Dr Annette Dowd

Cortie, M.B., Xiao, L.H., Erdei, L., Kealley, C.S., Dowd, A.R., Kimpton, J.A. & McDonagh, A.M. 2011, 'Thermal Stability of (KxNayH1-x-y)2Ti6O13 Nanofibers', European Journal Of Inorganic Chemistry, vol. 2011, no. 33, pp. 5087-5095.
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Potassium-rich titanate nanofibers were produced by digesting TiO2 in concentrated KOH solutions under hydrothermal conditions. The nanofibers were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and thermogravimetric analysis. A hexatitanate structure was assigned, in contrast to the trititanate structure usually resulting from NaOH treatment of TiO2. The potassium cations could be exchanged with others, such as sodium, hydrogen, and ammonium. The potassium-rich hexatitanate was found to be photocatalytic in its as-synthesized condition. The thermal stability of the fibers during calcination was followed in situ using X-ray diffraction and was found to be strongly dependent on the chemical composition. The potassium-rich titanate converted to anatase at only 480 ¦C, whereas the hydrogen- and ammonium-rich materials had to be heated to over 600 ¦C before conversion took place. Conversion was notably slowest in the ammonium-rich material. Surprisingly, the sodium-rich hexatitanate did not form anatase at temperatures up to 800 ¦C and instead recrystallized.

Porkovich, A., Arnold, M.D., Kouzmina, G., Hingley, B., Dowd, A.R. & Cortie, M.B. 2011, 'Calorimetric sensor for use in hydrogen peroxide aqueous solutions', Sensor Letters, vol. 9, no. 2, pp. 695-697.
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A sensor for characterising aqueous solutions of hydrogen peroxide is described. The sensor is based on the calorimetric signal obtained when catalysing the decomposition of H(2)O(2). The system is quick and simple, and is suitable for determinations of H(2)O(2) concentration between 0% and at least 50% (w/w).

Cortie, M.B., Giddings, J.A. & Dowd, A.R. 2010, 'Optical Properties And Plasmon Resonances Of Titanium Nitride Nanostructures', Nanotechnology, vol. 21, no. 11, pp. 1-8.
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We examine the optical properties of nanostructures comprised of titanium nitride, TiN, an electrically conducting intermetallic-like compound. This material can be deposited in the form of durable films by physical vapor deposition. Use of nanosphere te

Bai, H., Cortie, M.B., Maaroof, A.I., Dowd, A.R., Kealley, C.S. & Smith, G.B. 2009, 'The preparation of a plasmonically resonant VO2 thermochromic pigment', Nanotechnology, vol. 20, no. 8, pp. 1-9.
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Vanadium dioxide (VO2) undergoes a reversible metal-insulator transition, normally at similar to 68 degrees C. While the properties of continuous semi-transparent coatings of VO2 are well known, there is far less information available concerning the potential use of discrete VO2 nanoparticles as a thermochromic pigment in opaque coatings. Individual VO2 nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO2 nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO2 powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties.

Bhatia, V.K., Levey, F.C., Kealley, C.S., Dowd, A.R. & Cortie, M.B. 2009, 'The aluminium-copper-gold ternary system', Gold Bulletin, vol. 42, no. 3, pp. 201-208.
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Despite Au, Al and Cu being individually very well-known elements, their ternary phase diagram has not been studied in as much detail as those of many other Au-containing ternaries. Here we review what is known, and consider the prospects for technological exploitation of some of the ternary compositions. The components of greatest interest in Al-Au-Cu may be the P-phases, at least two of which have shape memory properties. Of these, 'Spangold', which has the nominal stoichiometry Au7Cu5Al4, has received some attention for jewellery applications, while the edge compound Cu3Al is a well-known shape memory composition with corresponding specialised industrial uses. The properties of other beta-phase compositions in the system have been scarcely investigated. The system also contains an extensive gamma-phase, Al4AuxCu9-x, where x ranges from 0 to similar to 6.5, and the purple gold phase AuAl2.

Cortie, M.B., Dowd, A.R., Harris, N. & Ford, M.J. 2007, 'Core-shell Nanoparticles With Self-regulating Plasmonic Functionality', Physical Review B, vol. 75, no. 11, pp. 113405-1-113405-4.
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We propose a smart nanoparticle, a regulatron, that exploits a cycle of dynamic plasmonic feedback to self-regulate its temperature to a fixed range. One kind of regulatron can be conceived from VO2 and Au; the temperature of this particle when illuminat

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+.

Johnston, M.B., Dowd, A.R., Driver, R., Linfield, E.H., Davies, A.G. & Whittaker, D.M. 2004, 'Emission of collimated THz pulses from photo-excited semiconductors', Semiconductor Science and Technology, vol. 19, no. 4, pp. 449-451.
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It is shown experimentally that surface-field terahertz (THz) emitters can produce well-collimated beams of THz radiation, making them useful devices for time-domain spectroscopy applications. Simulations of the carrier-dynamics are used to explain the mechanism of THz generation in InAs and GaAs, and it is shown that inter-valley scattering of electrons must be considered in order to fully describe THz emission from InAs.

Johnston, M.B., Whittaker, D.M., Dowd, A.R., Davies, A.G., Linfield, E.H., Li, X. & Ritchie, D.A. 2002, 'Generation of high-power terahertz pulses in a prism', Optics Letters, vol. 27, no. 21, pp. 1935-1937.
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A compact, high-power emitter of half-cycle terahertz (THz) radiation is demonstrated. The device consists of an epitaxial InAs emitter upon a GaAs prism and produces THz pulses that are 20 times more powerful than those from conventional planar InAs emitters. This improvement is a direct result of reorienting the transient THz dipole such that its axis is not perpendicular to the emitting surface. (C) 2002 Optical Society of America.

Johnston, M.B., Corchia, A., Dowd, A.R., Linfield, E.H., Davies, A.G., McLaughlin, R., Arnone, D.D. & Pepper, M. 2002, 'Magnetic-field-induced enhancement of terahertz emission from III-V semiconductor surfaces', Physica E: Low-dimensional Systems and Nanostructures, vol. 13, no. 2-4, pp. 896-899.
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We discuss the origins of the magnetic-field-induced enhancement of terahertz (THz) emission from bulk semiconductor surfaces. The principal effect of the magnetic field is to rotate the THz dipole and hence dramatically increase the THz power radiated through the semiconductor surface. It also significantly affects the ability of the photo-created carriers to screen surface electric fields. The sensitivity of THz emission to the motion of photo-created carriers makes this an ideal probe of hot carrier dynamics both in bulk semiconductors and sophisticated heterostructures.

Dowd, A.R., Elliman, R.G. & Luther-Davies, B. 2001, 'Linear optical properties of Ge nanocrystals in silica', Applied Physics Letters, vol. 79, no. 15, pp. 2327-2329.
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The absorption and extinction spectra of Ge nanocrystals in silica formed by ion implantation are studied using photothermal deflection and transmission spectroscopies. It is found that scattering makes a significant contribution to the extinction spectrum, damping the spectral features and resulting in a Rayleigh scattering-like omega4 dependence. In contrast, the spectra measured by photothermal deflection clearly show features such as the E1/E1 + Delta1 transitions. The Tauc gap is extracted to be ~0.7-¦0.1 eV.

Dowd, A.R., Llewellyn, D., Elliman, R.G., Luther-Davies, B., Samoc, M. & Fitz Gerald, J.D. 2001, 'Physical and optical characterisation of Ge-implanted silica', Nuclear Instruments & Methods In Physics Research Section B-Beam Interactions With Materials And Atoms, vol. 175, pp. 637-640.
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Ge nanocrystals formed in silica by implantation with 1.0 MeV Ge ions and subsequent annealing at 1100-¦C were characterised by transmission electron microscopy and Raman spectroscopy. The nanocrystals were found to be approximately spherical in shape and to have a structure consistent with that of bulk Ge. The average size of the crystallites increased with increasing fluence and for a fluence of 1++1017 Ge cmÔ++2 the size varied from 2.5 to 12 nm. The nonlinear optical response of the material was measured at a wavelength of 800 nm using degenerative four wave mixing and z-scan techniques. The former provided information about the magnitude and temporal response of the nonlinearity whilst the latter provided information about the operative mechanism. The magnitude of the nonlinear refractive index, n2 , was shown to be more than three-orders of magnitude larger than that of pure silica and to have a relaxation time of the order of picoseconds. The mechanism causing this nonlinear response is shown to be absorptive and to increase with increasing implant fluence as a consequence.

Dowd, A.R., Samoc, M., Luther-Davies, B. & Elliman, R.G. 1999, 'Nonlinear Optical Properties Of Semiconducting Nanocrystals In Fused Silica', Nuclear Instruments & Methods In Physics Research Section B-beam Interactions With Materials And Atoms, vol. 148, no. 1-4, pp. 964-968.
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Degenerate four-wave mixing (DFWM) is used to examine the nonlinear optical response of Ge nanocrystals in a silica matrix. The nanocrystals are formed by implanting 1.0 MeV Ge ions into silica to a dose of 3.0x10(17) Ge cm(-2) and annealing at 1100 degr

Dowd, A.R., Elliman, R.G., Samoc, M. & Luther-Davies, B. 1999, 'Nonlinear Optical Response Of Ge Nanocrystals In A Silica Matrix', Applied Physics Letters, vol. 74, no. 2, pp. 239-241.
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Time-resolved degenerate-four-wave-mixing measurements were used to study the nonlinear optical response (intensity-dependent refractive index! of Ge nanocrystallites embedded in a silica matrix. Nanocrystals were fabricated by ion-implanting silica with

Samoc, M., Samoc, A., Luther-Davies, B., Dowd, A.R. & McDonnell, M. 1997, 'Photocurrent Autocorrelation Of Femtosecond Laser Pulses In Poly(p-phenylenevinylene)', Journal Of Physics D-Applied Physics, vol. 30, no. 5, pp. 895-899.
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Photoconductive thin-film cells made from a pi-conjugated polymer, poly-(p-phenylenevinylene) (PPV) can be used for diagnostics of femtosecond laser pulses utilizing the phenomenon of photocurrent autocorrelation. In general, the autocorrelation photocur

Bhatia, V.K., Thorogood, G., Dowd, A.R. & Cortie, M.B. 2011, 'Thin Films of AuCuAl Shape Memory Alloy for Use in Plasmonic Nano-actuators', MRS Fall Meeting, Boston, MA, November 2010 in MRS Proceedings, ed See MRS online proceedings library, Cambridge University Press, Online, pp. n01-n08.
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Vijay Bhatia, Gordon Thorogood, Annette Dowd and Michael B. Cortie (2011). Thin Films of AuCuAl Shape Memory Alloy for Use in Plasmonic Nano-actuators. MRS Proceedings, 1295 , mrsf10-1295-n01-08 doi:10.1557/opl.2011.180

Edgar, J.A., Zareie, H.M., Blaber, M.G., Dowd, A.R. & Cortie, M.B. 2008, 'Synthesis of hollow gold nanoparticles and rings using silver templates', IEEE International Conference on Nanoscience and Nanotechnology, Melbourne, Australia, February 2008 in International Conference on Nanoscience and Nanotechnology, ICONN 2008, ed P Mulvaney, IEEE, Piscataway, USA, pp. 36-39.
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Gold nanoshells have gained attention recently due to their versatile optical properties. In particular, their spectrally selective extinction has been exploited for experimental medical applications, functional coatings and contrast enhancement for analytical techniques. Here we discuss nanoshells and the formation of gold nanorings by the galvanic replacement of Ag nanosphere template particles. Hollow Au/Ag nanoshells can be converted to nanorings upon addition of excess HAuCl4. Nanorings present a distinct particle geometry, with optical properties exhibiting characteristics of both nanorods and nanoshells.

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

Vella, A., Whitley, R.J., Armstrong, N.G., Dowd, A.R. & Cline, J.P. 2006, 'Analysis of admixed CeO2 nanoparticles via TEM and x-ray diffraction techniques', Annual Condensed matter and materials meeting, Wagga Wagga, February 2006 in 30th Annual Condensed matter and materials meeting, ed Avdeev M, AIP, Australia, pp. 1-4.
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The techniques used to identify nanoparticle size and shape characteristics are o vital importance in the developemnt of functional nanoparticles. Each technique offers different advantages: this work compares the two techniques of transmission electron microscopy (TEM) and x-ray diffraction (XRD) analysis by charactering CeO2 nanoparticle specimens. Whole Powder Pattern Modelling (WPPM) is used to quantify the specimens dislocations and size characteristics from XRD data. Using admixed samples we test and extend the techniques. We show that XRD accurately characterises small crystallite distributions and that larger crystallite distributions necessitate further investigation.

Armstrong, N.G., Dowd, A.R., Cline, J.P. & Kalceff, W. 2005, 'Bayesian analysis of ceria nanoparticles from line profile data', Denver X-Ray Conference, Steamboat Springs, USA, June 2005 in Advances in X-ray analysis - Volume 48, ed Huang, T.C., International Centre for Diffraction Data, Pennsylvania, USA, pp. 59-66.
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A Bayesian/Maximum entropy (MaxEnt) emthod is applied to quantify the broadening of X-ray line profiles in terms of the nanocrystallite size effects in ceria. The analysis is in general agreemetn with transmission electron microscopy results, while demonstrating the importance of appropriate a priori information needed in the method. The analysis also identifies other microstructural effects, such as the presence of dislocations and shape anisotropic effects which may be influencing the size distributions determined from the Bayesian/Max-Ent method.

Dowd, A.R., Johnston, M.B., Whittaker, D.M., Davies, A.G. & Linfield, E.H. 2002, 'Enhancement of THz emission from semiconductor devices', COMMAD, Sydney, Australia, December 2002 in 2002 Conference on Optoelectronic and Microelectronic Materials and Devices. COMMAD 2002. Proceedings, ed Gal, M, IEEE, Piscataway, NJ, USA, pp. 281-284.
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We have studied the emission of coherent terahertz (THz) frequency electromagnetic pulses from semiconductor surfaces. Collimated beams of THz radiation are observed from surface-field emitters and the efficiency of these emitters is shown to be improved by (a) modifying the effective refractive index at the surface of the emitter and (b) reorienting the THz dipole with respect to the surface. A ~ 20 enhancement in emitted THz power was seen in a GaAs/InAs prism emitter

Dowd, A.R., Llewellyn, D., Fitz Gerald, J.D., Elliman, R.G. 2001, 'The size distribution of Ge nanocrystals in implanted and annealed silica', Microstructural Processes in Irradiated Materials - 2000, Boston, MA, USA, November 2000 in Microstructural Processes in Irradiated Materials - 2000. Symposium (Mater. Res. Soc. Proceedings Vol. 650), ed Lucas GE; Snead LL; Kirk MA; Elliman RG, Mater. Res. Soc., Warrendale, PA, USA, pp. R3.39.1-R3.39.6.
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Effect of implantation and annealing parameters on the formation of Ge crystallites in ion implanted silica are examined. Samples were implanted at room temperature or -196degrees C with 1.0 MeV Ge+ ions to fluences in the range from 0.6 to 31017 Gecm-2. Ge nanocrystals were not observed in samples implanted at -196degrees C but were observed in samples irradiated at room temperature. Nanocrystals were observed in all samples after annealing and their size distribution was found to be almost independent of the implant fluence. The distributions were also shown to be asymmetrical with depth, with smaller nanocrystals located on the near surface side of the implant distribution