Angus commenced working at UTS in 2000 undertaking research part-time during his undergraduate degrees. After completing a PhD at UTS in 2008, Nanostructured Thin Films – Plasmon Resonance Phenomena, he began his post-doctoral endeavours with a year at the UNSW School of Photovoltaics and Renewable Energy Engineering working on Si Quantum Dot Solar cells.
Returning to UTS as a post-doctoral fellow in 2009, he has worked on various projects including: A ARC Discovery Project on Radiative Cooling using sky-window spectral selectivity; and a CSIRO Flagship Transparent Electrodes cluster project developing multi-layered transparent electrodes for OPV and OLED devices. He is currently working on an ARC Discovery Project which involves producing innovative structures which incorporate combined angular and spectral control.
Much of his work involves looking at applied scalable solutions to real-world problems, such that the greatest impacts can be achieved from the research endeavours.
Tai, M.C., Gentle, A.R., Arnold, M.D. & Cortie, M.B. 2018, 'Spontaneous growth of polarizing refractory metal 'nano-fins'.', Nanotechnology, vol. 29, no. 10, p. 105702.View/Download from: Publisher's site
Traditional polymer polarizers degrade in harsh environments and at high temperatures, reducing the polarization effect. In contrast, polarizers produced with refractory metals have vastly improved thermal stability and resistance to harsh environments but are expensive to fabricate. Here we demonstrate prototype refractory metal wire grid polarizers produced by co-sputtering molybdenum and aluminum under specific conditions. Removal of the aluminum through selective dissolution enables the nanostructure array to transmit light. The polarization spans 500-1100 nm and the extinction ratio significantly increases to >100. Possessing broadband polarization and sufficient extinction ratios, the new polarizing film has potential applications in coatings for sunglasses, windows, pyrometers, scientific instruments, and LCD panels.
Angeloski, A., Gentle, A.R., Scott, J.A., Cortie, M.B., Hook, J.M., Westerhausen, M.T., Bhadbhade, M., Baker, A.T. & McDonagh, A.M. 2018, 'From Lead(II) Dithiocarbamate Precursors to a Fast Response PbS Positive Temperature Coefficient Thermistor.', Inorganic chemistry, vol. 57, no. 4, pp. 2132-2140.View/Download from: Publisher's site
PbS submicron crystals were formed by thermolysis of two different lead dithiocarbamate complexes. These precursors were readily synthesized and fully characterized, and in situ synchrotron powder diffraction experiments were performed to characterize their decomposition. The structure and purity of resultant PbS was examined using scanning electron and transmission electron microscopies, powder X-ray diffraction, and infrared spectroscopy. Submicron crystalline PbS was used to create a new PbS thermistor with excellent sensitivity and an ultrarapid thermal response time.
Bilokur, M., Gentle, A., Arnold, M.D., Cortie, M.B. & Smith, G.B. 2017, 'High Temperature Spectrally Selective Solar Absorbers Using Plasmonic AuAl 2 :AlN Nanoparticle Composites', Solar RRL, vol. 1, no. 10, pp. 1700092-1700092.View/Download from: Publisher's site
Tran, T.T., Kianinia, M., Bray, K., Kim, S., Xu, Z.-.Q., Gentle, A., Sontheimer, B., Bradac, C. & Aharonovich, I. 2017, 'Nanodiamonds with photostable, sub-gigahertz linewidth quantum emitters', APL Photonics, vol. 2, no. 11, pp. 116103-116103.View/Download from: Publisher's site
De Silva, K.S.B., Keast, V.J., Gentle, A. & Cortie, M.B. 2017, 'Optical properties and oxidation of -phase Ag-Al thin films.', Nanotechnology, vol. 28, no. 9, p. 095202.View/Download from: UTS OPUS or Publisher's site
We investigate a series of Ag-Al thin films containing up to 12 at% Al with the purpose of discovering whether these alloys would be a better choice for nanophotonic applications than pure Ag. Variable angle spectroscopic ellipsometry, AFM, x-ray diffraction and density functional theory are applied to explore and characterize the materials. Electromagnetic simulations of optical properties are used to place the results into a theoretical framework. We find that the increase in electron-to-atom ratio associated with the Al additions changes the optical properties: additions of the order of 1-2 at% Al are beneficial as they are associated with favorable changes in the dielectric function, but for greater additions of Al there is a flattening of the absorption edge and an increase in optical loss. In addition, contents of more than about 2 at% Al are associated with the onset of time-dependent intergranular oxidation, which causes a pronounced dip in the reflectance spectrum at about 2.3-2.4 eV (500-540 nm).
Choi, S., Rogers, D.J., Sandana, E.V., Bove, P., Teherani, F.H., Nenstiel, C., Hoffmann, A., McClintock, R., Razeghi, M., Look, D., Gentle, A., Phillips, M.R. & Ton-That, C. 2017, 'Author Correction: Radiative recombination of confined electrons at the MgZnO/ZnO heterojunction interface.', Scientific reports, vol. 7, no. 1, p. 15912.View/Download from: Publisher's site
A correction to this article has been published and is linked from the HTML version of this paper. The error has been fixed in the paper.
Choi, S., Rogers, D.J., Sandana, E.V., Bove, P., Teherani, F.H., Nenstiel, C., Hoffmann, A., McClintock, R., Razeghi, M., Look, D., Gentle, A., Phillips, M.R. & Ton-That, C. 2017, 'Radiative recombination of confined electrons at the MgZnO/ZnO heterojunction interface.', Scientific reports, vol. 7, no. 1, p. 7457.View/Download from: Publisher's site
We investigate the optical signature of the interface in a single MgZnO/ZnO heterojunction, which exhibits two orders of magnitude lower resistivity and 10 times higher electron mobility compared with the MgZnO/Al2O3 film grown under the same conditions. These impressive transport properties are attributed to increased mobility of electrons at the MgZnO/ZnO heterojunction interface. Depth-resolved cathodoluminescence and photoluminescence studies reveal a 3.2eV H-band optical emission from the heterointerface, which exhibits excitonic properties and a localization energy of 19.6meV. The emission is attributed to band-bending due to the polarization discontinuity at the interface, which leads to formation of a triangular quantum well and localized excitons by electrostatic coupling.
Rahman, M.A., Westerhausen, M.T., Nenstiel, C., Choi, S., Hoffmann, A., Gentle, A., Phillips, M.R. & Ton-That, C. 2017, 'Charge state switching of Cu acceptors in ZnO nanorods', Applied Physics Letters, vol. 110, no. 12.View/Download from: UTS OPUS or Publisher's site
© 2017 Author(s). Undoped and Ga-doped ZnO nanorods both exhibit an intense green luminescence (GL) band centered at 2.4 eV. Unlike the defect-related GL in undoped nanorods, the GL band in Ga-doped nanorods displays a periodic fine structure separated by 72 meV, which consists of doublets with an energy spacing of 30 ± 3 meV. The emergence of the structured GL is due to the Cu + state being stabilized by the rise in the Fermi level above the 0/- (Cu 2+ /Cu + ) charge transfer level as a result of Ga donor incorporation. From a combination of optical characterization and simulation using the Brownian oscillator model, the doublet fine structures are shown to originate from two hole transitions with the Cu + state located at 390 meV above the valence band.
Gali, M.A., Gentle, A.R., Arnold, M.D. & Smith, G.B. 2017, 'Extending the applicability of the four-flux radiative transfer method.', Applied optics, vol. 56, no. 31, pp. 8699-8709.View/Download from: Publisher's site
A generalized four-flux method capable of modeling and tuning the spectral reflectance of a diverse range of complex composite coatings is presented. An example application is exploring and maximizing the visible and near-infrared (IR) spectral reflectance available from the diverse structures arising from combinations of the many practical paint ingredients that are available or can be made when applied to different substrates. This requires consideration of scatterers that can differ in composition, particle size, size distribution, and fill factor, and are held in place by a variety of organic binders, which typically partially absorb in the near IR. This extended model is further enhanced by an explicit matrix algorithm that allows analysis of diverse multilayer stacks. This is applied to a multilayer and is designed to model useful changes that result from varying the pigment fill factor as a function of depth within a layer. What we believe is a novel feature is the way the scattering affects matrix absorptance. The model includes contributions to total absorptance from the scattering pigments and from the paint binder that can arise in different bands or simultaneously at the same wavelengths. Model accuracy is demonstrated by example results when compared to experimental data on dried single layer paint profiles using imaged cross sections. The model input covering the actual pigment and binder properties used are material, shape, size, and size distributions, mass added, and the measured optical constants from 400 nm to 2,500 nm of the undoped binder resin layer. One interesting result is the comparison of a two-layered stack, with bigger particles in the first layer and smaller ones in the second, to one with the opposite depth profile.
Ben-David, J., Stapleton, A.J., Gibson, C.T., Sharma, A., Gentle, A.R., Lewis, D.A. & Ellis, A.V. 2016, 'Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-free silver nanowire/single walled carbon nanotube transparent electrodes using graphene oxide', Thin Solid Films, vol. 616, pp. 515-520.View/Download from: Publisher's site
© 2016 Elsevier B.V. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is often used in transparent electrodes as a transparent conductive polymer, however encapsulation away from atmospheric water is often required. Here, we fabricate transparent, flexible silver nanowire (AgNW):single walled carbon nanotube (SWCNT) electrodes using graphene oxide (GO), mitigating the use of PEDOT:PSS. These GO/AgNW:SWCNT electrodes were found to be highly conductive with a sheet resistance of 2.2 /–5.9 / and a work function of ~ 4.8 eV. The optical transmittance was 75.00 ± 0.02% with a haze value of 21.8 ± 0.8%. The figure of merit was shown to be comparable to indium tin oxide (ITO), at 297 1 . Finally, the electrodes were shown to be flexible with no reduction in conductivity after 1000 bend cycle/cycles. These PEDOT:PSS free electrodes have the potential to replace rigid commercial ITO electrodes in applications that require flexible, highly conductive transparent electrodes.
Jiang, Y., Soufiani, A.M., Gentle, A., Huang, F., Ho-Baillie, A. & Green, M.A. 2016, 'Temperature dependent optical properties of CH3NH3PbI3perovskite by spectroscopic ellipsometry', Applied Physics Letters, vol. 108, no. 6.View/Download from: UTS OPUS or Publisher's site
© 2016 AIP Publishing LLC. Mixed organic-inorganic halide perovskites have emerged as a promising new class of semiconductors for photovoltaics with excellent light harvesting properties. Thorough understanding of the optical properties of these materials is important for photovoltaic device optimization and the insight this provides for the knowledge of energy band structures. Here we present an investigation of the sub-room temperature dependent optical properties of polycrystalline thin films of CH 3 NH 3 PbI 3 perovskites that are of increasing interest for photovoltaics. The complex dielectric function of CH 3 NH 3 PbI 3 in the energy range of 0.5-4.1 eV is determined between 77 K and 297 K using spectroscopic ellipsometry. An increase in optical permittivity as the temperature decreases is illustrated for CH 3 NH 3 PbI 3 . Optical transitions and critical points were analyzed using the energy dependent second derivative of these dielectric functions as a function of temperature.
Gentle, A.R. & Smith, G.B. 2016, 'Is enhanced radiative cooling of solar cell modules worth pursuing?', SOLAR ENERGY MATERIALS AND SOLAR CELLS, vol. 150, pp. 39-42.View/Download from: UTS OPUS or Publisher's site
Gentle, A.R., Yambem, S.D., Burn, P.L., Meredith, P. & Smith, G.B. 2016, 'AZO/Ag/AZO anode for resonant cavity red, blue, and yellow organic light emitting diodes', JOURNAL OF APPLIED PHYSICS, vol. 119, no. 24.View/Download from: UTS OPUS or Publisher's site
Schmerl, N.M., Gentle, A.R., Quinton, J.S., Smith, G.B. & Andersson, G.G. 2016, 'Surface and Near Surface Area Density of States for Magnetron-Sputtered ZnO and Al-ZnO: A MIES, UPS, and VBXPS Study Investigating Ultrahigh Vacuum Sputter Cleaning and UV Oxygen Plasma', Journal of Physical Chemistry C, vol. 120, no. 29, pp. 15772-15784.View/Download from: Publisher's site
© 2016 American Chemical Society. The impact of nonsolvent-based cleaning methods on zinc oxide and aluminum-doped zinc oxide was investigated across a range of doping concentrations up to 25% aluminum. A combination of electron spectroscopic techniques was utilized in order to characterize the electronic states present on the surface and to discern the differences between the near surface area and outermost layer valence band states. Understanding the differences between the near surface area and outermost layer of an interface is crucial when optimizing devices for charge transfer. The techniques were valence band X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and metastable-induced electron spectroscopy. The band gap was also measured via ultraviolet/visible spectroscopy.
Scajev, P., Malinauskas, T., Seniutinas, G., Arnold, M.D., Gentle, A., Aharonovich, I., Gervinskas, G., Michaux, P., Hartley, J.S., Mayes, E.L.H., Stoddart, P.R. & Juodkazis, S. 2016, 'Light-induced reflectivity transients in black-Si nanoneedles', SOLAR ENERGY MATERIALS AND SOLAR CELLS, vol. 144, pp. 221-227.View/Download from: UTS OPUS or Publisher's site
Shahcheraghi, N., Keast, V.J., Gentle, A.R., Arnold, M.D. & Cortie, M.B. 2016, 'Anomalously strong plasmon resonances in aluminium bronze by modification of the electronic density-of-states.', Journal of physics. Condensed matter : an Institute of Physics journal, vol. 28, no. 40, p. 405501.View/Download from: UTS OPUS or Publisher's site
We use a combination of experimental measurements and density functional theory calculations to show that modification of the band structure of Cu by additions of Al causes an unexpected enhancement of the dielectric properties. The effect is optimized in alloys with Al contents between 10 and 15 at.% and would result in strong localized surface plasmon resonances at suitable wavelengths of light. This result is surprising as, in general, alloying of Cu increases its DC resistivity and would be expected to increase optical loss. The wavelengths for the plasmon resonances in the optimized alloy are significantly blue-shifted relative to those of pure Cu and provide a new material selection option for the range 2.2-2.8eV.
Smith, G., Gentle, A., Arnold, M. & Cortie, M. 2016, 'Nanophotonics-enabled smart windows, buildings and wearables', Nanophotonics, vol. 5, no. 1, pp. 55-73.View/Download from: UTS OPUS or Publisher's site
© 2016 Geoff Smith et al., published by De Gruyter Open.Design and production of spectrally smart windows, walls, roofs and fabrics has a long history, which includes early examples of applied nanophotonics. Evolving nanoscience has a special role to play as it provides the means to improve the functionality of these everyday materials. Improvement in the quality of human experience in any location at any time of year is the goal. Energy savings, thermal and visual comfort indoors and outdoors, visual experience, air quality and better health are all made possible by materials, whose "smartness" is aimed at designed responses to environmental energy flows. The spectral and angle of incidence responses of these nanomaterials must thus take account of the spectral and directional aspects of solar energy and of atmospheric thermal radiation plus the visible and color sensitivity of the human eye. The structures required may use resonant absorption, multilayer stacks, optical anisotropy and scattering to achieve their functionality. These structures are, in turn, constructed out of particles, columns, ultrathin layers, voids, wires, pure and doped oxides, metals, polymers or transparent conductors (TCs). The need to cater for wavelengths stretching from 0.3 to 35 m including ultraviolet-visible, near-infrared (IR) and thermal or Planck radiation, with a spectrally and directionally complex atmosphere, and both being dynamic, means that hierarchical and graded nanostructures often feature. Nature has evolved to deal with the same energy flows, so biomimicry is sometimes a useful guide.
Tai, M.C., Gentle, A., Arnold, M.D. & Cortie, M.B. 2016, 'Optical: In situ study of de-alloying kinetics in nanoporous gold sponges', RSC Advances, vol. 6, no. 89, pp. 85773-85778.View/Download from: UTS OPUS or Publisher's site
© 2016 The Royal Society of Chemistry. Nanoporous gold sponges are useful for a variety of applications but the kinetics of the dissolution process used to make them is not well understood. Here we show how optical transmittance can be used to determine the rate at which sponges form from thin film precursors. The technique also provides a means by which de-alloying can be terminated at a target thickness. Analysis revealed three stages during the de-alloying process: initial depassivation, bulk dissolution and, finally, delamination. The dissolution rate is linear with hydroxide concentration, and exponential with temperature, with an activation energy of approximately 0.5 eV.
King, S.R., Shimmon, S., Gentle, A.R., Westerhausen, M.T., Dowd, A. & McDonagh, A.M. 2016, 'Remarkable thermal stability of gold nanoparticles functionalised with ruthenium phthalocyanine complexes.', Nanotechnology, vol. 27, no. 21, p. 215702.View/Download from: UTS OPUS or Publisher's site
A gold nanoparticle (AuNP) ruthenium phthalocyanine (RuPc) nanocomposite has been synthesised that exhibits high thermal stability. Electrical resistance measurements revealed that the nanocomposite is stable up to 320 °C. Examination of the nanocomposite and the RuPc stabiliser complex using thermogravimetric analysis and differential scanning calorimetry show that the remarkable thermal stability is due to the RuPc molecules, which provide an effective barrier to sintering of the AuNPs.
Castro Aguilar, J.L., Gentle, A.R., Smith, G.B. & Chen, D. 2015, 'A method to measure total atmospheric long-wave down-welling radiation using a low cost infrared thermometer tilted to the vertical', Energy, vol. 81, pp. 233-244.View/Download from: UTS OPUS or Publisher's site
Atmospheric long-wave down-welling radiation is a fundamental element of climate change and of input to thermal simulation. Measuring long-wave radiation is needed to calculate locally total energy flows to the earth's surface and night cooling rates in urban precincts. It is an important parameter for the weather files used by energy building simulation software to calculate the thermal performance of buildings and their energy efficiency. Currently, atmospheric down-welling radiation is usually measured by a pyrgeometer, for radiation beyond 3 m. This is expensive and bulky. A simple methodology for measurement and calculation, with good accuracy, of average atmospheric long-wave down-welling radiation using a tilted, low-cost infrared thermometer is described. Tilt setting, comparison to data gathered by the pyrgeometer, and comparison of simulation studies with both data sets is described. A link of the magnitude of divergence between instant data pairs and radiant intensity is demonstrated and shown to depend on asymmetry in cloud density.
Gentle, A.R., Yambem, S.D., Smith, G.B., Burn, P.L. & Meredith, P. 2015, 'Optimized multilayer indium-free electrodes for organic photovoltaics', PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, vol. 212, no. 2, pp. 348-355.View/Download from: UTS OPUS or Publisher's site
De Silva, K.S.B., Gentle, A., Arnold, M., Keast, V.J. & Cortie, M.B. 2015, 'Dielectric function and its predicted effect on localized plasmon resonances of equiatomic Au-Cu', Journal of Physics D: Applied Physics, vol. 48, no. 21.View/Download from: UTS OPUS or Publisher's site
Equiatomic (Au,Cu) solid solution orders below 658 K to form a tetragonal AuCu (I) phase with significant changes in physical properties and the crystal structure. The effect of ordering on the dielectric function of the material is controversial however, with inconsistent results reported in the literature. Since the nature of any localized surface plasmon resonance (LSPR) in the nanostructures is very sensitive to the dielectric function, this uncertainty hinders the use of AuCu in plasmonic devices or structures. Therefore, we re-examine the question using a combination of measurements and computations. We find that no significant change in the dielectric function occurs when this material becomes ordered, at least over the range of photon energies relevant to LSPRs. The likely properties of LSPRs in plasmonic devices made of AuCu are analyzed. Use of the alloy offers some advantages over pure Cu, however pure Au would still be the superior option in most situations.
Keast, V.J., Wallace, J.W., Wrightson, C.J., Tai, M., Gentle, A., Arnold, M.D. & Cortie, M.B. 2015, 'The effect of vacancies on the optical properties of AuAl2', JOURNAL OF PHYSICS-CONDENSED MATTER, vol. 27, no. 50.View/Download from: UTS OPUS or Publisher's site
Tai, M.C., Gentle, A., de Silva, K.S.B., Arnold, M.D., van der Lingen, E. & Cortie, M.B. 2015, 'Thermal Stability of Nanoporous Raney Gold Catalyst', METALS, vol. 5, no. 3, pp. 1197-1211.View/Download from: UTS OPUS or Publisher's site
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.View/Download from: UTS OPUS or Publisher's site
Supansomboon, S., Dowd, A., Gentle, A., Van Der Lingen, E. & Cortie, M.B. 2015, 'Thin films of PtAl2 and AuAl2 by solid-state reactive synthesis', Thin Solid Films, vol. 589, pp. 805-812.View/Download from: UTS OPUS or Publisher's site
© 2015 Elsevier B.V. The intermetallic compounds AuAl < inf > 2 < /inf > and PtAl < inf > 2 < /inf > are colored purple and yellow respectively. In the past they have been prepared by bulk melting techniques or by co-deposition in a magnetron sputterer. Here, however, we investigate films of AuAl < inf > 2 < /inf > , PtAl < inf > 2 < /inf > and (Au,Pt)Al < inf > 2 < /inf > prepared by sequential physical vapor deposition of the elements, followed by in situ solid-state reaction. The microstructure, dielectric functions, optical properties and thermal stability of the resulting films are characterized and compared to those prepared by bulk melting or co-deposition. The (Au,Pt)Al < inf > 2 < /inf > films show a color gamut that stretches from purple to brassy yellow depending on composition and microstructure. High temperature synchrotron X-ray diffraction experiments show that the (Au,Pt)Al < inf > 2 < /inf > phase is metastable, decomposing when heated above 420 °C. In contrast, the pure AuAl < inf > 2 < /inf > or PtAl < inf > 2 < /inf > phases are stable to about 580 °C before they oxidize or decompose. The alternative possibility of producing the purple-to-yellow color gamut by depositing optical stacks of very thin films of AuAl < inf > 2 < /inf > and PtAl < inf > 2 < /inf > is also assessed. Either scheme will provide a range of colors lying between those of the binary compound endpoints. Calculations predict that deposition of AuAl < inf > 2 < /inf > onto PtAl < inf > 2 < /inf > will produce more intense colors than vice versa, an unexpected finding that is worth further investigation.
Castelletto, S., Bodrog, Z., Magyar, A.P., Gentle, A., Gali, A. & Aharonovich, I. 2014, 'Quantum-confined single photon emission at room temperature from SiC tetrapods', NANOSCALE, vol. 6, no. 17, pp. 10027-10032.View/Download from: UTS OPUS or Publisher's site
Gentle, A.R. & Smith, G.B. 2014, 'Procedure for measuring simultaneously the solar and visible properties of glazing with complex internal or external structures', Applied Optics, vol. 53, no. 30, pp. 7157-7157.View/Download from: UTS OPUS or Publisher's site
McPherson, D.J., Supansomboon, S., Zwan, B., Keast, V.J., Cortie, D.L., Gentle, A., Dowd, A. & Cortie, M.B. 2014, 'Strategies to control the spectral properties of Au-Ni thin films', THIN SOLID FILMS, vol. 551, pp. 200-204.View/Download from: UTS OPUS or Publisher's site
Gentle, A.R., Smith, G.H. & Watkins, S. 2013, 'Discharge amplified photo-emission from ultra-thin films applied to tuning work function of transparent electrodes in organic opto-electronic devices', Applied Surface Science, vol. 285, no. B, pp. 110-114.View/Download from: UTS OPUS or Publisher's site
A novel photoemission technique utilising localised discharge amplification of photo-yield is reported. It enables fast, accurate measurement of work function and ionisation potential for ultra-thin buffer layers vacuum deposited onto single and multilay
Smith, G., Gentle, A.R. & Dybdal, K.L. 2013, 'Polymeric Mesh For Durable Infra-red Transparent Convection Shields: Applications In Cool Roofs And Sky Cooling', Solar Energy Materials and Solar Cells, vol. 115, no. NA, pp. 79-85.View/Download from: UTS OPUS or Publisher's site
Polyethylene (PE) mesh is shown to strongly suppress convective gain at night and to have a high black body transmittance, making it suited to use in radiative cooling. Advantages over previous non-porous cover systems include; self-supporting for large areas, good mechanical stability, low cost, retractable, and a long outdoor lifetime. This study compares performance with a PE mesh cover to that of an impermeable PE cover and to no cover. Convective suppression and net cooling for different wind speeds and ambient temperatures are examined. The impact of such a mesh on night sky cooling rates for a mesh over water, then over a roof is presented. For the roof the associated rise in surface temperature is also measured and modelled in the daytime. Effective permeabilities are not the same as geometric permeability. They are extracted by comparing simulation results with data and are found to depend only weakly on wind speed. They are most sensitive to magnitude and sign of the difference between roof and ambient temperatures. They differ significantly between night and day, that is for convective warming and cooling respectively.
Smith, G., Castro Aguilar, J.L., Gentle, A.R. & Chen, D. 2012, 'Multi-parameter Sensitivity Analysis: A Design Methodology Applied To Energy Efficiency In Temperate Climate Houses', Energy And Buildings, vol. 55, no. NA, pp. 668-673.View/Download from: UTS OPUS or Publisher's site
Quantified sensitivities of heating and cooling loads to different variables that influence heat gain and loss in a building provides a valuable basis for energy efficient design, especially in temperate climate zones where particular parameter settings
So, Y., Gentle, A.R., A, H., Sj, C. & G, G. 2011, 'Size Dependent Optical Properties Of Si Quantum Dots In Si-Rich Nitride/Si(3)N(4) Superlattice Synthesized By Magnetron Sputtering', Journal Of Applied Physics, vol. 109, no. 6, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
A spectroscopic ellipsometry compatible approach is reported for the optical study of Si quantum dots (QDs) in Si-rich nitride/silicon nitride (SRN/Si(3)N(4)) superlattice, which based on Tauc-Lorentz model and Bruggeman effective medium approximation. I
Gentle, A.R., Aguilar, J.L. & Smith, G. 2011, 'Optimized cool roofs: Integrating albedo and thermal emittance with R-value', Solar Energy Materials and Solar Cells, vol. 95, pp. 3207-3215.View/Download from: UTS OPUS or Publisher's site
For cool roofs the combined effect of the three parameters that define heat gain and loss from a roof, namely solar albedo a, thermal emittance E, and sub-roof R-value, must be considered. An accurate contribution of night sky cooling, and hence humidity and total down-welling atmospheric radiation is needed. A systematic analysis of the contribution of a roof to average cooling load per day and to peak load reductions is presented for a temperate climate zone over 6 cooling months using an hour-by-hour analysis. Eighteen 3-parameter sets (a,E,R) demonstrate the over-riding importance of a high a, while sensitivity to R-value and E drops away as albedo rises. Up-front cost per unit reductions in peak demand or average energy use per day always rises strongly as R rises unless albedo is low. A moderate R similar to 1.63 is superior to high R unless a roof is dark, or winter heating demand is high. We indicate briefly why the roof typically does not present a dominant influence on average winter heating needs in most temperate zones, enhancing the benefits of cool roofs.
Di, D., Perez-Wurfl, I., Gentle, A., Kim, D.-.H., Hao, X., Shi, L., Conibeer, G. & Green, M.A. 2010, 'Impacts of Post-metallisation Processes on the Electrical and Photovoltaic Properties of Si Quantum Dot Solar Cells.', Nanoscale research letters, vol. 5, no. 11, pp. 1762-1767.View/Download from: Publisher's site
As an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO(2)) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (H(3)PO(4)) etching, nitrogen (N(2)) gas anneal and forming gas (Ar: H(2)) anneal on the cells' electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I-V, light I-V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement.
Gentle, A.R. & Smith, G. 2010, 'Radiative heat pumping from the earth using surface phonon resonant nanoparticles', Nano Letters, vol. 10, no. 2, pp. 373-379.View/Download from: UTS OPUS or Publisher's site
Nanoparticles that have narrow absorption bands that lie entirely within the atmospheres transparent window from 7.9 to 13 ?m can be used to radiatively cool to temperatures that are well below ambient. Heating from incoming atmospheric radiation in the remainder of the Planck radiation spectrum, where the atmosphere is nearly black, is reduced if the particles are dopants in infrared transmitting polymers, or in transmitting coatings on low emittance substrates. Crystalline SiC nanoparticles stand out with a surface phonon resonance from 10.5 to 13 ?m clear of the atmospheric ozone band. Resonant SiO2 nanoparticles are complementary, absorbing from 8 to 10 ?m, which includes atmospheric ozone emissions. Their spectral location has made SiC nanoparticles in space dust a feature in ground-based IR astronomy. Optical properties are presented and subambient cooling performance analyzed for doped polyethylene on aluminum. A mixture of SiC and SiO2 nanoparticles yields high performance cooling at low cost within a practical cooling rig.
Perez-Wurfl, I., Hao, X., Gentle, A., Kim, D.H., Conibeer, G. & Green, M.A. 2009, 'Si nanocrystal p-i-n diodes fabricated on quartz substrates for third generation solar cell applications', Applied Physics Letters, vol. 95, no. 15.View/Download from: Publisher's site
We fabricated p-i-n diodes by sputtering alternating layers of silicon dioxide and silicon rich oxide with a nominal atomic ratio O/Si=0.7 onto quartz substrates with in situ boron for p -type and phosphorus for n -type doping. After crystallization, dark and illuminated I-V characteristics show a diode behavior with an open circuit voltage of 373 mV. Due to the thinness of the layers and their corresponding high resistivity, lateral current flow results in severe current crowding. This effect is taken into account when extracting the electronic bandgap based on temperature dependent diode I-V measurements. © 2009 American Institute of Physics.
Gentle, A.R., Smith, G. & Maaroof, A.I. 2009, 'Frequency And Percolation Dependence Of The Observed Phase Transition In Nanostructured And Doped Vo2 Thin Films', Journal of Nanophotonics, vol. 3, no. 031505, pp. 1-15.View/Download from: UTS OPUS or Publisher's site
The response to applied electric fields of vanadium dioxide thin films above and below the phase transition depends on the size of grains if below ~200nm across, and on aluminum doping above a critical concentration. Tc drops as doping level increases, but does not depend on grain size. The observed phase transition undergoes a remarkable qualitative shift as the applied field goes from optical to low frequencies. The expected insulator to metal transition is found at optical frequencies, but at low frequencies an insulator-to-insulator transition occurs. Optical switching at both T < Tc and T > Tc is nearly independent of doping level and grain size. In contrast dc properties in both phases are sensitive to both factors. The band gaps from optical and dc data differ, and densities of states change with doping level. Such behaviour can arise if there is a transient phase change. The way doping and grain size can support such a phase is discussed. Only individual nanograins need to switch phases coherently to explain data, not the whole sample. Resistance as a function of composition across the transition was derived using effective medium compositional analysis of optical data in the hysteresis zone. The percolation thresholds are not at the usual Tc values.
Gentle, A.R. & Smith, G. 2008, 'Dual metal-insulator and insulator-insulator switching in nanoscale and Al doped VO2', Journal Of Physics D-Applied Physics, vol. 41, no. 1, pp. 1-5.View/Download from: UTS OPUS or Publisher's site
Thin films of VO2 doped with aluminium, or with nanoscale grain sizes, have been produced. They display semiconductor resistive behaviour above the transition temperature T-c, but a metallic and plasmonic optical response. All samples optically switch ov
Gentle, A.R. & Smith, G. 2008, 'Five layer narrow band position variable filters for sharp colours and ultra low emittance', Applied Physics B-Lasers And Optics, vol. 92, no. 1, pp. 67-72.View/Download from: UTS OPUS or Publisher's site
A simplified approach to creating narrow visible and near IR transmission bands with thin films is outlined utilising just five layers on glass, three of which are thin silver. These films have very high reflection at most wavelengths except for a narrow
Gentle, A.R., Maaroof, A.I. & Smith, G. 2008, 'Temperature dependence of optical and transport properties in VO2 with high temperature anomalies', Current Applied Physics, vol. 8, no. 3-4, pp. 229-232.View/Download from: UTS OPUS or Publisher's site
Thermochromic VO2 is of interest for energy efficient glazing, and for fast telecommunications because it optically switches in the near IR. Despite extensive study several aspects of its apparently diverse behaviour have not been explained satisfactorily. The visible-NIR permittivity and dc electrical conductivity of high quality thin films of VO2, across the metal-insulator phase transition and well into the metallic phase to temperatures up to 100 Â°C above Tc are studied as a function of temperature and grain size. Experimental behaviour is partly explained with effective medium models, existing band structures and classical transport theory. Anomalies however include: unphysically fast relaxation rate, counter-intuitive and significant differences between optical and dc, and bulk and thin film parameters; and residual "non-metallic" features above the transition in highly oriented films. Residual, but transient high temperature d-electron singlet pairing on V dimers, which is sensitive to nanostructure, is examined as a source of some anomalies. Â© 2007 Elsevier B.V. All rights reserved.
Swift, P.D., Lawlor, R., Smith, G. & Gentle, A.R. 2008, 'Rectangular-section mirror light pipes', Solar Energy Materials And Solar Cells, vol. 92, no. 8, pp. 969-975.View/Download from: UTS OPUS or Publisher's site
Using an integrated-ray approach an expression for the transmission of rectangular section mirror light pipe (MLP) has been derived for the case of collimated light input. The transmittance and the irradiance distribution at the exit aperture of rectangu
Gentle, A.R., Maaroof, A.I. & Smith, G. 2007, 'Nanograin VO2 in the Metal Phase: A Plasmonic System with falling DC Resistivity as Temperature Rises', Nanotechnology, vol. 18, no. 2, pp. 025202-25209.View/Download from: UTS OPUS
Thin films of vanadium dioxide with grain size smaller than 60nm have a metallic phase with excellent plasmonic response,but their dc resistivity falls as temperature rises to values above the metal-insulator transition. At the transition optical switching is complete, but the switch in dc resistance is incomplete. In the metallic phase nanograin and large grain samples have similar values of both plasma frequency and relaxation rate. However, plasmonic response in nanograins is stronger due to the absence of a low energy interband transition foun din large grain fims. Conductivity rises with thermal activation energy of 108 meV, which is well below that in rthe semiconductor phase. Possible mechanisms for non-metal' like dc behaviour in this plasmonic system are briefly discussed. They include fluctuations which are coherent in nanograins but incoherent for larger grains. Nanoscale systems seem preferable for optical switching applications and large grain structures for dc switching work.
Maaroof, A.I., Cortie, M.B., Gentle, A.R. & Smith, G. 2007, 'Mesoporous gold sponge as a prototype 'metamaterial'', Physica B: Condensed Matter, vol. 394, no. 2, pp. 167-170.View/Download from: UTS OPUS or Publisher's site
Mesoporous gold sponge has optical properties that can be intermediate between those of metals and insulators with a flat spectral response that is unlike that of bulk gold. Films of different thicknesses were produced and an extension of the Lorentz-Drude (LD) model used to model their spectral behaviour. We found that it was necessary to include an additional special oscillator centered at 1.4eV in order to model the unusual spectral response. This is quite unlike bulk gold, which can be mideled using a standard two-oscillator LD model.
Maaroof, A.I., Gentle, A.R., Smith, G. & Cortie, M.B. 2007, 'Bulk and surface plasmons in highly nanoporous gold films', Journal of Physics D: Applied Physics, vol. 40, no. 18, pp. 5675-5682.View/Download from: UTS OPUS or Publisher's site
The far field plasmonic behaviour of nanoporous gold films with void densities ranging from 60% to 90% has been investigated and modelled. These layers have good dc conductivity and quite different nanostructure to traditional porous layers in which the metal percolates. Our gold films with void density f above 70% have high thermal emittance fora conductor at their thickness and their flat spectral response at visible and near infrared wavelengths is not metal like. We derive effective optical constants which become plasmonic at wavelengths between 1.8 and 4um for f from 72 to 87%. This onset is much longer than that in bulk gold. For void densities below 70% the onset of plasmonic behaviour is much closer to the dense material. A simple test is implemented to test for surface plasmon polaritons (SPPs) under illumination. The more porous films show no evidence of SPP, while the less porous films display weak evidence. Thus by tailoring void content in these nanostructures we can taolor the onset of efefctive plasmonic response across a wide range from 0.8 to 4 um and emittance from around0.9 down to low values. An effective uniform metal response is this found in the presence o fsurface nanostructure without the interface absorption found in dense gold layers with sturctured surfaces.
Smith, G., Maaroof, A.I. & Gentle, A.R. 2007, 'Homogenized Lorentz-Drude optical response in highly nanoporous conducting gold layers produced by de-alloying', Optics Communications, vol. 271, no. 1, pp. 263-268.View/Download from: UTS OPUS or Publisher's site
Nanoporousgold films produced by de-alloying AuAl2 with void densities between 45% and 65% retain high infra-red reflectance and good conductivity. They act optically like a homogenous Lorentz-Drude metal with a unique wp and an inter-band transition energy unchanged from that of dense gold. The link between wp and wp in dense gold is found using a cimplification of the Bergmann expansio for permittivity valid at infra-red wavelengths. The carrier relaxation time of the effective metal becomes the actual relaxation time in the Au netowork and the complex refractive indices (n.k) found using normal incidence spectrophotometry and oblique incidence ellipsometry agree closely with each other. The single pole approximation for the ratio wp/wp in the infra-red allows estimates of void content and the apparent shift in carrier effective mass. It is then possible to model with no adjustable parameters, the full UV-visible-NR spectral response, giving excellent agreemtn with data. A range of films with these properties are presented.
Smith, G., Gentle, A.R., Swift, P.D., Earp, A.A. & Mronga, N. 2003, 'Coloured paints based on coated flakes of metal as the pigment, for enhanced solar reflectance and cooler interiors: description and theory', Solar Energy Materials And Solar Cells, vol. 79, no. 2, pp. 163-177.View/Download from: UTS OPUS or Publisher's site
Smith, G., Gentle, A.R., Swift, P.D., Earp, A.A. & Mronga, N. 2003, 'Coloured paints based on iron oxide and silicon oxide coated flakes of aluminium as the pigment, for energy efficient paint: optical and thermal experiments', Solar Energy Materials And Solar Cells, vol. 79, no. 2, pp. 179-197.View/Download from: UTS OPUS or Publisher's site
Smith, G., Deller, C.A., Swift, P.D., Gentle, A.R., Garrett, P.D. & Fisher, W.K. 2002, 'Nanoparticle-doped polymer foils for use in solar control glazing', Journal of nanoparticle Research, vol. 4, no. N/A, pp. 157-165.View/Download from: UTS OPUS
Smith, G.B., Deller, C.A., Swift, P.D., Gentle, A., Garrett, P.D. & Fisher, W.K. 2002, 'Nanoparticle-doped polymer foils for use in solar control glazing', JOURNAL OF NANOPARTICLE RESEARCH, vol. 4, no. 1-2, pp. 157-165.View/Download from: Publisher's site
Smith, G., Hossain, A.K. & Gentle, A.R. 2001, 'Near Infra-Red Radiation Squeezing Through 20nm Voids in Obliquely Deposited Metal Films', Applied Physics Letters, vol. 78, no. 15, pp. 2144-2413.View/Download from: UTS OPUS
Castro Aguilar, J.L., Smith, G., Gentle, A.R. & Chen, D. 2012, 'Making cool roofs compatible with low heating and cooling loads' in Mendez-Vilas, A., BrownWalker & Raton, B. (eds), Fuelling the Future: Advances in Science and Technologies for Energy Generation, Transmission and St, Brown Walker Press, United States, pp. 530-534.View/Download from: UTS OPUS
Bilokur, M., Gentle, A., Arnold, M., Cortie, M. & Smith, G. 2017, 'An advanced plasmonic cermet solar absorber for high temperature solar energy conversion applications', Proceedings of SPIE - The International Society for Optical Engineering.View/Download from: Publisher's site
© 2017 SPIE. Cermet coatings based on nanoparticles of Au or Ag in a stable dielectric matrix provide a combination of spectral-selectivity and microstructural stability at elevated temperatures. The nanoparticles provide an absorption peak due to their localized surface plasmon resonance and the dielectric matrix provides red-shifting and intrinsic absorption from defects. The matrix and two separated cermet layers combined add mechanical support, greater thermal stability and extra absorptance. The coatings may be prepared by magnetron sputtering. They have solar absorptance ranging between 91% and 97% with low thermal emittance making them suitable for application in solar thermal conversion installations.
Gentle, A.R., Nuhoglu, A., Arnold, M.D. & Smith, G.B. 2017, '3D printable optical structures for sub-ambient sky cooling', Proceedings of SPIE - The International Society for Optical Engineering.View/Download from: Publisher's site
© 2017 SPIE. There has been continued recent interest in radiative sky cooling of coated flat surfaces that are able to passively attain sub-ambient temperatures. As the lowest incoming infrared radiation from a clear sky occurs at the zenith, a surface which sees mainly this region of the sky will receive much lower levels of sky radiation than one which views the whole sky, since the near-horizon contains significantly more incoming radiation. Two approaches to extra cooling are thus angular selectivity, which limits oblique outgoing as well as incoming radiation, and macroscopic reflectors which block oblique incoming sky radiation, while directing most outgoing emitted radiation towards the near zenith. This work focuses on the second of these techniques. We maximise cooling potential via coated 3D printed structures which can passively maintain a thermal reservoir below ambient temperature throughout the night and day. Novel design methods are used to fabricate and test structures which maximise outgoing thermal radiation from a surface, while minimising its illumination by incoming radiation from the sky and sun. Preliminary results gave 10°C below ambient both day and night during a Sydney spring. 3D printing allows the production of complex designed mirror cones with relatively low thermal conductivity. Post processing of the 3D printed structures allows the desired surface textures and optical properties to be created.
Tai, M.C., Gentle, A.R., Arnold, M.D. & Smith, G.B. 2017, 'Optical anisotropy due to perpendicular azimuth serial bideposition', Proceedings of SPIE - The International Society for Optical Engineering.View/Download from: Publisher's site
© 2017 SPIE. Angled columnar structures produced by oblique angle deposition possess useful optical polarization effects. It is well known that this is due to structural anisotropy but the relative contributions of factors affecting this anisotropy are not fully understood in all cases. Serial bideposited films where the azimuth is changed during deposition can have greater birefringence if the azimuths are directly opposed. In contrast, in this article the properties of perpendicular azimuth films are studied: silicon films at tilt angles 50-80° were deposited and analyzed. Electron microscopy confirmed that the silicon nanostructures were formed off-axis, meaning they did not develop along the deposition axes but followed the averaged azimuth. Optical measurements confirm that the maximum birefringence occurs closer to glancing angles, and optical modelling demonstrates that in contrast to fixed azimuth films the birefringence in these perpendicular azimuth films is primarily modulated by depolarization factors.
Gali, M.A., Arnold, M.D., Gentle, A.R. & Smith, G.B. 2017, 'Super-cool paints: Optimizing composition with a modified four-flux model', Proceedings of SPIE - The International Society for Optical Engineering.View/Download from: Publisher's site
© 2017 SPIE. The scope for maximizing the albedo of a painted surface to produce low cost new and retro-fitted super-cool roofing is explored systematically. The aim is easy to apply, low cost paint formulations yielding albedos in the range 0.90 to 0.95. This requires raising the near-infrared (NIR) spectral reflectance into this range, while not reducing the more easily obtained high visible reflectance values. Our modified version of the four-flux method has enabled results on more complex composites. Key parameters to be optimized include; fill factors, particle size and material, using more than one mean size, thickness, substrate and binder materials. The model used is a variation of the classical four-flux method that solves the energy transfer problem through four balance differential equations. We use a different approach to the characteristic parameters to define the absorptance and scattering of the complete composite. This generalization allows extension to inclusion of size dispersion of the pigment particle and various binder resins, including those most commonly in use based on acrylics. Thus, the pigment scattering model has to take account of the matrix having loss in the NIR. A paint ranking index aimed specifically at separating paints with albedo above 0.80 is introduced representing the fraction of time at a sub-ambient temperature.
Bilokur, M., Gentle, A., Arnold, M., Cortie, M.B. & Smith, G.B. 2015, 'Optical properties of refractory TiN, AlN and (Ti,Al)N coatings', MICRO+NANO MATERIALS, DEVICES, AND SYSTEMS.View/Download from: UTS OPUS or Publisher's site
Gali, M.A., Tai, M.C., Arnold, M.D., Cortie, M.B., Gentle, A.R. & Smith, G.B. 2015, 'Plasmonic response in nanoporous metal: dependence on network topology', MICRO+NANO MATERIALS, DEVICES, AND SYSTEMS.View/Download from: UTS OPUS or Publisher's site
Aguilar, J.C., Gentle, A.R. & Smith, G.B. 2014, 'Managing and monitoring radiant and convective heat flows intemperate zone urban environments', Proceedings of the Third International Conference on Countermeasures to the Urban heat island, International Conference on Countermeasures to the Urban heat island, http://www.ic2uhi.unimore.it, Venice, pp. 1482-204-1492-204.View/Download from: UTS OPUS
Modeling and experimental techniques for studying the impact of facades and roofing materials plus building layouts, on the UHI and interior energy use have been carried out for Sydney, which has a temperate zone climate. Cool roofing is treated as a multi-parameter sensitivity problem where changes in one of: solar reflectance, sub-roof R-value, and roof thermal mass (via material type or with phase change layers), plus change from cooling to heating season, alter the sensitivity of energy use and external surface temperatures to all of the other design settings. For high-rise layouts the issue of aspect ratio (height/spacing) plus spacing cover were considered. Special attention was paid to the night-time as an indicator of UHI problems and hence to flows of thermal radiation from the sky and from surfaces. Models needed to be accurate on this influence while a low cost, compact and portable technique for monitoring thermal radiation flows has been developed and calibrated using simultaneous full sky data from a pyrgeometer. An additional aspect of cool roofing has recently emerged involving modification to convective flow and cool air flow towards ground from varieties of multilayer roofing, including proliferation of solar modules on urban roofs, and additional layers involving polymer mesh or another solid layer.
Castro Aguilar, J.L., Smith, G., Gentle, A.R. & Chen, D. 2013, 'Optimum Integration of Albedo sub-roof r-value and phase change material for cool roofs', Proceedings of BS2013:13th International Conference of the International Building Performance Simulation Association, International Conference of the International Building Performance Simulation Association, International Building Performance Simulation Association (IBPSA), Chambery France, pp. 1315-1321.View/Download from: UTS OPUS
Bonnie, F., Arnold, M.D., Smith, G. & Gentle, A.R. 2013, 'Modes of interaction between nanostructured metal and a conducting mirror as a function of separation and incident polarization', Proc. SPIE 8818, Nanostructured Thin Films, anostructured Thin Films, SPIE, San Diego. USA, pp. 1-10.View/Download from: UTS OPUS or Publisher's site
The optical resonances that occur in nanostructured metal layers are modulated in thin film stacks if the nanostructured layer is separate from a reflecting conducting layer by various thickness of thin dielectric.
Gentle, A.R. & Smith, G. 2010, 'Performance comparisons of sky window spectral selective and high emittance radiant cooling systems under varying atmospheric conditions', Solar 2010 : Proceedings of the 48th AuSES Annual Conference, Solar2010, the 48th AuSES Annual Conference, Australian Solar Energy Society, Canberra, Australia, pp. 1-8.View/Download from: UTS OPUS
The need for alternative low energy methods for cooling buildings is being realised. This work investigates radiative cooling as a viable option. The use of a novel convection suppressant cover material allows a durable system capable of sub-ambient temperatures. The system's performance using a high emittance radiative surface is evaluated under various atmospheric conditions.
Smith, G., Gentle, A.R. & Edmonds, I. 2010, 'Urban growth, albedo and global warming', Solar 2010 : Proceedings of the 48th AuSES Annual Conference, Solar2010, the 48th AuSES Annual Conference, Australian Solar Energy Society, Canberra, pp. 1-8.View/Download from: UTS OPUS
Traditional town and city growth adds to the "urban heat island" (UHI) problem, which raises cooling demand, degrades the microclimate and adds directly to global warming. Low solar albedos and local energy use both contribute to the UHI but it is not widely appreciated that the former can have by far the dominant impact. These relative impacts, locally and globally, are quantized per square kilometre of typical Australian urban area for shifts in solar albedo and for the extra coal power demanded. This analysis shows that as a matter of urgency urban planning rules and building codes need to change. The energy savings and global cooling associated with improved rules and codes provide a higher environmental return on investment than most renewables and other energy efficiency measures.
Gentle, A.R. & Smith, G. 2010, 'Optimized infra-red spectral response of surfaces for sub-ambient sky cooling as a function of humidity and operating temperature', Proceedings of SPIE - The International Society for Optical Engineering - Photonics for Solar Energy Systems III, Photonics for Solar Energy Systems, SPIE, Brussels, Belgium, pp. 77250Z-0.
The preferred surface spectral response for sub-ambient sky cooling varies according to the amount of water vapor in the atmosphere and the operating difference (Ta-Ts) between ambient and emitter surface temperatures. While all good candidates average h
Smith, G.B. & Gentle, A.R. 2009, 'Angular selectivity: impact on optimised coatings for night sky radiative cooling', Proc SPIE 2009, 7404, SPIE Nanostructured Thin Films II, SPIE, San Diego CA USA, pp. 19-27.View/Download from: UTS OPUS
To achieve strong net thermal radiation emission from surfaces whose temperature is at or below ambient it is important to have high absorptance between 7.9 m to 13 m where the atmosphere is most transparent. Outside of this band the atmosphere behaves like a black body emitter and hence at these wavelengths net radiant heat loss is normally not possible at sub-ambient temperatures. It becomes possible using two types of angular selectivity, which also improve emission between 7.9 m to 13 m. One is coating based, and one uses external heat mirrors. In the latter low emittance mirrors replace the higher emitting segments of the atmosphere. The coating's net gain is a result of its reflectance rise countering the atmosphere's drop in transparency as ray angles to the zenith approach the horizontal. These ideas are examined in the context of experimental data on coatings which rely on nanostructure to largely limit their spectral absorption to the atmosphere's transparent band. The angular selective coating becomes possible in two multilayer types (a) one nano-layer is strongly reflective (b) one layer has much higher index than the other. Type (a) materials as nanoparticles provide surface phonon resonance in the desired absorption band.
Rahman, H.U., Gentle, A., Gauja, E. & Ramer, R. 2008, 'Characterisation of Dielectric Properties ofPECVD Silicon Nitride for RF MEMS Applications', IEEE INMIC 2008: 12th IEEE International Multitopic Conference - Conference Proceedings, pp. 91-96.View/Download from: Publisher's site
Synthesis of Silicon Nitride thin films is important in the semiconductor industry. The properties of the films make them valuable for oxidation masks, protection and passivation barrier layers, etch stop layer and inter level insulators. In the present study, we prepared silicon nitride films with different refractive index. We used various conditions of PECVD atmosphere with the purpose of obtaining high quality near stoichiometric films. Different deposition routines were employed, including variable flow ratio of silane and ammonia on to a silicon substrate. The quality and stoichiometry of the film was investigated using reflectance measurements. Measured process parameters were the deposition rate, film thickness, refractive index, breakdown voltage, dielectric constant, surface morphology and film composition. The thickness of the film was measured using AFM, DEKTAK and ellipsometer measurements. Fitting of reflectance spectra with WVASE ellipsometric software provided the optical constants for silicon nitride and allowed analysis of the films. A Bruggeman effective medium approximation was utilized to model the refractive index of the films. Reflective measurements were carried out in the range 210nm-2500nm.
Rahman, H.U., Gentle, A., Gauja, E. & Ramer, R. 2008, 'Characterization and optimisation of PECVD silicon nitride as dielectric layer for rf MEMS using reflectance measurements', ISAPE 2008 - The 8th International Symposium on Antennas, Propagation and EM Theory Proceedings, pp. 500-503.View/Download from: Publisher's site
Synthesis of Silicon Nitride thin films is important in the semiconductor industry. The properties of the films make them valuable for oxidation masks, protection and passivation barrier layers, etch stop layer and inter level insulators. In the present study, we prepared silicon nitride films with different refractive index. We used various conditions of PECVD atmosphere with the purpose of obtaining high quality near stoichiometric films. Different deposition routines were employed, including variable flow ratio of silane and ammonia on to a silicon substrate. The quality and stoichiometry of the film was investigated using reflectance measurements of the films. Measured process parameters were the deposition rate, film thickness, refractive index, breakdown voltage, dielectric constant, surface morphology and film composition. The thickness of the film was measured by using AFM, DEKTAK and ellipsometer measurements. Fitting of reflectance spectra with WVASE ellipsometric software provided us with optical constants for silicon nitride and allowed analysis of the films. A Bruggeman effective medium approximation was utilized to model the refractive index of the films. Reflective measurements were carried out in the range 210nm-2500nm. © 2008 IEEE.
Gentle, A.R., Smith, G.B. & Maaroof, A.I. 2008, 'Frequency and percolation dependence of the observed phase transition in nanostructured and doped VO(2) thin films', NANOSTRUCTURED THIN FILMS.View/Download from: Publisher's site
Gentle, A.R., Maaroof, A.I., Cortie, M.B. & Smith, G. 2007, 'Optical and electrical switching in nanostructured coatings of VO2', Nanocoatings. Proceedings of SPIE vol 6647, SPIE, SPIE, San Diego, California, USA, pp. 1-8.View/Download from: UTS OPUS or Publisher's site
Vanadium dioxide udergoes a reversible metal-insulator phase transition at about 68 degrees C. Cooatings iof this compound are reflective in the infrared above this temperature, and transmissive or absorptive below it, while resistivity changes by several orders of magnitude. We present a convenient methods for deposting films with nano-sized grains, which are then optically and electrically characterised. Emphasis in this study is the impact of aluminium doping and grain sturcture. The optical hysteresis is rpesnted and its switching range is not altered at different soping levels but he value of transition temperature Tc does shift. In contrast hysteresis in dc resistance does change with a strong correlation between the fall in resistance in the semiconductor state with doping, in the drop in Tc and the electrica properties in the metal state. For grain sizes under about 180 nm the conductivity in the mtal phase is not linear in temperature but is thermally activated, with activation enegies delta E dependent on both grain size G and doping level.
Gentle, A.R., Maaroof, A.I., Smith, G. & Cortie, M.B. 2005, 'Optical properties and applications to production of plasmonic thin film nanostructures of self-ordered columnar alumina arrays on glass', Photonics: Design, Technology, And Packaging II, Conference on Photonics - Design, Technology and Packaging II, SPIE, Brisbane, Australia, pp. 3816-3816.View/Download from: UTS OPUS or Publisher's site
In this paper we report on new techniques for making self-ordered porous layers of alumina of varying aspect ratios on glass, without the use of lithographic or masking techniques. Use of RF etching in one of the hole forming steps and also when filling
Smith, G.B., Maaroof, A., Dowd, A., Gentle, A. & Cortie, M. 2006, 'Tuning plasma frequency for improved solar control glazing using mesoporous nanostructures - art. no. 61970T', Photonics for Solar Energy Systems, pp. T1970-T1970.View/Download from: Publisher's site
Ford, M., Kirkup, L., Gentle, A.R., Zareie, H.M. & Cortie, M.B. 2005, 'How reliable are scanning tunneling microscopy measurements of electron transport in molecules? - art. no. 603604', Biomems And Nanotechnology Ii, Conference on BioMEMS and Nanotechnology II, Spie-Int Society Optical Engineering, Brisbane, AUSTRALIA, pp. 3604-3604.View/Download from: UTS OPUS or Publisher's site
Scanning tunneling microscopy measurements of tunneling through molecules adsorbed on a surface have been simulated using a standard empirical model based upon the Wentzel-Kramer-Brillouin method applied to tunneling through a barrier. The Gaussian noise