Materials Research Society Symposium - Proceedings, p. G3.30.
Electron beam induced electromigration of ON + and H+ impurities in unintentionally n-doped GaN was investigated using cathodoluminescence (CL) kinetics profiling, CL imaging of regions pre-irradiated with a stationary electron beam, and wavelength dispersive x-ray spectrometry (WDS). The presented results (i) illustrate induced impurity diffusion in wide bandgap semiconductors, (ii) provide experimental evidence for the (VGa-ON)2- model of yellow luminescence in GaN with low Si content, (iii) confirm the roles of O in frequently reported bound exciton and donor-acceptor pair emissions and (iv) suggest the involvement of ON + and hydrogenated gallium vacancies in a blue emission in autodoped GaN.
Kim, Y., Yuan, S., Leon, R., Clark, A., Jagadish, C., Johnston, M.B., Burke, P., Gal, M., Zou, J., Cockayne, D., Phillips, M.R. & Kalceff, M.A.S. 1996, 'V-grooved GaAs/AlGaAs quantum wires with side wall quantum wells intermixed by pulsed anodization and rapid thermal annealing', Conference on Optoelectronic & Microelectronic Materials and Devices, Proceedings, COMMAD, pp. 200-203.
Novel impurity-free interdiffusion (IFID) technique, namely, pulsed anodization and subsequent rapid thermal annealing, is applied to study GaAs/AlGaAs multiple quantum wires grown by metalorganic chemical vapour deposition on V-grooved GaAs substrate. Photoluminescence (PL) and cathodoluminescence (CL) emissions are observed from GaAs quantum wires. IFID increases both carrier confinement in quantum wires and the efficiency of excess carrier transferring from sidewall quantum wells to quantum wires, where the excess carriers are generated either by optical pumping (PL) or electron pumping (CL).

Journal articles

Choi, S., Phillips, M.R., Aharonovich, I., Pornsuwan, S., Cowie, B.C.C. & Ton-That, C. 2015, 'Photophysics of Point Defects in ZnO Nanoparticles', Advanced Optical Materials, vol. 3, no. 6, pp. 821-827.
View/Download from: UTS OPUS or Publisher's site
&copy; 2015 WILEY-VCH Verlag GmbH & Co. Zinc oxide (ZnO) nanoparticles have recently been identified as a promising candidate for advanced nanophotonics applications and quantum technologies. This work reports the formation of luminescent point defects and describes their photophysical properties. In particular, it is shown using correlative photoluminescence, cathodoluminescence, electron paramagnetic resonance (EPR), and X-ray absorption near-edge spectroscopy that green luminescence at 2.48 eV and an EPR line at g = 2.00 belong to a surface oxygen vacancy (V<inf>o,s</inf><sup>+</sup>) center, while a second green emission at 2.28 eV is associated with zinc vacancy (V<inf>Zn</inf>) centers. It is established that radiative point defects can be excited in the visible that exhibits nanosecond lifetimes using both above bandgap and sub-bandgap 405 and 532 nm excitation. This work provides important knowledge towards employment of point defects in ZnO in nanophotonics technologies.
Choi, S., Berhane, A.M., Gentle, A., Ton-That, C., Phillips, M.R. & Aharonovich, I. 2015, 'Electroluminescence from Localized Defects in Zinc Oxide: Toward Electrically Driven Single Photon Sources at Room Temperature', ACS Applied Materials and Interfaces, vol. 7, no. 10, pp. 5619-5623.
View/Download from: UTS OPUS or Publisher's site
&copy; 2015 American Chemical Society. Single photon sources are required for a wide range of applications in quantum information science, quantum cryptography, and quantum communications. However, the majority of room temperature emitters to date are only excited optically, which limits their proper integration into scalable devices. In this work, we overcome this limitation and present room temperature electrically driven light emission from localized defects in zinc oxide (ZnO) nanoparticles and thin films. The devices emit in the red spectral range and show excellent rectifying behavior. The emission is stable over an extensive period of time, providing an important prerequisite for practical devices. Our results open possibilities for building new ZnO-based quantum integrated devices that incorporate solid-state single photon sources for quantum information technologies. (Graph Presented).
Ton-That, C., Zhu, L., Lockrey, M.N., Phillips, M.R., Cowie, B.C.C., Tadich, A., Thomsen, L., Khachadorian, S., Schlichting, S., Jankowski, N. & Hoffmann, A. 2015, 'Molecular nitrogen acceptors in ZnO nanowires induced by nitrogen plasma annealing', Physical Review B - Condensed Matter and Materials Physics, vol. 92, no. 2.
View/Download from: UTS OPUS or Publisher's site
&copy;2015 American Physical Society. X-ray absorption near-edge spectroscopy, photoluminescence, cathodoluminescence, and Raman spectroscopy have been used to investigate the chemical states of nitrogen dopants in ZnO nanowires. It is found that nitrogen exists in multiple states: N<inf>O</inf>,N<inf>Zn</inf>, and loosely bound N<inf>2</inf> molecule. The results establish a direct link between a donor-acceptor pair emission at 3.232 eV and the concentration of loosely bound N<inf>2</inf>. This work confirms that N<inf>2</inf> at Zn site is a potential candidate for producing a shallow acceptor state in N-doped ZnO as theoretically predicted by Lambrecht and Boonchun [Phys. Rev. B 87, 195207 (2013)10.1103/PhysRevB.87.195207]. Additionally, shallow acceptor states arising from N<inf>O</inf> complexes have been ruled out in this paper.
Zhu, L., Phillips, M.R. & Ton-That, C. 2015, 'Coalescence of ZnO nanowires grown from monodisperse Au nanoparticles', CrystEngComm, vol. 17, no. 27, pp. 4987-4991.
View/Download from: UTS OPUS or Publisher's site
This journal is &copy; The Royal Society of Chemistry. New insights into control of nanowire merging phenomena are demonstrated in the growth of thin ZnO nanowires using monodisperse Au colloidal nanoparticles as a catalyst. Both the nanowire diameter and density were found to be strongly dependent on the density of Au nanoparticles. Structural analysis and spectral cathodoluminescence imaging of the c-plane nanowire cross-sections reveal that the thin isolated nanowires growing from the Au nanoparticles begin to merge and coalesce with neighbouring nanowires to form larger nanowires when their separation reaches a threshold distance. Green luminescence, which originated from the remnants of constituent nanowires before merging, is detected at the core of the fused nanowires. The distribution of nanowire diameters and green emission were found to be strongly dependent on the density of the Au nanoparticles. The merging phenomenon is attributed to electrostatic interactions between the nanowire c-facets during growth and well-described by a cantilever bending model.
Anantachaisilp, S., Smith, S.M., Ton-That, C., Pornsuwan, S., Moon, A.R., Nenstiel, C., Hoffmann, A. & Phillips, M.R. 2015, 'Nature of red luminescence in oxygen treated hydrothermally grown zinc oxide nanorods', Journal of Luminescence, vol. 168, pp. 20-25.
View/Download from: UTS OPUS or Publisher's site
&copy; 2015 Published by Elsevier B.V. A strong broad red luminescence (RL) peak centered at 1.69 eV (FWHM=0.57 eV) at 15 K [1.78 eV (FWHM=0.69 eV) at 300 K] is formed in ZnO nanorods hydrothermally grown at low temperature following thermal annealing at 650 &deg;C for 30 min in an O<inf>2</inf> gas environment. The optical properties of this peak were comprehensively studied using a range of characterization techniques, including photoluminescence and cathodoluminescence spectroscopy, X-ray absorption near edge spectroscopy and electron paramagnetic resonance spectroscopy. With decreasing temperature the RL peak position red shifted and its FWHM became narrower in accordance with the configuration coordinate model. Using these results, the RL has been assigned to highly lattice coupled V<inf>Zn</inf>-related acceptor-like centers. No correlation was found between the observed red luminescence and nitrogen impurities.
Khachadorian, S., Gillen, R., Choi, S., Ton-That, C., Kliem, A., Maultzsch, J., Phillips, M.R. & Hoffmann, A. 2015, 'Effects of annealing on optical and structural properties of zinc oxide nanocrystals', Physica Status Solidi (B) Basic Research, vol. 252, no. 11, pp. 2620-2625.
View/Download from: UTS OPUS or Publisher's site
& Co. KGaA, Weinheim. The optical and vibrational properties of zinc oxide nanocrystals (ZnO NCs), grown by chemical precipitation method, were investigated following thermal annealing treatments in oxygen, argon, and zinc vapors at temperatures up to 900{ring operator}C. Raman scattering and photoluminescence techniques were utilized to show the effect of temperature annealing in various environments on optical and structural properties of ZnO NCs, referring them to the reduction and increase of certain intrinsic defect concentrations. The experimental results are complemented by density functional theory calculations for understanding the correlation between Raman modes induced with different annealing procedures and certain intrinsic point defects. &copy; 2015 WILEY-VCH Verlag GmbH
Choi, S., Johnson, B.C., Castelletto, S., Ton-That, C., Phillips, M.R. & Aharonovich, I. 2014, 'Single photon emission from ZnO nanoparticles', Applied Physics Letters, vol. 104, no. 26.
View/Download from: UTS OPUS or Publisher's site
Room temperature single photon emitters are very important resources for photonics and emerging quantum technologies. In this work, we study single photon emission from defect centers in 20 nm zinc oxide (ZnO) nanoparticles. The emitters exhibit bright broadband fluorescence in the red spectral range centered at 640 nm with polarized excitation and emission. The studied emitters showed continuous blinking; however, bleaching can be suppressed using a polymethyl methacrylate coating. Furthermore, hydrogen termination increased the density of single photon emitters. Our results will contribute to the identification of quantum systems in ZnO. &copy; 2014 AIP Publishing LLC.
Lem, L.L.C., Phillips, M.R. & Ton-That, C. 2014, 'Controlling the visible luminescence in hydrothermal ZnO', Journal of Luminescence, vol. 154, pp. 387-391.
View/Download from: UTS OPUS or Publisher's site
Cathodoluminescence spectra have been measured in hydrothermal and hydrogen-doped ZnO at different excitation densities and temperatures to investigate the emission efficiencies of near-band-edge (NBE), green and yellow luminescence bands. The NBE intensity depends linearly on the electron beam excitation as expected for excitonic recombination character. The intensities of the green and yellow bands are highly dependent not only on the excitation density but also on temperature. At high excitation densities ZnO exhibits dominant green emission at room temperature; the intensity of the green band can be further controlled by doping ZnO with hydrogen, which passivates green luminescence centers. Conversely at small excitation densities (< 0.1 nA) and low temperatures the visible luminescence from ZnO is predominantly yellow due to the abundance of Li in hydrothermal ZnO. The results are explained by differences in the recombination kinetics and the relative concentrations of the green and yellow centers, and illustrate that single-color emission can be achieved in ZnO by adjusting the excitation power and temperature. &copy; 2014 Published by Elsevier B.V. All rights reserved.
Chan, K.S., Ton-That, C., Vines, L., Choi, S., Phillips, M.R., Svensson, B.G., Jagadish, C. & Wong-Leung, J. 2014, 'Effects of high temperature annealing on defects and luminescence properties in H implanted ZnO', Journal of Physics D: Applied Physics, vol. 47, no. 34.
View/Download from: UTS OPUS or Publisher's site
The evolution of luminescence properties and voids formation with respect to annealing temperature in H implanted ZnO was investigated by depth-resolved cathodoluminescence spectroscopy (DRCLS), transmission electron microscopy and secondary ion mass spectrometry (SIMS). The annealing temperature is found to induce noticeable changes to the shape, size and empty volume density of the cavities. DRCLS results also reveal that the green emission is influenced by different annealing temperatures. In particular, the 600 &deg;C anneal produces a strong quenching of the green emission in the implanted region, while after the 800 &deg;C anneal a significant enhancement near the surface is observed. The annealing at 600 &deg;C also results in an uncommon violet emission at ?3.1 eV that is not observed after a higher annealing temperature. A clear correlation between the violet emission, vacancies and Li is revealed from comparison between the DRCLS intensities and SIMS data. &copy; 2014 IOP Publishing Ltd.
Ton-That, C., Lem, L.L.C., Phillips, M.R., Reisdorffer, F., Mevellec, J., Nguyen, T.P., Nenstiel, C. & Hoffmann, A. 2014, 'Shallow carrier traps in hydrothermal ZnO crystals', New Journal of Physics, vol. 16.
View/Download from: UTS OPUS or Publisher's site
Native and hydrogen-plasma induced shallow traps in hydrothermally grown ZnO crystals have been investigated by charge-based deep level transient spectroscopy, photoluminescence and cathodoluminescence microanalysis. The as-grown ZnO exhibits a trap state at 23 meV, while H-doped ZnO produced by plasma doping shows two levels at 22 meV and 11 meV below the conduction band. As-grown ZnO displays the expected thermal decay of bound excitons with increasing temperature from 7 K, while we observed an anomalous behaviour of the excitonic emission in H-doped ZnO, in which its intensity increases with increasing temperature in the range 140-300 K. Based on a multitude of optical results, a qualitative model is developed which explains the Y line structural defects, which act as an electron trap with an activation energy of 11 meV, being responsible for the anomalous temperature-dependent cathodoluminescence of H-doped ZnO. &copy; 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Callsen, G., Wagner, M.R., Reparaz, J.S., Nippert, F., Kure, T., Kalinowski, S., Hoffmann, A., Ford, M.J., Phillips, M.R., Dalmau, R.F., Schlesser, R., Collazo, R. & Sitar, Z. 2014, 'Phonon pressure coefficients and deformation potentials of wurtzite AlN determined by uniaxial pressure-dependent Raman measurements', Physical Review B - Condensed Matter and Materials Physics, vol. 90, no. 20.
View/Download from: UTS OPUS or Publisher's site
&copy; 2014 American Physical Society. We studied bulk crystals of wurtzite AlN by means of uniaxial pressure-dependent Raman measurements. As a result, we derive the phonon pressure coefficients and deformation potentials for all zone center optical phonon modes. For the A1 and E1 modes, we further experimentally determined the uniaxial pressure dependence of their longitudinal optical-transverse optical (LO-TO) splittings. Our experimental approach delivers new insight into the large variance among previously reported phonon deformation potentials, which are predominantly based on heteroepitaxial growth of AlN and the ball-on-ring technique. Additionally, the measured phonon pressure coefficients are compared to their theoretical counterparts obtained by density functional theory implemented in the siesta package. Generally, we observe a good agreement between the calculated and measured phonon pressure coefficients but some particular Raman modes exhibit significant discrepancies similar to the case of wurtzite GaN and ZnO, clearly motivating the presented uniaxial pressure-dependent Raman measurements on bulk AlN crystals.
Anantachaisilp, S., Smith, S.M., Ton-That, C., Osotchan, T., Moon, A.R. & Phillips, M.R. 2014, 'Tailoring deep level surface defects in ZnO nanorods for high sensitivity ammonia gas sensing', Journal of Physical Chemistry C, vol. 118, no. 46, pp. 27150-27156.
View/Download from: UTS OPUS or Publisher's site
&copy; 2014 American Chemical Society. The influence of deep level surface defects on electrical and gas sensing properties of ZnO nanorods NH3(g) sensors was studied. ZnO nanorods 50-60 nm in diameter were synthesized via low-temperature hydrothermal growth at 90&deg;C on sapphire substrates. The as-grown nanorods exhibited a cathodoluminescence (CL) peak centered at 1.90 eV (YL), attributed to LiZn deep acceptors or O interstitials. Subsequent annealing in O2 at 1 atm and Zn vapor at 650&deg;C produced broad CL peaks centered at 1.70 eV (RL) and 2.44 eV (GL), respectively. The RL and GL have been ascribed to acceptor-like VZn and donor-like VO related centers, respectively. Electrical and gas sensing measurements established that the NH3 gas response sensitivity was 22.6 for O2 anneal (RL), 1.4 for Zn vapor anneal (GL), and 4.1 for the as-grown (YL) samples. Additionally, treatment in H-plasma quenched the RL and inverted the NH3 electrical response due to the incorporation of H donors. Changes in the gas sensing response are explained by a shift in the position of the ZnO Fermi level relative to the chemical potential of NH3 gas due to the creation of near surface donor or acceptors. These data confirm that ZnO nanorods arrays can be tailored to detect specific gas species. (Chemical Equation Presented).
Chan, K.S., Ton-That, C., Vines, L., Choi, S., Phillips, M.R., Svensson, B.G., Jagadish, C. & Wong-Leung, J. 2014, 'Effects of high temperature annealing on defects and luminescence properties in H implanted ZnO', Journal of Physics D: Applied Physics, vol. 47, no. 34.
View/Download from: Publisher's site
The evolution of luminescence properties and voids formation with respect to annealing temperature in H implanted ZnO was investigated by depth-resolved cathodoluminescence spectroscopy (DRCLS), transmission electron microscopy and secondary ion mass spectrometry (SIMS). The annealing temperature is found to induce noticeable changes to the shape, size and empty volume density of the cavities. DRCLS results also reveal that the green emission is influenced by different annealing temperatures. In particular, the 600 &deg;C anneal produces a strong quenching of the green emission in the implanted region, while after the 800 &deg;C anneal a significant enhancement near the surface is observed. The annealing at 600 &deg;C also results in an uncommon violet emission at ?3.1 eV that is not observed after a higher annealing temperature. A clear correlation between the violet emission, vacancies and Li is revealed from comparison between the DRCLS intensities and SIMS data. &copy; 2014 IOP Publishing Ltd.
Davis, J., Short, K., Wuhrer, R., Phillips, M.R., Lumpkin, G.R. & Whittle, K.R. 2013, 'Electron backscatter diffraction characterization of plasma immersion ion implantation effects in stainless steel', Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, vol. 295, pp. 38-41.
View/Download from: UTS OPUS or Publisher's site
In these experiments plasma immersion ion implantation is utilised to simulate some of the radiation effects in a nuclear reactor environment. Scanning electron microscopy using the angular selective backscatter detector has revealed observable changes in crystallographic contrast after irradiation with helium ions. Further studies using electron backscatter diffraction in both plan and cross section view allow us to visualize the extent and depth of damage and observe differences in the behavior of different crystalline phases present in several grades of stainless steel. &copy; 2012 Elsevier B.V. All rights reserved.
Zhu, L., Ton-That, C. & Phillips, M.R. 2013, 'Nitrogen incorporation in ZnO nanowires using N2O dopant gas', Materials Letters, vol. 99, pp. 42-45.
View/Download from: UTS OPUS or Publisher's site
Aligned nitrogen-doped ZnO nanowires were grown by chemical vapour deposition using Au catalyst. N incorporation was achieved through the introduction of N2O gas as a dopant source and confirmed by Raman spectroscopy, which reveals additional N-related modes at 275, 580 and 642 cm-1. The nanowires have a hexagonal faceted shape and are predominantly grown along the [001] direction. The nanowire morphology is unaffected by N incorporation. The luminescence peak at 3.24 eV was monitored as a function of N2O content. Intensity analysis of this band reveals that it can be partly attributed to donor-acceptor pair (DAP) emission originating from the N doping. &copy; 2013 Elsevier B.V. All rights reserved.
Khachadorian, S., Papagelis, K., Ogata, K., Hofmann, S., Phillips, M.R. & Thomsen, C. 2013, 'Elastic properties of crystalline-amorphous core-shell silicon nanowires', Journal of Physical Chemistry C, vol. 117, no. 8, pp. 4219-4226.
View/Download from: UTS OPUS or Publisher's site
The pressure behavior of Raman frequencies and line widths of crystalline core-amorphous shell silicon nanowires (SiNWs) with two different core-to-shell ratio thicknesses was studied at pressures up to 8 GPa. The obtained isothermal compressibility (bulk modulus) of SiNWs with a core-to-shell ratio of about 1.8 is ?20% higher (lower) than reported values for bulk Si. For SiNWs with smaller core-to-shell ratios, a plastic deformation of the shell was observed together with a strain relaxation. A significant increase in the full width at half-maximum of the Raman LTO-peak due to phonon decay was used to determine the critical pressure at which LTO-phonons decay into LO + TA phonons. Our results reveal that this critical pressure in strained core-shell SiNWs (?4 GPa) is different from the reported value for bulk Si (?7 GPa), whereas no change is observed for relaxed core-shell SiNWs. &copy; 2013 American Chemical Society.
Martin, A.A., Phillips, M.R. & Toth, M. 2013, 'Dynamic surface site activation: A rate limiting process in electron beam induced etching', ACS Applied Materials and Interfaces, vol. 5, no. 16, pp. 8002-8007.
View/Download from: UTS OPUS or Publisher's site
We report a new mechanism that limits the rate of electron beam induced etching (EBIE). Typically, the etch rate is assumed to scale directly with the precursor adsorbate dissociation rate. Here, we show that this is a special case, and that the rate can instead be limited by the concentration of active sites at the surface. Novel etch kinetics are expected if surface sites are activated during EBIE, and observed experimentally using the electron sensitive material ultra nanocrystalline diamond (UNCD). In practice, etch kinetics are of interest because they affect resolution, throughput, proximity effects, and the topography of nanostructures and nanostructured devices fabricated by EBIE. &copy; 2013 American Chemical Society.
Wagner, M.R., Callsen, G., Reparaz, J.S., Kirste, R., Hoffmann, A., Rodina, A.V., Schleife, A., Bechstedt, F. & Phillips, M.R. 2013, 'Effects of strain on the valence band structure and exciton-polariton energies in ZnO', Physical Review B - Condensed Matter and Materials Physics, vol. 88, no. 23.
View/Download from: Publisher's site
The uniaxial stress dependence of the band structure and the exciton-polariton transitions in wurtzite ZnO is thoroughly studied using modern first-principles calculations based on the HSE+G0W0 approach, kp modeling using the deformation potential framework, and polarized photoluminescence measurements. The ordering of the valence bands [A(?7), B(?9), C(?7)] is found to be robust even for high uniaxial and biaxial strains. Theoretical results for the uniaxial pressure coefficients and splitting rates of the A, B, and C valence bands and their optical transitions are obtained including the effects of the spin-orbit interaction. The excitonic deformation potentials are derived and the stress rates for hydrostatic pressure are determined based on the results for uniaxial and biaxial stress. In addition, the theory for the stress dependence of the exchange interaction and longitudinal-transversal splitting of the exciton polaritons is developed using the basic exciton functions of the quasicubic approximation and taking the interaction between all exciton states into account. It is shown that the consideration of these effects is crucial for an accurate description of the stress dependence of the optical spectra in ZnO. The theoretical results are compared to polarized photoluminescence measurements of different ZnO substrates as function of uniaxial pressure and experimental values reported in the literature demonstrating an excellent agreement with the computed pressure coefficients. &copy; 2013 American Physical Society.
Choi, S., Ton-That, C., Phillips, M.R. & Aharonovich, I. 2013, 'Observation of whispering gallery modes from hexagonal ZnO microdisks using cathodoluminescence spectroscopy', Applied Physics Letters, vol. 103, no. 17.
View/Download from: Publisher's site
Zinc oxide hexagonal microdisks with diameters ranging from 3 ?m up to 15 ?m were fabricated by thermal chemical vapour deposition. Optical characterisation of ZnO microdisks was performed using low temperature (80 K) cathodoluminescence (CL) imaging and spectroscopy. The microdisks exhibited green luminescence locally distributed near the hexagonal boundary of the ZnO microdisks. High resolution CL spectra of the ZnO microdisks revealed whispering gallery modes (WGMs) emission. The experimentally observed WGMs were in excellent agreement with the predicted theoretical positions calculated using a plane wave model. This work could provide the means for ZnO microdisk devices operating in the green spectral range. &copy; 2013 AIP Publishing LLC.
Gogova, D., Petrov, P.P., Buegler, M., Wagner, M.R., Nenstiel, C., Callsen, G., Schmidbauer, M., Kucharski, R., Zajac, M., Dwilinski, R., Phillips, M.R., Hoffmann, A. & Fornari, R. 2013, 'Structural and optical investigation of non-polar (1-100) GaN grown by the ammonothermal method', JOURNAL OF APPLIED PHYSICS, vol. 113, no. 20.
View/Download from: UTS OPUS or Publisher's site
He, R., Tang, B., Ton-That, C., Phillips, M. & Tsuzuki, T. 2013, 'Physical structure and optical properties of Co-doped ZnO nanoparticles prepared by co-precipitation', Journal of Nanoparticle Research, vol. 15, no. 11.
View/Download from: Publisher's site
The structural and optical properties of cobalt-doped zinc oxide (Co-doped ZnO) nanoparticles have been investigated. The nanopowder with Co concentrations up to 5 at% was synthesized by a coprecipitation method. The physical structure and the chemical states of the Co-doped ZnO were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-Visible reflectance and cathodoluminescence (CL) spectroscopy. The results show that cobalt ions predominantly occupy Zn2+ sites in the wurtzite crystal lattice and possess a valence state of 2+. CL analysis revealed that the incorporation of Co2+ creates a new emission band at 1.85 eV, but quenched the near-band-edge luminescence. &copy; Springer Science+Business Media 2013.
Ton-That, C., Foley, M., Phillips, M.R., Tsuzuki, T. & Smith, Z. 2012, 'Correlation between the structural and optical properties of Mn-doped ZnO nanoparticles', Journal of Alloys and Compounds, vol. 522, pp. 114-117.
View/Download from: UTS OPUS or Publisher's site
The crystallographic and optical properties of Mn-doped ZnO nanoparticles prepared by a sol-gel process have been investigated by X-ray diffraction, UV-visible absorption spectroscopy and cathodoluminescence microanalysis. X-ray diffraction reveals that the nanoparticles have hexagonal wurtzite crystal structure, with the lattice constants along the a- and c-axes increasing with increasing Mn concentration from 0 to 2.4 at%. For all Mn concentrations in this range, the nanoparticles are essentially free of native point defects so that they exhibit only band-edge luminescence. The optical bandgap and band-edge emission energies for Mn-doped ZnO were found to increase in proportion to the lattice constants. The direct correlation between the bandgap and crystal structure suggests that the band-edge optical properties of Mn-doped ZnO is predominantly influenced by the amount of Mn atoms substituting Zn on the lattice sites. &copy; 2012 Elsevier B.V. All rights reserved.
Weston, L., Ton-That, C. & Phillips, M.R. 2012, 'Doping properties of hydrogen in ZnO', Journal of Materials Research, vol. 27, no. 17, pp. 2220-2224.
View/Download from: UTS OPUS or Publisher's site
The doping properties and stability of hydrogen in zinc oxide (ZnO) crystals have been investigated by cathodoluminescence (CL) spectroscopy. Hydrogen incorporation was achieved by hydrogen plasma at 200 &deg;C. The ZnO near-band-edge (NBE) peak is dramatically enhanced, while the green emission at 2.4 eV is quenched with increasing hydrogen incorporation. These effects are attributed to hydrogen passivating green luminescence centers, which are most likely negatively charged zinc vacancy defects. E-beam irradiation of H-doped ZnO crystals by an intense electron beam with ?W power reverses the hydrogen doping process. This effect is ascribed to the dissociation of H-related defects, formation of Chidden H2, and electromigration of H + under the influence of the local trapped charge-induced electric field. These results highlight the potential to modify the local luminescent properties of ZnO by e-beam irradiation. &copy; 2012 Materials Research Society.
Ton-That, C., Weston, L. & Phillips, M.R. 2012, 'Characteristics of point defects in the green luminescence from Zn- and O-rich ZnO', Physical Review B - Condensed Matter and Materials Physics, vol. 86, no. 11.
View/Download from: UTS OPUS or Publisher's site
Cathodoluminescence spectra have been measured to determine the characteristics of ubiquitous green luminescence (GL) in nonstoichiometric zinc oxide (ZnO). Zn- and O-rich ZnO were found to exhibit characteristic emissions at 2.53 eV [full width at half-maximum (FWHM) 340 meV] and 2.30 eV (FWHM 450 meV), respectively. Hydrogen was used to probe the physical nature of GL centers. The Zn-rich GL is enhanced upon H incorporation, whereas the O-rich GL is completely quenched as its underlying acceptor-like V Zn centers are passivated by H. The GL emission bands each exhibit remarkably different excitation-power dependencies. The Zn-rich GL follows a close to linear relationship with excitation power, while the O-rich GL exhibits a square-root dependence. Calculations based on bimolecular recombination equations show the defect concentration in Zn-rich ZnO is three orders of magnitude greater than that in O-rich ZnO, indicating V O is more readily formed than V Zn in thermochemical treatments of ZnO. &copy; 2012 American Physical Society.
Bishop, J., Toth, M., Phillips, M. & Lobo, C. 2012, 'Effects of oxygen on electron beam induced deposition of SiO2 using physisorbed and chemisorbed tetraethoxysilane', Applied Physics Letters, vol. 101, no. 21.
View/Download from: UTS OPUS or Publisher's site
Electron beam induced deposition (EBID) is limited by low throughput and purity of as-grown material. Co-injection of O2 with the growth precursor is known to increase both the purity and deposition rate of materials such as SiO2 at room temperature. Here, we show that O2 inhibits rather than enhances EBID from tetraethoxysilane (TEOS) precursor at elevated temperatures. This behavior is attributed to surface site competition between chemisorbates at elevated temperature, and TEOS decomposition by atomic oxygen produced through electron dissociation of physisorbed O2 at room temperature. &copy; 2012 American Institute of Physics.
Bishop, J., Lobo, C.J., Martin, A., Ford, M., Phillips, M. & Toth, M. 2012, 'Role of activated chemisorption in gas-mediated electron beam induced deposition', Physical Review Letters, vol. 109, no. 14.
View/Download from: UTS OPUS or Publisher's site
Models of adsorbate dissociation by energetic electrons are generalized to account for activated sticking and chemisorption, and used to simulate the rate kinetics of electron beam induced chemical vapor deposition (EBID). The model predicts a novel temperature dependence caused by thermal transitions from physisorbed to chemisorbed states that govern adsorbate coverage and EBID rates at elevated temperatures. We verify these results by experiments that also show how EBID can be used to deposit high purity materials and characterize the rates and energy barriers that govern adsorption. &copy; 2012 American Physical Society.
Lobo, C.J., Martin, A., Phillips, M.R. & Toth, M. 2012, 'Electron beam induced chemical dry etching and imaging in gaseous NH 3 environments', Nanotechnology, vol. 23, no. 37.
View/Download from: UTS OPUS or Publisher's site
We report the use of ammonia (NH 3) vapor as a new precursor for nanoscale electron beam induced etching (EBIE) of carbon, and an efficient imaging medium for environmental scanning electron microscopy (ESEM). Etching is demonstrated using amorphous carbonaceous nanowires grown by electron beam induced deposition (EBID). It is ascribed to carbon volatilization by hydrogen radicals generated by electron dissociation of NH 3 adsorbates. The volatilization process is also effective at preventing the buildup of residual hydrocarbon impurities that often compromise EBIE, EBID and electron imaging. We also show that ammonia is a more efficient electron imaging medium than H 2O, which up to now has been the most commonly used ESEM imaging gas. &copy; 2012 IOP Publishing Ltd.
Demers, H., Poirier-Demers, N., Phillips, M.R., De Jonge, N. & Drouin, D. 2012, 'Three-dimensional electron energy deposition modeling of cathodoluminescence emission near threading dislocations in gan and electron-beam lithography exposure parameters for a PMMA resist', Microscopy and Microanalysis, vol. 18, no. 6, pp. 1220-1228.
View/Download from: UTS OPUS or Publisher's site
The Monte Carlo software CASINO has been expanded with new modules for the simulation of complex beam scanning patterns, for the simulation of cathodoluminescence (CL), and for the calculation of electron energy deposition in subregions of a three-dimensional (3D) volume. Two examples are presented of the application of these new capabilities of CASINO. First, the CL emission near threading dislocations in gallium nitride (GaN) was modeled. The CL emission simulation of threading dislocations in GaN demonstrated that a better signal-to-noise ratio was obtained with lower incident electron energy than with higher energy. Second, the capability to simulate the distribution of the deposited energy in 3D was used to determine exposure parameters for polymethylmethacrylate resist using electron-beam lithography (EBL). The energy deposition dose in the resist was compared for two different multibeam EBL schemes by changing the incident electron energy. &copy; 2012 Microscopy Society of America.
Roczen, M., Schade, M., Malguth, E., Callsen, G., Barthel, T., Gref, O., Töfflinger, J.A., Schöpke, A., Schmidt, M., Leipner, H.S., Ruske, F., Phillips, M.R., Hoffmann, A., Korte, L. & Rech, B. 2012, 'Structural investigations of silicon nanostructures grown by self-organized island formation for photovoltaic applications', Applied Physics A: Materials Science and Processing, vol. 108, no. 3, pp. 719-726.
View/Download from: UTS OPUS or Publisher's site
The self-organized growth of crystalline silicon nanodots and their structural characteristics are investigated. For the nanodot synthesis, thin amorphous silicon (a-Si) layers with different thicknesses have been deposited onto the ultrathin (2 nm) oxidized (111) surface of Si wafers by electron beam evaporation under ultrahigh vacuum conditions. The solid phase crystallization of the initial layer is induced by a subsequent in situ annealing step at 700&deg;C, which leads to the dewetting of the initial a-Si layer. This process results in the self-organized formation of highly crystalline Si nanodot islands. Scanning electron microscopy confirms that size, shape, and planar distribution of the nanodots depend on the thickness of the initial a-Si layer. Cross-sectional investigations reveal a single-crystalline structure of the nanodots. This characteristic is observed as long as the thickness of the initial a-Si layer remains under a certain threshold triggering coalescence. The underlying ultra-thin oxide is not structurally affected by the dewetting process. Furthermore, a method for the fabrication of close-packed stacks of nanodots is presented, in which each nanodot is covered by a 2 nm thick SiO 2 shell. The chemical composition of these ensembles exhibits an abrupt Si/SiO 2 interface with a low amount of suboxides. A minority charge carrier lifetime of 18 ?s inside of the nanodots is determined. &copy; 2012 Springer-Verlag.
Friend, R.H., Phillips, M., Rao, A., Wilson, M.W.B., Li, Z. & McNeill, C.R. 2012, 'Excitons and charges at organic semiconductor heterojunctions', Faraday Discussions, vol. 155, pp. 339-348.
View/Download from: Publisher's site
All-organic heterojunction solar cells now provide very high quantum efficiencies for charge generation and rapidly-improving power conversion efficiencies. Charge generation and separation however, must overcome the strong Coulomb interactions between electrons and holes in these materials that is manifest also through the large exchange energies usually observed. We show for a polymer-polymer system with low charge generation efficiency that this arises through intersystem crossing from the photogenerated charge-transfer state to a lower lying triplet state, mediated by the proton hyperfine interaction, and that the activation barrier for full separation of electrons and holes is of the order of 250 meV. We observe, using transient optical spectroscopy, the processes of charge separation, recombination and sweep-out in efficient polymer-fullerene devices. We report also on the process of singlet exciton fission to form a pair of triplet excitons in pentacene that can later be dissociated against a heterojunction formed with C 60. &copy; 2012 The Royal Society of Chemistry.
Lin, Z.W., Li, Y.J., Zhu, J.G., Wang, X.L., Dou, S.X., Guo, Y.G., Lei, G., Wang, Y., Philips, M., Cortie, M., Li, Y.C., Choi, K.Y. & Shi, X. 2011, 'Visualization of vortex motion in FeAs-based BaFe1.9Ni 0.1As2 single crystal by means of magneto-optical imaging', Journal of Applied Physics, vol. 109, no. 7.
View/Download from: UTS OPUS or Publisher's site
Superconductivity has been found in newly discovered iron-based compounds. This paper studies the motion of magnetic vortices in BaFe1.9Ni 0.1As2 single crystal by means of the magneto-optical imaging technique. A series of magneto-optical images reflecting magnetic flux distribution at the crystal surface were taken when the crystal was zero-field cooled to 10 K. The behavior of the vortices, including penetration into and expulsion from the single crystal with increasing and decreasing external fields, respectively, is discussed. The motion behavior is similar to that observed in high-Tc superconducting cuprates with strong vortex pinning; however, the flux-front is irregular due to randomly distributed defects in the crystal. &copy; 2011 American Institute of Physics.
Callsen, G., Reparaz, J.S., Wagner, M.R., Kirste, R., Nenstiel, C., Hoffmann, A. & Phillips, M.R. 2011, 'Phonon deformation potentials in wurtzite GaN and ZnO determined by uniaxial pressure dependent Raman measurements', Applied Physics Letters, vol. 98, no. 6.
View/Download from: UTS OPUS or Publisher's site
We report the phonon deformation potentials of wurtzite GaN and ZnO for all zone center optical phonon modes determined by Raman measurements as a function of uniaxial pressure. Despite all the structural and optical similarities between these two material systems, the pressure dependency of their vibrational spectra exhibits fundamental distinctions, which is attributed to their different bond ionicities. In addition, the LO-TO splitting of the A1 and E1 phonon modes is analyzed which yields insight into the uniaxial pressure dependency of Born's transverse effective charge e T*. &copy; 2011 American Institute of Physics.
Wagner, M.R., Callsen, G., Reparaz, J.S., Schulze, J.H., Kirste, R., Cobet, M., Ostapenko, I.A., Rodt, S., Nenstiel, C., Kaiser, M., Hoffmann, A., Rodina, A.V., Phillips, M.R., Lautenschläger, S., Eisermann, S. & Meyer, B.K. 2011, 'Bound excitons in ZnO: Structural defect complexes versus shallow impurity centers', Physical Review B - Condensed Matter and Materials Physics, vol. 84, no. 3.
View/Download from: UTS OPUS or Publisher's site
ZnO single crystals, epilayers, and nanostructures often exhibit a variety of narrow emission lines in the spectral range between 3.33 and 3.35 eV which are commonly attributed to deeply bound excitons (Y lines). In this work, we present a comprehensive study of the properties of the deeply bound excitons with particular focus on the Y0 transition at 3.333 eV. The electronic and optical properties of these centers are compared to those of the shallow impurity related exciton binding centers (I lines). In contrast to the shallow donors in ZnO, the deeply bound exciton complexes exhibit a large discrepancy between the thermal activation energy and localization energy of the excitons and cannot be described by an effective mass approach. The different properties between the shallow and deeply bound excitons are also reflected by an exceptionally small coupling of the deep centers to the lattice phonons and a small splitting between their two electron satellite transitions. Based on a multitude of different experimental results including magnetophotoluminescence, magnetoabsorption, excitation spectroscopy (PLE), time resolved photoluminescence (TRPL), and uniaxial pressure measurements, a qualitative defect model is developed which explains all Y lines as radiative recombinations of excitons bound to extended structural defect complexes. These defect complexes introduce additional donor states in ZnO. Furthermore, the spatially localized character of the defect centers is visualized in contrast to the homogeneous distribution of shallow impurity centers by monochromatic cathodoluminescence imaging. A possible relation between the defect bound excitons and the green luminescence band in ZnO is discussed. The optical properties of the defect transitions are compared to similar luminescence lines related to defect and dislocation bound excitons in other II-VI and III-V semiconductors. &copy; 2011 American Physical Society.
Callsen, G., Reparaz, J.S., Wagner, M.R., Vierck, A., Phillips, M.R., Thomsen, C. & Hoffmann, A. 2011, 'Titanium-assisted growth of silica nanowires: From surface-matched to free-standing morphologies', Nanotechnology, vol. 22, no. 40.
View/Download from: UTS OPUS or Publisher's site
We report on an oxide-assisted growth technique for silica nanowires which allows tuning the growth from surface-matched nanowires to free-standing morphologies based on growth control by Ti in the role of a catalyst and surfactant. Using an adjustable Ti concentration, we grew silica nanowires with lengths ranging from 100nm up to several millimetres whose defect chemistry was analysed by electron microscopy tools, monochromatic cathodoluminescence imaging and time resolved photoluminescence spectroscopy. The knowledge of the luminescence properties and the related defect occurrence along with their spatial distribution is pivotal for advancing silica nanowire growth in order to realize successful device designs based on self-assembled Si/SiOx nanostructures. We demonstrate a core-shell structure of the grown nanowires with a highly luminescent 150nm thick shell and outstandingly fast decaying dynamics (?1ns) for glass-like materials. The conjunction of the observed efficient and stable luminescences with their attributed decaying behaviours suggests applications for silica nanowires such as active and passive optical interconnectors and white light phosphors. The identification of a time domain difference for the spectral regime from 2.3 to 3.3eV, within the confined spatial dimensions of a single nanowire, is very promising for future, e.g.data transmission applications, employing silica nanowires which exhibit achievable compatibility with commonly applied silicon-based electronics. A qualitative growth model based on silica particle diffusion and Ti-assisted seed formation is developed for the various types of segregated silica nanowires which extends commonly assumed oxide-assisted growth mechanisms. &copy; IOP Publishing Ltd.
Chen, P.P.T., Downes, J.E., Fernandes, A.J., Butcher, K.S.A., Wintrebert-Fouquet, M., Wuhrer, R. & Phillips, M.R. 2011, 'Effects of crystallinity and chemical variation on apparent band-gap shift in polycrystalline indium nitride', Thin Solid Films, vol. 519, no. 6, pp. 1831-1836.
View/Download from: UTS OPUS or Publisher's site
The nature of the apparent band-gap shift in polycrystalline indium nitride thin-films, grown by remote-plasma-enhanced chemical vapour deposition at 535 &plusmn; 10 &deg;C, has been investigated separately in relation to growth temperature dependent crystallinity and chemical variation. Substrates of sapphire and gallium nitride on sapphire were used to study the effect of a stress-reduced template on indium nitride crystallite quality and apparent band-gap. To mimic surface growth temperature variations two glass substrates of differing thickness and thermal conductivity were intentionally used for the same growth conditions. The samples were characterised using optical transmission, scanning electron microscope, X-ray diffraction, and high-resolution X-ray photoelectron spectroscopy. The results indicate that the apparent band-gap shift in polycrystalline narrow band-gap indium nitride thin-films is not primarily determined by the quality of indium nitride crystallites but rather it is associated with growth temperature dependent chemical variations in the films. &copy; 2010 Elsevier B.V. All rights reserved.
Lem, L.L.C., Ton-That, C. & Phillips, M.R. 2011, 'Distribution of visible luminescence centers in hydrogen-doped ZnO', Journal of Materials Research, vol. 26, no. 23, pp. 2912-2915.
View/Download from: UTS OPUS or Publisher's site
ZnO crystals have been investigated by scanning cathodoluminescence microscopy and spectroscopy at 80 K following hydrogen incorporation by plasma exposure. The intensity of the ZnO near-band-edge (NBE) emission is greatly enhanced while the defect-related green emission is quenched following plasma treatment. These effects are attributed to the passivation of zinc vacancies by hydrogen. The green and yellow intensities and their intensity ratios to the NBE vary with excitation depth for both undoped and H-doped ZnO crystals. The intensities of the green and yellow emissions exhibit sublinear dependencies on electron beam excitation density while the NBE intensity increases linearly with the excitation density. These saturation effects with increasing excitation density must be taken into account when assessing defects in ZnO by luminescence characterization. &copy; Copyright Materials Research Society 2011.
Sprouster, D.J., Ruffell, S., Bradby, J.E., Williams, J.S., Lockrey, M.N., Phillips, M.R., Major, R.C. & Warren, O.L. 2011, 'Structural characterization of B-doped diamond nanoindentation tips', Journal of Materials Research, vol. 26, no. 24, pp. 3051-3057.
View/Download from: UTS OPUS or Publisher's site
Copyright &copy; Materials Research Society 2011. We report on the electrical and structural properties of boron-doped diamond tips commonly used for in-situ electromechanical testing during nanoindentation. The boron dopant environment, as evidenced by cathodoluminescence (CL) microscopy, revealed significantly different boron states within each tip. Characteristic emission bands of both electrically activated and nonelectrically activated boron centers were identified in all boron-doped tips. Surface CL mapping also revealed vastly different surface properties, confirming a high amount of nonelectrically activated boron clusters at the tip surface. Raman microspectroscopy analysis showed that structural characteristics at the atomic scale for boron-doped tips also differ significantly when compared to an undoped diamond tip. Furthermore, the active boron concentration, as inferred via the Raman analysis, varied greatly from tip-to-tip. It was found that tips (or tip areas) with low overall boron concentration have a higher number of electrically inactive boron, and thus non-Ohmic contacts were made when these tips contacted metallic substrates. Conversely, tips that have higher boron concentrations and a higher number of electrically active boron centers display Ohmic-like contacts. Our results demonstrate the necessity to understand and fully characterize the boron environments, boron concentrations, and atomic structure of the tips prior to performing in situ electromechanical experiments, particularly if quantitative electrical data are required.
Lockrey, M.N. & Phillips, M.R. 2011, 'Characterisation of the optical properties of InGaN MQW structures using a combined SEM and CL spectral mapping system', Journal of Semiconductors, vol. 32, no. 1.
View/Download from: UTS OPUS or Publisher's site
We demonstrate the ability of a combined scanning electron microscope and cathodoluminescence (CL) spectral mapping system to provide important spatially resolved information. The degree of inhomogeneity in spectral output across a multi-quantum well sample is measured using the SEM-CL system as well as measuring the efficiency roll-off with increasing carrier concentration. The effects of low energy electron beam modification on the InGaN/GaN multi quantum wells have also been characterized.
Foley, M., Ton-That, C. & Phillips, M.R. 2010, 'Luminescent properties of ZnO structures grown with a vapour transport method', Thin Solid Films, vol. 518, no. 15, pp. 4231-4233.
View/Download from: UTS OPUS or Publisher's site
ZnO structures were synthesised on the sapphire (112?0) substrate by a vapour transport method in a gas flowing furnace. The influence of the oxygen content in the gas mixture on the morphology and luminescent properties of ZnO structures grown on a strip-like substrate was investigated, with all other growth parameters being kept nominally identical. Integrated electron microscopy and cathodoluminescence analysis shows gradual variations of structural and optical emission properties for ZnO structures grown on the long substrate. Defect-related green luminescence of ZnO is found to be highly dependent on the oxygen vapour in the growth region of the furnace. Our findings demonstrate that the green luminescence is associated with oxygen deficiency in ZnO. &copy; 2009 Elsevier B.V. All rights reserved.
White, R., Thomas, P., Phillips, M.R., Moran, K. & Wuhrer, R. 2010, 'X-ray mapping and scatter diagram analysis of the discoloring products resulting from the interaction of artist's pigments', Microscopy and Microanalysis, vol. 16, no. 5, pp. 594-598.
View/Download from: UTS OPUS or Publisher's site
The discoloring interaction between the artist's pigments cadmium yellow and the copper-containing malachite, an interaction that is conjectured to cause black spotting in oil paintings of the 19th and early 20th centuries, was examined using X-ray mapping and scatter diagram analysis. The application of these coupled techniques confirmed that copper sulfide phases were produced during discoloration reaction. Scatter diagram analysis indicated that two copper sulfide stoichiometries (CuS and Cu3S2) were present as reaction products where previously only crystalline CuS (covellite) had been identified by X-ray diffraction. The results demonstrate the potential of X-ray mapping coupled with scatter diagram analysis for the identification of both crystalline and X-ray amorphous phases produced by such complex heterogeneous interactions and their applicability to the investigation of interactions of artists' pigments. &copy; Microscopy Society of America 2010.
Coutts, M.J., Zareie, H.M., Cortie, M.B., Phillips, M.R., Wuhrer, R. & McDonagh, A.M. 2010, 'Exploiting zinc oxide re-emission to fabricate periodic arrays', ACS Applied Materials and Interfaces, vol. 2, no. 6, pp. 1774-1779.
View/Download from: UTS OPUS or Publisher's site
The synthesis of hexagonal ring-shaped structures of zinc oxide using nanosphere lithography and metal/metal oxide sputtering is demonstrated. This synthesis exploits the surface re-emission of zinc oxide to deposit material in regions lying out of the line-of-sight of the sputtering source. These rings can nucleate the hydrothermal growth of zinc oxide crystals. Control over the growth could be exercised by varying growth solution concentration or temperature or by applying an external potential. &copy; 2010 American Chemical Society.
Ton-That, C., Foley, M., Lem, L.L.C., McCredie, G., Phillips, M.R. & Cowie, B.C.C. 2010, 'Diffusion synthesis and electronic properties of Fe-doped ZnO', Materials Letters, vol. 64, no. 3, pp. 386-388.
View/Download from: UTS OPUS or Publisher's site
Fe-doped ZnO was successfully fabricated by thermal in-diffusion of Fe into ZnO crystals. X-ray absorption near edge structure (XANES), photoemission and cathodoluminescence (CL) spectroscopy have been combined to examine the Fe diffusion and its effects on the electronic and optical properties of the crystal. Depth-resolved CL demonstrates that Fe in-diffusion occurs to at least 4 ?m depth and results in intense green luminescence, whereas the undoped crystal exhibits only the ZnO near-band-edge emission. XANES and valence-band photoemission show that Fe is incorporated as Fe2+/3+ ions on substitutional Zn sites. The results suggest that the variation in the CL properties is due to a change in the oxygen vacancy charge state as a result of electron transfer from Fe. Crown Copyright &copy; 2009.
Pauc, N., Phillips, M.R., Aimez, V. & Drouin, D. 2010, 'Response to "comment on 'Carrier recombination near threading dislocations in GaN epilayers by low voltage cathodoluminescence'" [Appl. Phys. Lett. 97, 166101 (2010)]', Applied Physics Letters, vol. 97, no. 16.
View/Download from: Publisher's site
Phillips, M.R., Drouin, D., Moody, S.J. & Ton-That, C. 2009, 'Imaging fundamental electronic excitations at high spatial resolution using scanning cathodoluminescence microscopy', Microscopy and Microanalysis, vol. 15, no. SUPPL. 2, pp. 670-671.
View/Download from: UTS OPUS or Publisher's site
Godlewski, M., Wójcik-G?odowska, A., Guziewicz, E., Yatsunenko, S., Zakrzewski, A., Dumont, Y., Chikoidze, E. & Phillips, M.R. 2009, 'Optical properties of manganese doped wide band gap ZnS and ZnO', Optical Materials, vol. 31, no. 12, pp. 1768-1771.
View/Download from: UTS OPUS or Publisher's site
Optical properties of ZnMnO layers grown at low temperature by Atomic Layer Deposition and Metalorganic Vapor Phase Epitaxy are discussed and compared to results obtained for ZnMnS samples. Present results suggest a double valence of Mn ions in ZnO lattice. Strong absorption, with onset at about 2.1 eV, is tentatively related to Mn 2+ to 3+ photoionization. Mechanism of emission deactivation in ZnMnO is discussed and is explained by the processes following the assumed Mn 2+ to 3+ recharging. &copy; 2009 Elsevier B.V. All rights reserved.
Moody, S.J., Phillips, M.R. & Toth, M. 2009, 'Assessment of sem image quality using 1d power spectral density estimation', Microscopy and Microanalysis, vol. 15, no. SUPPL. 2, pp. 48-49.
View/Download from: Publisher's site
Bertinshaw, J., Kirkup, L., Phillips, M. & Placido, F. 2008, 'A system for supplying constant electrical power for postprocessing tin-doped indium oxide films', Review of Scientific Instruments, vol. 79, no. 7.
View/Download from: UTS OPUS or Publisher's site
Annealing tin doped indium oxide (ITO) thin films by self-heating shows potential for reducing the crystallization temperature required to optimize the optical and electrical properties of the films. It also shows promise as a cost effective method of studying the heat treatment process in situ. A computer based solution was developed to allow for a precise control over the annealing process. To anneal at a fixed temperature, a feedback loop senses changes in the resistance of the sample and adjusts the current across the load accordingly to ensure constant delivery of power to an ITO film. &copy; 2008 American Institute of Physics.
Malguth, E., Hoffmann, A. & Phillips, M.R. 2008, 'Fe in III-V and II-VI semiconductors', Physica Status Solidi (B) Basic Research, vol. 245, no. 3, pp. 455-480.
View/Download from: UTS OPUS or Publisher's site
Many theoretical and experimental studies deal with the realization of room-temperature ferromagnetism in dilute magnetic semiconductors (DMS). However, a detailed quantitative understanding of the electronic properties of transition metal doped semiconductors has often been neglected. This article points out which issues concerning electronic states and charge transfers need to be considered using Fe as an example. Methods to address these issues are outlined, and a wealth of data on the electronic properties of Fe doped III-V and II-VI compound semiconductors that have been obtained over a few decades is reviewed thoroughly. The review is complemented by new results on the effective-mass-like state consisting of a hole bound to Fe2+ forming a shallow acceptor state. The positions of established Fe3+/2+ and Fe2+/1+ charge transfer levels are summarized and predictions on the positions of further charge transfer levels are made based on the internal reference rule. The Fe3+/4+ level has not been identified unambiguously in any of the studied materials. Detailed term schemes of the observed charge states in tetrahedral and trigonal crystal field symmetry are presented including hyperfine structure, isotope effects and Jahn-Teller effect. Particularly, the radiative transitions Fe3+(4T 1 ? 1A1) and Fe2+(5E ? 5T2) are analyzed in great detail. An effective-mass-like state [Fe2+, h] consisting of a hole bound to Fe2+ is of great significance for a potential realization of spin-coupling in a DMS. New insights on this shallow acceptor state could be obtained by means of stress dependent and temperature dependent absorption experiments in the mK range. The binding energy and effective Bohr radius were determined for GaN, GaP, InP and GaAs and a weak exchange interaction between the hole and the Fe2+ center was detected. With regard to the Fe 3+ ground state, 6A1, in GaP and InP, the hyperfine structure level ?8 was found to be above the ?7 level. All results are discuss...
Ton-That, C., Phillips, M.R., Foley, M., Moody, S.J. & Stampfl, A.P.J. 2008, 'Surface electronic properties of ZnO nanoparticles', Applied Physics Letters, vol. 92, no. 26.
View/Download from: UTS OPUS or Publisher's site
The surface electronic structure of ZnO nanoparticles has been studied with photoemission and x-ray absorption spectroscopies. Contrary to expectation, ZnO:Zn phosphor nanoparticles were found to contain a lower oxygen vacancy density on the surface than undoped ZnO counterparts, but oxygen vacancies are in different chemical environments. Cathodoluminescence shows intense green luminescence from the ZnO:Zn surface, while the undoped nanoparticles exhibit only the near-band-edge emission. The results indicate the roles of surface oxygen vacancies and their environment in the previously unexplained green luminescence from the ZnO:Zn material. &copy; 2008 American Institute of Physics.
Foley, M., Ton-That, C. & Phillips, M.R. 2008, 'Cathodoluminescence inhomogeneity in ZnO nanorods', Applied Physics Letters, vol. 93, no. 24.
View/Download from: UTS OPUS or Publisher's site
Luminescence properties of vertically aligned, crystalline ZnO nanorods are studied by cathodoluminescence (CL) spectroscopy and microscopy. Results show that luminescence characteristics vary dramatically with location on the nanorod as well as CL excitation depth. CL inhomogeneity is observed between the nanorod tip and sidewalls, accompanied by a variation in the chemical environment of surface oxygen ions as probed by photoemission spectroscopy. Our findings demonstrate that CL can provide useful information on the local optical properties of nanostructured materials, which is simply beyond the capability of other methods. &copy; 2008 American Institute of Physics.
Morgan, S.W. & Phillips, M.R. 2008, 'High bandwidth secondary electron detection in variable pressure scanning electron microscopy using a Frisch grid', Journal of Physics D: Applied Physics, vol. 41, no. 5.
View/Download from: UTS OPUS or Publisher's site
The bandwidth and contrast of secondary electron (SE) images obtained using variable pressure scanning electron microscopy are enhanced when a grounded Frisch grid is placed between the SE detecting anode and the negatively biased stage. The improvement in SE image quality occurs as a consequence of the grounded Frisch grid electrostatically screening the 'slow' induced ion current signal, generated below the grid, from the induced current detected above the grid by the anode. Ion induced artefacts, such as image smearing at fast scan rates, are virtually eliminated using a Frisch grid. Gas amplification data are presented to illustrate that gas gain can be optimized by varying the Frisch grid-stage (amplification region) separation Frisch grid-anode (drift region) separation and stage bias. &copy; 2008 IOP Publishing Ltd.
Mokkapati, S., Wong-Leung, J., Tan, H.H., Jagadish, C., McBean, K.E. & Phillips, M.R. 2008, 'Tuning the bandgap of InAs quantum dots by selective-area MOCVD', Journal of Physics D: Applied Physics, vol. 41, no. 8.
View/Download from: UTS OPUS or Publisher's site
In-plane bandgap energy control of InAs quantum dots (QDs) grown on GaAs substrates is demonstrated using selective-area epitaxy. Transmission electron microscopy and cathodoluminescence are used for characterization of the selectively grown dots. A single-step growth of a thin InAs quantum well and InAs QDs emitting at 1010 and 1100 nm (at 77 K) on the same wafer is demonstrated. Non-uniform growth profile is reported for the selectively grown QDs in the mask openings. Surface migration of adatoms from higher order facets to (1 0 0) facets results in enhanced deposition rates closer to the edge of the openings and vapour phase diffusion of adatoms results in density variations across the openings over length scales greater than the surface migration length of the adatoms. &copy; 2008 IOP Publishing Ltd.
Zareie, H.M., Morgan, S.W., Moghaddam, M., Maaroof, A.I., Cortie, M.B. & Phillips, M.R. 2008, 'Nanocapacitive circuit elements', ACS Nano, vol. 2, no. 8, pp. 1615-1619.
View/Download from: UTS OPUS or Publisher's site
"Natural" lithography was used to prepare arrays of nanoscale capacitors on silicon. The capacitance was verified by a novel technique based on the interaction of a charged substrate with the electron beam of a scanning electron microscope. The "nanocapacitors" possessed a capacitance of ?1 10-16F and were observed to hold charge for over an hour. Our results indicate that fabricating nanostructures using natural lithography may provide a viable alternative for future nanoelectronic devices. &copy; 2008 American Chemical Society.
Wuhrer, R., Moran, K. & Phillips, M.R. 2008, 'Multi-detector x-ray mapping and generation of correction factor images for problem solving', Microscopy and Microanalysis, vol. 14, no. SUPPL. 2, pp. 1108-1109.
View/Download from: UTS OPUS or Publisher's site
Yang, J., Li, S., Li, Z.W., McBean, K. & Phillips, M.R. 2008, 'Origin of excitonic emission suppression in an individual ZnO nanobelt', Journal of Physical Chemistry C, vol. 112, no. 27, pp. 10095-10099.
View/Download from: UTS OPUS or Publisher's site
The near band edge emissions of an individual ZnO nanobelt were investigated by cathodoluminescence spectroscopy, which has unique advantages in higher spatial resolution, orientation, and environmental independence over the conventional photoluminescence spectroscopy. The results show that the presence of a large surface-to-volume ratio is the determinant to suppress the formation of excitons in ZnO nanobelts. Ab initio calculations show that a drastic decrease of density-of-state in the conduction band and increase in the valence band upon size reduction are the key consequence of the large surface-to-volume ratio, revealing the possible fundamental physical origin of exciton suppression. The weak exciton polarity also reduces the likelihood for an exciton to couple with longitudinal phonons. This causes a reduction in the first longitudinal phonon replica intensity and then a complete suppression of the second replica. Understanding the effect of large surface ratio upon the physical properties of ZnO nanomaterials may provide new insights into the fundamental science of nanotechnology for the development of optoelectronics. &copy; 2008 American Chemical Society.
Ton-That, C., Stockton, G., Phillips, M.R., Nguyen, T.P., Huang, C.H. & Cojocaru, A. 2008, 'Luminescence properties of poly- (phenylene vinylene) derivatives', Polymer International, vol. 57, no. 3, pp. 496-501.
View/Download from: UTS OPUS or Publisher's site
Background: Conjugated polymers, especially those of the poly(phenylene vinylene) (PPV) family, are promising candidates as emission material in light-emitting devices. The aim of this work was to investigate the dependence of the luminescence properties of PPV-based derivatives on their polymer structure, especially side groups. Results: Three PPV derivatives, BEHPPV, MEHPPV and MEHSPPV, were synthesised and characterised by photoluminescence (PL) and cathodoluminescence (CL) spectroscopies in the temperature range 10-300K. PL and CL spectra of the polymers exhibit similar luminescence peaks, which undergo a blue shift with increasing temperature. The shift in wavelength is accompanied by variations in the relative intensities of emission peaks. Both BEHPPV and MEHPPV display emission characteristics of the PPV backbone, but the peak of MEHPPV shifts to a longer wavelength in comparison with the corresponding peak of BEHPPV at the same temperature. The luminescence spectra of MEHSPPV, which has a sulfanyl incorporated in the side chain, are considerably different from those of the two other derivatives. Conclusions: The results demonstrate that the luminescence properties depend strongly on the chain conformations of the conjugated backbone, which are affected by polymer side chains. &copy; 2007 Society of Chemical Industry.
Ton-That, C., Foley, M. & Phillips, M.R. 2008, 'Luminescent properties of ZnO nanowires and as-grown ensembles', Nanotechnology, vol. 19, no. 41.
View/Download from: UTS OPUS or Publisher's site
Vertically aligned ZnO nanowires were synthesized on a sapphire (1120) substrate by vapour deposition and their light-emitting properties were characterized using photoluminescence and cathodoluminescence spectroscopies. Besides the nanowires, there exists a mosaic ZnO film on the substrate surface. Comparison of the luminescent properties of the as-grown ensemble and the nanowires extracted from it shows that the mosaic film is the major source of the defect-related green emission while the nanowires possess highly crystalline quality with virtually no defects. Photoemission spectroscopy shows that the valence band states associated with O 2p from the as-grown sample are diminished compared with those from the extracted nanowires. These findings suggest that the green emission partly arises from oxygen vacancies located on the surface of the mosaic film. &copy; IOP Publishing Ltd.
Ton-That, C., Phillips, M.R. & Nguyen, T.P. 2008, 'Blue shift in the luminescence spectra of MEH-PPV films containing ZnO nanoparticles', Journal of Luminescence, vol. 128, no. 12, pp. 2031-2034.
View/Download from: UTS OPUS or Publisher's site
Luminescence properties of nanocomposites consisting of ZnO nanoparticles in a conjugated polymer, poly [2-methoxy-5-(2?-ethyl hexyloxy)-phenylene vinylene] (MEH-PPV), were investigated. Photoluminescence measurements reveal a blue shift in the emission spectrum of MEH-PPV upon incorporation of ZnO nanoparticles into the polymer film while the emission is increasingly quenched with increasing ZnO concentration. In contrast, the structure of the polymer and its conjugation length are not affected by the presence of ZnO nanoparticles (up to 16 wt% ZnO) as revealed by Raman spectroscopy. The blue shift and photoluminescence quenching are explained by the separation of photogenerated electron-hole pairs at the MEH-PPV/ZnO interface and the charging of the nanoparticles. Crown Copyright &copy; 2008.
Malguth, E., Hoffmann, A. & Phillips, M.R. 2008, 'Structural and optical inhomogeneities of Fe doped GaN grown by hydride vapor phase epitaxy', Journal of Applied Physics, vol. 104, no. 12.
View/Download from: Publisher's site
We present the results of cathodoluminescence experiments on a set of Fe doped GaN samples with Fe concentrations of 5 1017, 1 1018, 1 1019, and 2 1020 cm -3. These specimens were grown by hydride vapor phase epitaxy with different concentrations of Fe. The introduction of Fe is found to promote the formation of structurally inhomogeneous regions of increased donor concentration. We detect a tendency of these regions to form hexagonal pits at the surface. The locally increased carrier concentration leads to enhanced emission from the band edge and the internal T4 1 (G) - A6 1 (S) transition of Fe3+. In these areas, the luminescence forms a finely structured highly symmetric pattern, which is attributed to defect migration along strain-field lines. Fe doping is found to quench the yellow defect luminescence band and to enhance the blue luminescence band due to the lowering of the Fermi level and the formation of point defects, respectively. &copy; 2008 American Institute of Physics.
Veal, T.D., Piper, L.F.J., Phillips, M.R., Zareie, M.H., Lu, H., Schaff, W.J. & McConville, C.F. 2007, 'Doping-dependence of subband energies in quantized electron accumulation at InN surfaces', Physica Status Solidi (A) Applications and Materials Science, vol. 204, no. 2, pp. 536-542.
View/Download from: UTS OPUS or Publisher's site
Electron tunnelling spectroscopy is used to investigate the quantized electron accumulation at the surfaces of wurtzite InN with different doping levels. The tunnelling spectra of InN-oxide-tip junctions recorded in air at room temperature exhibit a -0.6 V plateau, corresponding to the band gap of InN, and a gap between onsets of 1.3 V, consistent with the separation between the valence band maximum and the pinned Fermi level at the oxidized InN surface. Also observed within the tunnelling spectra are additional features between the conduction band minimum and the pinned Fermi level. These features are attributed to surface-bound quantized states associated with the. potential well formed by the downward band bending at the InN-oxide interface. Their energetic positions are dependent upon the doping level of the InN films and coincide with calculated subband energies. &copy; 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
Godlewski, M., Skrobot, M., Guziewicz, E. & Phillips, M.R. 2007, 'Color tuning of white light emission from thin films of ZnSe', Journal of Luminescence, vol. 125, no. 1-2, pp. 85-91.
View/Download from: UTS OPUS or Publisher's site
In this paper we discuss light emission from thin films of ZnSe obtained by atomic layer deposition (ALD). Due to the color mixing of band edge and two deep defect-related emissions of ZnSe, the ALD films emit white light. Tuning of color temperature is demonstrated in cathodoluminescence experiments. We report that chromaticity parameters can be varied by a change of accelerating voltage or excitation density. &copy; 2006 Elsevier B.V. All rights reserved.
Toth, M., Lobo, C.J., Knowles, W.R., Phillips, M.R., Postek, M.T. & Vladár, A.E. 2007, 'Nanostructure fabrication by ultra-high-resolution environmental scanning electron microscopy', Nano Letters, vol. 7, no. 2, pp. 525-530.
View/Download from: UTS OPUS or Publisher's site
Electron beam induced deposition (EBID) is a maskless nanofabrication technique capable of surpassing the resolution limits of resist-based lithography. However, EBID fabrication of functional nanostructures is limited by beam spread in bulk substrates, substrate charging, and delocalized film growth around deposits. Here, we overcome these problems by using environmental scanning electron microscopy (ESEM) to perform EBID and etching while eliminating charging artifacts at the nanoscale. Nanostructure morphology is tailored by slimming of deposits by ESEM imaging in the presence of a gaseous etch precursor and by pre-etching small features into a deposit (using a stationary or a scanned electron beam) prior to a final imaging process. The utility of this process is demonstrated by slimming of nanowires deposited by EBID, by the fabrication of gaps (between 4 and 7 nm wide) in the wires, and by the removal of thin films surrounding such nanowires. ESEM imaging provides a direct view of the slimming process, yielding process resolution that is limited by ESEM image resolution (~1 nm) and surface roughening occurring during etching. &copy; 2007 American Chemical Society.
Toth, M., Knowles, W.R. & Phillips, M.R. 2007, 'Imaging deep trap distributions by low vacuum scanning electron microscopy', Applied Physics Letters, vol. 90, no. 7.
View/Download from: UTS OPUS or Publisher's site
The distribution of deep traps in a bulk dielectric (Al2 O3) is imaged by low vacuum scanning electron microscopy (LVSEM). The image contrast corresponds to spatial variations in radiation-induced, field-enhanced conductivity. A methodology is presented for identification of such contrast, the behavior of which is explained by a model of charge generation and transport in dielectrics imaged by LVSEM. The technique presented is applicable to studies of charge traps in dielectrics, device failure modes, and contrast mechanisms in electron microscopy. &copy; 2007 American Institute of Physics.
Motlan, Zhu, G., Drozdowicz-Tomsia, K., McBean, K., Phillips, M.R. & Goldys, E.M. 2007, 'Annealing of ZnS nanocrystals grown by colloidal synthesis', Optical Materials, vol. 29, no. 12, pp. 1579-1583.
View/Download from: UTS OPUS or Publisher's site
ZnS nanocrystals (NCs) capped with tetramethylammonium (TMAH) were synthesized from ZnCl2 2H2O and thiourea using a wet chemical process. Further treatments of the nanocrystals such as aging, and annealing have been conducted to examine the stability of the grown samples. The X-ray diffraction spectra show that the crystal has a zinc blende structure with particle size of about 2 nm. The evidence of nanocrystalline character is also clear in the UV-Vis absorption that shows an excitonic peak at about 236 nm (5.2 eV) arising from band edge transitions. A photoluminescence emission peak centered at about 450 nm (2.7 eV) is attributed to transitions between shallow donors and Zn+ vacancies. Both absorption and photoluminescence spectra show that sample aging does not affect the characteristics of the sample, possibly due to protection by TMAH capping. Annealing at 700 &deg;C and 900 &deg;C results in the red shift of the photoluminescence. &copy; 2006.
White, R., Thomas, P.S., Philips, M.R., Wuhrer, R. & Guerbois, J.P. 2007, 'TG-MS characterization of the reaction products of cadmium yellow and malachite artist's pigments', Journal of Thermal Analysis and Calorimetry, vol. 88, no. 1, pp. 181-184.
View/Download from: UTS OPUS or Publisher's site
The deleterious interaction of some traditional sulphide artists pigments and copper ions results in the formation of black copper sulphides, in particular, covellite (CuS), and, hence, the discolouration of valuable artworks. In this paper the interaction of malachite, a source of copper(II) ions, with the pigment cadmium yellow, a sulphide pigment comprising of a solid solution of cadmium and zinc sulphides, is investigated by XRD and TG-MS. XRD showed the presence of the copper sulphide and cadmium carbonate phases, produced by a simple ion exchange mechanism. TG-MS showed the complexity of the range of metastable phases produced. The identification of these phases, however, requires further work. &copy; Springer-Verlag 2007.
Godlewski, M., Yatsunenko, S., Ivanov, V.Y., Drozdowicz-Tomsia, K., Goldys, E.M., Phillips, M.R., Klar, P.J. & Heimbrodt, W. 2007, 'Mechanisms of enhancement of light emission in nanostructures of II-VI compounds doped with manganese', Low Temperature Physics, vol. 33, no. 2, pp. 192-196.
View/Download from: UTS OPUS or Publisher's site
Intra-shell transitions of transition metal and rare earth ions are parity forbidden processes. For Mn2+ ions this is also a spin forbidden process, i.e., light emission should be inefficient. Surprisingly, it has been reported that in nanostructures of ZnMnS the T14 to A16 intra-shell transition of Mn2+ results in a bright photoluminescence characterized by a short PL decay time. The model of a quantum confined atom was introduced to explain the observed experimental results. It was later claimed that this model is incorrect. Based on the results of our photoluminescence, photoluminescence kinetics, time-resolved photoluminescence, electron spin resonance, and optically detected magnetic resonance investigations, we confirm photoluminescence enhancement and decrease of photoluminescence lifetime and relate these effects to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. This mechanism is active in both bulk and in low-dimensional structures, but is significantly enhanced in nanostructure samples. &copy; 2007 American Institute of Physics.
Godlewski, M., Bozek, R., Miasojedovas, S., Juršenas, S., Kazlauskas, K., &Zcaron;ukauskas, A., Phillips, M.R., Czernecki, R., Targowski, G., Perlin, P., Leszczy?ski, M., Böttcher, T., Figge, S. & Hommel, D. 2007, 'Micro-analysis of light emission properties of GaN-based laser diodes', Physica Status Solidi (C) Current Topics in Solid State Physics, vol. 4, no. 7, pp. 2818-2821.
View/Download from: Publisher's site
In-depth and in-plane changes of emission intensity from GaN-based laser diode structures were studied using cathodoluminescence, photoluminescence (PL), micro-PL and a Kelvin probe (potential fluctuations). We show that even at high excitation density potential fluctuations are not screened in active layers of laser diode structures. Potential fluctuations are enhanced in p-type doped layers. We also found that dislocations are formed there, which can penetrate to active region of LD devices. &copy; 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
Zhang, H.Z., Phillips, M.R., Fitz Gerald, J.D., Yu, J. & Chen, Y. 2006, 'Patterned growth and cathodoluminescence of conical boron nitride nanorods', Applied Physics Letters, vol. 88, no. 9.
View/Download from: UTS OPUS or Publisher's site
We demonstrate a simple and effective approach for growing large-scale, high-density, and well-patterned conical boron nitride nanorods. A catalyst layer of Fe (NO3) 3 was patterned on a silicon substrate by using a copper grid as a mask. The nanorods were grown via annealing milled boron carbide powders at 1300 &deg;C in a flow of nitrogen gas. The as-grown nanorods exhibit uniform morphology and the catalyst pattern precisely defines the position of nanorod deposition. Cathodoluminescence (CL) spectra of the nanorods show two broad emission bands centered at 3.75 and 1.85 eV. Panchromatic CL images reveal clear patterned structure. &copy; 2006 American Institute of Physics.
Chen, P.P.T., Butcher, K.S.A., Wintrebert-Fouquet, M., Wuhrer, R., Phillips, M.R., Prince, K.E., Timmers, H., Shrestha, S.K. & Usher, B.F. 2006, 'Apparent band-gap shift in InN films grown by remote-plasma-enhanced CVD', Journal of Crystal Growth, vol. 288, no. 2, pp. 241-246.
View/Download from: UTS OPUS or Publisher's site
The properties of indium nitride grown at various temperatures on c-plane sapphire and glass substrates, using remote plasma-enhanced chemical vapour deposition, have been investigated. The optical absorption spectra show a broad range of apparent band-gap values from approximately 2.3-0.9 eV, depending on the growth temperature. The influence of growth temperature on crystallinity, level of impurity incorporation, stoichiometry, and lattice distortion are analysed. The possible causes of the apparent band-gap shift in indium nitride are discussed. &copy; 2006 Elsevier B.V. All rights reserved.
Veal, T.D., Piper, L.F.J., Phillips, M.R., Zareie, M.H., Lu, H., Schaff, W.J. & McConville, C.F. 2006, 'Scanning tunnelling spectroscopy of quantized electron accumulation at in xGa 1-xN surfaces', Physica Status Solidi (A) Applications and Materials Science, vol. 203, no. 1, pp. 85-92.
View/Download from: UTS OPUS or Publisher's site
Electron tunnelling spectroscopy has been used to investigate quantized levels in electron accumulation layers at InGaN surfaces. The tunnelling spectra exhibit a plateau in the normalized conductance which widens with increasing Ga-content, corresponding to the band gap of InGaN. The measured In xGa 1-xN band gaps (between ?0.65 eV for x = 1 and 1.8 eV for x - 0.43) are consistent with the band gaps determined by previous optical absorption and cathodoluminescence spectroscopy. Additional structures in the spectra reflect the two-dimensional electronic subbands in the surface quantum well. The subband energies depend on Ga-content, bulk doping level and the resultant shape of the surface potential well. The tunnelling spectra are compared with calculations of the potential well, the charge-profile and the subband energies. &copy; 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Coleman, V.A., Buda, M., Tan, H.H., Jagadish, C., Phillips, M.R., Koike, K., Sasa, S., Inoue, M. & Yano, M. 2006, 'Observation of blue shifts in ZnO/ZnMgO multiple quantum well structures by ion-implantation induced intermixing', Semiconductor Science and Technology, vol. 21, no. 3, pp. L25-L28.
View/Download from: UTS OPUS or Publisher's site
Implantation with low-energy (80 keV) oxygen ions and subsequent rapid thermal annealing at 800 &deg;C are used to induce intermixing in a stack of 19 ZnO/Zn0.7Mg0.3O multiple quantum wells grown on sapphire by molecular beam epitaxy. Large blue shifts of more than 300 meV have been observed for doses up to 1 1016 cm-2, with no observation of saturation. This process is driven by the creation of defects by implantation which encourage the diffusion of Mg from the barrier layers into the ZnO quantum wells. Although defects are introduced during the implantation process, good recovery of the cathodoluminescence is seen following rapid thermal annealing. The Zn-Mg interdiffusion in this system has also been calculated for the corresponding ion doses, and the diffusion coefficient extracted. This study has significant implications for band gap engineering of ZnO/ZnMgO optoelectronic devices. &copy; 2006 IOP Publishing Ltd.
Zareie, H.M., McDonagh, A.M., Edgar, J., Ford, M.J., Cortie, M.B. & Phillips, M.R. 2006, 'Controlled assembly of 1,4-phenylenedimethanethiol molecular nanostructures', Chemistry of Materials, vol. 18, no. 9, pp. 2376-2380.
View/Download from: UTS OPUS or Publisher's site
We present here the first high-resolution scanning tunneling microscope images showing that 1,4-phenylenedimethanethiol forms mono- and multilayers on gold(111) substrates under particular solution-deposition conditions. The high-resolution images show that the deposition conditions strongly influence the type of surface structure formed. The molecular structures were also probed using molecular-etching techniques and through deposition and imaging of gold nanoparticles. The current-voltage (I-V) characteristics of the multilayer structures are significantly different from those of monolayers. For the first time, scanning electron microscopy experiments were used to investigate the homogeneity of larger surface areas of the surface structures. &copy; 2006 American Chemical Society.
Coleman, V.A., Bradby, J.E., Jagadish, C. & Phillips, M.R. 2006, 'Observation of enhanced defect emission and excitonic quenching from spherically indented ZnO', Applied Physics Letters, vol. 89, no. 8.
View/Download from: UTS OPUS or Publisher's site
The influence of spherical nanoindentation on the band edge and deep level emission of single crystal c-axis ZnO has been studied by cathodoluminescence (CL) spectroscopy and monochromatic imaging. Excitonic emission is quenched at the indent site and defect emission in the range of 450-720 nm is enhanced. Analysis of CL monochromatic images and spectra suggests that at least two different defect states are responsible for the broad defect emission band. Additionally, the indents result in a strong crystallographic dependence of the defect emission, producing a rosette feature with [112?0] [21?1?0], and [12?10] orientations that reflect the star-shaped luminescence quenching observed at the excitonic peak (390 nm). &copy; 2006 American Institute of Physics.
Phillips, M.R. 2006, 'Cathodoluminescence microscopy and spectroscopy of opto-electronic materials', Microchimica Acta, vol. 155, no. 1-2, pp. 51-58.
View/Download from: UTS OPUS or Publisher's site
Cathodoluminescence (CL) microscopy and spectroscopy are enabling techniques for the microcharacterisation of technologically important materials. Recent advances in SEM instrumentation have considerably expanded the microanalytical capabilities of the CL technique. In this paper, following a brief overview of the principles and practice of CL microscopy and spectroscopy, a number of examples are presented that demonstrate the utility of the technique for the microcharacterisation of advanced opto-electronic materials.
Pauc, N., Phillips, M.R., Aimez, V. & Drouin, D. 2006, 'Carrier diffusion processes near threading dislocations in GaN and GaN:Si characterized by low voltage cathodoluminescence', Superlattices and Microstructures, vol. 40, no. 4-6 SPEC. ISS., pp. 557-561.
View/Download from: UTS OPUS or Publisher's site
We present a low temperature study of GaN epilayers by means of low voltage cathodoluminescence (CL). We show that lowering the primary electrons accelerating voltage down to 1&nbsp;kV allows imaging of single threading dislocations. By using monochromatic or panchromatic low voltage CL microscopy, it is possible to extract different diffusion lengths related to free excitons, bound excitons or donor-to-acceptor pair transitions. &copy; 2006 Elsevier Ltd. All rights reserved.
Morgan, S.W. & Phillips, M.R. 2006, 'Transient analysis of gaseous electron-ion recombination in the environmental scanning electron microscope', Journal of Microscopy, vol. 221, no. 3, pp. 183-202.
View/Download from: UTS OPUS or Publisher's site
Most of the work carried out in relation to contrast mechanisms and signal formation in an environmental scanning electron microscope has yet to consider the time dependent aspects of image generation at a quantitative level. This paper quantitatively describes gaseous electron-ion recombination (also known as 'signal scavenging') in an environmental scanning electron microscope at a transient level by utilizing the dark shadows/streaks seen in gaseous secondary electron detector images of alumina (Al2O3) immediately after a region of enhanced secondary electron emission is encountered by a scanning electron beam. The investigation firstly derives a theoretical model of gaseous electron-ion recombination that takes into consideration transients caused by the time constant of the gaseous secondary electron detector electronics and external circuitry used to generate images. Experimental data of pixel intensity versus time of the streaks are then simulated using the model enabling the relative magnitudes of (i) ionization and recombination rates, (ii) recombination coefficients and (iii) electron drift velocities, as well as absolute values of the total time constant of the gaseous secondary electron detection system and external circuitry, to be determined as a function of microscope operating parameters such as gaseous secondary electron detector bias, sample-electrode separation, imaging gas pressure, and scan speed. The results revealed, for the first time, the exact dependence that the effects of secondary electron-ion recombination on signal formation has on reduced electric field and time in an environmental scanning electron microscope. Furthermore, the model implicitly demonstrated that signal loss as a consequence of field retardation due to ion space charges, although obviously present, is not the foremost phenomenon causing streaking in images, as previously thought. &copy; 2006 The Royal Microscopical Society.
Morgan, S.W. & Phillips, M.R. 2006, 'Gaseous scintillation detection and amplification in variable pressure scanning electron microscopy', Journal of Applied Physics, vol. 100, no. 7.
View/Download from: UTS OPUS or Publisher's site
This work investigates the generation and detection of gaseous scintillation signals produced in variable pressure scanning electron microscopy through electron-gas molecule excitation reactions. Here a gaseous scintillation detection (GSD) system is developed to efficiently detect photons produced via excitation reactions in electron cascades. Images acquired using GSD are compared to those obtained using conventional gaseous secondary electron detection (GSED) and demonstrate that images rich in secondary electron (SE) contrast can be achieved using the gaseous scintillation signal. A theoretical model, based on existing Townsend theories, is developed. It describes the production and amplification of photon signals generated by cascading SEs, high energy backscattered electrons, and primary beam electrons. Photon amplification (the total number of photons produced per sample emissive electron) is then investigated and compared to conventional electronic amplification over a wide range of microscope operating parameters, scintillating imaging gases, and photon collection geometries. These studies revealed that argon gas exhibited the largest GSD gain, followed by nitrogen then water vapor, exactly opposite to the trend observed for electron amplification data. It was also found that detected scintillation signals exhibit larger SE signal-to-background levels compared to those of conventional electronic signals detected via GSED. Finally, dragging the electron cascade towards the light pipe assemblage of GSD systems, or electrostatic focusing, dramatically increases the collection efficiency of photons. &copy; 2006 American Institute of Physics.
Godlewski, M., Phillips, M.R., Kazlauskas, K., Czernecki, R., Targowski, G., Perlin, P., Leszczy?ski, M., Figge, S. & Hommel, D. 2006, 'Profiling of light emission of GaN-based laser diodes with cathodoluminescence', Physica Status Solidi (A) Applications and Materials Science, vol. 203, no. 7, pp. 1811-1814.
View/Download from: UTS OPUS or Publisher's site
Cathodoluminescence is applied for evaluation of in-plane variations of light emission from GaN-based laser diode structures. We demonstrate that potential fluctuations affect significantly emission of laser diodes for e-beam currents above thresholds for a stimulated emission. &copy; 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
Malguth, E., Hoffmann, A., Gehlhoff, W., Gelhausen, O., Phillips, M.R. & Xu, X. 2006, 'Structural and electronic properties of Fe3+ and Fe2+ centers in GaN from optical and EPR experiments', Physical Review B - Condensed Matter and Materials Physics, vol. 74, no. 16.
View/Download from: UTS OPUS or Publisher's site
This work provides a consistent picture of the structural, optical, and electronic properties of Fe-doped GaN. A set of high-quality GaN crystals doped with Fe at concentrations ranging from 5 1017 cm-3 to 2 1020 cm-3 is systematically investigated by means of electron paramagnetic resonance and various optical techniques. Fe3+ is shown to be a stable charge state at concentrations from 1 1018 cm-3. The fine structure of its midgap states is successfully established, including an effective-mass-like state consisting of a hole bound to Fe2+ with a binding energy of 50&plusmn;10 meV. A major excitation mechanism of the Fe3+ (T14 ? A16) luminescence is identified to be the capture of free holes by Fe2+ centers. The holes are generated in a two-step process via the intrinsic defects involved in the yellow luminescence. The Fe3+/2+ charge-transfer level is found 2.863&plusmn;0.005 eV above the valence band, suggesting that the internal reference rule does not hold for the prediction of band offsets of heterojunctions between GaN and other III-V materials. The Fe2+ (E5 ? T25) transition is observed around 390 meV at any studied Fe concentration by means of Fourier transform infrared spectroscopy. Charge-transfer processes and the effective-mass-like state involving both Fe2+ states are observed. At Fe concentrations from 1 1019 cm-3, additional lines occur in electron paramagnetic resonance and photoluminescence spectra which are attributed to defect complexes involving Fe3+. With increasing Fe concentration, the Fermi level is shown to move from near the conduction band to the Fe3+/2+ charge-transfer level, where it stays pinned for concentrations from 1 1019 cm-3. Contrary to cubic II-VI and III-V materials, both electronic states are effected by only a weak Jahn-Teller interaction. &copy; 2006 The American Physical Society.
Phillips, M. & Drouin, D. 2006, 'Comparison of Low Voltage Cathodoluminescent Phosphors', Microscopy & Microanalysis, vol. 12, no. S2, pp. 1526-1527.
View/Download from: UTS OPUS
NA
Phillips, M., Drouin, D. & Goldys, E.M. 2006, 'Probing Carrier Behavior at the Nanoscale in Gallium Nitride using Low Voltage Cathodoluminescence', Microscopy & Microanalysis, vol. 12, no. S2, pp. 156-157.
View/Download from: UTS OPUS
NA
McBean, K.E., Phillips, M.R. & Goldys, E.M. 2006, 'Synthesis and characterization of doped and undoped ZnO nanostructures', Microscopy and Microanalysis, vol. 12, no. 4, pp. 327-330.
View/Download from: UTS OPUS or Publisher's site
Zinc oxide (ZnO) nanoparticles have been produced using precipitation methods from ethanolic solution. Rare-earth metal doping was performed, and the effect of lithium codoping on the luminescence properties of the rare-earth doped products was assessed. The resulting particles were characterized using cathodoluminescence and scanning electron microscopy. It was found that lithium significantly enhanced the cathodoluminescence signal from the rare-earth ions, which has been attributed to the increased integration of the rare-earth ions into the ZnO structure. The nanophase ZnO products were also annealed in argon, hydrogen, and oxygen, with hydrogen being the most successful for removing the broad defect emission present in as-grown samples and enhancing the ZnO near band edge emission. &copy; Microscopy Society of America 2006.
White, R., Phillips, M.R., Thomas, P. & Wuhrer, R. 2006, 'In-situ investigation of discolouration processes between historic oil paint pigments', Microchimica Acta, vol. 155, no. 1-2, pp. 319-322.
View/Download from: UTS OPUS or Publisher's site
Discolouring interactions between paint pigments have been observed since the mid 19th century. The source of some of these discolourations is the production of copper sulfides from an interaction between cadmium sulfide pigments and copper containing pigments. In this work, the discolouring interaction between cadmium yellow and malachite pigments was observed dynamically using the environmental scanning electron microscope (ESEM).
Pauc, N., Phillips, M.R., Aimez, V. & Drouin, D. 2006, 'Carrier recombination near threading dislocations in GaN epilayers by low voltage cathodoluminescence', Applied Physics Letters, vol. 89, no. 16.
View/Download from: Publisher's site
The authors present a low voltage cathodoluminescence (CL) study of as grown GaN and GaN:Si epilayers on sapphire. At 1 kV they resolve individual threading dislocations on the sample surface at low temperature (5 K), which appear as correlated dark spots. Analysis of CL intensity profiles across individual dislocation cores provides a direct measurement of the exciton and minority carrier diffusion lengths. Using this approach at 5 K, an exciton diffusion length of 62&plusmn;28 nm was found for GaN:Si (?3 1018 cm-3) compared with 81&plusmn;20 nm for a nominally undoped n -type GaN (?1 1016 cm-3). &copy; 2006 American Institute of Physics.
Skrobot, M., Godlewski, M., Guziewicz, E., Kopalko, K. & Phillips, M.R. 2006, 'Tuning of color chromaticity of light emission from ZnSe films grown on a GaAs substrate by atomic layer epitaxy', Acta Physica Polonica A, vol. 110, no. 3, pp. 359-367.
Monocrystalline films of sphalerite-type ZnSe were grown on GaAs(100) substrates from elemental Zn and Se precursors by atomic layer epitaxy in a gas flow system. Due to color mixing of band edge and deep defect-related emissions these layers emit intensive white light. Depth profiling cathodoluminescence indicates that green and red emissions mostly come from disordered regions of the films, close to the ZnSe/GaAs interface. We tested a possibility of tuning of chromaticity coordinates and of color temperature of the emission. We found that the chromaticity parameters (color perception) can be tuned by either regulating the appropriate accelerating voltage of electrons or current density of primary electrons in cathodoluminescence investigations. These properties of ZnSe films make them suitable for some practical applications as white light sources.
White, R.E., Thomas, P.S., Phillips, M.R. & Wuhrer, R. 2005, 'A DSC study of the effect of lead pigments on the drying of cold pressed linseed oil', Journal of Thermal Analysis and Calorimetry, vol. 80, no. 1, pp. 237-239.
View/Download from: UTS OPUS or Publisher's site
Cold pressed linseed oil and paints prepared using the inorganic pigments; lead white and red lead, were characterized using non-isothermal differential scanning calorimetry (DSC) in an air atmosphere to determine the effect of the pigment on the oxidative polymerisation of the drying oil medium. For each paint sample, the onset temperature for oxidation was reduced from 166&deg;C to the range 50 to 60&deg;C when a heating rate of 5 K min-1 was used. In order to determine the rate of drying, the non-isothermal experiments were carried out using a range of heating rates. A change in the mechanism oxidative polymerization was observed as the heating rate was increased. &copy; 2005 Akad&eacute;miai Kiad&oacute;, Budapest.
Scott, K., Butcher, A., Wintrebert-Fouquet, M., Chen, P.P.T., Wuhrer, R. & Phillips, M.R. 2005, 'Revisiting electrochromism in InN', Physica Status Solidi C: Conferences, vol. 2, no. 7, pp. 2293-2296.
View/Download from: UTS OPUS or Publisher's site
We confirm changes to the band-gap of InN thin films treated in an electrochemical cell in which water electrolysis is evident. Electrical properties of the films were also affected. It is suggested that the change in the film resistivity results from hydrogen incorporation or removal during the electrolysis (dependent on sample polarity). The presence of grain boundaries is believed to enhance the penetration of chemical species into the InN resulting in a greater net change in the observed properties. &copy; 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Scott, K., Butcher, A., Wintrebert-Fouquet, M., Chen, P.P.T., Prince, K.E., Timmers, H., Shrestha, S.K., Shubina, T.V., Ivanov, S.V., Wuhrer, R., Phillips, M.R. & Monemar, B. 2005, 'Non-stoichiometry and non-homogeneity in InN', Physica Status Solidi C: Conferences, vol. 2, no. 7, pp. 2263-2266.
View/Download from: UTS OPUS or Publisher's site
It is shown that the wide variation of apparent band-gap observed for thin films nominally referred to as InN is strongly influenced by variations in the nitrogen:indium stoichiometry. InN samples grown by remote plasma enhanced chemical vapour deposition show a change in band-gap between 1.8 and 1.0 eV that is not due to the Moss-Burstein effect, oxygen inclusion or quantum size effects, but for which changes in the growth temperature result in a strong change in stoichiometry. Material non-homogenity and non-stoichiometry appear to be general problems for InN growth. Excess nitrogen can be present at very high levels and indium rich material is also found. This work shows that the extent of the Moss-Burstein effect will have to be reassessed for InN. &copy; 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Godlewski, M., Ivanov, V.Y., ?usakowska, E., Bo?ek, R., Masojedovas, S., Juršénas, S., Kazlauskas, K., &Zcaron;ukauskas, A., Goldys, E.M., Phillips, M.R., Böttcher, T., Figge, S. & Hommel, D. 2005, 'Influence of n-type doping on light emission properties of GaN layers and GaN-based quantum well structures', Physica Status Solidi C: Conferences, vol. 2, no. 3, pp. 1056-1059.
View/Download from: UTS OPUS or Publisher's site
Effects of n-type doping of GaN epilayers and InGaN/GaN quantum well structures are studied. We evaluate the influence of n-type doping on a structural quality of the samples (using atomic force and scanning electron microscopy), on light emission intensity and on in-plane emission intensity variations. Possible mechanisms responsible for strong enhancement of light emission from doped samples are discussed. &copy; 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Tomaszewska-Grzeda, A., Lojkowski, W., Godlewski, M., Yatsunenko, S., Drozdowicz-Tomsia, K., Goldys, E.M. & Phillips, M.R. 2005, 'Growth and characterization of ZnO nanoparticles', ACTA PHYSICA POLONICA A, vol. 108, no. 5, pp. 897-902.
View/Download from: UTS OPUS
Godlewski, M., Phillips, M.R., Czernecki, R., Targowski, G., Perlin, P., Leszczynski, M. & Figge, S. 2005, 'Light emission properties of GaN-based laser diode structures', ACTA PHYSICA POLONICA A, vol. 108, no. 4, pp. 675-680.
View/Download from: UTS OPUS
Godlewski, M., Yatsunenko, S., Ivanov, V.Y.U., Khachapuridze, A., ?wia?tek, K., Goldys, E.M., Phillips, M.R., Klar, P.J. & Heimbrodt, W. 2005, 'Origin of ultrafast component of photoluminescence decay in nanostructures doped with transition metal or rare-earth ions', Acta Physica Polonica A, vol. 107, no. 1, pp. 65-74.
View/Download from: UTS OPUS
Bulk samples, layers, quantum well, and quantum dot structures of II-Mn-VI samples all show coexistence of slow and fast components of Mn2+ photoluminescence decay. Thus, fast photoluminescence decay cannot be related to low dimensionality of a host material. This also means that the model of the so-called quantum confined atom is incorrect. Based on the results of time-resolved photoluminescence and optically detected magnetic resonance investigations we relate the observed lifetime decrease in Mn2+ intra-shell transition to spin dependent magnetic interactions between localized spins of Mn2+ ions and between Mn2+ ions and spins/magnetic moments of free carriers. The latter mechanism is enhanced in nanostructures.
Wojcik, A., Kopalko, K., Godlewski, M., Lusakowska, E., Guziewicz, E., Minikayev, R., Paszkowicz, W., Swiatek, K., Klepka, M., Jakiela, R., Kiecana, M., Sawicki, M., Dybko, K. & Phillips, M.R. 2005, 'Thin films of ZnO and ZnMnO by atomic layer epitaxy', OPTICA APPLICATA, vol. 35, no. 3, pp. 413-417.
View/Download from: UTS OPUS
Mokkapati, S., Lever, P., Tan, H.H., Jagadish, C., McBean, K.E. & Phillips, M.R. 2005, 'Controlling the properties of InGaAs quantum dots by selective-area epitaxy', Applied Physics Letters, vol. 86, no. 11, pp. 1-3.
View/Download from: UTS OPUS or Publisher's site
Selective growth of InGaAs quantum dots on GaAs is reported. It is demonstrated that selective-area epitaxy can be used for in-plane bandgap energy control of quantum dots. Atomic force microscopy and cathodoluminescence are used for characterization of the selectively grown dots. Our results show that the composition, size, and uniformity of dots are determined by the dimensions of the mask used for patterning the substrate. Properties of dots can be selectively tuned by varying the mask dimensions. A single-step growth of a thin InGaAs quantum well and InGaAs quantum dots on the same wafer is demonstrated. By using a single-step growth, dots luminescing at different wavelengths, in the range 1150-1230 nm, in different parts of the same wafer are achieved. &copy; 2005 American Institute of Physics.
Drozdowicz-Tomsia, K., Goldys, E.M., Motlan, M., Zareie, H. & Phillips, M.R. 2005, 'Growth-temperature-dependent cathodoluminescence properties of GaSb/GaAs quantum-dot multilayer structures', Applied Physics Letters, vol. 86, no. 17, pp. 1-3.
View/Download from: UTS OPUS or Publisher's site
Multilayer GaSb/GaAs quantum-dot (QD) structures grown by atmospheric-pressure metalorganic chemical vapor deposition on semi-insulating GaAs (100) substrates with varying growth temperature of the confinement layers are studied by the cathodoluminescence (CL). Two main features assigned to wetting layer and QDs are observed in the CL spectra. Their relative positions strongly depend on the growth conditions of the confinement layers. The highest separation of 270 meV is achieved for GaAs confinement layers grown at 540 &deg;C. &copy; 2005 American Institute of Physics.
Godlewski, M., Yatsunenko, S., Drozdowicz-Tomsia, K., Goldys, E.M., Phillips, M.R., Klar, P.J. & Heimbrodt, W. 2005, 'Dynamics of light emission in CdMnS nanoparticles', ACTA PHYSICA POLONICA A, vol. 108, no. 4, pp. 681-688.
View/Download from: UTS OPUS
Godlewski, M., ?usakowska, E., Bozek, R., Goldys, E.M., Phillips, M.R., Böttcher, T., Figge, S. & Hommel, D. 2004, 'Cathodoluminescence and atomic force microscopy study of n-type doped GaN epilayers', Physica Status Solidi (A) Applied Research, vol. 201, no. 2, pp. 212-215.
View/Download from: UTS OPUS
We evaluate influence of n-type doping and of the doping level on structural and optical quality of GaN epilayers. We confirm reported previously strong enhancement of light emission from Si doped samples and discuss possible mechanisms of this enhancement. Kelvin probe measurements indicate smoothing of potential fluctuations in the doped layers. &copy; 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Godlewski, M., Goldys, E.M., Phillips, M.R., Böttcher, T., Figge, S., Hommel, D., Czernecki, R., Prystawko, P., Leszczynski, M., Perlin, P., Grzegory, I. & Porowski, S. 2004, 'In-depth and in-plane profiling of light emission properties of InGaN-based laser diode', Physica Status Solidi (A) Applied Research, vol. 201, no. 2, pp. 207-211.
View/Download from: UTS OPUS
We employ cathodoluminescence (CL) technique for evaluation of in-depth and in-plane instabilities of light emission in laser diode structure. We study light emission properties from laser structure and their relation to microstructure details. Large in-plane instabilities of light emission are also present for excitation densities, larger than the threshold densities for the stimulated emission, i.e., potential fluctuations are not fully screened in the active region of the laser even at large excitation densities. &copy; 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Guziewicz, E., Godlewski, M., Kopalko, K., ?usakowska, E., Dynowska, E., Guziewicz, M., Godlewski, M.M. & Phillips, M. 2004, 'Atomic layer deposition of thin films of ZnSe - Structural and optical characterization', Thin Solid Films, vol. 446, no. 2, pp. 172-177.
View/Download from: UTS OPUS or Publisher's site
Thin films of sphalerite-type ZnSe were grown by atomic layer deposition (ALD) from elemental Zn and Se precursors. These films, grown on various substrates, show bright blue 'edge' emission accompanied by donor-acceptor pair emissions in the blue, green and red spectral regions. Red, green and blue emissions mixed together give a white color, with a color temperature between 2400 and 4500 K depending on a layer thickness and temperature. ZnSe grown by ALD is in consequence a promising material for the fabrication of semiconductor-based white light emitting thin film electroluminescence displays. &copy; 2003 Elsevier B.V. All rights reserved.
Gelhausen, O., Phillips, M.R., Goldys, E.M., Paskova, T., Monemar, B., Strassburg, M. & Hoffmann, A. 2004, 'Dissociation of H-related defect complexes in Mg-doped GaN', PHYSICAL REVIEW B, vol. 69, no. 12.
View/Download from: UTS OPUS or Publisher's site
Gelhausen, O., Malguth, E., Phillips, M.R., Goldys, E.M., Strassburg, M., Hoffmann, A., Graf, T., Gjukic, M. & Stutzmann, M. 2004, 'Doping-level-dependent optical properties of GaN:Mn', Applied Physics Letters, vol. 84, no. 22, pp. 4514-4516.
View/Download from: UTS OPUS or Publisher's site
Cathodoluminescence (CL) and optical transmission spectroscopy were used to study the optical properties of molecular-beam-epitaxy (MBE) grown GaN with different doping levels. The 1-?m-thick samples were grown by plasma-induced MBE on c-plane Al 2O 3 substrate. The absorption measurements were performed at 2 K with a 250 W tungsten-halogen lamp. The CL measurements showed that Mn-doping concentrations around 10 20 cm -3 reduced the near band edge emission intensity by around one order of magnitude.
Phillips, M.R., Zareie, M.H., Gelhausen, O., Drago, M., Schmidtling, T. & Richter, W. 2004, 'Scanning tunneling and cathodoluminescence spectroscopy of indium nitride', Journal of Crystal Growth, vol. 269, no. 1, pp. 106-110.
View/Download from: UTS OPUS or Publisher's site
Indium nitride epilayers grown by metalorganic vapor-phase epitaxy have been studied by cathodoluminescence (CL) spectroscopy, scanning tunneling microscopy and scanning tunneling spectroscopy (STS). A broad CL emission peak centered at 0.8eV was observed at 80K. This peak was attributed to an excitonic radiative recombination mechanism as its emission intensity exhibited a super-linear dependence on beam current with a power-law exponent of m=2. A large spatial variation in the CL emission intensity was ascribed to the presence of threading dislocations, which act as non-radiative recombination centers. A surface band gap of ?1.4eV was estimated from STS I-V curves. &copy; 2004 Elsevier B.V. All rights reserved.
Godlewski, M., ?usakowska, E., Goldys, E.M., Phillips, M.R., Böttcher, T., Figge, S., Hommel, D., Prystawko, P., Leszczynski, M., Grzegory, I. & Porowski, S. 2004, 'Diffusion length of carriers and excitons in GaN - Influence of epilayer microstructure', Applied Surface Science, vol. 223, no. 4, pp. 294-302.
View/Download from: UTS OPUS or Publisher's site
We demonstrate a correlation between the microstructure of epilayers and the diffusion length of free carriers and excitons in heteroepitaxial and homoepitaxial GaN films. We show that the diffusion length is shorter than predicted for a given density of dislocations. With improving structural quality of the films and lower dislocation density the diffusion lengths of free carriers and excitons increase, which, in turn, increases the rate of nonradiative recombination at dislocations. This process may explain a surprisingly small change of light emission efficiency observed for GaN epilayers with varying densities of dislocations. &copy; 2003 Elsevier B.V. All rights reserved.
Godlewski, M., Yatsunenko, S., Khachapuridze, A., Ivanov, V.Y., Go?acki, Z., Karczewski, G., Bergman, P.J., Klar, P.J., Heimbrodt, W. & Phillips, M.R. 2004, 'Mechanism of intra-shell recombination of transition metal and rare earth ions in nanostructures of II-VI compounds', Journal of Alloys and Compounds, vol. 380, no. 1-2 SPEC. ISS., pp. 45-49.
View/Download from: UTS OPUS or Publisher's site
Based on the results of optically detected magnetic resonance (ODMR) and time-resolved investigations we relate the observed lifetime shortening of intra-shell Mn2+ emission to spin dependent magnetic interactions between localized spins of Mn2+ ions and spins/magnetic moments of free carriers. We show that this mechanism is active both in bulk and in low dimensional structures, such as quantum wells (QWs), quantum dots (QDs) and nanostructures. &copy; 2004 Elsevier B.V. All rights reserved.
Godlewski, M., Szmidt, J., Olszyna, A., Werbowy, A., ?usakowska, E., Phillips, M.R., Goldys, E.M. & Sokolowska, A. 2004, 'Luminescent properties of wide bandgap materials at room temperature', Physica Status Solidi C: Conferences, vol. 1, no. 2, pp. 213-218.
View/Download from: UTS OPUS or Publisher's site
Properties of nanocrystalline thin films of selected nitrides are discussed as possible buffer materials for obtaining freestanding GaN wafers. These films are grown by impulse plasma deposition on silicon substrates. We demonstrate high smoothness of these films. &copy; 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Kopalko, K., Godlewski, M., Lusakowska, E., Paszkowicz, W., Domagala, J.Z., Szczerbakow, A., Ivanov, V.Y., Godlewski, M.M. & Phillips, M.R. 2004, 'Monocrystalline ZnO films grown by atomic layer epitaxy - growth and characterization', 11TH INTERNATIONAL CONFERENCE ON II-VI COMPOUNDS (II-VI 2003), PROCEEDINGS, pp. 892-895.
View/Download from: UTS OPUS
Kopalko, K., Godlewski, M., Guziewicz, E., ?usakowska, E., Paszkowicz, W., Domaga?a, J., Dynowska, E., Szczerbakow, A., Wójcik, A. & Phillips, M.R. 2004, 'Monocrystalline thin films of ZnSe and ZnO grown by atomic layer epitaxy', Vacuum, vol. 74, no. 2, pp. 269-272.
View/Download from: UTS OPUS or Publisher's site
We report on the growth of monocrystalline thin films of ZnSe and ZnO by atomic layer epitaxy by simple reaction between elemental precursors. Structural and optical properties of these films are discussed with reference to the investigations performed with atomic force microscopy, scanning electron microscopy, cathodoluminescence and photoluminescence. &copy; 2004 Elsevier Ltd. All rights reserved.
Strassburg, M., Rodina, A., Dworzak, M., Haboeck, U., Krestnikov, I.L., Hoffmann, A., Gelhausen, O., Phillips, M.R., Alves, H.R., Zeuner, A., Hofmann, D.M. & Meyer, B.K. 2004, 'Identification of bound exciton complexes in ZnO', Physica Status Solidi (B) Basic Research, vol. 241, no. 3, pp. 607-611.
View/Download from: UTS OPUS or Publisher's site
An identification of shallow bound exciton centers in ZnO is presented based on magneto-optical measurements and diffusion experiments. The thermalization behavior of the Zeeman split components confirms that the I 4, I6, I8 and I9 exciton lines stem from donor bound exciton complexes. The results are supported by theoretical analysis of shallow bound exciton complexes revealing the ?7 symmetry of the upper valence band. The presence of two-electron satellites related to the respective transitions is further evidence for the donor bound complexes and enabled the determination of donor binding energies. Hydrogen, aluminum, gallium and indium were identified to origin the I4, I 6, I8 and I9 lines by doping, diffusion and annealing experiments combined with photoluminescence and secondary ion mass spectrometry. &copy; 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Phillips, M.R., Gelhausen, O. & Goldys, E.M. 2004, 'Cathodoluminescence properties of zinc oxide nanoparticiles', Physica Status Solidi (A) Applied Research, vol. 201, no. 2, pp. 229-234.
View/Download from: UTS OPUS
Zinc oxide nano-particles (25 nm) have been investigated by cathodoluminescence spectroscopy (300 nm-1700 nm) at 80 K and 300 K following thermal annealing in high purity H2/N2, N2, O2 and Ar gaseous atmospheres. The intensity of the ZnO near band edge peak was significantly increased after heat treatment in hydrogen. Conversely, thermal annealing in the other gas types decreased this emission. This effect is attributed to hydrogen passivation of competitive non-radiative defect centers, most likely bulk zinc vacancy centers. The appearance of a strong green emission centered at 2.4 eV following thermal annealing in all gas atmospheres is ascribed to the formation of bulk oxygen vacancy defects. A strong red shift of the near band edge emission with increasing beam current at 300 K is accredited to electron beam heating rather than to an increase in the carrier density. Electron beam heating is evidenced by the occurrence of a strong black body emission in the near infrared spectral region. &copy; 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Gelhausen, O., Phillips, M.R., Goldys, E.M., Paskova, T., Monemar, B., Strassburg, M. & Hoffmann, A. 2004, 'Dissociation of H-related defect complexes in Mg-doped GaN', Physical Review B - Condensed Matter and Materials Physics, vol. 69, no. 12, pp. 1252101-1252109.
Post-growth annealing and electron beam irradiation during cathodoluminescence were used to determine the chemical origin of the main optical emission lines in moderately and heavily Mg-doped GaN. The 3.27 eV donor-acceptor pair (DAP) emission line that dominates the emission spectrum in moderately Mg-doped (p-type) GaN was found to be strongly reduced by electron irradiation and of different chemical origin than the DAP at a similar energetic position in Si-doped (n-type) GaN. These results suggest that the acceptor responsible for the 3.27 eV DAP emission in Mg-doped GaN is Mg and that the donor (20-30 meV) is hydrogen-related, possibly a (VN-H) complex. This complex is dissociated either by electron irradiation or thermal annealing in N2 or O2 atmosphere. We found that upon electron irradiation, a deeper emission line (centered at 3.14 eV) emerged, which was assigned to a DAP consisting of the same Mg acceptor level and a deeper donor (100-200 meV) with a similar capture cross section as the donor in the 3.27 eV emission. Moreover, two different deep donor levels at 350&plusmn;30 and 440&plusmn;40 meV were identified as being responsible for the blue band (2.8-3.0 eV) in heavily Mg-doped GaN. The donor level at 350&plusmn;30 meV was strongly affected by electron irradiation and attributed to a H-related defect.
Gelhausen, O., Klein, H.N., Phillips, M.R. & Goldys, E.M. 2003, 'Low-energy electron-beam irradiation and yellow luminescence in activated Mg-doped GaN', Applied Physics Letters, vol. 83, no. 16, pp. 3293-3295.
View/Download from: UTS OPUS or Publisher's site
A study was performed on the effect of low-energy electron-beam irradiation (LEEBI) in activated Mg-doped GaN. The residual impurities and native defects in metalorganic-vapor-phase-epitaxy-grown, GaN were also studied. Excitation power density-resolved and temperature-resolved cathodoluminescence spectroscopy was used for the study. It was found that the LEEBI-treatment dissociated neutral Mg-H complexes and other hydrogenated defect complexes and gave rise to additional radiative recombination channels.
Dredge, P., Wuhrer, R. & Phillips, M.R. 2003, 'Monet's painting under the microscope', Microscopy and Microanalysis, vol. 9, no. 2, pp. 139-143.
View/Download from: UTS OPUS or Publisher's site
An oil painting by Claude Monet, Port-Goulphar, Belle-Ile 1887 (collection of the Art Gallery of New South Wales), was examined to determine both the identity of the pigments used by the artist in this painting and his technique of mixing colors and laying paint on the canvas. The extremely complex construction of the painting was revealed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and X-ray mapping (XRM) analysis of cross sections of paint flakes excised from damaged regions of Port-Goulphar, Belle-Ile. Nine different pigments were found on the painting. Many of the identified colors were modern pigments that became available only late in the 19th century as a result of scientific advances in pigment chemistry. Although similar colors were available in a natural mineral form, they lacked the vivid color of their manufactured counterparts. The use of these new synthetic metallic oxide colors by Monet accounts for the brilliance of his paintings. In addition, a separation between successive paint layers was observed in some areas of paint chip cross sections, indicating that oil-based paint was applied to paint that had dried, and consequently, Port-Goulphar, Belle-Ile was painted over a long period of time. This observation is contrary to the general perception of Monet's technique of painting freely and quickly.
Godlewski, M., Guziewicz, E., Kopalko, K., ?usakowska, E., Dynowska, E., Godlewski, M.M., Goldys, E.M. & Phillips, M.R. 2003, 'Origin of white color light emission in ALE-grown ZnSe', Journal of Luminescence, vol. 102-103, no. SPEC, pp. 455-459.
View/Download from: UTS OPUS or Publisher's site
We discuss light emission properties from thin films of ZnSe grown by atomic layer epitaxy on GaAs (100). White color emission is observed in photoluminescence and cathodoluminescence, due to the observation of three RGB emission bands. We demonstrate possibility of color tuning by either variation of film thickness or, in cathodoluminescence experiments, variation of an accelerating voltage. &copy; 2002 Elsevier Science B.V. All rights reserved.
Godlewski, M., Ivanov, V.Y., Goldys, E.M., Phillips, M., Böttcher, T., Figge, S., Hommel, D., Czernecki, R., Prystawko, P., Leszczynski, M., Perlin, P., Grzegory, I. & Porowski, S. 2003, 'Cathodoluminescence profiling of InGaN-based quantum well structures and laser diodes - In-plane instabilities of light emission', Acta Physica Polonica A, vol. 103, no. 6, pp. 689-694.
View/Download from: UTS OPUS
Instabilities of light emission and also of stimulated emission in series of GaN epilayers and InGaN quantum well structures, including laser diode structures, are studied. A stimulated emission is observed under electron beam pumping. This enabled us to study light emission properties from laser structures and their relation to microstructure details. We demonstrate large in-plane fluctuations of light emission and that these fluctuations are also present for excitation densities larger than the threshold densities for the stimulated emission.
Gelhausen, O., Phillips, M.R. & Goldys, E.M. 2003, 'A method to improve the light emission efficiency of Mg-doped GaN', Journal of Physics D: Applied Physics, vol. 36, no. 23, pp. 2976-2979.
View/Download from: UTS OPUS or Publisher's site
Scanning cathodoluminescence (CL) spectroscopy and imaging were used to study the effect of post-growth processing on the CL efficiency of metal-organic vapour phase epitaxy-grown Mg-doped GaN. In this work, two treatments, thermal annealing in high-purity gaseous atmospheres (N2, O2 and H2(5%)/N2) and low-energy electron beam irradiation (LEEBI), have been investigated. Post-growth annealing in a H2/N2 atmosphere followed by LEEBI leads to a significant enhancement of the free electron-to-bound Mg-acceptor (e, Mg) CL emission and a reduction of nonradiative centres involving native defects. The presented results demonstrate that the combination of post-growth annealing in a H2/N2 atmosphere and LEEBI dissociation of Mg-H complex acceptors significantly improves the light emitting efficiency of Mg-doped p-type GaN. Conversely, the samples annealed in a N2 or O2 atmosphere exhibit a reduced (e, Mg) emission after both annealing and LEEBI treatment.
Yatsunenko, S., Khachapuridze, A., Ivanov, V.Y., Godlewski, M., Van Khoi, L., Go?acki, Z., Karczewski, G., Goldys, E.M., Phillips, M., Klar, P.J. & Heimbrodt, W. 2003, 'Spin dependent interactions of free carriers and manganese ions in nanostructures of wide band gap II-Mn-VI semiconductors - Mechanism of lifetime reduction', Acta Physica Polonica A, vol. 103, no. 6, pp. 643-648.
View/Download from: UTS OPUS
The spin dependent interactions of free carriers and manganese ions in nanostructures of wide band gap were discussed. The observed lifetime shortening of intrashell manganese ion emission was related to spin dependent magnetic interactions. The mechanism was found to be active in both bulk and low dimensional structures.
Gelhausen, O., Klein, H.N., Phillips, M.R. & Goldys, E.M. 2003, 'Electron irradiation-induced electro-migration and diffusion of defects in Mg-doped GaN', Physica Status Solidi (B) Basic Research, vol. 239, no. 2, pp. 310-315.
View/Download from: UTS OPUS or Publisher's site
In-plane- and depth-resolved cathodoluminescence (CL) microanalysis and spectroscopy was carried out to study the impact of electron injection on electro-migration and diffusion of native defects and residual impurities in rapidly thermally annealed (RTA) Mg-doped p-type GaN. During intense electron beam irradiation (e.g. Eb, = 10 keV, Ib = 80 nA), an electric field is generated within the primary beam interaction volume. We observed the following two electric field-related effects: (i) an increased electron recombination length and a subsequent field-assisted charge spreading, which causes a dissociation of Mg-H complexes beyond the interaction volume of the primary electron beam, and ii) thermally assisted electro-migration of positively charged, mobile defects leading to the formation of deeper complexes, which are highly stable and act as nonradiative recombination pathways. Furthermore, the diffusion of electron beam-dissociated hydrogen was found to result in the passivation of Mg acceptors beyond the charge recombination volume. &copy; 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Phillips, M.R., Telg, H., Kucheyev, S.O., Gelhausen, O. & Toth, M. 2003, 'Cathodoluminescence efficiency dependence on excitation density in n-type gallium nitride', Microscopy and Microanalysis, vol. 9, no. 2, pp. 144-151.
View/Download from: UTS OPUS or Publisher's site
Cathodoluminescence (CL) spectra from silicon doped and undoped wurtzite n-type GaN have been measured in a SEM under a wide range of electron beam excitation conditions, which include accelerating voltage, beam current, magnification, beam diameter, and specimen temperature. The CL intensity dependence on excitation density was analyzed using a power-law model (ICL ? Jm) for each of the observed CL bands in this material. The yellow luminescence band present in both silicon and undoped GaN exhibits a close to cube root (m = 0.33) dependence on electron beam excitation at both 77 K and 300 K. However, the blue (at 300 K) and donor-acceptor pair (at 77 K) emission peaks observed in undoped GaN follow power laws with exponents of m = 1 and m = 0.5, respectively. As expected from its excitonic character, the near band edge emission intensity depends linearly (m = 1) in silicon doped GaN and superlinearly (m = 1.2) in undoped GaN on the electron beam current. Results show that the intensities of the CL bands are highly dependent not only on the defect concentration but also on the electron-hole pair density and injection rate. Furthermore, the size of the focussed electron beam was found to have a considerable effect on the relative intensities of the CL emission peaks. Hence SEM parameters such as the objective lens aperture size, astigmatism, and the condenser lens setting must also be considered when assessing CL data based on intensity measurements from this material.
Gelhausen, O., Klein, H.N., Phillips, M.R. & Goldys, E.M. 2002, 'Influence of low-energy electron beam irradiation on defects in activated Mg-doped GaN', Applied Physics Letters, vol. 81, no. 20, pp. 3747-3749.
View/Download from: UTS OPUS or Publisher's site
The influence of low-energy electron beam irradiation (LEEBI) on residual hydrogen impurities and defects in activated magnesium doped gallium nitride layers was studied. In-plane and depth-resolved cathodoluminescence imaging revealed the correlation between the spatial distribution of the injected carriers and the depth and lateral distribution of activated magnesium acceptors. It was found that the hydrogen dissociation results from electron-hole recombination at hydrogen defect complexes and is associated with the generation of additional defect centers.
Bradby, J.E., Kucheyev, S.O., Williams, J.S., Wong-Leung, J., Swain, M.V., Munroe, P., Li, G. & Phillips, M.R. 2002, 'Indentation-induced damage in GaN epilayers', Applied Physics Letters, vol. 80, no. 3, pp. 383-385.
View/Download from: UTS OPUS or Publisher's site
The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence (CL) monochromatic imaging. CL imaging of indents which exhibit plastic deformation (based on indentation data) shows an observable "footprint" of deformation-produced defects that result in a strong reduction in the intensity of CL emission. Multiple discontinuities are observed during loading when the maximum load is above the elastic-plastic threshold, and such a behavior can be correlated with multiple slip bands revealed by XTEM. No evidence of pressure-induced phase transformations is found from within the mechanically damaged regions using selected-area diffraction patterns. The main deformation mechanism appears to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes on further loading. XTEM reveals no cracking or delamination in any of the samples studied for loads of up to 250 mN. &copy; 2002 American Institute of Physics.
Kucheyev, S.O., Toth, M., Phillips, M.R., Williams, J.S., Jagadish, C. & Li, G. 2002, 'X-ray spectrometry investigation of electrical isolation in GaN', Journal of Applied Physics, vol. 91, no. 6, pp. 3940-3942.
View/Download from: UTS OPUS or Publisher's site
Electrical isolation of n-type GaN epilayers bombarded with MeV light ions is studied by energy dispersive x-ray spectrometry (EDS). We show that the maximum bremsstrahlung x-ray energy (the Duane-Hunt limit) can be used to monitor the isolation process in GaN. This method allows the dose region above the threshold dose for isolation to be conveniently studied, whereas the application of conventional (low-voltage) electrical techniques in this dose range with large sheet resistances of the material (?1011/sq) is often impossible due to comparable parasitic resistances of the experimental setup. A correlation of EDS and resistance measurements of GaN strongly suggests that the magnitude of sample charging scales with the number of ion-beam-produced deep electron traps which are empty at equilibrium. The results presented demonstrate the utility of EDS as a powerful and simple technique to study electrical isolation in wide band-gap semiconductors. &copy; 2002 American Institute of Physics.
Kucheyev, S.O., Toth, M., Phillips, M.R., Williams, J.S., Jagadish, C. & Li, G. 2002, 'Chemical origin of the yellow luminescence in GaN', Journal of Applied Physics, vol. 91, no. 9, pp. 5867-5874.
View/Download from: UTS OPUS or Publisher's site
The influence of ion-beam-produced lattice defects as well as H, B, C, N, O, and Si, introduced by ion implantation, on the luminescence properties of wurtzite GaN is studied by cathodoluminescence spectroscopy. Results indicate that intrinsic lattice defects produced by ion bombardment mainly act as nonradiative recombination centers and do not give rise to the yellow luminescence (YL) of GaN. Experimental data unequivocally shows that C is involved in the defect-impurity complex responsible for YL. In addition, C-related complexes appear to act as efficient nonradiative recombination centers. Implantation of H produces a broad luminescent peak which is slightly blueshifted with respect to the C-related YL band in the case of high excitation densities. The position of this H-related YL peak exhibits a blueshift with increasing excitation density. Based on this experimental data and results reported previously, the chemical origin of the YL band is discussed. &copy; 2002 American Institute of Physics.
Rémond, G., Nockolds, C., Phillips, M. & Roques-Carmes, C. 2002, 'Implications of polishing techniques in quantitative x-ray microanalysis', Journal of Research of the National Institute of Standards and Technology, vol. 107, no. 6, pp. 639-662.
View/Download from: UTS OPUS
The implications of the polishing techniques in quantative x-ray microanalysis were discussed. Two and three body abrasive wears, polishing procedures and techniques and characterization of polished surfaces were also discussed. Varying the nature of polishing materials was found to result in different surface and subsurface chemical, physical and textural damages.
Toth, M., Phillips, M.R., Craven, J.P., Thiel, B.L. & Donald, A.M. 2002, 'Electric fields produced by electron irradiation of insulators in a low vacuum environment', Journal of Applied Physics, vol. 91, no. 7, pp. 4492-4499.
View/Download from: UTS OPUS or Publisher's site
We report on the properties of electric fields generated as a result of electron irradiation of dielectrics in a low vacuum scanning electron microscope. Individual field components produced by (i) ionized gas molecules located outside the sample surface and (ii) subsurface trapped charge were detected by measurements of changes in (i) primary electron landing energy and (ii) secondary electron (SE) emission current, respectively. The results provide experimental evidence for a recently proposed model of field-enhanced SE emission from electron irradiated insulators in a low vacuum environment [Toth et al., J. Appl. Phys. 91, 4479 (2002)]. Errors introduced into x-ray microanalysis by the electric fields generated by ionized gas molecules can be alleviated by minimizing the steady state ion concentration by the provision of efficient ion neutralization routes. It is demonstrated how this can be achieved using simple sample-electrode geometries. &copy; 2002 American Institute of Physics. &copy; 2002 American Institute of Physics.
Toth, M., Phillips, M.R., Thiel, B.L. & Donald, A.M. 2002, 'Electron imaging of dielectrics under simultaneous electron-ion irradiation', Journal of Applied Physics, vol. 91, no. 7, pp. 4479-4491.
View/Download from: UTS OPUS or Publisher's site
We demonstrate that if charging caused by electron irradiation of an insulator is controlled by a defocused flux of soft-landing positive ions, secondary electron (SE) images can contain contrast due to lateral variations in (i) changes in the SE yield caused by subsurface trapped charge and (ii) the SE-ion recombination rate. Both contrast mechanisms can provide information on microscopic variations in dielectric properties. We present a model of SE contrast formation that accounts for localized charging and the effects of gas ions on the SE emission process, emitted electrons above the sample surface, and subsurface trapped charge. The model explains the ion flux dependence of charge-induced SE contrast, an increase in the sensitivity to surface contrast observed in SE images of charged dielectrics, and yields procedures for identification of contrast produced by localized sample charging. &copy; 2002 American Institute of Physics. &copy; 2002 American Institute of Physics.
Godlewski, M., Goldys, E.M., Phillips, M., Böttcher, T., Figge, S., Hommel, D., Czernecki, R., Prystawko, P., Leszczynski, M., Perlin, P., Wisniewski, P., Suski, T., Bockowski, M., Grzegory, I. & Porowski, S. 2002, 'Relationship between sample morphology and carrier diffusion length in GaN thin films', Acta Physica Polonica A, vol. 102, no. 4-5, pp. X627-X632.
View/Download from: UTS OPUS
Scanning and spot-mode cathodoluminescence investigations of homo-and hetero-epitaxial GaN films indicate a surprisingly small influence of their microstructure on overall intensity of a light, emission. This we explain by a correlation between structural quality of these films and diffusion length of free carriers and excitons. Diffusion length increases with improving structural quality of the samples, which, in turn, enhances the rate of nonradiative recombination on structural defects, such as dislocations.
Gauvin, R., Griffin, B., Nockolds, C., Phillips, M. & Joy, D.C. 2002, 'A method to measure the effective gas path length in the environmental or variable pressure scanning electron microscope', Scanning, vol. 24, no. 4, pp. 171-174.
View/Download from: UTS OPUS
A simple method is described to determine the effective gas path length when incident electrons scatter in the gas above the specimen. This method is based on the measurement of a characteristic x-ray line emitted from a region close to the incident beam. From various experimental measurements performed on various microscopes, it is shown that the effective gas path length may increase with the chamber pressure and that it is also often dependent of the type of x-ray bullet.
Rémond, G., Myklebust, R., Fialin, M., Nockolds, C., Phillips, M. & Roques-Carmes, C. 2002, 'Decomposition of wavelength dispersive x-ray spectra', Journal of Research of the National Institute of Standards and Technology, vol. 107, no. 6, pp. 509-529.
View/Download from: UTS OPUS
Line shapes of atomic lines and soft x-ray emission bands measured with a wavelength dispersive spectrometer (WDS) with the Electron Probe Micro Analyzer (EPMA) are reviewed. Least square fitting to pseudo-Voigt profiles of the digitally measured spectra are used to account for the presence of non-diagram features (high and low energy satellites) and instrumental induced distortions. The effect of line width and relative intensities on the quality of fits is illustrated. Spectral distortions resulting from the presence of absorption edges within the analyzed wavelength region are illustrated for the case of FeL?,? emission bands for pure Fe and iron oxides. For quantitative analysis, an analytical approach is presented where the measured soft x-ray emission bands are corrected for self absorption before extracting the intensities from the experimental data.
Bradby, J.E., Kucheyev, S.O., Williams, J.S., Jagadish, C., Swain, M.V., Munroe, P. & Phillips, M.R. 2002, 'Contact-induced defect propagation in ZnO', Applied Physics Letters, vol. 80, no. 24, pp. 4537-4539.
View/Download from: UTS OPUS or Publisher's site
Contact-induced damage has been studied in single-crystal (wurtzite) ZnO by cross-sectional transmission electron microscopy (XTEM) and scanning cathodoluminescence (CL) monochromatic imaging. XTEM reveals that the prime deformation mechanism in ZnO is the nucleation of slip on both the basal and pyramidal planes. Some indication of dislocation pinning was observed on the basal slip planes. No evidence of either a phase transformation or cracking was observed by XTEM in samples loaded up to 50 mN with an ?4.2 ?m radius spherical indenter. CL imaging reveals a quenching of near-gap emission by deformation-produced defects.Both XTEM and CL show that this comparatively soft material exhibits extensive deformation damage and that defects can propagate well beyond the deformed volume under contact. Results of this study have significant implications for the extent of contact-induced damage during fabrication of ZnO-based (opto)electronic devices. &copy; 2002 American Institute of Physics.
Godlewski, M., Goldys, E.M., Butcher, K.S.A., Phillips, M.R., Pakula, K. & Baranowski, J.M. 2001, 'Cathodoluminescence investigations of interfaces in InGaN/GaN/sapphire structures', PHYSICA STATUS SOLIDI B-BASIC RESEARCH, vol. 228, no. 1, pp. 179-182.
View/Download from: UTS OPUS or 3.3.CO;2-V">Publisher's site
Kucheyev, S.O., Toth, M., Phillips, M.R., Williams, J.S., Jagadish, C. & Li, G. 2001, 'Cathodoluminescence depth profiling of ion-implanted GaN', Applied Physics Letters, vol. 78, no. 1, pp. 34-36.
View/Download from: UTS OPUS or Publisher's site
Cathodoluminescence (CL) spectroscopy shows that even relatively low-dose keV light-ion bombardment (corresponding to the generation of ?5 1019 vacancies/cm3) of wurtzite GaN results in a dramatic quenching of visible CL emission. Postimplantation annealing at temperatures up to 1050&deg;C generally causes a partial recovery of measured CL intensities. However, CL depth profiles indicate that, in most cases, such a recovery results from CL emission from virgin GaN, beyond the implanted layer due to a reduction in the extent of light absorption within the implanted layer. In this case, CL emission from the implanted layer remains completely quenched even after such an annealing. These results show that an understanding of the effects of ion bombardment and postimplantation annealing on luminescence generation and light absorption is required for a correct interpretation of luminescence spectra of GaN optically doped by keV ion implantation. &copy; 2001 American Institute of Physics.
Danilatos, G.D., Phillips, M.R. & Nailon, J.V. 2001, 'Electron beam current loss at the high-vacuum-high-pressure boundary in the environmental scanning electron microscope', Microscopy and Microanalysis, vol. 7, no. 5, pp. 397-406.
View/Download from: UTS OPUS
A significant loss in electron probe current can occur before the electron beam enters the specimen chamber of an environmental scanning electron microscope (ESEM). This loss results from electron scattering in a gaseous jet formed inside and downstream (above) the pressure-limiting aperture (PLA), which separates the high-pressure and high-vacuum regions of the microscope. The electron beam loss above the PLA has been calculated for three different ESEMs, each with a different PLA geometry: an ElectroScan E3, a Philips XL30 ESEM, and a prototype instrument. The mass thickness of gas above the PLA in each case has been determined by Monte Carlo simulation of the gas density variation in the gas jet. It has been found that the PLA configurations used in the commercial instruments produce considerable loss in the electron probe current that dramatically degrades their performance at high chamber pressure and low accelerating voltage. These detrimental effects are minimized in the prototype instrument, which has an optimized thin-foil PLA design.
Gelhausen, O., Phillips, M.R. & Toth, M. 2001, 'Depth-resolved cathodoluminescence microanalysis of near-edge emission in III-nitride thin films', Journal of Applied Physics, vol. 89, no. 6, pp. 3535-3537.
View/Download from: UTS OPUS or Publisher's site
We describe an approach to assess the quality of III-nitride thin films using depth-resolved cathodoluminescence (CL) microanalysis. In this procedure, the depth-resolved peak shift due to self-absorption of the near-edge CL emission is calculated using Monte Carlo simulation techniques and compared with measured peak shift values. A discrepancy between the experimental and modeled data indicates the presence of an exciton peak shift due to strain, near-edge defects, and alloy fluctuation. Depth-resolved peak shift analysis of the near-edge CL from an undoped 700 nm thick Al0.057Ga0.943N film grown on a (0001) Al2O3 substrate is presented to demonstrate the utility of the method. &copy; 2001 American Institute of Physics.
Cooper, R., Smith, K.L., Colella, M., Vance, E.R. & Phillips, M. 2001, 'Optical emission due to ionic displacements in alkaline earth titanates', Journal of Nuclear Materials, vol. 289, no. 1-2, pp. 199-203.
View/Download from: UTS OPUS or Publisher's site
Optical emission spectra in the 300-700 nm range were collected from single crystal CaTiO3, SrTiO3 and BaTiO3, and polycrystalline CaTiO3 samples, that were irradiated at room temperature using a Febetron 706 variable energy pulsed-electron-beam generator. The long-lived emissions (up to microseconds after the electron pulse) consist of broad (halfwidths to approximately 100 nm) bands centred around 380, 425, and 445 nm for CaTiO3, SrTiO3 and BaTiO3, respectively. These emission bands are similar to cathodoluminescence emissions from 25 keV electron irradiation attributed by others to direct conduction-valence band transitions in unreduced samples and oxygen vacancies in reduced samples. CaTiO3, SrTiO3 and BaTiO3 all have emission thresholds of 0.26&plusmn;0.02 MeV. This corresponds to a threshold displacement energy for oxygen, Ed of 45&plusmn;4 eV.
Godlewski, M., Mackowski, S., Karczewski, G., Goldys, E.M. & Phillips, M.R. 2001, 'Cathodolfiminescence studies of self-organized cdTe/ZnTe quantum dot structure grown by MBE: In-plane and in-depth properties of the system', Semiconductor Science and Technology, vol. 16, no. 6, pp. 493-496.
View/Download from: UTS OPUS or Publisher's site
We report the results of low-temperature photoluminescence, room-temperature cathodoluminescence (CL) and scanning CL and electron microscopy of self-organized CdTe/ZnTe quantum dot (QD) structure. The in-depth profiling CL investigations were used to identify the microscopic origin of the CL emissions observed at 2.13,2.0-2.1 and 2.25 eV. In particular, we distinguish between CL emissions originating from the QD region of the structure and from the underlying buffer layers. Based on these measurements we assign the 2.13 eV CL band to the wetting layer and the 2.0-2.1 eV band to the QD emission. From the study of the in-plane and in-depth CL characteristics we demonstrate large in-plane fluctuations of the CL intensity and discuss their origin.
Godlewski, M., Goldys, E.M., Phillips, M.R., Pakula, K. & Baranowski, J.M. 2001, 'Cathodoluminescence and depth-profiling cathodoluminescence studies of interface properties in MOCVD-grown InGaN/GaN/sapphire structures: Role of GaN buffer layer', Applied Surface Science, vol. 177, no. 1-2, pp. 22-31.
View/Download from: UTS OPUS or Publisher's site
We report the results of room-temperature cathodoluminescence (CL) and of scanning CL and electron (SEM) microscopy of GaN/InGaN structure with a single InGaN quantum well on top. The structures were grown by MOCVD on sapphire with low-temperature (LT) GaN buffer. Depth-profiling CL investigations were used to identify the observed CL emissions, which show a complicated in-depth evolution. The influence of a LT GaN buffer on structural and optical properties of GaN/sapphire interface in the structure is discussed. Our results show that inter-diffusion of Al from sapphire to the GaN buffer layer takes place. A gradual improvement of film quality with increasing distance from interface is demonstrated. &copy; 2001 Elsevier Science B.V.
Godlewski, M., Guziewicz, E., Szczerbakow, A., Kopalko, K., Dynowska, E., Phillips, M.R., Cricenti, A. & Girasole, M. 2001, 'Optical and structural properties of thin films of ZnS grown by atomic layer epitaxy', Journal of Wide Bandgap Materials, vol. 9, no. 1-2, pp. 55-63.
View/Download from: Publisher's site
Monocrystalline films of sphalerite-type ZnS are produced on (001) GaAs substrates by atomic layer epitaxy (ALE) in a gas flow system employing reactions of three different types. Properties of these ZnS films are compared. The best quality ZnS layers are obtained using either zinc chloride or elemental zinc as source of cation and H2S vapors as source of sulfur. These layers show flat surfaces and good spectral properties. &copy; 2002 Sage Publications.
Kucheyev, S.O., Toth, M., Phillips, M.R., Williams, J.S. & Jagadish, C. 2001, 'Effects of excitation density on cathodoluminescence from GaN', Applied Physics Letters, vol. 79, no. 14, pp. 2154-2156.
View/Download from: UTS OPUS or Publisher's site
Wurtzite GaN epilayers are studied by cathodoluminescence (CL) spectroscopy. Results show that the intensities of donor-acceptor pair (DAP) and yellow luminescence (YL) peaks sublinearly depend on excitation density, presumably, due to saturation effects. The intensity of near-gap emission, however, exhibits a superlinear dependence on electron-beam excitation. In contrast to photoluminescence measurements, CL studies of GaN are usually performed in a regime with a strongly nonlinear dependence of luminescence intensities on excitation due to a large difference in carrier generation rates for these two techniques. As a result, the ratios of near-gap to YL and DAP emission intensities strongly depend on electron-beam current. Moreover, electron-beam spot size (i.e., beam focusing) dramatically affects CL intensity. An understanding of such saturation effects is necessary for a correct interpretation of CL spectra from GaN. &copy; 2001 American Institute of Physics.
Buyanova, I.A., Chen, W.M., Goldys, E.M., Phillips, M.R., Xin, H.P. & Tu, C.W. 2001, 'Strain relaxation in GaNxP1-x alloy: Effect on optical properties', Physica B: Condensed Matter, vol. 308-310, pp. 106-109.
View/Download from: UTS OPUS or Publisher's site
By using scanning electron microscopy and cathodoluminescence (CL), a decrease in radiative efficiency of GaNP alloy with increasing N content is seen due to the formation of structural defects. The defect formation is attributed to relaxation of tensile strain in the GaNP layer, which is lattice mismatched to GaP substrate. Several types of extended defects including dislocations, microcracks and pits are revealed in partly relaxed GaNxP1-x epilayers with x?1.9%, whereas coherently strained layers exhibit high crystalline quality for x up to 4%. According to the CL measurements, all extended defects act as competing, non-radiative channels leading to the observed strong decrease in the radiative efficiency. From CL mapping experiments, non-uniformity of strain distribution around the extended defects is partly responsible for the broadening of the photoluminescence (PL) spectra recorded in the macro-PL experiments. &copy; 2001 Elsevier Science B.V. All rights reserved.
Godlewski, M., Goldys, E.M., Butcher, K.S.A., Phillips, M.R., Pakula, K. & Baranowski, J.M. 2001, 'Cathodoluminescence investigations of interfaces in InGaN/GaN/sapphire structures', Physica Status Solidi (B) Basic Research, vol. 228, no. 1, pp. 179-182.
View/Download from: 3.0.CO;2-3">Publisher's site
Scanning electron microscopy and cathodoluminescence (CL) in spot and depth-profiling modes were used to evaluate the in-plane and in-depth uniformity of light emission from InGaN/GaN quantum well (QW) structures. The structures were grown by MOCVD on sapphire with a low-temperature (LT) GaN buffer. Depth-profiling CL investigations were used to identify the observed CL emissions, which show a complicated in-depth evolution. The influence of a LT GaN buffer on the structural and optical properties of the GaN/sapphire interface is discussed.
Godlewski, M., Goldys, E.M. & Phillips, M.R. 2000, 'Cathodoluminescence studies of in-plane and in-depth properties of GaN epilayers', Journal of Luminescence, vol. 87, pp. 1155-1157.
View/Download from: Publisher's site
The influence of sample morphology on optical properties of GaN epilayers is studied. We show that a granular/columnar structure of MOCVD- and MBE-grown films results in strong planar fluctuations of the 'edge' emission of GaN, which is strongly deactivated at grain boundaries. In contrast, the yellow emission of GaN is relatively in-plane homogeneous. We further show large in-depth inhomogeneity of GaN samples and discuss a possible origin of in-plane homogeneity of the yellow photoluminescence.
Godlewski, M., Goldys, E.M., Phillips, M.R., Langer, R. & Barski, A. 2000, 'Cathodoluminescence depth-profiling studies of GaN/AlGaN quantum-well structures', JOURNAL OF MATERIALS RESEARCH, vol. 15, no. 2, pp. 495-501.
View/Download from: Publisher's site
Toth, M., Kucheyev, S.O., Williams, J.S., Jagadish, C., Phillips, M.R. & Li, G. 2000, 'Imaging charge trap distributions in GaN using environmental scanning electron microscopy', Applied Physics Letters, vol. 77, no. 9, pp. 1342-1344.
We present direct experimental evidence for a field assisted component in images acquired using the gaseous secondary electron detector (GSED) employed in environmental scanning electron microscopes. Enhanced secondary electron (SE) emission was observed in GSED images of epitaxial GaN bombarded with MeV He ions. The increase in SE emission is attributed to an electric field generated by electrons trapped at defects produced by ion implantation. The presence of nonradiative recombination centers and of trapped charge in implanted GaN was established by cathodoluminescence spectroscopy and energy dispersive x-ray spectrometry. The field assisted SE component is distinguishable from the "normal" GSED signal by characteristic pressure and temperature dependencies. The presented results demonstrate the utility of the GSED for imaging charge trap distributions in semiconductors. &copy; 2000 American Institute of Physics.
Toth, M. & Phillips, M.R. 2000, 'The effects of space charge on contrast in images obtained using the environmental scanning electron microscope', SCANNING, vol. 22, no. 5, pp. 319-325.
Masens, C., Schulte, J., Phillips, M. & Dligatch, S. 2000, 'Ultra flat gold surfaces for use in chemical force microscopy: Scanning probe microscopy studies of the effect of preparation regime on surface morphology', Microscopy and Microanalysis, vol. 6, no. 2, pp. 113-120.
The preparation of ultra flat gold surfaces for use in chemical force microscopy (CFM) has been studied. The surfaces were studied in terms of substrate effects by comparing mica, Si (110) wafer and glass slides. The effect of different annealing regimes was also investigated. Measurements on these surfaces were made by both atomic force microscopy (AFM) (in contact and tapping mode) and by scanning tunneling microscopy (STM). The films contain different morphologies with respect to grain size and topography. Calculations of surface roughness present values less than 2.5 nm for all surfaces studied, making the choice of the "flattest" surface difficult if based on criteria of surface roughness alone. Additionally, it is shown that different acquisition parameters can produce dissimilar images that have stability and reproducibility.
Toth, M., Phillips, M. & Griffin, B. 2000, 'X-ray Microanalysis of Insulators in the ESEM', Microscopy & Microanalysis, vol. 6, no. 2, pp. 786-787.
Godlewski, M., Goldys, E. & Phillips, M. 2000, 'Cathodoluminescence Studies of in-plane and in-depth Properties of GaN Epilayers', Journal of Luminescence, vol. 87-89, pp. 1155-1157.
View/Download from: Publisher's site
Whittall, A., Phillips, M. & Suetsugu, Y. 2000, 'Cathodoluminescence Emission For Differentiating The Degree Of Carbonation In Apatites', Bioceramics, vol. 0, pp. 179-182.
Cathodoluminescence has recently been used successfully in detecting and determining the spatial location of the amorphous phase in plasma sprayed calcium phosphate coatings. The aim of this study is to determine whether this same technique can be used t
Meier, T., Koch, S.W., Phillips, M. & Wang, H. 2000, 'Strong coupling of heavy- and light-hole excitons induced by many-body correlations', Physical Review B, vol. 62, no. 19, pp. 12605-12608.
View/Download from: Publisher's site
Kucheyev, S.O., Bradby, J.E., Williams, J.S., Jagadish, C., Toth, M., Phillips, M.R. & Swain, M.V. 2000, 'Nanoindentation of epitaxial GaN films', Applied Physics Letters, vol. 77, no. 21, pp. 3373-3375.
Wurtzite GaN films grown on sapphire substrates are studied by nanoindentation with a spherical indenter. No systematic dependence of the mechanical properties of GaN epilayers on the film thickness (at least for thicknesses from 1.8 to 4 ?m) as well as on doping type is observed. Slip is identified as one of the physical mechanisms responsible for plastic deformation of GaN and may also contribute to the "pop-in" events observed during loading. No visible material cracking is found even after indentations at high loads (900 mN), but a pronounced elevation of the material surrounding the impression is observed. &copy; 2000 American Institute of Physics.
Toth, M. & Phillips, M.R. 2000, 'The role of induced contrast in images obtained using the environmental scanning electron microscope', Scanning, vol. 22, no. 6, pp. 370-379.
Generation of contrast in images obtained using the environmental scanning electron microscope (ESEM) is explained by interpretation of images acquired using the gaseous secondary electron detector (GSED), ion current, and the Everhart-Thornley detector. We present a previously unreported contrast component in GSED and ion current images attributed to signal induction by changes in the concentration of positive ions in the ESEM chamber during image acquisition. Changes in positive ion concentration are caused by changes in electron emission from the sample during image acquisition and by a discrepancy between the drift velocities of negative and positive charge carriers in the imaging gas. The proposed signal generation mechanism is used to explain contrast reversal in images produced using the GSED and ion current signals and accounts for discrepancies in contrast observed, under some conditions, in these types of images. Combined with existing models of signal generation in the ESEM, the proposed model provides a basis for correct interpretation of ESEM images.
Phillips, M.R. & Ott, D.M. 2000, 'Crosstalk caused by nonideal output filters in WDM lightwave systems', IEEE PHOTONICS TECHNOLOGY LETTERS, vol. 12, no. 8, pp. 1094-1096.
View/Download from: Publisher's site
Toth, M. & Phillips, M. 2000, 'Space Charge Artefacts in ESEM Images: Shadowing and Contrast', Microscopy & Microanalysis, vol. 6, no. 2, pp. 775-775.
Godlewski, M., Goldys, E.M., Phillips, M.R., Langer, R. & Barski, A. 2000, 'Cathodoluminescence depth-profiling studies of GaN/AlGaN quantum-well structures', Journal of Materials Research, vol. 15, no. 2, pp. 495-501.
In this paper we evaluate the in-depth homogeneity of GaN epilayers and the influence of electric field present in strained GaN/AlGaN heterostructures and quantum wells on the yellow and "edge" emission in GaN and AlGaN. Our depth-profiling cathodoluminescence measurements show an increased accumulation of defects at the interface. Inhomogeneities in the doping level are reflected by the enhancement of the yellow emission in the interface region. The piezoelectric effect is found to strongly reduce the emission from the strained AlGaN quantum-well barriers. We also show that Ga droplets, commonly found on surfaces of samples grown in Ga-rich conditions, screen the internal electric field in a structure and thus result in a local enhancement of the edge emission intensity.
Toth, M. & Phillips, M.R. 1999, 'Detection of Cr impurities in GaN by room temperature cathodoluminescence spectroscopy', Applied Physics Letters, vol. 75, no. 25, pp. 3983-3985.
Trace levels of Cr impurities in epitaxial GaN grown on sapphire substrates were investigated using cathodoluminescence (CL) spectroscopy. CL emissions characteristic of Cr in an octahedral crystal field were observed from ?-Ga2O3 overlayers produced on GaN by post-growth thermal annealing in dry O2. Cr luminescence was also observed from the sapphire substrates, a likely source of the Cr contaminant. The presented results illustrate the use of ?-Ga2O3 overlayers as high sensitivity indicators of the presence of Cr in GaN. &copy; 1999 American Institute of Physics.
Phillips, M.R. & Ott, D.M. 1999, 'WDM lightwave system crosstalk by optical Kerr effect with polarisation-dependent loss', ELECTRONICS LETTERS, vol. 35, no. 20, pp. 1764-1765.
View/Download from: Publisher's site
Phillips, M.R., Toth, M. & Drouin, D. 1999, 'Depletion layer imaging using a gaseous secondary electron detector in an environmental scanning electron microscope', Applied Physics Letters, vol. 75, no. 1, pp. 76-78.
View/Download from: UTS OPUS
We present a method for imaging depletion layers using the gaseous secondary electron detector (GSED) employed in environmental scanning electron microscopes. GSED images of a p-n junction were obtained from a Si P+PN power diode. Behavior of the junction contrast as a function of imaging conditions is unrelated to reported GSED contrast formation mechanisms [ A. L. Fletcher, B. L. Thiel, and A. M. Donald, J. Phys. D 30, 2249 (1997)]. Optimum imaging conditions are presented, and the contrast behavior is interpreted in terms of a previously unreported induced current component in GSED images. The presented technique is unique as it will enable imaging of depletion layers in uncoated semiconductor/oxide devices in controlled gaseous environments at elevated specimen temperatures. &copy; 1999 American Institute of Physics.
Toth, M., Fleischer, K. & Phillips, M.R. 1999, 'Electron beam induced impurity electro-migration in unintentionally doped GaN', MRS Internet Journal of Nitride Semiconductor Research, vol. 4, no. SUPPL. 1, p. 6d.
Electron beam induced electromigration of O N + and H + impurities in unintentionally n-doped GaN was investigated using cathodoluminescence (CL) kinetics profiling, CL imaging of regions pre-irradiated with a stationary electron beam, and wavelength dispersive x-ray spectrometry (WDS). The presented results (i) illustrate induced impurity diffusion in wide bandgap semiconductors, (ii) provide experimental evidence for the (V Ga-O N) 2- model of yellow luminescence in GaN with low Si content 1, (iii) confirm the roles of O in frequently reported bound exciton and donor-acceptor pair emissions and (iv) suggest the involvement of O N + and hydrogenated gallium vacancies in a blue emission in autodoped GaN.
Leon, R., Okuno, J.O., Lawton, R.A., Stevens-Kalceff, M., Phillips, M.R., Zou, J., Cockayne, D.J.H. & Lobo, C. 1999, 'Dislocation-induced changes in quantum dots: Step alignment and radiative emission', Applied Physics Letters, vol. 74, no. 16, pp. 2301-2303.
A new type of quantum dot (QD) alignment for an InGaAs/GaAs QD multilayered structure has been observed. In addition to two distinct types of InGaAs dot alignment in vicinal GaAs (001), an abrupt transition in QD sizes and concentrations was seen. This was accompanied by bright QD emission, even after formation of a dislocation array, and different behaviors with thermal intermixing.
Fleischer, K., Toth, M., Phillips, M.R., Zou, J., Li, G. & Chua, S.J. 1999, 'Depth profiling of GaN by cathodoluminescence microanalysis', Applied Physics Letters, vol. 74, no. 8, pp. 1114-1116.
View/Download from: Publisher's site
We present the results of a depth-resolved cathodoluminescence (CL) and transmission electron microscopy study of autodoped GaN grown on sapphire. Depth-resolved CL analysis can be used for depth profiling of the yellow luminescence (YL) center concentration which was found to increase with depth. The results are consistent with the (ON-VGa)2- complex model of YL centers [J. Neugebauer and C. G. Van de Walle, Appl. Phys. Lett. 69, 503 (1996) and T. Mattila and R. M. Nieminen, Phys. Rev. B 55, 9571 (1996)]. Depth profiling of the near-edge emission in GaN layers thicker than ?0.5 ?m is not possible due to strong self-absorption. &copy; 1999 American Institute of Physics.
Phillips, M. & Wang, H. 1999, 'Coherent oscillation in four-wave mixing of interacting excitons', Solid State Communications, vol. 111, no. 6, pp. 317-321.
View/Download from: Publisher's site
Toth, M., Fleischer, K. & Phillips, M.R. 1999, 'Direct experimental evidence for the role of oxygen in the luminescent properties of GaN', Physical Review B - Condensed Matter and Materials Physics, vol. 59, no. 3, pp. 1575-1578.
We present experimental evidence of electron-beam-induced diffusion of O and H in unintentionally doped n-type GaN grown on a sapphire substrate. Impurity diffusion was investigated using cathodoluminescence kinetics and imaging at 4 and 300 K and by wavelength dispersive x-ray analysis. The results illustrate the significance of electron-beam-induced electromigration in wide band gap semiconductors, confirm the roles of ON . in bound exciton, donor-acceptor pair and yellow emissions and suggest the involvement of ON . and hydrogenated gallium vacancies in the previously unexplained blue luminescence. &copy;1999 The American Physical Society.
Kim, D.G., Seong, T.Y., Baik, Y.J., Stevens Kalceff, M.A. & Phillips, M.R. 1999, 'Cathodoluminescence of diamond films grown on pretreated Si (001) substrates by microwave plasma chemical vapour deposition', Diamond and Related Materials, vol. 8, no. 2-5, pp. 712-716.
Diamond films were grown on a.c. bias-enhanced nucleated Si(001) wafers using different CH4 concentrations by microwave plasma chemical vapour deposition. Cathodoluminescence (CL) spectra from the films exhibit emission components which are associated with defects such as neutral atomic vacancies, nitrogen-vacancy complexes and structural defects such as dislocations. The luminescence intensities of the related peaks were found to depend on the BEN and CH4 concentrations. Comparison of the CL and SEM images indicates that a nitrogen-associated defect is primarily distributed in the {001} growth facets of the diamond grains. However, the structural defect-related centres are found to be located mainly near grain boundaries and {111} growth facets.
Phillips, M.R. & Ott, D.M. 1999, 'Crosstalk due to optical fiber nonlinearities in WDM CATV lightwave systems', JOURNAL OF LIGHTWAVE TECHNOLOGY, vol. 17, no. 10, pp. 1782-1792.
View/Download from: Publisher's site
Stevens Kalceff, M.A., Phillips, M.R., Toth, M., Moon, A.R., Jamieson, D.N., Orwa, J.O. & Prawer, S. 1999, 'Cathodoluminescence microanalysis of electron irradiation damage in wide band gap materials', Materials Research Society Symposium - Proceedings, vol. 540, pp. 43-48.
Cathodoluminescence(CL)microanalysis(spectroscopyandmicroscopy) inanelectronmicroscopeenablesbothpre- existingandirradiationinducedlocalvariationsinthebulkandsurfacedefectstructureof widebandgapmaterialstobecharacterizedwithhighspatial(lateralanddepth) resolutionandsensitivity. CLmicroanalyticaltechniquesallowtheinsitumonitoringofelectronirradiationinducedd amage,thepostirradiationassessmentofdamageinducedbyotherenergeticradiation, andtheinvestigationofirradiationinducedelectromigrationofmobilechargeddefectspec ies.ElectronirradiatedsilicondioxidepolymorphsandMeVH +ionimplantedTypeHadiamondhavebeeninvestigatedusingCLmicroanalyticaltechnique s.&copy;1999MaterialsResearchSociety.
Godlewski, M., Goldys, E.M., Phillips, M.R., Langer, R. & Barski, A. 1998, 'Influence of the surface morphology on the yellow and "edge" emissions in wurtzite GaN', Applied Physics Letters, vol. 73, no. 25, pp. 3686-3688.
View/Download from: Publisher's site
In this letter we examine an influence of surface morphology on yellow and edge emissions in wurtzite phase GaN. Our cathodoluminescence measurements show that the yellow emission does not correlate with the surface morphology, but simultaneously the "edge" emission shows very strong spatial fluctuations. The observed effect is attributed to granular structures in GaN films and enhancement of the yellow emission in the interface region. &copy; 1998 American Institute of Physics.
Gross, K.A. & Phillips, M.R. 1998, 'Identification and mapping of the amorphous phase in plasma-sprayed hydroxyapatite coatings using scanning cathodoluminescence microscopy', Journal of Materials Science: Materials in Medicine, vol. 9, no. 12, pp. 797-802.
View/Download from: Publisher's site
The presence and distribution of the amorphous phase is a key factor in the performance and bone-bonding behavior of plasma-sprayed hydroxyapatite coatings. Microanalysis of coatings was conducted with microprobe Raman and scanning cathodoluminescence microscopy. It was confirmed that the darker regions in polished cross sections represent the amorphous phase. The more intense cathodoluminescence emission from the amorphous phase during electron-beam irradiation compared with the crystalline phase was used to detect the two structurally different areas within the sample. By selecting the peak of the emission at 450 nm it was possible to raster the surface with the electron beam and produce a map of the amorphous phase in polished sections, a fracture surface and an as-sprayed surface of the plasma-sprayed coating. Cathodoluminescence microscopy, based on the different light emission from the amorphous phase and hydroxyapatite, is a useful tool for identifying and mapping of the amorphous-phase constituent in plasma-sprayed coatings.
Toth, M. & Phillips, M.R. 1998, 'Monte Carlo modeling of cathodoluminescence generation using electron energy loss curves', Scanning, vol. 20, no. 6, pp. 425-432.
This work demonstrates the validity of approximating cathodoluminescence generation throughout the electron interaction volume by the total electron energy loss profile. The energy loss profiles in multilayer specimens were accurately calculated using the Monte Carlo simulation CASINO. Resolution of cathodoluminescence images can be estimated from the electron beam spot diameter, the electron penetration range, and the minority carrier diffusion length.
Godlewski, M., Suski, T., Grzegory, I., Porowski, S., Langer, R., Barski, A., Bergman, J.P., Monemar, B., Goldys, E.M. & Phillips, M.R. 1998, 'Mechanisms of yellow and red photoluminescence in wurtzite and cubic GaN', Acta Physica Polonica A, vol. 94, no. 2, pp. 326-330.
The origin of two "deep" photoluminescence (PL) emissions observed in wurtzite (yellow PL) and cubic (red PL) GaN is discussed. PL and time-resolved PL studies confirm donor-acceptor pair character of the yellow band in wurtzite GaN and point to participation of shallow donors in this emission. A similar PL mechanism is proposed for the red emission of cubic GaN. We further show a puzzling property of both yellow and red PLs. Both yellow and red emissions show spatial homogeneity and are only weakly dependent on surface morphology.
Szczerbakow, A., Godlewski, M., Dynowska, E., Ivanov, V.Y., Swiatek, K., Goldys, E.M. & Phillips, M.R. 1998, 'Structure, surface morphology and optical properties of thin films of ZnS and CdS grown by atomic layer epitaxy', ACTA PHYSICA POLONICA A, vol. 94, no. 3, pp. 579-582.
Goldys, E.M., Zuo, H.Y., Tansley, T.L., Phillips, M.R. & Contessa, C.M. 1998, 'Band offsets in In0.15Ga0.85As/GaAs and In0.15Ga0.85As/Al0.15Ga0.85As studied by photoluminescence and cathodoluminescence', Superlattices and Microstructures, vol. 23, no. 6, pp. 1223-1226.
Photoluminescence and cathodoluminescence measurements of strained undoped In0.15 Ga0.85As/GaAs and In0.15Ga0.85As/Al0.15Ga0.85As quantum well structures with emission lines attributed to the first electron-first heavy hole and first electron-first light hole excitonic transitions have been analysed theoretically within the eight-band effective mass approximation. For In0.15Ga0.85As/GaAs the results are consistent with either type I or type II alignment of the light hole band. In the case of In0.15Ga0.85As/Al0.15Ga0.85As our results indicate type II alignment for the light hole band and offset ratio of Q = 0.83. &copy; 1998 Academic Press Limited.
Goldys, E.M., Zuo, H.Y., Phillips, M.R., Contessa, C.M., Vaughan, M.R. & Tansley, T.L. 1997, 'Type I and type II alignment of the light hole band in In0.15Ga0.85As/GaAs and in In0.15Ga0.85As/Al0.15Ga0.85As strained quantum wells', Journal of Electronic Materials, vol. 26, no. 8, pp. 922-927.
View/Download from: UTS OPUS
We present results of photoluminescence and cathodoluminescence measurements of strained undoped In0.15Ga0.85AsXGaAs and In0.15Ga0.85As/Al0.15Ga0.85As quantum well structures, designed to throw light on the current controversy over light-hole band alignment at low In content. We compare these data with theoretical calculations of the confined state energies within the eight band effective mass approximation. Our analysis shows that for In0.15Ga0 85As/GaAs, the observed two transitions are consistent with either type I or type II alignment of the light hole band for band offset ratios within the accepted range. In the case of In0.15Ga0 85As/Al0.15Ga0 85As, however, our results clearly indicate type II alignment for the light hole band. We derive the band offset ratio Q, defined here as Q = ?Ec/?Eg where ?Ec is the conduction band offset and ?Eg is the bandgap difference between the quantum well and the barrier in the presence of strain, for the In0.15Ga0.85As/Al0.15Ga0.85As system to be Q = 0.83 and discuss it in the context of the common anion rule.
Stevens Kalceff, M.A., Phillips, M.R., Moon, A.R. & Smallwood, A. 1997, 'Cathodoluminescence microanalysis of natural hydrated amorphous SiO2; opal', Physics and Chemistry of Minerals, vol. 24, no. 2, pp. 131-138.
Natural amorphous hydrated silicon dioxide (opal) has been investigated for the first time using Cathodoluminescence microanalysis in a Scanning Electron Microscope. Defect centers have been identified and imaged with high sensitivity and high spatial resolution, Intrinsic defects identified include the non bridging oxygen hole center (NBOHC) and the oxygen deficient centers (ODC). Impurities are strongly correlated with the grain structure of the precious opal and a higher than average concentration of impurity defects are observed at grain boundaries and cracks. Impurity associated defect centers include the NBOHC with -OH precursor, and the charge compensated substitutional A1, Ti, and Fe centers. Cathodoluminescence microanalysis provides important information about the defect structure and long term stability of precious opal.
Wuhrer, R., Yeung, W.Y., Phillips, M.R. & McCredie, G. 1996, 'Study on d.c. magnetron sputter deposition of titanium aluminium nitride thin films: Effect of aluminium content on coating', Thin Solid Films, vol. 290-291, pp. 339-342.
View/Download from: Publisher's site
Titanium aluminium nitride thin films have been deposited on glass slides using a dual unbalanced d.c. magnetron sputter arrangement with separate titanium and aluminium targets. A range of Ti/Al/N compositions were produced by varying the aluminium target magnetron current. The thin films were then examined using an atomic force microscope (AFM) and a field emission scanning electron microscope. Aluminium, titanium and nitrogen compositions (wt.%) were determined by using energy dispersive X-ray spectroscopy. It was found that as the aluminium magnetron current increased from 0.1 to 0.4 A, the titanium decreased from 77 wt.% to 53 wt.%, the aluminium increased from 6 wt.% to 25 wt.% and the colour changed from gold to a blue-grey. An increase in the aluminium content had a significant effect on the grain size of the film. Surface measurement analysis using the AFM results revealed that as the aluminium content increased both the rms roughness (6.5 nm ? 3.2 nm) and grain size (120 nm ? 90 nm) decreased. It is believed that the above effects could result from the increase in aluminium atom bombardment rate with the higher aluminium magnetron current.
Stevens Kalceff, M.A., Phillips, M.R. & Moon, A.R. 1996, 'Electron irradiation-induced changes in the surface topography of silicon dioxide', Journal of Applied Physics, vol. 80, no. 8, pp. 4308-4314.
The irradiation of crystalline (?-SiO2) and amorphous (?-SiO2) silicon dioxide with a stationary electron beam produces characteristic changes in the surface topography. The development of these changes has been investigated using cathodoluminescence spectroscopy and microscopy, scanning probe (atomic force) microscopy, and scanning electron microscopy. Electron irradiation produces a permanent volume increase on (crystalline) ?-SiO2, while in (amorphous) ?-SiO2 an initial small volume increase is followed by volume loss as irradiation continues. The observed changes are consistent with electromigration of oxygen under the influence of the electric field induced by charge trapping at preexisting or irradiation-induced defects. Oxygen enrichment may produce expansion of the surface region due to the formation of peroxy linkage defects. In ?-SiO2, charges trapped by defects at grain boundaries produce enhanced electric fields which may result in volume reduction at the surface, when critical field strengths are exceeded. The observed volume reductions may be attributed to electron stimulated desorption of constituents, in particular oxygen mass loss, and densification of the surface region associated with the formation of oxygen-deficient defect centers. &copy; 1996 American Institute of Physics.
Ariyavisitakul, S., Darcie, T.E., Greenstein, L.J., Phillips, M.R. & Shankaranarayanan, N.K. 1996, 'Performance of simulcast wireless techniques for personal communication systems', IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, vol. 14, no. 4, pp. 632-643.
View/Download from: Publisher's site
Kim, Y., Yuan, S., Leon, R., Jagadish, C., Gal, M., Johnston, M.B., Phillips, M.R., Stevens Kalceff, M.A., Zou, J. & Cockayne, D.J.H. 1996, 'Effects of anodic oxide induced intermixing on the structural and optical properties of quantum wire structure grown on nonplanar GaAs substrate', Journal of Applied Physics, vol. 80, no. 9, pp. 5014-5020.
Effects of anodic oxide induced intermixing on the structural and optical properties of stacked GaAs quantum wire (QWR) structures grown on a sawtooth-type nonplanar GaAs substrate are investigated. Cross-sectional transmission electron microscope (XTEM) observation, temperature dependent photoluminescence (PL) and cathodoluminescence (CL) imaging were used. Intermixing was achieved by pulsed anodic oxidation of the GaAs cap layer and subsequent rapid thermal annealing, was verified by XTEM analysis. A significant enhancement of QWR PL is observed accompanied by a notable blueshift of the sidewall quantum well (SQWL) PL due to the intermixing. Furthermore, an extended necking region is observed after the intermixing by spatially resolved CL. The temperature dependence of the PL intensities of both SQWL and QWR show maxima at approximately T ?110 K indicating the role of the extended necking region in feeding carriers to SQWL and QWR. &copy; 1996 American Institute of Physics.
Kalceff, M.A.S. & Phillips, M.R. 1995, 'Cathodoluminescence microcharacterization of the defect structure of quartz', Physical Review B, vol. 52, no. 5, pp. 3122-3134.
View/Download from: Publisher's site
Cathodoluminescence (CL) spectroscopy has been used to investigate the irradiation-sensitive defect structure of ultrapure synthetic quartz at 295 and 80 K. CL emissions are identified with particular defect centers. Insight into the processes of defect formation and subsequent electromigration resulting from the trapped-charge-induced electric field following irradiation by a stationary continuous electron beam are presented. The CL emissions are associated with either a nonbridging oxygen hole center (NBOHC) or trapped-electron Si3- center (1.91 eV); NBOHC with OH precursor (1.95 eV); the radiative recombination of the self-trapped exciton (STE) in irradiation-induced amorphous SiO2 outgrowths (2.28 eV); an extrinsic process (2.46 eV); the radiative recombination of the STE associated with the E1 center in -SiO2 (2.72 eV); an additional component at 80 K due to the radiative recombination of the STE associated with the E2 center (2.69 eV); an intrinsic process (2.95 eV); and the charge-compensated substitutional aluminum center (3.12 eV). &copy; 1995 The American Physical Society.
Zhou, B., Li, X., Tansley, T.L., Butcher, K.S.A. & Phillips, M.R. 1995, 'Growth of GaN films by combined laser and microwave plasma enhanced chemical vapour deposition', Journal of Crystal Growth, vol. 151, no. 3-4, pp. 249-253.
GaN films have been grown on quartz and (011&#x0304;2) sapphire substrates using combined ultraviolet excimer laser and microwave plasma enhanced metalorganic chemical vapour deposition (MOCVD) at a substrate temperature of 500&deg;C. Film compositions were analysed by X-ray photoelectron spectroscopy (XPS) and less than 5% residual impurity, principally carbon and oxygen was found. Films grown on quartz were polycrystalline wurtzite with a preferential (0002) orientation, while (0002) and (21&#x0304;1&#x0304;0) orientations were both found on (011&#x0304;2) sapphire. Electron carrier concentration was found to be controllable between 1017 and 1014 cm-3 via control of ammonia plasma injection rate, whilst electron mobility also increased proportionally with the flow rate of the plasma. A room-temperature mobility of 95 cm2 V-1 s-1 was obtained for films on (011&#x0304;2) sapphire, saturating at a plasma flow rate of 100 ml/min. The results are interpreted as showing a reduction of nitrogen vacancies by an increase in the reacting species liberated in the plasma. &copy; 1995.
Stevens Kalceff, M.A. & Phillips, M.R. 1995, 'Electron irradiation induced outgrowths from quartz', Journal of Applied Physics, vol. 77, no. 8, pp. 4125-4127.
View/Download from: Publisher's site
The irradiation of natural and ultrapure synthetic crystalline quartz by a stationary electron beam produces surface outgrowths, which have been analyzed using scanning electron microscopy, atomic force microscopy, cathodoluminescence spectroscopy, and microscopy. Oxygen enrichment of the quartz surface occurs due to electromigration resulting from the trapped charge induced electric field. It is proposed that the accumulated oxygen is incorporated into the quartz surface structure as peroxy linkages, the formation of which results in the permanent volume increase observed as amorphous outgrowths on crystalline quartz. A cathodoluminescence emission at 2.3 eV localized on the outgrowths, is attributed to an intrinsic process. &copy; 1995 American Institute of Physics.
Moon, A.R. & Phillips, M.R. 1994, 'Defect clustering and color in Fe,Ti: ?-Al2O3', Journal of the American Ceramic Society, vol. 77, no. 2, pp. 356-367.
A comprehensive theory is presented which successfully explains the polarization, isothermal, and isochronal behavior of the optical absorption bands responsible for the color in blue and blue-green sapphire (Fe,Ti: ?-Al2O3). The experimental study on which this theory is based has conclusively shown that (Fe,Ti) and (Fe,Fe) vacancy-containing defect clusters are responsible for the optical properties of Fe,Ti: ?-Al2O3 and H,Fe,Ti: ?-Al2O3. The experimental results also prove that V?Al is the charge-compensating defect for TiAl in Fe,Ti and Ti: ?-Al2O3 with an [TiAl ] = 3[V?Al] electroneutrality condition and that Vo provides the charge balance for Fe?Al in Fe: ?-Al2O3 with an [Fe?Al] = 2[Vo ] electroneutrality condition. Defect clusters were found to form via diffusion-limited solid-state reactions where the relative concentration of charged and neutral point defects depends on both the association energy and the diffusivity of the defects participating in the clustering reactions. In this paper, a model is presented which attempts to explain both the origin and the thermal behavior of the optical bands responsible for the color of Fe,Ti: ?-Al2O3.
FRIGO, N.J., PHILLIPS, M.R. & BODEEP, G.E. 1993, 'CLIPPING DISTORTION IN LIGHTWAVE CATV SYSTEMS - MODELS, SIMULATIONS, AND MEASUREMENTS', JOURNAL OF LIGHTWAVE TECHNOLOGY, vol. 11, no. 1, pp. 138-146.
View/Download from: Publisher's site
Pillai, S., Xu, Z., Gal, M., Glaisher, R., Phillips, M. & Cockayne, D. 1992, 'Cathodoluminescence From Porous Silicon', Japanese Journal Of Applied Physics Part 2-letters, vol. 31, no. 12A, pp. 1-2.
Spatially resolved cathodoluminescence (CL) spectra were measured on porous silicon. The CL spectra showed bands and prominent peaks ranging in energy between 1.45 eV and 3 eV and were unlike the photoluminescence spectra measured on the same samples, wh
Pillai, S.M., Xu, Z.Y., Gal, M., Glaisher, R., Phillips, M. & Cockayne, D. 1992, 'Cathodoluminescence from porous silicon', Japanese Journal of Applied Physics, Part 2: Letters, vol. 31, no. 12 A, pp. L1702-L1705.
Spatially resolved cathodoluminescence (CL) spectra were measured on porous silicon. The CL spectra showed bands and prominent peaks ranging in energy between 1.45 eV and 3 eV and were unlike the photoluminescence spectra measured on the same samples, which consisted of the well known single, broad band peaking in the visible or near infrared region. Two possible models are discussed to explain these observations.
PHILLIPS, M.R. & DARCIE, T.E. 1991, 'NUMERICAL-SIMULATION OF CLIPPING-INDUCED DISTORTION IN ANALOG LIGHTWAVE SYSTEMS', IEEE PHOTONICS TECHNOLOGY LETTERS, vol. 3, no. 12, pp. 1153-1155.
View/Download from: Publisher's site
Moon, A.R. & Phillips, M.R. 1991, 'Titania precipitation in sapphire containing iron and titanium', Physics and Chemistry of Minerals, vol. 18, no. 4, pp. 251-258.
View/Download from: Publisher's site
Titania, TiO2, precipitation in natural blue sapphire (Fe, Ti: ?-Al2O3) has been investigated using high resolution and analytical transmission electron microscopy. The structure and habit of the TiO2 precipitate depends on both the Ti4+ concentration and the temperature at which the precipitate formed. Tetragonal TiO2 (Rutile) grows at 1350&deg; C but at 1150&deg; C an orthorhombic non-equilibrium TiO2 polymorph precipitates. Both TiO2 polymorphs nucleate in the (0001)s plane as lens shaped discs twinned along their diameter. The crystallographic alignment of each type of TiO2 precipitate with respect to the ?-Al2O3 host matrix provides a high degree of structural coherency with minimal lattice mismatch. Electron diffraction analysis established the following precipitate/host orientation relationships: tetragonal TiO2: {011}r{norm of matrix} {11 {Mathematical expression}07B;100}r{norm of matrix}(0001)s and ?01 {Mathematical expression}?r?10 {Mathematical expression}0?s twinned along the (011)r planeand orthorhombic TiO2: {021}?{norm of matrix}{11 {Mathematical expression}0}s, {100}?{norm of matrix}(0001)s and ?0 {Mathematical expression}2? ?{norm of matrix}?10 {Mathematical expression}0?s twinned along the (021)? plane. &copy; 1991 Springer-Verlag.
MOON, A.R. & PHILLIPS, M.R. 1991, 'ACCURATE OH BOND ANGLE DETERMINATION IN TRIGONAL CRYSTALS', APPLIED SPECTROSCOPY, vol. 45, no. 6, pp. 1051-1053.
View/Download from: Publisher's site
PHILLIPS, M.R., DARCIE, T.E., MARCUSE, D., BODEEP, G.E. & FRIGO, N.J. 1991, 'NONLINEAR DISTORTION GENERATED BY DISPERSIVE TRANSMISSION OF CHIRPED INTENSITY-MODULATED SIGNALS', IEEE PHOTONICS TECHNOLOGY LETTERS, vol. 3, no. 5, pp. 481-483.
View/Download from: Publisher's site
McCredie, G.M., Phillips, M.R. & Moon, A.R. 1991, 'Optimization of thinning rates in an argon ion beam thinner', Review of Scientific Instruments, vol. 62, no. 7, pp. 1855-1856.
View/Download from: Publisher's site
A simple and inexpensive ''feedback'' circuit has been devised that regulates the gas flow in an argon ion gun system and thus optimizes the specimen thinning rate. The circuit is easily adapted to suit a broad range of similar applications.
Moon, A.R. & Phillips, M.R. 1991, 'Defect clustering in H,Ti:?-Al2O3', Journal of Physics and Chemistry of Solids, vol. 52, no. 9, pp. 1087-1099.
View/Download from: Publisher's site
In order to investigate the defect structure of Ti:?-Al2O3, protons were incorporated into aluminium oxide single crystals doped with tetravalent titanium. This produced a set of sharp bands in the i.r. spectrum with stretching frequencies around 3300 cm-1, characteristic of OH bands. The thermal behaviour of these bands was investigated in a series of isochronal and isothermal heating experiments, monitored using FTIR spectroscopy. The i.r. spectra consisted of three main absorption bands at 3309cm-1, 3232cm-1 and 3187cm-1. The i.r. band at 3309cm-1 has been assigned to a (Ti. AlV'''AlOH. oTi. Al)x defect cluster. The lower energy bands at 3232cm-1 and 3187cm-1 were assigned to two structural variants of a (Ti. AlV'''AlOH. o)' defect cluster. The (Ti. AlV'''AlOH. oTi. Al)x defect cluster forms via the following reversible internal diffusion-limited association reaction Ti. Al + (Ti. AlV'''AlOH. o)' ? (Ti. AlV'''AlOH. o)x. The binding enthalpy for this reaction was determined to be 1.06 &plusmn; 0.20 eV. The clustering reaction was observed to follow first order reaction kinetics. An activation energy of 2.5 &plusmn;0.1 eV was determined for the (Ti. AlV'''AlOH. o)' cluster. The relative concentration of all charged and neutral defect associates was found to critically depend on the thermal history of the crystal. The defect structure of Ti4+:?-Al2O3 is also discussed with reference to this study. &copy; 1991.
MOON, A.R. & PHILLIPS, M.R. 1991, 'IRON AND SPINEL PRECIPITATION IN IRON-DOPED SAPPHIRE', JOURNAL OF THE AMERICAN CERAMIC SOCIETY, vol. 74, no. 4, pp. 865-868.
View/Download from: Publisher's site
Moon, A.R., Phillips, M.R. & Blair, D.G. 1990, 'Equilibration in defect clustering reactions', Solid State Communications, vol. 76, no. 7, pp. 881-882.
View/Download from: Publisher's site
A technique is presented for calculating the optimum cooling profile of a sample to ensure that a given defect cluster concentration is obtained in the shortest possible time. &copy; 1990.
Moon, A.R. & Phillips, M.R. 1984, 'An electron microscopy study of exsolved phases in natural black Australian sapphire', Micron And Microscopica Acta, vol. 15, no. 3, pp. 143-146.
View/Download from: Publisher's site
Natural Australian sapphire (?-Al2O3 with around 1% Fe and up to 0.03% Ti) occurs in many colours, generally with an abundance of exsolved phases. Such 'silky' stones, cut en cabochon, exhibit the well-known phenomenon of asterism. For stones with a well-defined 'star' needle-like precipitate phases can be seen under an optical microscope. The needle axes are perpendicular to the star axes and generally parallel to the prism a-axes. (For artificial star sapphire the precipitate needle axes are perpendicular to the prism axes, e.g. Phillips et al., 1980.) Many authors have assumed that these precipitate phases in natural sapphire were needles of rutile (TiO2) only, as is the case for artificial sapphire (Phillips et al., 1980). Our studies on natural Australian black sapphire, however, confirm the existence of a variety of iron/titanium rich phases, as well as rutile. Sample specimens were prepared by illuminating a polished basal plane with a He-Ne laser to obtain the star directions and then cutting slices of the stone parallel to the star axes. The polished sections were then ion-beam thinned and examined in a JEOL 100CX (S)TEM, equipped with an energy dispersive X-ray spectrometer. Precipitate phases were identified by electron diffraction and from their X-ray spectrum. &copy; 1984.
Moon, A.R. & Phillips, M.R. 1984, 'The physics of asterism in sapphire.', Schweizerische Mineralogische und Petrographische Mitteilungen, vol. 64, no. 3, pp. 329-334.
The star image in silky sapphire (asterism) is shown to result from the incoherent superposition of reflected Fraunhofer diffraction patterns. These arise when light is scattered from precipitates strictly oriented within the sapphire host. The theory explains why long, thin precipitates produce sharper stars than their shorter and wider counterparts and why a cabochon is normally required to observe the star image. -W.S.