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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, MTEE - Materials and Technology for Energy Efficiency
Core Member, CCET - Centre for Clean Energy Technology
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 Arbiol, J. & Xiong, Q. (eds), Semiconductor Nanowires, Woodhead Publising, Cambridge, England, pp. 393-408.
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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.
Stevens-Kalceff, M.A., Phillips, M., Moon, T. & Kalceff, W. 2000, 'Cathodoluminescence Microcharacterisation of Silicon Dioxide Polymorphs' in Pagel, M., Barbin, V., Blanc, P. & Ohnenstetter, D. (eds), Cathodoluminescence in Geosciences, Springer-Verlag, Berlin, Germany, 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., Hardy, T., Merklein, M., Wintrebert-Fouquet, M. & Phillips, M. 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, Conference on Optoelectronic and Microelectronic Materials and Devices, IEEE, Canberra, ACT, pp. 139-140.
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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
Nenstiel, C., Switaisky, T., Alic, M., Suski, T., Albecht, M., Phillips, M. & Hoffmann, A.V. 2010, 'Luminescence of InGaN MQWs grown on misorientated GaN substrates', Conference on Optoelectronic and Microelectronic Materials and Devices, Proceedings, COMMAD, Conference on Optoelectronic and Microelectronic Materials and Devices, IEEE, Canberra, ACT, pp. 135-136.
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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 thi
Foley, M., Ton-That, C. & Phillips, M. 2010, 'Cathodoluminescence characterisation of vapour transport grown ZnO structures', Proceedings of the 2010 International Conference on Nanoscience and Nanotechnology, International Conference On Nanoscience and Nanotechnology, IEEE Explorer, Sydney, Australia, pp. 207-209.
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ZnO structures grown under controlled vapourphase 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 influence.
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.
Malguth, E., Hoffmann, A.V., Phillips, M. & Gehlhoff, W. 2005, 'Fe-centers in GaN as candidates for spintronics applications', GaN, AlN, InN And Related Materials, Symposium on GaN, AIN, InN Related Materials, Materials Research Society, Boston, MA, pp. 131-136.
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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 mu m thick freestanding HVPE grown GaN:Fe crystals with
Zareie, H.M., Sarikaya, M., McDonagh, A.M., Barber, J., Cortie, M.B. & Phillips, M. 2007, 'Self-organised materials: from organic molecules to genetically engineered gold-binding proteins', 2006 International Conference on Nanoscience and Nanotechnology, ICONN, IEEE, Brisbane, Australia, pp. 517-519.
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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 whos 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).
Phillips, M. & Morgan, S.W. 2006, 'Enhanced high speed SE imaging using a VPSEM using a Frisch Grid', Proceedings of Microscopy & Microanalysis 12, Suppl. 2 2006, Microscopy & Microanalysis, Cambridge university Press, Chicago, USA, pp. 1480-1481.
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Secondary electron (SE) imaging in a variable pressure SEM has necessitated the development of new detector technologies. One approach is to measure the charge, Q, induced on a positive electrode placed at some distance, r, from the specimen stage which is a ground potential. Gas ionization by sufficiently energetic SEs produces electron-ion pairs which are charge separated by the applied electric field. Electrons drift towards the anode causing further gas ionization in a cascade process, and the ions drift towards the stage (cathode). The total Q induced at the anode will include charge components induced by the motion of both electrons, QE, and ions, QI.
Wuhrer, R., Moran, K., Phillips, M. & Davey, P. 2006, 'X-ray mapping using a multiple-EDS (DUAL) detector', Proceedings of Microscopy & Microanalysis 12, suppl. 2, 2006, Microscopy & Microanalysis, Cambridge University Press, Chicago USA, pp. 1406-1407.
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X-ray mapping (XRM) is an extremely useful problem solving tool. However, the two major problems for energy dispersive spectroscopy are interpretation of results under non ideal conditions (strong overlap and small peak size relative to background), and the time required to obtain a good quality 256x256 pixel map (1 to 3 hours). XRM has been considered a slow technique, claiming many hours of SEM time and often relegated to out-of-hours (overnight) mapping. With the development of high count rate silicon high resolution drift detectors (SDD) [1, 2] and multi-detector systems [3], the time required to acquire XRM decreases. With a single EDS detector at 20kcps output, a good 512x512 quantitative map can be obtained in around 4 to 8 hours for major elements (>10wt% evenly distributed) and minor elements (>1wt% localised).
Phillips, M. & Drouin, D. 2006, 'Comparison of low voltage phosphers', Proceedings of Microscopy & Microanalysis 12, Suppl. 2, 2006, Microscopy & Microanalysis, Cambridge University Press, Chicago, USA, pp. 1526-1527.
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Progress in field emission display (FED) technology requires the parallel development of phosphors that exhibit high cathodoluminescence (CL) efficiency at low voltage (< 1 kV) excitation and long term CL stability when subjected to high current densities. Five commercial phosphors, ZnO:Zn, YSiO5:Ce, Y2O3:Eu, SrGa2S4:Ce and SrGa2S4:Eu have been studied using low voltage scanning cathodoluminescence microscopy and spectroscopy at 300 K. All samples were powders with a 0.5 10 &igrave;m particle size (Figure 1). ZnO:Zn was the only specimen that did not display any charging effects at 1 kV when using the in-lens secondary electron image mode, reflecting its good electrical conductivity compared with the other phosphors.
McBean, K.E., Phillips, M. & Drouin, D. 2006, 'Effects of lithium doping and post-processing on the cathodoluminescence of zinc oxide nanoparticles', Proceedings of Microscopy & Microanalysis 12, Suppl. 2, 2006, Microscopy & Microanalysis, Cambridge University Press, Chicago, USA, pp. 1510-1511.
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Zinc oxide (ZnO) is a wide band-gap (3.37 eV) semiconductor with a large exciton binding energy of 60 meV. Because of these properties, ZnO is a good candidate for a wide range of applications, including varistors, phosphors as well as a large range of optical devices. Although the optical properties of ZnO have been extensively studied, there is still intensive debate as to the origin of a number of the luminescence centers observed.
Mokhapati, S., Tan, H.H., Jagadish, C., McBean, K.E. & Phillips, M. 2006, 'Integration of quantum dots devices by selective area epitaxy', Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology, International Conference on Nanoscience & Nanotechnology, IEEE, Brisbane, Australia, pp. 442-445.
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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 lase integrated with a quantum well waveguide.
Drouin, D., Pauc, N., Phillips, M., Poissant, P., Delample, V. & Souifi, A. 2006, 'SEM characterisation of nanodevices and nanomaterials', Proceedings of the 2006 International Conference on Nanosacience and Nanotechnology, International Confrence on Nanoscience and Nanotechnology, IEEE, Brisbane QLD Australia, pp. 596-599.
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The scanning electron microsope (SEM) cna be used to study and characterise a wide variety of materials used in nanoelectronic and photonic applications. Several different techniques make use of this versatile tool. These include voltage conrtast in secondary electron imaging, charge colletion for semiconductor samples and cathodoluminescnece. These techniques are important in device nanofabrication process development and nanomaterials characterisation.
Phillips, M., Drouin, D. & Pauc, N. 2006, 'Probing carrier behaviour at the nanoscale in gallium nitride using low voltage cathodoluminescence', Proceedings of Microscopy & Microanalysis 12, Suppl. 2 2006, Microscopy & Microanalysis, Cambridge Univesity Press, Chicago USA, pp. 156-157.
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The increasing application of GaN in blue and UV light emitting diodes and lasers has generated considerable interest in its optical and electrical properties. These optical devices exhibit extremely high emission efficiencies despite the presence of a very high concentration of threading dislocations (108 1010 cm-2) that act as non-radiative recombination channels. This perceived contradiction can be been explained by small (< 100 nm) carrier diffusion lengths which effectively negate the effect of the threading dislocations on the radiative recombination efficiency. These short exciton and minority carrier diffusion lengths in GaN can be explored by cathodoluminescence (CL) microscopy and spectroscopy using a SEM equipped with a Schottky field emission gun operating at 1 kV.
Wuhrer, R., Moran, K. & Phillips, M. 2006, 'X-ray mapping and post processing', Proceedings of Microscopy & Microanalysis 12 Suppl. 2, 2006, Microscopy & Microanalysis, Cambridge university Press, Chicago USA, pp. 1404-1405.
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Characterisation of materials frequently involves the determination of variation in composition, structure and microstructure, by the use of a variety of imaging and analysis techniques. There is an increasing need to understand materials phenomena and processes and to learn more about exploiting subtle changes in the distribution of elements in materials technology. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS) and the combination of these techniques through x-ray mapping (XRM) has become an excellent tool for characterising the distribution of elements and phases in materials. This analytical technique provides a high magnification image related to the distribution and relative abundance of elements within a given specimen and thus makes XRM particularly useful for: identifying the location of individual elements and mapping the spatial distribution of specific elements and phases within a sample (material surface).
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.
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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 - art. no. 60380J', Photonics: Design, Technology, and Packaging II, pp. J380-J380.
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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.
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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 &plusmn; 0.01 eV above the valence band maximum considerably lower than the previously reported value of 3.17 &plusmn; 0.10 eV. A bound state of the form (Fe2+, hVB) with a binding energy of 50 &plusmn; 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. &copy; 2006 Materials Research Society.
Butcher, K.S., Ferris, J.M., Phillips, M., Wintrebert-Fouquet, M., Jong Wah, J.W., Jovanovic, N. & Vyverman, W. 2004, 'A luminescence study of porous diatoms', Materials Science & Engineering C-Biomimetic And Supramolecular Systems, Symposium on Current Trends in Nanoscience - From Materials to Applications held at the EMRS Spring Meeting, Elsevier, Strasbourg, France, pp. 658-663.
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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 ther
Wuhrer, R., Moran, K., Phillips, M. & Davey, P. 2005, 'X-ray Mapping using Multiple EDS and WDS Detectors', Proceeding Microscopy and Microanalysis Vol 11 (Suppl2), Microscopy and Microanalysis, Cambridge University Press, Honolulu, USA, pp. 1678-1679.
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High quality x-ray mapping (XRM) has been used for over 30 years by experienced wavelength dispersive spectroscopy (WDS) operators. Manufacturers have been developing similar techniques using energy dispersive spectroscopy (EDS) over the last 20 years. This has been generally unsuccssful due to a number of problems such as poor computer specifications, cost, time to map and generally poor peak to bacjground ratios (P:B). With improvements in all the above parameters EDS mapping is now gaining in popularity.
Wuhrer, R., Huggett, P.G., Moran, K., Phillips, M. & Ben-Nissan, B. 2005, 'EBSD and XRM of Phases in Vacuum Cast Composite Alloys', Proceeding Microscopy and Microanalysis Vol 11 (S2), Microscopy and Microanalysis, Cambridge University Press, Honolulu, Hawaii, pp. 1678-1679.
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There have been a number f new processes developed that allow the joining of very dissimilar materials such as titanium alloys, wear resistant white irons, cast irons and ceramic materials to ferrous (mild steel) and non-ferrous (aluminium) alloys. These new processes have allowed the development of more complex composite shapes to be produced. However, with any new process development, an undertsnating of the mechanism of bonding is required. through the use of x-ray mapping (XRM), chemical phase imaging as well as electron back scattered diffraction (EBSD) analsysis, very useful information on the mass transport across the interface as well as phase segregation, texture variations and phase distribution within the bond interface can be obtained. results from this investigation on a number of bonded materials are presented and the importance of XRM and EBSD in providing a better understanding of the physical and chemical processes involved in metallurgical bonding/welding of dissimilar materials discussed.
Phillips, M. & Morgan, S.W. 2005, 'Direct Comparison of Various Gaseous Secondary Electron Detectors in the Variable Pressure Scanning Electron Microscope', Proceeding Microscopy and Microanalysis vol 11 (Suppl 2), Microscopy and Microanalysis, Cambridge University Press, Honolulu, Hawaii, pp. 398-399.
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The conventional Everhart-Thornely scintillation-photomultiplier secondary electron (SE) detector cannot function at elevated pressures due to the high voltage (~ +12kV) involved in its operation. As a result, SE imaging in the variable pressure scanning electron microscope (VPSEM) has required the development of a new generation of SE detectors that operate under low vacuum conditions. To date, three different methods have been devised to measure the secondary electron (SE) emission signal in a VPSEM. Each of these approaches involves the excitation of the chamber gas by the placement of a low voltage (< +1000V) positively biased electrode in the vicinity of the specimen. A SE image can be obtained by measuring the current induced in either the positive electrode (the gaseous secondary electron detector) or the grounded stage (the ion current detector) or via a photomultiplier that detects light emission from the gas (the gas luminescence detector). In this work, the performance of each of these three low vacuum SE detector types has been compared under identical operating conditions using a Zeiss Supra 55VPSEM and FEI XL30 ESEM.
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.
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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. &copy; 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&deg;C to 1200&deg;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. &copy; 2005 Materials Research Society.
Wójcik, A., Kopalko, K., Godlewski, M., Łusakowska, E., Guziewicz, E., Minikayev, R., Paszkowicz, W., Światek, K., Klepka, M., Jakieła, 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.
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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. &copy; 2005 IEEE.
Godlewski, M., Phillips, M.R., Czernecki, R., Targowski, G., Perlin, P., Leszczyński, 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-Grzda, 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.
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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. &copy;2005 IEEE.
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', Materials Research Society, Symposium Proceedings Volume 798, GaN and Related Alloys, Materials Research Society, Boston, USA, pp. 569-574.
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Gelhausen, O., Phillips, M., Goldys, E.M., Paskova, T., Monemar, B., Strassburg, M. & Hoffmann, A.V. 2003, 'Formation and dissociation of hydrogen-related defect centres in Mg-doped GaN', Materials Research Society, Symposium Proceedings Volume 798, GaN and Related Alloys, Materials Research Society, Boston, USA, pp. 497-502.
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Wuhrer, R., Moran, K., Huggett, P.G., Phillips, M. & Ben-Nissan, B. 2004, 'X-Ray Mapping and Electron Back-Scattered Diffraction of Phases in Welded Materials', Proceedings Microscopy and Microanalysis 2004, Microscopy & Microanalysis, Cambridge University Press, Savannah, USA, pp. 916-917.
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Wuhrer, R., Phillips, M., Mason, K., Roux, C.P., Maniago, J. & Hales, S. 2004, 'GSR analysis in the Environmental Scanning Electron Microscope', Proceedings Microscopy and Microanalysis 2004, Microscopy & Microanalysis, Cambridge University Press, Savannah, USA, pp. 1362-1363.
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White, R.E., Phillips, M., Thomas, P., Wuhrer, R. & Dredge, P. 2004, 'Interactions between pigments in 19th and early 20th century oil paintings - in situ studies using environmental scanning electron microscopy', Proceedings Microscopy and Microanalysis 2004, Microscopy and Microanalysis, Cambridge University Press, Savannah, USA, pp. 132-133.
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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. & McBean, K.E. 2004, 'In-situ evaluation of post growth treatments on the cathodomluminescence properties of fluorescent nanoparticles in the Environmental Scanning Electron Microscope', Proceedings Microscopy and Microanalysis 2004, Microscopy & Microanalysis, Cambridge University Press, Savannah, USA, pp. 1064-1065.
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Phillips, M.R., Gelhausen, O. & Goldys, E.M. 2004, 'Cathodoluminescence properties of zinc oxide nanoparticles', Physica Status Solidi C: Conferences, pp. 229-234.
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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.
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.
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.
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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.
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Toth, M., Craven, J.P., Phillips, M., Thiel, B.L. & Donald, A.M. 2002, 'X-ray microanalysis of insulators in a variable pressure environment', Proceedings of Microscopy and Microanalysis 2002, Vol 11 (suppl 2), Microscopy & Microanalysis, Cambridge University Press, Quebec, Canada, pp. 1478-1479.
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Phillips, M. & Morgan, S.W. 2002, 'Time resolved analysis of the positive ion dynamics in the variable pressure scanning electron microscope', Proceedings of Microscopy and Microanalysis 2002, Vol 8 (Suppl 2), Microscopy & Microanalysis, Cambridge University Press, Canada, pp. 446-477.
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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.
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Whittall, A., Phillips, M. & Suetsugu, Y. 2001, 'Cathodoluminescence Emission for Differentiating the Degree of Carbonation in Apatites', Key Engineering Materials Vols. 192-195 Proeedings of the 13th Int. Symp. On Ceramics in Medicine, 13th Int. Symp. On Ceramics in Medicine, Trans tech Publications Ltd, Bologna, pp. 179-182.
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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.
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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.
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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., Phillips, M. & Cazaux, J. 2000, 'Charging Phenomena of Wide Bandgap Materials in a VP-SEM', 2nd Conference of the Internatioanl Union Microbeam Analysis Societies, Institute of Physics, Hawaii, pp. 269-270.
Phillips, M. & Toth, M. 2000, 'Charge Neutralisation of Insulators in anESEM', 2nd Conference of the Internatioanl Union Microbeam Analysis Societies, Institute of Physics, Hawaii, pp. 273-274.
Toth, M., Phillips, M., Kucheyev, S.O., Williams, J.S., Jagadish, C. & Li, G. 2000, 'Charge Contrast in SE Images Obtained Using the ESEM', 2nd Conference of the Internatioanl Union Microbeam Analysis Societies, Institute of Physics, Hawaii, pp. 275-276.
Griffin, B., Nockolds, C., Phillips, M. & Remond, G. 2000, 'New Needs for Imaging and X-ray Microanalysis Standards: ESEM, CHIME and Low Voltage Microanalysis', 2nd Conference of the Internatioanl Union Microbeam Analysis Societies, Institute of Physics, Hawaii, pp. 395-396.
Wuhrer, R., Yeung, W.Y. & Phillips, M. 2000, 'SEM/EDS, AFM and XRD Analysis of Ternary Nitride Coatings Produced by Magnetron Co-Sputtering at Different Nitrogen Pressures', 2nd Conference of the International Union Microbeam Analysis Societies, Institute of Physics, 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

Khachadorian, S., Gillen, R., Ton-That, C., Zhu, L., Maultzsch, J., Phillips, M.R. & Hoffmann, A. 2016, 'Revealing the origin of high-energy Raman local mode in nitrogen doped ZnO nanowires', Physica Status Solidi - Rapid Research Letters.
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&copy; 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Raman scattering experiments complemented by density functional theory (DFT) calculations of phonon frequencies have been performed to understand the origin of observed high-energy local Raman modes at 2269 cm-1 and 2282 cm-1 on N-plasma treated ZnO nanowires (NWs). We show that these modes increase in intensity with prolonged N-plasma treatment. Our results reveal that the origin of the high-energy Raman local mode is a loosely bound N2 molecule in the vicinity of a zinc vacancy, which according to our latest work acts as a shallow acceptor and leads to the donor-acceptor-pair transition at 3.232 eV [Phys. Rev. B 92, 024103 (2015)]. Moreover the results provide a more thorough description of nitrogen related complexes in ZnO NWs.
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.
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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 & INTERFACES, vol. 7, no. 10, pp. 5619-5623.
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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, vol. 92, no. 2.
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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.
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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.
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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 SOLID STATE PHYSICS, vol. 252, no. 11, pp. 2620-2625.
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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.
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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 20nm zinc oxide (ZnO) nanoparticles. The emitters exhibit bright broadband fluorescence in the red spectral range centered at 640nm 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. (C) 2014 AIP Publishing LLC.
Lee Cheong Lem, L.O., Phillips, M. & Ton-That, C. 2014, 'Controlling the visible luminescence in hydrothermal ZnO', Journal of Luminescence, vol. 154, pp. 387-391.
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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 (vol 47, 342001, 2014)', JOURNAL OF PHYSICS D-APPLIED PHYSICS, vol. 47.
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Ton-That, C., Lee Cheong Lem, L.O., Phillips, M., Reisdorffer, F., Mevellec, J., Nguyen, T., Nenstiel, C. & Hoffmann, A. 2014, 'Shallow carrier traps in hydrothermal ZnO crystals', New Journal of Physics, vol. 16, p. 083040.
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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, vol. 90, no. 20.
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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, pp. 27150-27156.
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The influence of deep level surface defects on electrical and gas sensing properties of ZnO nanorods NH3(g) sensors was studied. ZnO nanorods 5060 nm in diameter were synthesized via low-temperature hydrothermal growth at 90 degrees 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 degrees 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 O-2 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.
Davis, J., Short, K., Wuhrer, R., Phillips, M., Lumpkin, G.R. & Whittle, K.R. 2013, 'Electron backscatter diffraction characterization of plasma immersion ion implantation effects in stainless steel', Nuclear Instruments & Methods In Physics Research Section B-Beam Interactions With Materials And Atoms, vol. 295, pp. 38-41.
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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.
Zhu, L., Ton-That, C. & Phillips, M. 2013, 'Nitrogen incorporation in ZnO nanowires using N2O dopant gas', Materials Letters, vol. 99, no. 1, pp. 42-45.
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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 con?rmed by Raman spectroscopy, which reveals additional N-related modes at 275, 580 and 642 cm1 . 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 donoracceptor pair (DAP) emission originating from the N doping
Khachadorian, S., Papagelis, K., Ogata, K., Hofmann, S., Phillips, M. & Thomsen, C. 2013, 'Elastic Properties Of Crystalline-amorphous Core-shell Silicon Nanowires', Journal of Physical Chemistry C, vol. 117, no. 8, pp. 4219-4226.
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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 coreshell SiNWs (4 GPa) is different from the reported value for bulk Si (7 GPa), whereas no change is observed for relaxed coreshell SiNWs
Martin, A.A., Phillips, M. & Toth, M. 2013, 'Dynamic surface site activation: A rate limiting process in electron beam induced etching', ACS Applied Materials & Interfaces, vol. 5, no. 16, pp. 8002-8007.
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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.
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, vol. 88, no. 23.
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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.
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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, pp. 203513-203513.
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We studied the structural and optical properties of state-of-the-art non-polar bulk GaN grown by the ammonothermal method. The investigated samples have an extremely low dislocation density (DD) of less than 5 104cm2, which results in very narrow high-resolution x-ray rocking curves. The a and c lattice parameters of these stress-free GaN samples were precisely determined by using an x-ray diffraction technique based on the modified Bond method. The obtained values are compared to the lattice parameters of free-standing GaN from different methods and sources. The observed differences are discussed in terms of free-electron concentrations, point defects, and DD. Micro Raman spectroscopy revealed a very narrow phonon linewidth and negligible built-in strain in accordance with the high-resolution x-ray diffraction data. The optical transitions were investigated by cathodoluminescence measurements. The analysis of the experimental data clearly demonstrates the excellent crystalline perfection of ammonothermal GaN material and its potential for fabrication of non-polar substrates for homoepitaxial growth of GaN based device structures.
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.
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Ton-That, C., Foley, M., Phillips, M., Tsuzuki, T. & Smith, Z. 2012, 'Correlation between the structural and optical properties of Mn-doped ZnO', Journal Of Alloys And Compounds, vol. 522, pp. 114-117.
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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.
Weston, L., Ton-That, C. & Phillips, M. 2012, 'Doping properties of hydrogen in ZnO', Journal of Materials Research, vol. 27, no. 17, pp. 2220-2224.
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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 &micro;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
Ton-That, C., Weston, L. & Phillips, M. 2012, 'Characteristics of point defects in the green luminescence from Zn- and O-rich ZnO', Physical Review B, vol. 86, no. 11, pp. 1-5.
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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.
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, p. 211605.
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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.
Bishop, J.D., Lobo, C., Martin, A.A., Ford, M., Phillips, M. & Toth, M. 2012, 'Role of activated chemisorption in gas-mediated electron beam induced deposition', Physical Review Letters, vol. 109, p. 146103.
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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.
Lobo, C., Martin, A.A., Phillips, M. & Toth, M. 2012, 'Electron beam induced chemical dry etching and imaging in gaseous NH3 environments', Nanotechnology, vol. 23, p. 375302.
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We report the use of ammonia (NH3) 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 NH3 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 H2O, which up to now has been the most commonly used ESEM imaging gas.
Demers, H., Poirier-demers, N., Phillips, M., 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 & Microanalysis, vol. 18, no. 6, pp. 1220-1228.
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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-dimens
Roczen, M., Schade, M., Malguth, E., Callsen, G., Barthel, T., Gref, O., Tofflinger, J.A., Schopke, A., Schmidt, M., Leipner, H., Ruske, F., Phillips, M., 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 & Processing, vol. 108, no. 3, pp. 719-726.
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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) oxid
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.
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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., Li, Y., Zhu, J., Wang, X., Dou, S.X., Guo, Y., Lei, G., Wang, Y., Phillips, M., Cortie, M.B., Li, Y., Choi, K. & Shi, X. 2011, 'Visualization Of Vortex Motion In Feas-Based Bafe(1.9)Ni(0.1)As(2) Single Crystal By Means Of Magneto-Optical Imaging', Journal Of Applied Physics, vol. 109, no. 7, pp. 0-0.
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Superconductivity has been found in newly discovered iron-based compounds. This paper studies the motion of magnetic vortices in BaFe(1.9)Ni(0.1)As(2) single crystal by means of the magneto-optical imaging technique. A series of magneto-optical images re
Callsen, G., Reparaz, J., Wagner, M.R., Kirste, R., Nenstiel, C., Hoffmann, A.V. & Phillips, M. 2011, 'Phonon Deformation Potentials In Wurtzite Gan And Zno Determined By Uniaxial Pressure Dependent Raman Measurements', Applied Physics Letters, vol. 98, no. 6, pp. 1-3.
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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 materi
Wagner, M.R., Callsen, G., Reparaz, J., Schulze, J., Kirste, R., Cobet, M., Ostapenko, I., Rodt, S., Nenstiel, C., Kaiser, M., Hoffmann, A.V., Rodina, A., Phillips, M., Lautenschlager, S., Eisermann, S. & Meyer, B.K. 2011, 'Bound Excitons In Zno: Structural Defect Complexes Versus Shallow Impurity Centers', Physical Review B, vol. 84, no. 3.
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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 Y(0) 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.
Callsen, G., Reparaz, J., Wagner, M.R., Vierck, A., Phillips, M., Thomsen, C. & Hoffmann, A.V. 2011, 'Titanium-assisted growth of silica nanowires: from surface-matched to free-standing morphologies', Nanotechnology, vol. 22, no. 40, pp. 1-6.
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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 100 nm 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/SiO(x) nanostructures. We demonstrate a core-shell structure of the grown nanowires with a highly luminescent 150 nm thick shell and outstandingly fast decaying dynamics (approximate to 1 ns) 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 3.3 eV, 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.
Chen, P., Downes, J., Fernandes, A., Butcher, K., Wintrebert-Fouquet, M., Wuhrer, R. & Phillips, M. 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.
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The nature of the apparent band-gap shift in polycrystalline indium nitride thin-films, grown by remote-plasma-enhanced chemical vapour deposition at 535 +/- 10 degrees 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
Lem, L.L., Ton-That, C. & Phillips, M. 2011, 'Distribution of visible luminescence centers in hydrogen-doped ZnO', Journal of Materials Research, vol. 26, no. 23, pp. 2912-2915.
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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.
Sprouster, D.J., Ruffell, S., Bradby, J.E., Williams, J.S., Lockrey, M.N., Phillips, M., 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.
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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. 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, pp. 0-0.
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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. 2010, 'Luminescent properties of ZnO structures grown with a vapour transport method', Thin Solid Films, vol. 518, no. 15, pp. 4231-4233.
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ZnO structures were synthesised on the sapphire (112 0) substrate by a vapour transport method in a gas !owing furnace. The in!uence 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 "ndings demonstrate that the green luminescence is associated with oxygen de"ciency in ZnO.
White, R.J., Thomas, P., Phillips, M., 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 & Microanalysis, vol. 16, no. 5, pp. 594-598.
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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 mappi
Coutts, M.J., Zareie, H.M., Cortie, M.B., Phillips, M., Wuhrer, R. & McDonagh, A.M. 2010, 'Exploiting Zinc Oxide Re-Emission To Fabricate Periodic Arrays', ACS Applied Materials & Interfaces, vol. 2, no. 6, pp. 1774-1779.
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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 l
Ton-That, C., Foley, M., Lee Cheong Lem, L.O., McCredie, G., Phillips, M. & Cowie, B. 2010, 'Diffusion synthesis and electronic properties of Fe-doped ZnO', Materials Letters, vol. 64, no. 3, pp. 386-388.
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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 &micro;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.
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.
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Phillips, M., Drouin, D., Moody, S.J. & Ton-That, C. 2009, 'Imaging Fundamental Electronic Excitations at High Spatial Resolution Using Scanning Cathodoluminescence Microscopy', Microscopy & Microanalysis, vol. 15, no. S2, pp. 670-671.
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Godlewski, M., Wojcik-Glodowska, A., Guziewicz, E., Yatsunenko, S., Zakrzewski, A., Dumont, Y., Chikoidze, E. & Phillips, M. 2009, 'Optical properties of manganese doped wide band gap ZnS and ZnO', Optical Materials, vol. 31, pp. 1768-1771.
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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.
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.
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Bertinshaw, J.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, pp. 1-3.
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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
Malguth, E., Hoffmann, A.V. & Phillips, M. 2008, 'Fe in III-V and II-VI semiconductors', Physica Status Solidi B - Basic Research, vol. 245, no. 3, pp. 455-480.
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Ton-That, C., Phillips, M., Foley, M., Moody, S.J. & Stampfl, A. 2008, 'Surface electronic properties of ZnO nanoparticles', Applied Physics Letters, vol. 92, no. 26, pp. 1-3.
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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.
Foley, M., Ton-That, C. & Phillips, M. 2008, 'Cathodoluminescence Inhomogeneity In ZnO Nanorods', Applied Physics Letters, vol. 93, no. 24, pp. 1-3.
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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.
Morgan, S.W. & Phillips, M. 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, pp. 1-6.
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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
Mokkapati, S., Wong-Leung, J., Tan, H.H., Jagadish, C., McBean, K.E. & Phillips, M. 2008, 'Tuning the bandgap of InAs quantum dots by selective-area MOCVD', Journal Of Physics D-Applied Physics, vol. 41, no. 8, pp. 0-0.
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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 sing
Zareie, H.M., Morgan, S.W., Moghaddam, M., Maaroof, A.I., Cortie, M.B. & Phillips, M. 2008, 'Nanocapacitive circuit elements', ACS Nano, vol. 2, no. 8, pp. 1615-1619.
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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 nanocapacit
Wuhrer, R., Moran, K. & Phillips, M. 2008, 'Multi-Detector X-Ray Mapping and Generation of Correction Factor Images for Problem Solving', Microscopy & Microanalysis, vol. 14, no. S2, pp. 1108-1109.
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X-ray mapping with Silicon Drift detectors (SDDs) and multi-EDS detector systems has become an invaluable analysis technique because the time to perform an x-ray map is reduced considerably. Live x-ray imaging can now been performed with so much data collected in a matter of minutes. The use of multi-EDS detector systems has made this form of mapping even quicker and has also given users the ability to map minor and trace elements very accurately. How the data is collected and summed with multi-EDS detectors is very critical for accurate quantitative x-ray mapping (QXRM).
Yang, J., Li, S.S., Li, Z.W., McBean, K.E. & Phillips, M. 2008, 'Origin of excitonic emission suppression in an individual ZnO nanobelt', Journal Of Physical Chemistry C, vol. 112, no. 27, pp. 10095-10099.
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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 photoluminescenc
Ton-That, C., Stockton, G., Phillips, M., Nguyen, T., Huang, C. & Cojocaru, A. 2008, 'Luminescence properties of poly- (phenylene vinylene) derivatives', Polymer International, vol. 57, no. 3, pp. 496-501.
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BACKGROUND: Conjugated polymers, especially those of the poly(phenylene vinylene) (PPV) family, are promising candidates as emission material in fight-emitting devices. The aim of this work was to investigate the dependence of the luminescence properties
Ton-That, C., Foley, M. & Phillips, M. 2008, 'Luminescent properties of ZnO nanowires and as-grown ensembles', Nanotechnology, vol. 19, no. 41, pp. 1-5.
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Vertically aligned ZnO nanowires were synthesized on a sapphire (11 (2) over bar0) 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.
Ton-That, C., Phillips, M. & Nguyen, T. 2008, 'Blue shift in the luminescence spectra of MEH-PPV films containing ZnO nanoparticles', Journal Of Luminescence, vol. 128, no. 12, pp. 2031-2034.
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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 electronhole pairs at the MEH-PPV/ZnO interface and the charging of the nanoparticles.
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.
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Veal, T.D., Piper, L., Phillips, M., Zareie, H.M., Lu, H., Schaff, W. & Mcconville, C. 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.
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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 simi
Godlewski, M., Skrobot, M., Guziewicz, E. & Phillips, M. 2007, 'Color tuning of white light emission from thin films of ZnSe', Journal Of Luminescence, vol. 125, no. 1-2, pp. 85-91.
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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.
Toth, M., Lobo, C.J., Knowles, W.R., Phillips, M.R., Postek, M.T. & Vladar, A.E. 2007, 'Nanostructure fabrication by ultra-high-resolution environmental scanning electron microscopy', Nano Letters, vol. 7, pp. 525-530.
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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 (similar to 1 nm) and surface roughening occurring during etching.
Toth, M., Knowles, W. & Phillips, M. 2007, 'Imaging Deep Trap Distributions By Low Vacuum Scanning Electron Microscopy', Applied Physics Letters, vol. 90, no. 7, pp. 0-0.
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The distribution of deep traps in a bulk dielectric (Al2O3) 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 f
Motlan, M., Zhu, G., Gh, D., McBean, K.E., Phillips, M. & Goldys, E.M. 2007, 'Annealing Of ZnS Nanocrystals Grown By Colloidal Synthesis', Optical Materials, vol. 29, no. 12, pp. 1579-1583.
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ZnS nanocrystals (NCs) capped with tetramethylammonium (TMAH) were synthesized from ZnCl2 . 2H(2)O and thiourea using a wet chemical process. Further treatments of the nanocrystals such as aging, and annealing have been conducted to examine the stability
White, R.E., Thomas, P., Phillips, M., Wuhrer, R. & Guerbois, J.L. 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.
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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 interacti
Godlewski, M., Yatsunenko, S., Ivanov, V., Drozdowicz-Tomasia, K., Goldys, E.M., Phillips, M., 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. 2-3, pp. 192-196.
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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 4T1 to 6A1 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
Godlewski, M., Bozek, R., Miasojedovas, S., Juršenas, S., Kazlauskas, K., Žukauskas, A., Phillips, M.R., Czernecki, R., Targowski, G., Perlin, P., Leszczyński, 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.
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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., Phillips, M., Fitzgerald, J.D., Yu, J.X. & Chen, Y. 2006, 'Patterned growth and cathodoluminescence of conical boron nitride nanorods', Applied Physics Letters, vol. 88, no. 9, pp. 1-3.
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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 we
Chen, P., Butcher, K.S., Wintrebert-Fouquet, M., Wuhrer, R., Phillips, M., Prince, K., Timmers, H., Shrestha, S. & 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.
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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-g
Veal, T.D., Piper, L., Phillips, M., Zareie, H.M., Lu, H., Schaff, W. & Mcconville, C. 2006, 'Scanning tunnelling spectroscopy of quantized electron accumulation at InxGa1-xN surfaces', Physica Status Solidi A-Applications And Materials Science, vol. 203, no. 1, pp. 85-92.
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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, correspondin
Coleman, V., Buda, M., Tan, H.H., Jagadish, C., Phillips, M., Koike, K., Sasa, S., Inoue, M. & Yano, M. 2006, 'Observation of blue shifts in ZnOZnMgO multiple quantum well structures by ion-implantation induced intermixing', Semiconductor Science And Technology, vol. 21, no. 3, pp. 25-28.
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Implantation with low-energy (80 keV) oxygen ions and subsequent rapid thermal annealing at 800 degrees C are used to induce intermixing in a stack of 19 ZnO/Zn0.7Mg0.3O multiple quantum wells grown oil sapphire by molecular beam epitaxy. Large blue shif
Zareie, H.M., McDonagh, A.M., Edgar, J.A., Ford, M., Cortie, M.B. & Phillips, M. 2006, 'Controlled assembly of 1,4-phenylenedimethanethiol molecular nanostructures', Chemistry Of Materials, vol. 18, no. 9, pp. 2376-2380.
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We present here the first high-resolution scanning tunneling microscope images showing that 1,4phenylenedimethanethiol forms mono- and multilayers on gold(1 11) substrates under particular solution-deposition conditions. The high-resolution images show t
Coleman, V., Bradby, J., Jagadish, C. & Phillips, M. 2006, 'Observation of enhanced defect emission and excitonic quenching from spherically indented ZnO', Applied Physics Letters, vol. 89, no. 8, pp. 1-3.
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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 de
Phillips, M. 2006, 'Cathodoluminescence microscopy and spectroscopy of opto-electronic materials', Microchimica Acta, vol. 155, no. 1-2, pp. 51-58.
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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 C
Pauc, N., Phillips, M., 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, pp. 557-561.
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We present a low temperature study of GaN eiplayers by means of low voltage cathodoluminescence (CL). We show that lowering the primary electrons accelerating voltage down to 1 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 donot-to-acceptor pair transitions.
Morgan, S.W. & Phillips, M. 2006, 'Transient analysis of gaseous electron-ion recombination in the environmental scanning electron microscope', Journal Of Microscopy-Oxford, vol. 221, pp. 183-202.
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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 de
Morgan, S.W. & Phillips, M. 2006, 'Gaseous scintillation detection and amplification in variable pressure scanning electron microscopy', Journal Of Applied Physics, vol. 100, no. 7, pp. 1-16.
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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 dev
Godlewski, M., Phillips, M., Kazlauskas, K., Czernecki, R., Targowski, G., Perlin, P., Leszczynski, 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.
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Cathodoluminescence is applied for eveluation 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.
Malguth, E., Hoffmann, A.V., Gehlhoff, W., Gelhausen, O., Phillips, M. & Xu, X. 2006, 'Structural and electronic properties of Fe3+ and Fe2+ centers in GaN from optical and EPR experiments', Physical Review B, vol. 74, no. 16, pp. 1-12.
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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 5x10(17) cm(-3) to 2x10(20) cm(-3) is systematically investigat
Phillips, M. & Drouin, D. 2006, 'Comparison of Low Voltage Cathodoluminescent Phosphors', Microscopy & Microanalysis, vol. 12, no. S2, pp. 1526-1527.
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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.
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NA
McBean, K.E., Phillips, M. & Goldys, E.M. 2006, 'Synthesis and characterization of doped and undoped ZnO nanostructures', Microscopy And Microanalysis, vol. 12, no. 4, pp. 327-330.
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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.
White, R.E., Phillips, M., 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.
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Discolouring interactions between paint pigments have been observed since the mid 19(th) century. The source of some of these discolourations is the production of copper sulfides from an interaction between cadmium sulfide pigments and copper containing
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.
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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., Phillips, M. & 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.
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Cold pressed linseed oil and paints prepared using the inorganic pigments; lead white and red lead, were characterised using non-isothermal differential scanning calorimetry (DSC) in an air atmosphere to determine the effect of the pigment on the oxidati
Scott, K., Butcher, A., Wintrebert-Fouquet, M., Chen, P., Wuhrer, R. & Phillips, M. 2005, 'Revisiting electrochromism in InN', Physica Status Solidi C, vol. 2, no. 7, pp. 2293-2296.
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We confirm changes to the band-gap of InN thin films treated in an electrochemical cell in which water ebetrolysis is evident. Electrical properties of the films were also affected. It is suggested fhat 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.
Scott, K., Butcher, K.S., Wintrebert-Fouquet, M., Chen, P., Prince, C., Timmers, H., Shrestha, S., Shubina, T., Ivanov, S., Wuhrer, R., Phillips, M. & Monemar, B. 2005, 'Non-stoichiometry and non-homogeneity in InN', Physica Status Solidi C, vol. 2, no. 7, pp. 2263-2266.
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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 1.0eV that is not due to the Moss-Burstein effetc, oxygen inclusion or quantumn size effects, but for which changes in the growth temperature result in a strong change in stoichiometry. Material non-homogeneity and non-stoichiometry appear to be general rpoblems for inN growth. Excess nitrogen can be present at very high levels and indium rich materials is also found. This work shwos that the extent of the Moss-Burstein effects will have to be reassessed for InN.
Godlewski, M., Ivanov, V., Lusakowska, E., Bozek, R., Miasojedovas, S., Jursenas, S., Kazlauskas, K., Zukauskas, A., Goldys, E.M., Phillips, M., Bottcher, 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, vol. 2, no. 3, pp. 1056-1059.
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Effects of n-type doping of GaN epilayers and InGaN 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.
Tomaszewska-Grzeda, A., Lojkowski, W., Godlewski, M., Yatsunenko, S., Drozdowicz-Tomsia, K., Goldys, E.M. & Phillips, M. 2005, 'Growth and characterisation of ZnO nanoparticles', ACTA Physica Polonica, vol. 108, no. 5, pp. 897-902.
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In this work we evaluate structural and optical properties of ZnO nanoparticles grown by wet chemistry method. Light emission properties of these nanoparticles are studies with cathodoluminescence and microphotoluminescence. Even at the room temperature excitonic emission is well resolved, due to high exciton binding energy of ZnO. Decay kinetics of photoluminescence emisssions 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., Phillips, M., Czernecki, R., Targowski, G., Perlin, P., Leszczynski, M., Figge, S. & Hommel, D. 2005, 'Light emission properties of GaN-based laser diode structures', ACTA Physica Polonica, vol. 108, no. 4, pp. 675-680.
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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.
Godlewski, M., Yatsunenko, S., Ivanov, V., Khachapuridze, A., Swiatek, K., Goldys, E.M., Phillips, M., Klar, P.J. & Heimbrodt, W. 2005, 'Origin of ultrafast component of photoluminescence decay in nanostructures dopes with transition metal or rare-earth ions', ACTA Physica Polonica, vol. 107, no. 1, pp. 65-74.
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NA
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. 2005, 'Thin films of ZnO and ZnMnO by atomic layer epitaxy', Optica Applicata, vol. 35, no. 3, pp. 413-417.
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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. 2005, 'Controlling the properties of InGaAs quantum dots by selective-area epitaxy', Applied Physics Letters, vol. 86, no. 11, pp. 1-3.
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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
Drozdowicz-Tomsia, K., Goldys, E.M., Motlan, M., Zareie, H.M. & Phillips, M. 2005, 'Growth-temperature-dependent cathodoluminescence properties of GaSb/GaAs quantum-dot multilayer structures', Applied Physics Letters, vol. 86, no. 17, pp. 1-3.
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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 cathodoluminescenc
Godlewski, M., Yatsunenko, S., Drozdowicz-Tomsia, K., Goldys, E.M., Phillips, M., Klar, P.J. & Heimbrodt, W. 2005, 'Dynamics of light emission in CdMnS nanoparticles', ACTA Physica Polonica, vol. 108, no. 4, pp. 681-688.
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We demonstrate coexistence of slow and fast components of photoluminescence decay of the Mn&sup2;^(+) intra-shell emission in nanoparticles of CdMnS. We explain the observed decrease in PL lifetime of the Mn&sup2;^(+) intra-shell transition by high efficiency of spin dependent magnetic interactions between localized spins of Mn&sup2;^(+) ions and free carriers. This mechanism is enhanced in nanostructures, but it is also present in bulk samples.
Godlewski, M., Lusakowska, E., Bozek, R., Goldys, E.M., Phillips, M., Bottcher, 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, pp. 212-215.
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Godlewski, M., Goldys, E.M., Phillips, M., 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, pp. 207-211.
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Guziewicz, E., Godlewski, M., Kopalko, K., Lusakowska, 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.
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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 donoracceptor 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.
Gelhausen, O., Phillips, M., Goldys, E.M., Paskova, T., Monemar, B., Strassburg, M. & Hoffmann, A.V. 2004, 'Dissociation of H-related defect complexes in Mg-doped GaN', Physical Review B, vol. 69, no. 12, pp. 1-9.
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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 (2030 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 (100200 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 (2.83.0 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., Malguth, E., Phillips, M., Goldys, E.M., Strassburg, M., Hoffmann, A.V., 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.
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The optical properties of molecular-beam-epitaxy-grown GaN with different Mn-doping levels (5231019 cm3) were studied by cathodoluminescence (CL) and optical transmission spectroscopy. Transmission measurements at 2 K revealed an absorption peak at 1.414&plusmn;0.002 eV, which was attributed to an internal 5T2-->5E transition of the neutral Mn3+ state. The intensity of this Mn-related transmission peak was found to scale with the Mn3+ concentration. The CL measurements showed that Mn-doping concentrations around 1020 cm3 reduced the near band edge emission intensity by around one order of magnitude. A complete quenching of the donoracceptor-pair band at 3.27 eV and strong decrease of the yellow luminescence centered at 2.2 eV were attributed to a reduced concentration of VGa. In the infrared spectral range of 0.81.4 eV three broad, Mn-doping related CL emission bands centered at 1.01&plusmn;0.02, 1.09&plusmn;0.02, and 1.25&plusmn;0.03 eV were observed. Their origin is attributed to deep donor complexes, which are generated as a result of the heavy Mn-doping.
Phillips, M., Zareie, H.M., Gelhausen, O., Drago, M., Schmidtling, T. & Richter, W. 2004, 'Scanning tunnelling and cathodoluminescence spectroscopy of indium nitride', Journal of Crystal Growth, vol. 269, no. 1, pp. 106-110.
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ndium 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 0.8 eV was observed at 80 K. 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 not, vert, similar1.4 eV was estimated from STS IV curves.
Godlewski, M., Lusakowska, E., Goldys, E.M., Phillips, M., Bottcher, T., Figge, S., Hommel, D., Leszczynski, M., Grzegory, I. & Porowski, S. 2004, 'Diffusion length of carriers and excitons in GaN - influence of epilayer microstructure', Applied Surface Science, vol. 223, pp. 294-302.
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We demonstrate a correlation between the microsturcture of epilayers and the diffusion length of free carriers and excitons in heteroepitaxial and homeopitaxial GaN films. We show that the diffusion length is shorter than predicted for a given density of dislocations. With improving strutucal 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.
Godlewski, M., Yatsunenko, S., Khachapuridze, A., Ivanov, V., Golacki, Z., Karczewski, G., Bergman, P.J., Klar, P.J., Heimbrodt, W. & Phillips, M. 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, pp. 45-49.
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Godlewski, M., Szmidt, J., Olszyna, A., Werbowy, A., Lusakowska, E., Phillips, M., Goldys, E.M. & Sokolowska, A. 2004, 'Luminescent properties of wide bandgap materials at room temperature', Physica Status Solidi C, vol. 1, no. 2, pp. 213-218.
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Properties of nanocrystalline thin films of selected nitrides are discussed as possible biffer materials for obtaining freestanding GaN wafers. These films are grown by impulse plasma deposition on silicon substrates. We demonstrate high smoothness of these films.
Kopalko, K., Godlewski, M., Lusakowska, E., Paskowicz, W., Domagala, J., Szczerbakow, A., Ivanov, V., Godlewski, M.M. & Phillips, M. 2004, 'Monocrystalline ZnO films grown by atomic layer epitaxy - growth and characterisation', Physica Status Solidi C, vol. 1, no. 4, pp. 892-895.
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We report successful growth of thin films ZnO by atomic layer epitaxy (ALE). Properties of the ZnO films grown by ALE on GaN/sapphire are described in relation to those grown by the same sequential procedure on uncoated sapphire and glass substrates.
Kopalko, K., Godlewski, M., Guziewicz, E., Lusakowska, E., Paszkowicz, W., Domagala, J., Dynowska, E., Szczerbakow, A., Wojcik, A. & Phillips, M. 2004, 'Monocrystalline thin films of ZnSe and ZnO grown by atomic layer epitaxy', Vacuum, vol. 74, pp. 269-272.
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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 witha tomic force microscopy, scanning electron microscopy, cathodoluminescence and photoluminescence.
Strassburg, M., Rodina, A., Dworzak, M., Haboeck, U., Krestnikov, I.L., Hoffmann, A.V., Gelhausen, O., Phillips, M., 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.
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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 I4, 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, I6, I8 and I9 lines by doping, diffusion and annealing experiments combined with photoluminescence and secondary ion mass spectrometry.
Phillips, M., Gelhausen, O. & Goldys, E.M. 2004, 'Cathodoluminescence properties of zinc oxide nanoparticles', Physica Status Solidi A-Applied Research, vol. 201, pp. 229-234.
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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., Phillips, M. & 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.
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The effect of low-energy electron-beam irradiation (LEEBI) on native defects and residual impurities in metalorganic-vapor-phase-epitaxy-grown, lightly Mg-doped, p-type GaN was studied by temperature-resolved and excitation power density-resolved cathodoluminescence spectroscopy. Following the LEEBI treatment, the ubiquitous shallow donoracceptor-pair emission at 3.27 eV decreased, while a deeper DAP emission at ~3.1 eV dramatically increased in intensity, and a broad yellow luminescence band centered at 2.2 eV evolved. The results clearly indicate that the centers involved in the 3.27 eV transition are not stable during irradiation by low-energy electrons. Further, we report that the LEEBI-treatment not only dissociates neutral Mg-H complexes as intended, but simultaneously dissociates other hydrogenated defect complexes, giving rise to additional radiative recombination channels.
Dredge, P., Wuhrer, R. & Phillips, M. 2003, 'Monet's painting under the microscope', Microscopy And Microanalysis, vol. 9, no. 2, pp. 139-143.
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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., Lusakowska, E., Dynowska, E., Godlewski, M.M., Goldys, E.M. & Phillips, M. 2003, 'Origin of white color light emission in ALE-grown ZnSe', Journal Of Luminescence, vol. 102-103, no. 1, pp. 455-459.
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We discuss light emission properties from thin films of ZnSe grown by atomic layer epitaxy on GaAs (1 0 0). 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.
Godlewski, M.M., Ivanov, V., 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 sturctures and laser diodes - in-plane instabilities of light emission', ACTA Physica Polonica, vol. 103, no. 6, pp. 689-694.
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Gelhausen, O., Phillips, M. & 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.
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Scanning cathodoluminescence (CL) spectroscopy and imaging were used to study the effect of post-growth processing on the CL efficiency of metalorganic 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 MgH 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., Godlewski, M.M., Khoi, L., Golacki, 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, vol. 103, no. 6, pp. 643-648.
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Based on the results of optically detected magnetic resonance 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 in both bulk and in low dimensional structures, such as quantum wells, quantum dots, and nanostructures.
Gelhausen, O., Klein, H., Phillips, M. & 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.
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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.
Phillips, M., 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.
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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 [is proportional to] 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., Phillips, M. & 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.
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The effect of low-energy electron beam irradiation (LEEBI) on residual hydrogen impurities and native defects in activated metalorganic vapor phase epitaxy-grown Mg-doped (p-type) GaN layers was studied by cathodoluminescence (CL) microanalysis and spectroscopy at temperatures between 80 and 300 K. The LEEBI treatment dissociates (MgH)0 complexes producing (i) at 300 K, a significant increase in a free-to-bound transition (e,Mg0) centered at 3.26 eV and (ii) at 80 K, a substantial decrease in a HMg donoracceptor pair emission at 3.27 eV. In-plane and depth-resolved CL imaging reveals a direct correlation between the spatial distribution of the injected carriers and the depth and lateral distribution of activated Mg acceptors. This finding strongly suggests that hydrogen dissociation results from electron-hole recombination at hydrogen defect complexes rather than heating by the electron beam. The results at 80 K indicate that the process of dissociation of hydrogen from (MgH)0 complexes is accompanied by a generation of additional defect centers. It is proposed that following LEEBI hydrogen does not leave the specimen, but instead associates with nitrogen vacancies, generating additional recombination channels
Bradby, J., Kucheyev, S.O., Williams, J.S., Wong-Leung, J., Swain, M.V., Munroe, P., Li, G. & Phillips, M. 2002, 'Indentation-induced damage in GaN epilayers', Applied Physics Letters, vol. 80, no. 3, pp. 383-385.
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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.
Kucheyev, S.O., Toth, M., Phillips, M., Williams, J.S., Jagadish, C. & Li, G. 2002, 'X-ray spectometry investigation of electrical isolation in GaN', Journal of Applied Physics, vol. 91, no. 6, pp. 3940-3942.
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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.
Kucheyev, S.O., Toth, M., Phillips, M., 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.
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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
Remond, 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.
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Toth, M., Phillips, M., 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.
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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.
Toth, M., Phillips, M., 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.
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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.
Godlewski, M., Goldys, E.M., Phillips, M., Bottcher, 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. 627-630.
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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.
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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 efefctive gas path length may increase with the chamber pressure and that it is also often dependent on the type of x-ray bullet.
Remond, G., Myklebust, R.L., 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.
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Bradby, J., Kucheyev, S.O., Williams, J.S., Jagadish, C., Swain, M.V., Munroe, P. & Phillips, M. 2002, 'Contact-induced defect propagation in ZnO', Applied Physics Letters, vol. 80, no. 24, pp. 4537-4539.
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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 &micro;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.
Godlewski, M., Goldys, E.M., Butcher, K.S., Phillips, M., Pakula, K. & Baranowski, J. 2001, 'Cathodoluminescence Investigations of Interfaces in InGaN/Sapphire Structures', Physica Status Solidi B - Basic Research, vol. 228, no. 1, pp. 179-182.
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Kucheyev, S.O., Toth, M., Phillips, M., Williams, J.S., Jagadish, C. & Li, G. 2001, 'Cathodoluminescnece Depth Profiling of Ion-Implanted GaN', Applied Physics Letters, vol. 78, no. 1, pp. 34-36.
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Danilatos, G., Phillips, M. & Nailon, J.V. 2001, 'Electron Beam Current Loss at the High Vacuum High Pressure Boundary in the Environmental Scanning Electron Microscope', Microscopy & Microanalysis, vol. 7, no. 5, pp. 397-406.
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Gelhausen, O., Phillips, M. & Toth, M. 2001, 'Depth-Resolved Cathodoluminescence Microanalysis of Near-Edge Emission in Ill-Nitride Thin Films', Journal of Applied Physics, vol. 89, no. 6, pp. 3535-3537.
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Cooper, R., Smith, K., Colella, M., Vance, E.R. & Phillips, M. 2001, 'Optical Emission Due to Ionic Displacement in Alkaline Earth Titanates', Journal of Nuclear Materials, vol. 289, pp. 199-203.
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Godlewski, M., Mackowski, S., Karczewski, G., Goldys, E.M. & Phillips, M. 2001, 'Cathodoluminescence Studies of Self-Organised CdTe/ZnTe Quantum Dot Structure Grown by MBE: In-Plane and In-Depth Properties of the System', Semiconductor Science & Technology, vol. 16, pp. 493-496.
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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, 2.02.1 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 2.02.1 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., Pakula, K. & Baranowski, J. 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, pp. 22-31.
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Kucheyev, S.O., Toth, M., Phillips, M., Williams, J.S., Jagadish, C. & Li, G. 2001, 'Effects of Excitation Density on Cathodoluminescence from GaN', Applied Physics Letters, vol. 79, no. 14, pp. 2154-2156.
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Buyanova, I., Chen, W., Goldys, E.M., Phillips, M., Xin, H.P. & Tu, C.W. 2001, 'Strain Relation in GaNxP1-x Alloy: Effect on Optical Properties', Physica B: Condensed Matter, vol. 308-310, pp. 106-109.
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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.
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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. 2000, 'Cathodoluminescence studies of in-plane and in-depth properties of GaN Epilayers', Journal of Luminescence, vol. 87-89, no. 0, pp. 1155-1157.
Godlewski, M., Goldys, E.M., Phillips, M., Langer, R. & Barski, A. 2000, 'Cathodoluminescence depth-profiling Studies of GaN/ARGaN Quantum-Well Structures', Journal of Materials Research, vol. 15, no. 2, pp. 495-501.
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Toth, M., Kucheyev, S.O., Williams, J.S., Jagadish, C., Phillips, M. & Li, G. 2000, 'Imaging Charge Trap Distirbution in GaN Using Environmental Scanning Electron Microscopy', Applied Physics Letters, vol. 77, no. 9, pp. 1342-1344.
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Toth, M. & Phillips, M. 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.D., 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 & Microanalysis, vol. 6, no. 2, pp. 113-120.
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.
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Phillips, M. 2000, '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.
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., 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.
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The differential absorption of a GaAs single quantum well is studied for resonant pumping at either the heavy- or light-hole exciton resonances using different polarization configurations. For all excitation conditions the observed spectra show bleaching
Kucheyev, S.O., Bradby, J., Williams, J.S., Jagadish, C., Toth, M., Phillips, M. & Swain, M.V. 2000, 'Nanoindentation of epitaxial GaN Films', Applied Physics Letters, vol. 77, no. 21, pp. 3373-3375.
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Toth, M. & Phillips, M. 2000, 'The Role of Induced Contrast in Images Obtained Using the Environmental Scanning Electron Microscope', Scanning, vol. 22, no. 6, pp. 370-379.
Phillips, M. & Ott, D. 2000, 'Crosstalk Caused By Nonideal Output Filters In Wdm Lightwave Systems', IEEE Photonics Technology Letters, vol. 12, no. 8, pp. 1094-1096.
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Crosstalk mechanisms due to imperfections of the output demultiplexer in a 1550-nm wavelength-division multiplexed system are explored for the cable television frequency range of 50-800 MHz. Analytic and experimental results show significant crosstalk ca
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. 1999, 'Detection of Cr impurities in GaN by room temperature cathodoluminescence spectroscopy', Applied Physics Letters, vol. 75, no. 25, pp. 3983-3985.
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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 beta-Ga2O3 overlayers produced
Phillips, M. & Ott, D. 1999, 'Wdm Lightwave System Crosstalk By Optical Kerr Effect With Polarisation-dependent Loss', Electronics Letters, vol. 35, no. 20, pp. 1764-1765.
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WDM-system crosstalk is generated by nonlinear polarisation modulation (the optical Kerr effect) followed by polarisation dependent loss (PDL). Theory and experiment Show that at typical PDL values, this crosstalk. can exceed that from stimulated Raman s
Phillips, M., 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.
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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 junctio
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, pp. 2301-2303.
Fleischer, K., Toth, M., Phillips, M., 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.
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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 concentra
Phillips, M. & Wang, H. 1999, 'Coherent Oscillation In Four-wave Mixing Of Interacting Excitons', Solid State Communications, vol. 111, no. 6, pp. 317-321.
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We report the observation of quantum beat-like oscillations in transient four-wave mixing (FWM) of heavy-hole and light-hole excitonic transitions that share no common upper or lower states. Theoretical analysis shows that these oscillations arise from p
Toth, M., Fleischer, K. & Phillips, M. 1999, 'Direct experimental evidence for the role of oxygen in the luminescent properties of GaN', Physical Review B, vol. 59, no. 3, pp. 1575-1578.
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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 wav
Kim, D., Seong, T., Baik, Y., Kalceff, M.S. & Phillips, M. 1999, 'Cathodoluminescence of diamond films grown on pretreated Si (001) substrates by microwave plasma chemical vapour deposition', Diamond and Related Materials, vol. 8, pp. 712-716.
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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 wi
Phillips, M. & Ott, D. 1999, 'Crosstalk Due To Optical Fiber Nonlinearities In Wdm Catv Lightwave Systems', Journal Of Lightwave Technology, vol. 17, no. 10, pp. 1782-1792.
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CrosstaIk in a two-wavelength 1550-nm standard fiber system at subcarrier frequencies 50-800 MHz is investigated. The dependence of the crosstalk on subcarrier frequency, wavelength spacing, and optical power is measured and analyzed. The observed crosst
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.
Toth, M., Fleischer, K. & Phillips, M. 1998, 'Electron beam induced impurity electro-migration in unintentionally doped GaN', MRS Internet Journal of Nitride Semiconductor Research, vol. 537, pp. 1-6.
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 dis
Godlewski, M., Goldys, E.M., Phillips, M., 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.
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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 edg
Whittall, A. & Phillips, M. 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.
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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 mi
Toth, M. & Phillips, M. 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 th
Godlewski, M., Suski, T., Grzegory, I., Porowski, S., Langer, R., Barski, A., Bergman, J.P. & Monemar, B. 1998, 'Mechanisms Of Yellow And Red Photoluminescence In Wurtzite And Cubic Gan', ACTA Physica Polonica, vol. 94, no. 2, pp. 326-330.
The origin of two deep photoluminescence (PL) emissions observed in wurtzite (yellow FL) and cubic (red FL) GaN is discussed. PL and time-resolved PL studies confirm donor-acceptor pair character of the yellow band in wurtzite GaN and point to participat
Szczerbakow, A., Godlewski, M., Dynowska, E., Ivanov, V., Swiatek, K., Goldys, E.M. & Phillips, M. 1998, 'Structure, Surface Morphology And Optical Properties Of Thin Films Of Zns And CdS Grown By Atomic Layer Epitaxy', ACTA Physica Polonica, vol. 94, no. 3, pp. 579-582.
In this communication we report successful growth of monocrystalline cubic ZnS and monocrystalline and polycrystalline cubic and wurtzite films of CdS by atomic layer epitaxy. Structural and optical properties of these films are analysed. ZnS (and CdSZnS
Goldys, E.M., Zuo, H.Y., Tansley, T.L., Phillips, M. & 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.
Goldys, E.M., Zuo, H., Phillips, M., Contessa, C., Vaughan, M.R. & Tansley, T. 1997, 'Type I And Type II Alignment Of The Light Hole Band In In0.15Ga0.85AsGaAs And In In0.15Ga0.85AsAl0.15Ga0.85As Strained Quantum Wells', Journal Of Electronic Materials, vol. 26, no. 8, pp. 922-927.
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We present results of photoluminescence and cathddoluminescence measurements of strained undoped In0.15Ga0.85AsGaAs and In0.15Ga0.85AsAl0.15Ga0.85As quantum well structures, designed to throw light on the current controversy ever light-hole band alignmen
Kalceff, M., Phillips, M., Moon, T. & Smallwood, A.G. 1997, 'Cathodoluminescence Microanalysis Of Natural Hydrated Amorphous Sio2; Opal', Physics And Chemistry Of Minerals, vol. 24, no. 2, pp. 131-138.
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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 re
Wuhrer, R., Yeung, W.Y., Phillips, M. & 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.
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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 TiperAl/N compositions were produced by varying the aluminium ta
Kalceff, M.S., Phillips, M. & Moon, T. 1996, 'Electron irradiationinduced changes in the surface topography of silicon dioxide', Journal of Applied Physics, vol. 80, no. 8, pp. 4308-4314.
The irradiation of crystalline (alpha-SiO2) and amorphous (a-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
Ariyavisitakul, S., Darcie, T.E., Greenstein, L., Phillips, M. & Shankaranarayanan, N. 1996, 'Performance Of Simulcast Wireless Techniques For Personal Communication Systems', IEEE Journal On Selected Areas In Communications, vol. 14, no. 4, pp. 632-643.
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Broadband analog transport facilities using fiber or fibercoax cable can play a significant role in the evolution of the network infrastructure for personal communications services (PCSs), Low-power PCS systems require a dense grid of radio ports to prov
Kim, Y., Yuan, S., Leon, R., Jagadish, C., Gal, M., Johnston, M.B., Phillips, M., Kalceff, M.S., Zou, J. & Cockayne, D.J. 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.
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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)
Kalceff, M. & Phillips, M. 1995, 'Cathodoluminescence Microcharacterization Of The Defect Structure Of Quartz', Physical Review B, vol. 52, no. 5, pp. 3122-3134.
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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
Zhou, B., Li, X., Tansley, T., Butcher, K.S. & Phillips, M. 1995, 'Growth of GaN films by combined laser and microwave plasma enhanced chemical vapour deposition', Journal of Crystal Growth, vol. 151, pp. 249-253.
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GaN films have been grown on quartz and (01 (1) over bar 2) sapphire substrates using combined ultraviolet excimer laser and microwave plasma enhanced metalorganic chemical vapour deposition (MOCVD) at a substrate temperature of 500 degrees C. Film compo
Kalceff, M.S. & Phillips, M. 1995, 'Electron irradiation induced outgrowths from quartz', Journal Of Applied Physics, vol. 77, no. 8, pp. 4125-4127.
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Moon, T. & Phillips, M. 1994, 'Defect clustering and color in Fe,Ti: alpha-Al2O3', Journal Of The American Ceramic Society, vol. 77, no. 2, pp. 356-367.
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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 alpha-Al2O3). The experimental study on
Frigo, N., Phillips, M. & Bodeep, G. 1993, 'Clipping Distortion In Lightwave Catv Systems - Models, Simulations, And Measurements', Journal Of Lightwave Technology, vol. 11, no. 1, pp. 138-146.
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We report theoretical, numerical, and experimental investigations of clipping distortion in CATV systems. After reviewing Salehs calculation of the carrier to nonlinear distortion ratio (CNLD), we extend its applicability by incorporating a more precise
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. & 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.
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Clipping is a fundamental source of distortion in subcarrier multiplexed lightwave systems. We numerically simulate the clipping nonlinear distortion for typical CATV systems. The simulation results agree well with the Saleh clipping limit for effectiv
Moon, T. & Phillips, M. 1991, 'Titania Precipitation In Sapphire Containing Iron And Titanium', Physics And Chemistry Of Minerals, vol. 18, no. 4, pp. 251-258.
Titania, TiO2, precipitation in natural blue sapphire (Fe, Ti alpha-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+ concentrati
Moon, T. & Phillips, M. 1991, 'Accurate Oh Bond Angle Determination In Trigonal Crystals', Applied Spectroscopy, vol. 45, no. 6, pp. 1051-1053.
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Phillips, M., Darcie, T.E., Marcuse, D., Bodeep, G. & Frigo, N. 1991, 'Nonlinear Distortion Generated By Dispersive Transmission Of Chirped Intensity-modulated Signals', IEEE Photonics Technology Letters, vol. 3, no. 5, pp. 481-483.
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Transmission through dispersive and nonlinear optical fibers produces distortion in subcarrier intensity-modulated systems. Analytic expressions for second- and third-order distortion are derived using the time-domain form of the field envelope wave equ
McCredie, G., Phillips, M. & Moon, T. 1991, 'Optimization Of Thinning Rates In An Argon Ion-beam Thinner', Review Of Scientific Instruments, vol. 62, no. 7, pp. 1855-1856.
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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, T. & Phillips, M. 1991, 'Defect Clustering In H,Ti-alpha-Al2o3', Journal Of Physics And Chemistry Of Solids, vol. 52, no. 9, pp. 1087-1099.
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In order to investigate the defect structure of Ti alpha-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 33
Moon, T. & Phillips, M. 1991, 'Iron And Spinel Precipitation In Iron-doped Sapphire', Journal Of The American Ceramic Society, vol. 74, no. 4, pp. 865-868.
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Single crystals of Al2O3 containing 0.5 wt% Fe were exposed to low po2 atmospheres at 1500-degrees-C to produce precipitate phases. Analytical TEM identified the precipitate phases as spinel (hercynite) and iron, with the following orientation relations
Moon, T., Phillips, M. & Su, K. 1990, 'Equilibration In Defect Clustering Reactions', Solid State Communications, vol. 76, no. 7, pp. 881-882.
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Moon, T. & Phillips, M. 1984, 'An Electron-microscopy Study Of Exsolved Phases In Natural Black Australian Sapphire', Micron And Microscopica ACTA, vol. 15, no. 3, pp. 143-146.
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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.