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Dr Cuong Ton-That

Biography

Cuong Ton-That obtained a BSc in Physics (Honours, University Medal) from UTS and a PhD degree in the field of surface science from the Robert Gordon University, UK in 2000. He joined UTS in 2003 as a lecturer. Prior to working at UTS, he was a postdoctoral research associate in the Nanoscience Centre, University of Cambridge from 2000-2003.

His research is focused upon the development of oxide materials and nanostructures for solid state lighting applications. He has expertise in the growth and characterisation of zinc oxide nanostructures together with experience in cathodoluminescence, synchrotron-based X-ray spectroscopy, deep-level transient spectroscopy and scanning probe microscopy techniques.

He is currently the Leader of Research and Development in the School of Physics and Advanced Materials.

Image of Cuong Ton-That
Senior Lecturer, School of Physics and Advanced Materials
Program Director, School of Physics and Advanced Materials
Core Member, Research Strength Materials and Technology for Energy Efficiency Member
Research Fellow, Institute for Nanoscale Technology
Core Member, Research Strength Materials and Technology for Energy Efficiency Member
BSc (Hons) (UTS), PhD (Aberdeen)
 
Phone
+61 2 9514 2201
Room
CB01.12.19
Can supervise: Yes

Conference Papers

Foley, M., Ton-That, C. & Phillips, M.R. 2010, 'Cathodoluminescence characterisation of vapour transport grown ZnO structures', International Conference On Nanoscience and Nanotechnology, Sydney, Australia, February 2010 in Proceedings of the 2010 International Conference on Nanoscience and Nanotechnology, ed Andrew Dzurak, IEEE Explorer, Piscataway, NJ, U.S.A., 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, K.B. & Phillips, M.R. 2008, 'Cathodoluminescence for High Resolution Non-Destructive Luminescence Depth Profiling.', Sydney, Australia, July 2008 in IUMRS-ICEM 2008 COMMAD 2008, ed J Williams, A-MRS, Parkville, VIC.
Foley, M., Ton-That, C. & Kirkup, L. 2007, 'Electrical Properties of Pure and Oxygen-Intercalated Fullerene Films', Annual Condensed Matter and Materials Meeting, Wagga Wagga, Australia, February 2007 in Proceedings of the 31st Annual Condensed Matter and Materials Meeting, ed Barnhoorn, A; Fitz Gerald, J D; Jackson I; Senden, TJ, Australian National University, ACT, Australia, pp. 1-3.
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The conductivity of polycrystalline fullerene films as a function of oxygen concentration was investigated and found to be affected significantly by changes in oxygen partial pressure. The conductivity of the film was fitted to an Arrhenius curve. Analysis of the data indicated that a change of 0.11eV in activation energy occurred as the oxygen pressure was varied over two orders of magnitude.
Dowd, A.R., Johansson, K.B., Armstrong, N.G., Ton-That, C. & Phillips, M.R. 2006, 'Cathodoluminescence as a method of extracting detailed information from nanophotonics systems: a study of silicon nanocrystals', Conference on Microelectronics - Design, Technology and Packaging II, Brisbane, Australia, December 2005 in Photonics: Design, Technology, And Packaging Ii, ed Abbott, D; Kivshar, YS; RubinszteinDunlop, HH; Fan, S, SPIE-Int Society Optical Engineering, Bellingham, USA, pp. J380-1-J380-10.
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We investigated Si nanocaystal samples produced by high dose 600 keV Si+ implantation of fused silica and annealing using cathodoluminescence (CL). CL spectra collected under 5-25 keV electron irradiation show similar features to reported photoluminescence

Journal Articles

Zhu, L., Ton-That, C. & Phillips, M.R. 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 donor+acceptor pair (DAP) emission originating from the N doping
Ton-That, C., Nguyen, T. & Dan, Y. 2013, 'Enhanced Photoluminescence Of Polyfluorene By Incorporation Of Al-doped Zno Nanoparticles', Thin Solid Films, vol. 538, no. NA, pp. 85-88.
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Photoluminescent and structural properties of nanocomposite films consisting of green-emitting polyfluorene (PF) and Al-doped ZnO (AZO) nanoparticles were investigated. Topographical analysis shows that AZO nanoparticles can be homogeneously dispersed in PF films with less than 10 wt.% AZO. Photoluminescence of the composite films was investigated under wavelength selective excitation of AZO. Photoexcitation with laser energy below the AZO bandgap produces a slight increase in the PF emission intensity with increasing AZO concentration, accompanied by a spectral blueshift. These effects are attributed to separation of polymer chains and twisting of the PF backbone as revealed by Raman spectroscopy. On the other hand, photoexcitation above the AZO bandgap shows a remarkable enhancement, with the intensity at 5+10 wt.% AZO being three times greater than that of pure PF. The luminescence enhancement is attributed to the efficient transfer of energy from AZO nanoparticles to PF.
Cortie, M.B., Coutts, M.J., Ton-That, C., Dowd, A.R., Keast, V. & McDonagh, A.M. 2013, 'On The Coalescence Of Nanoparticulate Gold Sinter Ink', Journal Of Physical Chemistry C, vol. 117, no. 21, pp. 11377-11384.
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We examine the mechanism by which thiol-protected gold nanoparticle inks can sinter at surprisingly low temperatures. At room temperature the sample is comprised of randomly close-packed gold nanoparticles of about 2.3 nm diameter with a ligand shell of
He, R., Tang, B., Ton-That, C., Phillips, M.R. & Tsuzuki, T. 2013, 'Physical structure and optical properties of Co-doped ZnO nanoparticles prepared by co-precipitation', Journal of nanoparticle Research, vol. 15, no. 1, pp. 2030-1-2030-8.
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The structural and optical properties of cobalt-doped zinc oxide (Co-doped ZnO) nanoparticles have been investigated. The nanopowder with Co concentrations up to 5 at% was synthesized by a co-precipitation method. The physical structure and the chemical states of the Co-doped ZnO were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV+Visible reflectance and cathodoluminescence (CL) spectroscopy. The results show that cobalt ions predominantly occupy Zn2+ sites in the wurtzite crystal lattice and possess a valence state of 2+. CL analysis revealed that the incorporation of Co2+ creates a new emission band at 1.85 eV, but quenched the near-band-edge luminescence.
Choi, S., Ton-That, C., Phillips, M.R. & Aharonovich, I. 2013, 'Observation of Whispering Gallery Modes from hexagonal ZnO microdisks using cathodoluminescence', Applied Physics Letters, vol. 103, no. 17, pp. 171102-1-171102-5.
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Zinc oxide hexagonal microdisks with diameters ranging from 3?m up to 15?m were fabricated by thermal chemical vapour deposition. Optical characterisation of ZnO microdisks was performed using low temperature (80?K) cathodoluminescence (CL) imaging and spectroscopy. The microdisks exhibited green luminescence locally distributed near the hexagonal boundary of the ZnO microdisks. High resolution CL spectra of the ZnO microdisks revealed whispering gallery modes (WGMs) emission. The experimentally observed WGMs were in excellent agreement with the predicted theoretical positions calculated using a plane wave model. This work could provide the means for ZnO microdisk devices operating in the green spectral range.
Ton-That, C., Foley, M., Phillips, M.R., 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.R. 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 C. The ZnO near-band-edge (NBE) peak is dramatically enhanced, while the green emission at 2.4 eV is quenched with increasing hydrogen incorporation. These effects are attributed to hydrogen passivating green luminescence centers, which are most likely negatively charged zinc vacancy defects. E-beam irradiation of H-doped ZnO crystals by an intense electron beam with W power reverses the hydrogen doping process. This effect is ascribed to the dissociation of H-related defects, formation of Chidden H2, and electromigration of H + under the influence of the local trapped charge-induced electric field. These results highlight the potential to modify the local luminescent properties of ZnO by e-beam irradiation
Ton-That, C., Weston, L. & Phillips, M.R. 2012, 'Characteristics of point defects in the green luminescence from Zn- and O-rich ZnO', Physical Review B, 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.
Zou, J., Le Rendu, P., Musa, I., Yang, S., Dan, Y., Ton-That, C. & Nguyen, T. 2011, 'Investigation of the optical properties of polyfluorene/ZnO nanocomposites', Thin Solid Films, vol. 519, no. 12 Special Issue, pp. 3997-4003.
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Polyfluorene (PF) and its derivatives are very promising candidates for organic light emitting diodes (OLEDs) in lighting applications because of their high photoluminescence and electroluminescence efficiencies. Recent investigations of potential materials for OLEDs have shown that introducing n-type inorganic nanoparticles into conjugated polymers is efficient to produce stable and high performance devices. In this study, composite thin films made by incorporation of zinc oxide (ZnO) nanoparticles into a PF derivative have been prepared and their optical properties have been investigated. The prepared thin films were stored in different media (in air, in vacuum, in the dark or exposed to light) in order to study environmental influences on the material stability. Analysis of spectral data obtained from infrared (IR), Raman, UV-vis, and photoluminescence (PL) measurements shows a large enhancement in luminescence for polymer nanocomposites while using high nanoparticle concentrations (within a limit of 10% ZnO). Time-resolved PL performed on those nanocomposite films corroborated the above result: it indicated that the light-emission enhancement can be explained by efficient energy transfer from nanoparticles to the polymer chains and increase of the chain separation distance. In addition, the nanocomposites were found to be more stable than pristine polymer films whatever the storage conditions were used. It was confirmed by IR analysis that incorporation of nanoparticles into polymers prohibited the formation of fluorenonyl groups in PF chains, which was identified as the main cause of the degradation of the polymer under photo-oxidation.
Lem, L.L., Ton-That, C. & Phillips, M.R. 2011, 'Distribution of visible luminescence centers in hydrogen-doped ZnO', Journal of Materials Research, vol. 26, no. 23, pp. 2912-2915.
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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.
Ton-That, C., Foley, M., Lee Cheong Lem, L.O., McCredie, G.M., Phillips, M.R. & 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 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.
Foley, M., Ton-That, C. & Phillips, M.R. 2010, 'Luminescent properties of ZnO structures grown with a vapour transport method', Thin Solid Films, vol. 518, no. 15, pp. 4231-4233.
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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.
Phillips, M.R., Drouin, D., Moody, S.J. & Ton-That, C. 2009, 'Imaging Fundamental Electronic Excitations at High Spatial Resolution Using Scanning Cathodoluminescence Microscopy', Microscopy & Microanalysis, vol. 15, no. S2, pp. 670-671.
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Ton-That, C., Stockton, G., Phillips, M.R., 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., Phillips, M.R., 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.
Ton-That, C., Foley, M. & Phillips, M.R. 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.R. & 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 electron+hole pairs at the MEH-PPV/ZnO interface and the charging of the nanoparticles.
Foley, M., Ton-That, C. & Phillips, M.R. 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.
Ton-That, C., Dowd, A.R., Shard, A.G., Dhanak, V.R., Taninaka, A., Shinohara, H. & Welland, M.E. 2007, 'Electronic structure of potassium-doped La@C82 metallofullerene studied with photoelectron spectroscopy', Physical Review B, vol. 76, no. 16, pp. 1-7.
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The electronic structure of potassium-doped La@C82 has been studied with synchrotron-radiation photoelectron spectroscopy. Ultraviolet photoemission measurements indicate evolution of the valence-band states of La@C82 with increasing potassium content, but KxLa@C82 remains semiconducting for all x between 0 and 6, with a band gap of at least 0.4 eV, in contrast to K-doped C60. The valence-band features, including those which arise from the interactions of C82 cages with La and K, show oscillatory behavior of photoemission intensity with incident photon energy. The strength of the oscillations varies between the states, and we associate diminished oscillations with increased localization of electron density. Finally, although core and valence states of La@C82 change considerably with potassium dosage, the encapsulated La atom is well shielded from the outside chemical environment and its valency remains close to 3+.
Ton-That, C., Shard, A.G., Dhanak, V.R., Shinohara, H., Bendall, J. & Welland, M.E. 2006, 'Electronic structure of pristine and potassium-doped Y@C-82 metallofullerene', Physical Review B, vol. 73, no. 20, pp. 205406/1-205406/6.
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Ultraviolet photoelectron spectra (UPS) of Y@C-82 have been measured with a synchrotron light source. UPS spectra reveal the photoelectron onset at 0.3 eV below the Fermi level, indicating the semiconducting nature of the metallofullerene, and contain lo
Ton-That, C., Welland, M.E., Larsson, J.A., Greer, J.C., Shard, A.G., Dhanak, V.R., Taninaka, A. & Shinohara, H. 2005, 'Electrostatic ordering of the lanthanum endoatom in La@C-82 adsorbed on metal surfaces', Physical Review B, vol. 71, no. 4, pp. 1-6.
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An investigation of the dynamic behavior of the endohedral La atom in La@C-82 adsorbed on Ag(111) or Cu(111) using the normal-incidence x-ray standing wavefield (NIXSW) technique is presented. For the surface-normal (111) reflection, NIXSW demonstrates d
Shard, A.G., Ton-That, C., Campbell, P.A. & Dhanak, V.R. 2004, 'Site occupancy of chlorine on Cu(111) using normal-incidence x-ray standing waves: The energy difference between fcc and hcp hollow sites', Physical Review B, vol. 70, no. 15, pp. 155409-155417.
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t has previously been established that the lowest energy site for chlorine atoms on Cu(111) is the fcc hollow. However, substantial population of the hcp hollow at room temperature indicates that there is a relatively small difference in energy between the two sites. We show that this energy difference must be less than 10 meV by measuring the relative populations using normal-incidence x-ray standing waves and comparing the results to Monte Carlo simulations. This result is consistent with recent density functional theory calculations which indicate an energy difference of approximately 5 meV
Ton-That, C., Shard, A.G., Egger, S., Dhanak, V.R. & Welland, M.E. 2003, 'Modulations of valence-band photoemission spectrum from C-60 monolayers on Ag(111)', Physical Review B, vol. 67, no. 15, pp. 1-6.
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The photon-energy dependences of valence-band photoemission spectra have been investigated for monolayer, submonolayer, and multilayer C60 films on Ag(111). The intensity ratios of the highest and next-highest occupied molecular orbitals (the HOMO and NHOMO) of the films are found to oscillate with the same period as the incident photon energy is varied, but the amplitude of the oscillation is smaller with lower film coverage. Since the characteristics of the molecular orbitals of C60 in the monolayers are considerably different from those of the thick film due to the charge-transfer interaction between the metallic surface and the molecule the observation opposes the proposal in which the oscillation is entirely dependent on the nature of the empty and occupied states involved in the photoemission process. The results instead support the photoelectron interference model by Hasegawa et al. [Phys. Rev. B 58, 4927 (1998)]. Variation of the oscillation amplitude with C60 coverage is explained in terms of hybridization of the HOMO and NHOMO with the surface. Depositing C60 onto Ag(111) held at a high temperature produces a single-phase (2sqrt[3]2sqrt[3]) R30 C60 monolayer. Angle-resolved photoemission experiments reveal changes in the relative intensities of the two bands with the azimuth-emission angle, measured with respect to the symmetry axes of the ordered monolayer. The intensity modulation is due to anisotropic scattering of photoelectrons along various molecular axes.
Ton-That, C., Shard, A.G., Egger, S., Dhanak, V.R., Taninaka, A., Shinohara, H. & Welland, M.E. 2003, 'Orientation and constraints of endohedral lanthanum in La@C82 molecules adsorbed on Cu(111)', Physical Review B, vol. 68, no. 4, pp. 1-6.
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The orientation of the endohedral La atom in La@C82 adsorbed on Cu(111) has been determined using the normal-incidence x-ray standing wave (NIXSW) technique. The NIXSW measurements were carried out using both the normal ?111? and 70.5 off-normal ?111? Bragg reflections. The La ?111? profiles of the La@C82 monolayer and submonolayers are found to be similar to the ?111? profile of the multilayer, while the ?111? profiles of the monolayer and submonolayers are distinctly different with much lower peak height. This indicates significant ordering of the La atoms in the monolayers with respect to height above the Cu surface but little lateral ordering. The results of curve fits to the monolayer profiles show that the La atoms are regionally located at 1.62 (0.77) + above an extended scattering plane from the crystal. Cooling the monolayers to a temperature of 170 K increases ordering of the La atoms with respect to height above the surface. The NIXSW results demonstrate that the endohedral molecules adopt a restricted orientation upon adsorbing on the surface and the La atom resides on either the upper or lower half of the cage. Theoretical calculations show that the most stable La positions are located in the top half of the fullerene cage, which supports the La upper configuration. The results are explained in terms of electrostatic interactions between the endohedral atom, the fullerene cage, and the substrate.
Ton-That, C., Shard, A.G., Egger, S., Taninaka, A., Shinohara, H. & Welland, M.E. 2003, 'Structural and electronic properties of ordered La@C82 films on Si(111)', Surface Science, vol. 522, no. 1-3, pp. L15-L20.
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The growth of endohedral fullerene La@C82 films on Si(1 1 1) has been explored by scanning tunneling microscopy (STM). The STM images reveal the molecules are hexagonally close-packed in multilayer films with the inter-molecular separation similar to that of the La@C82 crystal. Electronic properties of the films have been investigated by ultraviolet photoelectron spectroscopy (UPS) and tunneling spectroscopy, which provide comparable results for the electronic structure of the occupied electronic states. Tunneling spectroscopy also gives an insight into the unoccupied states and shows that the edges of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) both approach the Fermi level, indicating that the film is metallic or semi-metallic. An electronic structure of the La@C82 film is proposed from the spectroscopic results.
Ton-That, C., Shard, A.G. & Bradley, R.H. 2002, 'Surface feature size of spin-cast PS/PMMA blends', Polymer, vol. 43, no. 18, pp. 4973-4977.
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Thin films of polystyrene (PS)/polymethylmethacrylate (PMMA) blends have been spin cast on mica from chloroform solutions. When the concentration of PMMA in the casting solution is less than that of PS a pitted morphology is formed. The average sizes of the pits are shown to increase with both the total concentration of the casting solution and the relative concentration of PMMA. The change in pit size is explained in terms of incomplete dewetting of a PMMA solution from an underlying PS solution. For a given ratio of PMMA/PS the average pit diameters appear to increase linearly with the square of the film thickness, the gradient of which is dependent on the film composition.
Ton-That, C., Shard, A.G., Teare, D.O. & Bradley, R.H. 2001, 'XPS and AFM surface studies of solvent-cast PS/PMMA blends', Polymer, vol. 42, no. 3, pp. 1121-1129.
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Films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) blends of two different thicknesses have been examined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Blends with different compositions were spin-cast onto a mica substrate with chloroform as the mutual solvent. XPS measurements revealed surface enrichment of PMMA in all compositions. The thicker (66 nm) films exhibit a higher degree of PMMA surface enrichment than the thinner (17 nm) films. AFM imaging allows distinctions to be drawn between blends with differing compositions. The blend films with less than 50% PMMA bulk concentration generally exhibit pitted surfaces; the pit size varies with film thickness and bulk composition. When the PMMA bulk concentration is greater than 50%, the film surface changes to show island-like phase-separated structure. The surface segregation and morphology are explained in terms of solubilities of the two polymers in the solvent and dewetting of PMMA relative to PS. The phase domains on the film surface have also been resolved by frictional force microscopy (FFM) using hydrophilic tips bearing hydroxyl groups.
Teare, D.O., Ton-That, C., Emmison, N. & Bradley, R.H. 2001, 'Effects of serum on the kinetics of CHO cell attachment to ultraviolet-ozone modified polystyrene surfaces', Journal of Colloid and Intrface Science, vol. 234, pp. 84-89.
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Ton-That, C., Teare, D.O. & Bradley, R.H. 2000, 'Friction, surface oxidation, and polar free energy for polymer surfaces by chemical force microscopy', Chemistry of Materials, vol. 12, pp. 2106-2111.
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Ton-That, C., Shard, A.G. & Bradley, R.H. 2000, 'Thickness of spin-cast polymer thin films determined by angle-resolved XPS and AFM tip-scratch methods', Langmuir, vol. 16, no. 5, pp. 2281-2284.
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Polystyrene (PS) and poly(methyl methacrylate) (PMMA) thin films (<100 nm thickness) have been spin-cast from chloroform solution onto cleaved mica surfaces (roughness within 0.2 nm). An algorithm for calculating the film thicknesses based on the relative intensities of the C 1s peak of the films and the Si 2s peak of the mica from angle-resolved X-ray photoelectron spectroscopy (XPS) is presented. The film thickness changes as a function of casting conditions. Data from this approach are comparable with thickness measured by an atomic force microscopy (AFM) tip-scratch method in the range 1.5-5.5 nm. Thicknesses of the films are shown to increase linearly with concentration of cast solutions.
Teare, D.O., Ton-That, C. & Bradley, R.H. 2000, 'Surface characterization and ageing of ultraviolet-ozone treated polymers using atomic force microscopy and x-ray photoelectron spectroscopy', Surface and Interface Analysis, vol. 29, no. 4, pp. 276-283.
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Ultraviolet-ozone (UVO) treatment of poly(ethyleneterephthalate) (PET) films and polystyrene (PS) dishes of up to 10 min exposure has been studied. Surface polarity, oxygen chemisorption and topographical change were analysed by contact angle measurement, x-ray photoelectron spectroscopy and atomic force microscopy. Studies of the treated surface reveal the chemistry behind the increasing oxygen content. The oxidation process is shown to proceed via different mechanisms for the two polymers. Polyethyleneterephthalate appears to undergo a Norrish-type chain depolymerization reaction, whereas PS undergoes a much more random chain scission attack. Atomic force microscopy analysis shows an increase in the surface roughness with increasing exposure to UVO for both polymers, with grains of low-molecular-weight oxidized material (LMWOM) forming at the surface. This material can be removed by washing. Surfaces that remain after washing have a higher concentration of oxygen species than the native surfaces. Analysis of aged surfaces shows that for oxidized PET a relaxation process occurs, lowering the levels of surface oxygen. This appears to occur due to the diffusion of LMWOM into the PET bulk. Relaxation of the oxidized PS surface is less thermodynamically favourable owing to the apolar nature of the PS
Ricketts, B. & Ton-That, C. 2000, 'Self-discharge of carbon-based supercapacitors with organic electrolytes', Journal of Power Sources, vol. 89, pp. 64-69.
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Ton-That, C., Shard, A.G., Daley, R. & Bradley, R.H. 2000, 'Effects Of Annealing On The Surface Composition And Morphology Of PS/PMMA Blend', Macromolecules, vol. 33, no. 22, pp. 8453-8459.
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Films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) blend have been annealed at a temperature above their glass transition temperatures for up to 48 h. Surface chemical compositions of the cast and annealed films were measured by X-ray photoelectron spectroscopy (XPS) while surface topographical changes were followed by atomic force microscopy (AFM). The blend films spin-cast from chloroform produce nonequilibrium surfaces with a significant excess of PMMA. The polymer component with a lower surface free energy, PS, is shown to segregate to the surface upon annealing. The PS surface concentration of the films, containing 50% PS:50% PMMA in the bulk, was evaluated using the ester peak in XPS C Is spectra (sampling depth similar to9 nm) and found to increase from similar to5% (freshly spin-cast film) to a saturated level of similar to 47% after 17 h of annealing. AFM imaging reveals evolution of blend morphology with annealing time. The spin-cast films prior to annealing exhibit pitted topography with typical pit size of similar to1.2 mum and depth of 30-40 nm. As the annealing process proceeds, these pits get continually shallower. Frictional force microscopy with hydroxylated tips recorded surface phase separations for the films of 2-4 h annealing. As the annealing continues to above 14 h, the pitted structure becomes distorted. The surface enrichment and morphology changes upon annealing are explained by dewetting of PMMA relative to PS.
Teare, D.O., Emmison, N., Ton-That, C. & Bradley, R.H. 2000, 'Cellular Attachment To Ultraviolet Ozone Modified Polystyrene Surfaces', Langmuir, vol. 16, no. 6, pp. 2818-2824.
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The surfaces of standard untreated polystyrene cell culture dishes have been oxidatively modified for up to 8 min exposure time using an ultraviolet ozone treater in order to promote cell adhesion. Surface oxygen chemisorption and topographical modification has been characterized using monochromatic X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The oxidation process is shown to proceed at low exposure times (<60 s) via the formation of C-OR groups, although some R2C=O and RO-C=O groups are also formed. At longer treatments, RO-C=O groups become the dominant species, although the other groups are also present. The maximum level of oxygen reached is 36 atomic 8. Some of the oxygen present at surfaces treated at times of >60 s is in the form of loosely bound low molecular weight oxidized material (LMWOM) which is produced by oxidative scission of the PS backbone. Water washing leads to a reduction in surface oxygen content mainly by the removal of RO-C=O and R2C=O functional groups. The residual stable oxygen levels, which can be introduced, are approximately 20-25 atomic %. Surface chemistry changes are accompanied by the formation of surface spikes which are about 30 nm high and 300-400 nm wide. A correlation between treatment time/oxygen level and overall roughness is observed. The effect of washing upon the topography is to slightly increase the surface roughness, although not to a significant degree. The attachment kinetics of adhesion for Chinese hamster ovary cells show that adhesion occurs much more rapidly for oxidized surfaces than for untreated control materials. A direct correlation between the levels of oxidation and the rate of cell adhesion is demonstrated.
Ton-That, C., Teare, D.O., Campbell, P.A. & Bradley, R.H. 1999, 'Surface characterisation of ultrviolet-ozone treated PET using atomic force microscopy and x-ray photoelectron spectroscopy', Surface Science, vol. 435, pp. 278-282.
Kirkup, L. & Ton-That, C. 1998, 'A direct reading thermometer based on a silicon diode', Physics Education, vol. 33, pp. 302-305.