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Emeritus Professor Geoff Smith


Geoff Smith is Emeritus Professor in Applied Physics. He is renowned for contributions to science and technology in energy, coatings and nanotechnology and is a world leader in green nanotechnology.

Based at UTS since 1973, his solar energy work started in 1974 after a PhD at Monash University and two years at the University of Sussex, UK. Professor Smith has spent periods on renewable energy projects at Chalmers University of Technology, and University of Uppsala Sweden, The University of Houston, Texas and Lawrence Berkeley Laboratory, California, USA. His group has worked with large corporations from Germany, USA, Japan, UK and Australia.

He carried out the daylighting design and polymer roofing studies for Australia stadium - as seen in the 2000 Olympics.

Contributions include over 190 refereed publications plus around 15 patents, including four in 2009 on cooling technologies. His output encompasses, fundamental new optical physics of nanostructures, pigmented materials and coatings interacting with solar and atmospheric radiation, applied physics of solar absorbers, passive cooling to temperatures well below ambient, solar control windows, roof glazing and skylights, daylight collection and its delivery from luminescent concentrators with e light pipes.

Several products have flowed from his industrial collaborations. He has shown how nanostructures and microstructures inside materials and films, and on surfaces, can achieve the low cost/high performance goals in commodity scale products, which are urgently needed to combat global warming, while maintaining living standards and quality of life.

Geoff has chaired an annual international conference "Nanostructured Thin Films" in the USA from 2007-2009. His energy and materials work has been recognised with a number of local and international awards including a PhD (honoris causa) from the University of Uppsala in Sweden. He has contributed to Australia's Energy Efficient Building Codes and chairs its skylight and roof glazing standards committee.


Fellow Australian Institute of Physics Fellow Australian Institute of Energy Member SPIE (International Applied Optics) Member ANZSES (International Solar Energy) Member OSA (Optics)Affiliated with SIA (Skylight Industry Association)Member ABCB Technical Committee on glazing within energy efficiency building codes.Chair Australian Standards Committee for Skylights and Roof GlazingAssociate Editor Journal of Nanophotonics

Image of Geoff Smith
Senior Lecturer, School of Mathematical and Physical Sciences
Core Member, Research Strength Materials and Technology for Energy Efficiency Member
BSc (UNE), PhD honoris causa (UU), PhD (Monash)
Fellow, Australian Institute of Energy
Fellow, Australian Institute of Physics
Member, Australian Optical Society
+61 2 9514 2224

Research Interests

Professor Smith’s team is a world leader in technologies for saving energy, and mitigating global warming and its impacts.

His research covers materials for use in solar energy and energy efficiency with emphasis on utilising nanostructures to optimally tune material responses to environmental energy flows (solar, thermal radiation from the atmosphere, and air flow) to achieve desired functions, which include human needs for thermal comfort, lighting and a view, and energy.

He and his group of fellows and research students have been at the forefront of aspects of photonics and optics of thin films and composites, and special polymers. Several large well-known corporations, local and international, have collaborated in this work. This has led to a number of new products and changed practices and standards. His group utilises vacuum deposition systems, optical and electrical characterization equipment and associated software, and electron microscopy for imaging nanostructures. The theoretical links between optical responses and nanostructure and its applications is a group forte.

Specific research interests
Cool roofs
Radiative cooling
Solar control windows
Solar control paints (white and coloured)
Daylighting and lighting
Modelling of Buildng energy use
Cool urban precincts and the urban heat island
Land use and global warming
Novel solar power systems
New approaches to water collection and salt water based agriculture
Efficient solar distillation
Core science
Optical properties of thin films
Nanostructured thin metal films
New plasmon resonant structures
Combining angular and spectral selectivity
Surface phonon resonant nanoparticles
Nanoparticle-polymer composites
Effective medium theory in optics
Infra-red transparent polymers

A detailed coverage and introduction to most aspects of this diverse field can be found in Geoff’s recent 460 page book (individual chapters can be bought online) :
"Green Nanotechnology: Solutions for sustainability and energy in the built environment" G.B. Smith and C. G Granqvist, CRC press (Taylor and Francis), Boca Raton, USA, September, 2010. ISBN 978-1-4200-8532-7

Can supervise: Yes


Smith, G. & Granqvist, C.G. 2010, Green Nanotechnology: Solutions for sustainability and energy in the built environment, 1, CRC Press (Taylor & Francis), USA.
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A focuses exploration of the role nanotechnology plays in meeting the challenges inherent in minimizing environmental impacts while maximizing energy resources, this book provides an overview of our energy supply, increasing energy production while reducing cost, and offering novel energy sources. It explores the ways in which nanotechnologies can improve structural engineering of energy sources, create novel methods of cooling, and inspire new approaches to water supply and treatment. In addressing these critical issues, the book provides an authoritative resource that provides the foundation for new research and product development.
Wilson, M., Kanangara, Raguse, B., Simmons, M. & Smith, G.B. 2002, Nanotechnology: Basic Science and Emerging Technologies, UNSW CRS Press.


Cortie, M.B., Stokes, N.L., Heness, G.L. & Smith, G. 2014, 'Applications of Nanotechnology in the Building Industry' in David Rickerby (ed), Nanotechnology for Sustainable Manufacturing, CRC Press, USA.
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.
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Smith, G.B., Lakhtakia, A. & Lee, C.C. 2009, 'Nanostructured Thin Films II'.
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Smith, G. 2007, 'Combining energy efficiency with aesthetic appeal using advanced optical materials' in Choudhury, P.K. & Singh, O.N. (eds), Frontiers in Optical Technology: Materials and Devices, Nova Science Publishers Inc., New York, USA, pp. 125-158.
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Energy efficiency in interior spaces concerns supply of lighting needs and maximising thermal comfort, with minimum use of electrical power fom the grid and of fossil fuels. It is relevant to all classes of buildings. and also. to transport. The world is faced with two apparently conflicting demands right now. A rapid growth in demand for better living standards and lifestyles, and an urgent need to cut greenhollse gas emissions. If this "conflict" can be eliminated or softened. then the process of scaling back our negative impact on the environment will accelerate. If it cannot, all living standards are at risk in the long term. Such a changeover, in common with past technology driven shifts in human activity, will also generate wide ranging opportunities tor economic growth in all regions of the world. There is much new science needed to optimise these technologies. and optics is playing a central role. Examples of two science based systems for better use of natural lighting are in fig. I.
Schelm, S. & Smith, G.B. 2007, 'Self assembled gold nanoparticles with organic linkers' in Nanotechnology in Biology and Medicine, CRC Press.
Botten, L.C., McPhedran, R.C., Nicorovici, N.A., Asatryan, A.A., de Sterke, C.M., Robinson, P.A., Busch, K., Smith, G.H. & Langtry, T.N. 2003, 'Rayleigh multipole methods for photonic crystal calculations', pp. 21-60.
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Multipole methods have evolved to be an important class of theoretical and computational techniques in the study of photonic crystals and related problems. In this chapter, we present a systematic and unified development of the theory, and apply it to a range of scattering problems including finite sets of cylinders, two-dimensional stacks of grating and the calculation of band diagrams from the scattering matrices of grating layers. We also demonstrate its utility in studies of finite systems that involve the computation of the local density of states.


Aguilar, J.C., Gentle, A.R. & Smith, G.B. 2014, 'Managing and monitoring radiant and convective heat flows intemperate zone urban environments', nThird International Conference on Countermeasures to the Urban heat island, Third International Conference on Countermeasures to the Urban heat island, http://www.ic2uhi.unimore.it, Venice, pp. 1482-204-1492-204.
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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.
Franklin, J.B., Smith, G.B. & Earp, A.E. 2013, 'A critical hurdle to widespread use of polymer based luminescent solar concentrators', Proceedings of SPIE - The International Society for Optical Engineering.
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Luminescent solar concentrators have been studied and improved for over 30 years. Of all moderate gain solar concentrator systems they are fundamentally the most attractive from a range of geometric and optical perspectives for many solar cell materials, for daylighting via light guides, and for some bio-applications. Of most significance is their étendue advantages over mirror and lens systems in terms of best dealing with the diffuse component and varying beam directions of solar radiation. Despite this and some attempted commercial ventures they have yet to achieve their potential. This paper addresses what is for the dominant class of such concentrators, those involving fluorophore doped polymers, especially PMMA, a core residual problem. Their long-term stability outdoors is insufficient. This is not due to UV effects and dye quenching, which can be controlled, but to fast local photo-thermal interactions between the activated dye molecules and the host material. Production of char like nanoscale absorbers may result. These absorb over a broad-band and though very dilute lower output transport efficiency in practical sizes. Data which led to this conclusion is presented, plus possible solutions. Other improvements in LSC polymer technology only have practical value if this core problem is first mitigated. © 2013 SPIE.
Bonnie, F., Arnold, M.D., Smith, G.B. & Gentle, A.R. 2013, 'Modes of interaction between nanostructured metal and a conducting mirror as a function of separation and incident polarization', Proceedings of SPIE - The International Society for Optical Engineering.
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The optical resonances that occur in nanostructured metal layers are modulated in thin film stacks if the nanostructured layer is separated from a reflecting conducting layer by various thicknesses of thin dielectric. We have measured and modeled the optical response of interacting silver layers, with alumina spacer thickness ranging from a few nm to 50 nm, for s- and p-polarized incident light, and a range of incident angles. Standard thin film models, including standard effective medium models for the nanostructured layer, will break down for spacer thickness below a critical threshold. For example, with polarisation in the film plane and some nano-islands, it may occur at around 10 nm depending on spacer refractive index. Of particular interest here are novel effects observed with the onset of percolation in the nanolayer. Hot spot effects can be modified by nearby mirrors. Other modes to consider include (a) a two-particle mode involving a particle and its mirror image (b) A Fano resonance from hybridisation of localized and de-localised plasmon modes (c) a Babinet's core-(partial) shell particle with metal core-dielectric shell in metal (d) spacing dependent phase modulation (e) the impact of field gradients induced by the mirror at the nano-layer. © 2013 Copyright SPIE.
Aguilar, J.L.C., Smith, G.B., Gentle, A.R. & Chen, D. 2013, 'Optimum integration of albedo, sub-roof R-value, and phase change material for cool roofs', Proceedings of BS 2013: 13th Conference of the International Building Performance Simulation Association, pp. 1315-1321.
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A cool roof aims to reduce total seasonal cooling loads and peak summer loads. It is often rated just in terms of its solar reflectance Rsol (or albedo), with some impact of infrared emittance considered. However the sensitivity of cooling loads to Rsolvaries as the R-value of sub-roof insulation changes. Knowing joint impacts led to better integrated energy savings design with R-value chosen on the basis of Rsol and local climate. This study extends previous work (Gentle et al., 2011) (Smith et al., 2012) (Aguilar et al., 2012) by considering the impact of phase change materials (PCM) within a roofing module on energy savings. The aim is to show how building simulation helps pinpoint the optimum combination. Copyright © 2011 by IPAC'11/EPS-AG.
Smith, G.B. 2011, 'Green nanotechnology', Proceedings of SPIE - The International Society for Optical Engineering.
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Nanotechnology, in particular nanophotonics, is proving essential to achieving green outcomes of sustainability and renewable energy at the scales needed. Coatings, composites and polymeric structures used in windows, roof and wall coatings, energy storage, insulation and other components in energy efficient buildings will increasingly involve nanostructure, as will solar cells. Nanostructures have the potential to revolutionize thermoelectric power and may one day provide efficient refrigerant free cooling. Nanomaterials enable optimization of optical, opto-electrical and thermal responses to this urgent task. Optical harmonization of material responses to environmental energy flows involves (i) large changes in spectral response over limited wavelength bands (ii) tailoring to environmental dynamics. The latter includes engineering angle of incidence dependencies and switchable (or chromogenic) responses. Nanomaterials can be made at sufficient scale and low enough cost to be both economic and to have a high impact on a short time scale. Issues to be addressed include human safety and property changes induced during manufacture, handling and outdoor use. Unexpected bonuses have arisen in this work, for example the savings and environmental benefits of cool roofs extend beyond the more obvious benefit of reduced heat flows from the roof into the building. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
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.
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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.
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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.B. 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.
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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 high emittance from 7.9 ?m to 13 ?m, where the atmosphere is most transparent (the IR "sky window"), the preferred spectral response in the remainder of the Planck spectrum depends on a number of factors. Emittances E in studies to date have been near the two extremes of a high E ?0.85 to 0.95, and an E value between 0.3 to 0.4 for surfaces which emit strongly only in the sky window. Cooling rates and ideal spectral properties vary with operating conditions. The reasons behind this will be explained for select different coatings, using spectral densities for emitted outgoing radiation, which is Ts dependent, and the incoming radiation that is absorbed, which is fixed unless the atmosphere changes. Higher E surfaces always work best above and just below ambient but external factors that reduce incoming radiation from the atmosphere, including very low humidity or heat mirror apertures, extend this preference down to lower surface temperatures. Sky window spectrally selective coatings do not benefit as much because they already absorb little incoming radiation, but always have the potential to achieve very much colder temperatures if non-radiative heat gains are kept low. © 2010 Copyright SPIE - The International Society for Optical Engineering.
Arnold, M.D. & Smith, G.B. 2009, 'Comparisons of enhanced absorption in closely-coupled grating-mirror and random particle-mirror systems', Proceedings of SPIE - The International Society for Optical Engineering.
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The grating-mirror geometry is a particularly rich plasmonic system due to the coupling of localized and global modes, and it is applicable to negative index materials, plasmonic imaging, and spectral filters. Recently absorption in sub-percolative films was found to be greatly enhanced by the addition of a mirror - a situation that is also reasonably modeled by a grating-mirror geometry. A great deal of attention has been focused on the coupling of barely-sub-wavelength periodic grating modes to surface plasmon polaritons that exhibit sharp spectral features. In contrast, island films have only quasi-periodicity at a few tens of nanometers, and produce broader spectral features, suggesting the influence of localized surface plasmons. In this work we examine how absorption is affected by variations in geometry of grating-mirror systems, to identify basic physics for future investigations of particle-mirror systems. © 2009 SPIE.
Gentle, A.R. & Smith, G.B. 2009, 'Angular selectivity: Impact on optimised coatings for night sky radiative cooling', Proceedings of SPIE - The International Society for Optical Engineering.
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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 electivity, 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. © 2009 SPIE.
Dowd, A.R., Lewis, R.A., Maaroof, A.I., Gentle, A.R. & Smith, G. 2008, 'Temperature dependence of infrared optical properties of vanadium dioxide', AIP 18th National Congress, AIP, Adelaide, SA.
Gentle, A.R., Smith, G.B. & Maaroof, A.I. 2008, 'Frequency and percolation dependence of the observed phase transition in nanostructured and doped VO2 thin films', Proceedings of SPIE - The International Society for Optical Engineering.
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The response to applied electric fields of vanadium dioxide thin films above and below the phase transition is shown experimentally to depend 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 quite sensitive to both factors. The band gaps predicted by optical and dc data differ, and densities of states change with doping level. Lattice or electron dynamics alone cannot yield such behaviour, but it 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 at temperatures in the hysteresis zone. Expected percolation behaviour does not arise in such an analysis, with the observed thresholds different when heating and cooling, and they occur at temperatures which differ from the usual Tc values.
Smith, G.B. & Lakhtakia, A. 2008, 'Proceedings of SPIE - Nanostructured Thin Films: Introduction', Proceedings of SPIE - The International Society for Optical Engineering, p. ix.
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Tomkin, D.F., Thomas, L.E., Day, M.B., Burke, P.F., Franklin, J., Smith, G., Louviere, J.J. & Street, D. 2007, 'Solar Light for rooms without windows', Sustainable Innovation 07, Farnham, Surrey, UK.
Gentle, A.R., Maaroof, A.I., Cortie, M.B. & Smith, G.B. 2007, 'Optical and electrical switching in nanostructured coatings of VO 2', Proceedings of SPIE - The International Society for Optical Engineering.
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Vanadium dioxide undergoes a reversible metal-insulator phase transition at about 68&deg;C. Coatings of 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 method for depositing films with nano-size grains, which are then optically and electrically characterised. Emphasis in this study is the impact of aluminum doping and grain structure. The optical hysteresis is presented and its switching range is not altered at different doping levels but the 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, the drop in Tc and the electrical properties in the metal state. For grain sizes under about 180 nm the conductivity in the metal phase is not linear in temperature but is thermally activated, with activation energies AE dependent on both grain size G and doping level. Simple mathematical relationships are found connecting ?E with G and with carrier density in the semiconductor state. ?E ranges in our samples from 0.15 eV in the smallest grain sizes to around 0.06 eV. This anomalous low frequency metal response is linked to excitations that arise in the metal phase associated with transient singlet pairing on neighbouring sites. Such pairing is weakened by doping, and in large grains appears to be present but incoherent.
Maaroof, A.I., Gentle, A.R., Cortie, M.B. & Smith, G.B. 2007, 'Nanoporous plasmonic coatings', Proceedings of SPIE - The International Society for Optical Engineering.
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The electrical and optical properties of mesoporous gold are compared to those of thin porous gold films and a simulated thin film made by randomly distributing voids in gold, until the voids fill 76% of film volume. All layers are electrically conducting but in some cases the critical percolation thresholds are close to zero, so conduction is possible at very high void content. Significant qualitative differences are apparent between the properties of mesoporous gold, and very thin sputtered gold containing voids, in plasmonic responses at optical frequencies and in dc resistance, both as a function of fill factor. The mesoporous films have an effective plasma frequency determined by void fill factor and structure, but do not support surface plasmons. In contrast thin porous gold layers display optical features associated with localized and de-localized surface plasmons. Sputtered porous gold is 2-dimensional and its percolation threshold requires a "Swiss-cheese" rather than particle cluster model. Thicker mesoporous layers have critical parameters consistent with very high connectivity, or equivalently large hyper-dimensionality. Our meso-gold samples display various hyper- dimensionalities from 3 to above 10.
Smith, G.B. & Cortie, M.B. 2007, 'Proceedings of SPIE - The International Society of Optical Engineering: Introduction', Proceedings of SPIE - The International Society for Optical Engineering, p. vii.
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Jumrusprasert, P., Smith, G. & Kirkup, L. 2007, 'Comparing the efficiency of fixed solar cell panels in a tropical location', ISES Solar World Congress 2007, ISES 2007, pp. 1478-1483.
Monocrystalline, polycrystalline and amorphous silicon solar cell panels were installed side-by-side on the same fixed rig to determine the relative performance in a tropical location. This study was conducted at Nakhon Ratchasima Rajabhat University, Thailand. The fixed panel rig was positioned at a tilt angle of 30&deg;, facing south. Overall performance of the solar cell panels is given via both annual output and an average conversion efficiency over one whole year. The results show that for a fixed orientation the monocrystalline, polycrystalline and amorphous panels, had average conversion efficiencies of 6.8%&plusmn;2.4%, 5.7%&plusmn;2.0% and 4.2%&plusmn;1.5% respectively in terms of total incident solar energies on the plane of cells which were 809.4 kWa/m2, 860.8 kWa/m2 and 820.6 kW.year/m2 respectively. The uncertainties shown represent the standard deviation in the conversion efficiencies determined over the 12 month period of the study. These conversion efficiencies are lower than expected but are in part due to local conditions and their significant impact on movements in the maximum power point, which was not tracked in these fixed load experiments. This study also examined the effects of ambient air temperature and wind speed close to the panels which in this locale had very little impact on conversion efficiency. A detailed economic analysis was then carried out including relative maintenance costs. In terms of return on investment the panels ranked in their performance order; fixed monocrystalline, then polycrystalline and finally amorphous but the overall economics was not attractive and significant system cost reductions are needed.
Gentle, A., Maaroof, A., Smith, G. & Cortie, M. 2006, 'Optical properties and applications to production of plasmonic thin film nanostructures of self-ordered columnar alumina arrays on glass', Proceedings of SPIE - The International Society for Optical Engineering.
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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 the holes with sputtered metal is shown to be advantageous over additional anodisation. These hole arrays have intrinsically interesting optical responses which will be reported, but their main use is for nano-patterning of subsequent deposited layers either as templates or as masks. High resolution images demonstrate the uniformity in nanohole diameter and in the spacing between holes, which can be achieved when care is used in production. While many nanostructured materials can be deposited using these Porous Anodic Alumina (PAA) templates we focus here on filling the vertical cylindrical holes with silver. Etching during hole filling leads to better-controlled structures and more efficient processes. Novel optical data on the resultant conducting columnar rings will be presented. Spectrally much sharper plasmon resonant features are found than those reported for classical and more random silver column and island arrays. The optical properties are analysed from an effective medium perspective using data from spectrophotometry and ellipsometry. Fitting this data gives modelled layer thickness and the vertical profile in close agreement with direct SEM imaging. The effective refractive indices of the silver columnar layer have interesting and potentially useful dispersion characteristics.
Smith, G.B., Maaroof, A., Dowd, A., Gentle, A. & Cortie, M. 2006, 'Tuning plasma frequency for improved solar control glazing using mesoporous nanostructures', Proceedings of SPIE - The International Society for Optical Engineering.
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The role of the plasma frequency ?p of conductors in their use for various solar energy and energy efficiency tasks, especially in transparent solar control window coatings, is analysed for a range of materials including noble and other metals, transparent compound conductors and the metallic phase of VO2. Ways of adjusting ?P for improved functionality are considered, including novel mesoporous metals and composites that can have an "apparent" or effective plasma frequency. While high ?p is needed for high thermal infra-red (IR) reflectance and strong surface plasmon resonant absorption, it is not the only requirement. The location of inter-band terms relative to ?p and the solar infra-red, effective bandwidth, and a high relaxation frequency can each alter these responses substantially. Two materials with elevated carrier relaxation rates, in one case when intrinsic, and in another due to mesostructure, are used to demonstrate this impact. Solar control and visible performance of a mesoporous gold film is analysed.
Deller, C.A., Franklin, J.B. & Smith, G.B. 2006, 'Lighting simulations using smoothed LED profiles compared with measured profiles', Proceedings of SPIE - The International Society for Optical Engineering.
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Ray tracing simulations of LED lighting systems typically use the smooth angular intensity profiles supplied by the LED manufacturer. However, measurements of a range of 5 mm LEDs presented in this paper show bright regions in the LEDs' angular distributions. The intensity patterns and bright regions vary between different LEDs, even when the measured angle for 50% integrated light output (as measured using an integrating sphere) is similar. When non-diffuse or partially diffuse optical elements such as clear light guides are part of a lighting system design, this source profile unevenness is intensified, so that bright caustic rings are formed. We have performed lighting simulations using coloured LEDs coupled into a clear light guide, and compared the light output using smoothed LED profiles with that using actual measured profiles. The simulated light patterns projected from the end of a light guide onto a screen are compared with that obtained by experiment. It is shown that the uniqueness of individual LED beam patterns needs to be taken into account for simulation accuracy. This is particularly important when the lighting system combines the output from several LEDs. It is also shown to be crucial in optimising the amount and type of diffusion required for homogenising the light distribution.
Cortie, M., Maaroof, A. & Smith, G.B. 2006, 'Functional metamaterials based on mesoscale gold sponges, particulate aggregates, and their composites with dielectric materials', Materials Research Society Symposium Proceedings, pp. 25-30.
The optical properties of some nanoscale composites may deviate from that expected from a simple law of mixture of their individual components. In these cases the resulting structure can be considered to be a type of 'metamateriar. Here we explore some of the possibilities for nanoscale composite structures comprised of gold and VO2 - the latter being a functional material that undergoes a reversible insulator to metallic phase transition at 68&deg;C. Two microstructures are examined: aggregates of gold nanoparticles surrounded by VO2 as the continuous phase, and its geometric inverse, mesoporous gold sponge with discontinuous VO2 inclusions. A composite, right-angled parallelepiped measuring 40100100 nm is taken as representative of the mixture, and calculations of the optical properties performed using the discrete dip&oacute;le approximation code of Draine and Flatau. The VO2 matrix strongly attenuates the dipole-dipole plasmon resonance of the gold structure, and thermochromic switching of the remaining plasmon resonance occurs. &copy; 2007 Materials Research Society.
Cortie, M., Xu, X., Chowdhury, H., Zareie, H. & Smith, G. 2005, 'Plasmonic heating of gold nanoparticles and its exploitation', Proceedings of SPIE - The International Society for Optical Engineering, pp. 565-573.
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Nanoscale particles of metals such as gold can interact with light by means of a plasmon resonance, even though they are much smaller than the wavelengths of visible light. The proportions of light that are absorbed and scattered vary with wavelength. Any light that is absorbed will cause heating of the particles, and this effect may potentially be exploited for solar glazing coatings, nanoscale lithography or medical treatments. The position of maximum absorption of an isolated spherical nanoparticle is 518 nm, but this may be significantly red-shifted by means of decreasing the symmetry to an prolate spheroid or 'nanorod', or by producing a metal 'nanoshell' on a dielectric core, or by aggregating insulated spherical particles. Absorption peaks in the vicinity of 655 nm for aggregated particles and 780 nm for prolate spheroids are demonstrated here. Absorbed energy is released as heat into the environment of the particles, and will cause a temperature rise within the particle the magnitude of which depends upon the value of the effective heat transfer coefficient between particle and environment. The latter is not known, but we show how highly localized temperature rises of some tens of Celsius might be conceivable in systems illuminated by sunlight.
Smith, G., Cortie, M.B. & Maaroof, A.I. 2005, 'The apparent optical indices of spongy nanoporous gold', Proceedings of the 16th National Congress of the Australian Institute of Physics, National Congress of the AIP, Australian Institute of Physics, Canberra, pp. 177-180.
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Very thin spongy nanoporous gold films have a unique nanostructure and hence unusual properties. Our interest in these materials is also due to their wide range of potential application (1,2). An optical study for such nanostructured films is of fundamental interest for understanding how light interacts with such a spongy nanoporous structure. In general the gold either percolates or is very closely packed. This surface plasmons, and surface plasmon resonant effects, are expected to play a key role given the large surface area of metal and the metal backbone of the nanostructure. The ropological complexity of the nano-void network is also expected to be a major influence. The optical response has, for a metal system, quite unusual dispersion relations for the effective complex refractive index components n*, k*. Once these are better understood new optical engineering possibilities arise. We are not aware of any optical studies for spongy metal film nanostructures apart from a brief preliminary report of our own on one such film 93) whose nanstructure was different to the spongy nanoporous films presented here. We check the internal consistency and physical accpetability of the results with a Kramers-Kronig analysis of the spectrumn of n*, k* values, because of their unusual spectral character.
Earp, A.A., Franklin, J. & Smith, G. 2005, 'Extraction of trapped light from luminescent solar concentration', Proceedings of the 16th National Congress of the Australian Institute of physics, National Congress of the AIP, Australian Institute of Physics, Canberra, Australia, pp. 104-107.
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In modern light sources such as Luminescent Solar Concentrators (LSC's) and Light Emitting Diodes (LED's), light is emitted within a light-guiding structure of high refractive index. Some of this light is trapped and will not be able to escape. Similar problems are observed when collecting fluorescent radiation in waveguides (1) and scintillation detectors (2). For lighting applications, this trapped light should be ablet o escape the light-guiding structure. In LED's this is commonly achieved witha special profile in the active zone. However, inLSC's the small light-emitting zone is remote from the large light collector so a different approach must betaken. This paper will focus on the extraction of emitted light from rectangular LSc's and propose a way of extracting a large fraction of the trapped light.
Smith, G.B., Maaroof, A.I., Allan, R.S., Schelm, S., Anstis, G.R. & Cortie, M.B. 2004, 'Optical response of nanostructured metal/dielectric composites and multilayers', Proceedings of SPIE - The International Society for Optical Engineering, pp. 192-205.
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The homogeneous optical response in conducting nanostructured layers, and in insulating layers containing dense arrays of self assembled conducting nanoparticles separated by organic linkers, is examined experimentally through their effective complex indices (n*, k*). Classical effective medium models, modified to account for the 3-phase nanostructure, are shown to explain (n*, k*) in dense particulate systems but not inhomogeneous layers with macroscopic conductance for which a different approach to homogenisation is discussed, (n*, k*) data on thin granular metal films, thin mesoporous gold, and on thin metal layers containing ordered arrays of voids, is linked to properties of the surface plasmon states which span the nanostructured film. Coupling between evanescent waves at either surface counterbalanced by electron scattering losses must be considered. Virtual bound states for resonant photons result, with the associated transit delay leading to a large rise in n* in many nanostructures. Overcoating n-Ag with alumina is shown to alter (n*, k*) through its impact on the SP coupling. In contrast to classical optical homogenisation, effective indices depend on film thickness. Supporting high resolution SEM images are presented.
Schelm, S. & Smith, G.B. 2004, 'Field profiles for spherical conductive nanoparticles and metallic-shell/dielectric-core nano-composites', Proceedings of SPIE - The International Society for Optical Engineering, pp. 160-169.
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Profiles of the electric field strength |E|2/|E 0|2 for spherical metallic shells on a dielectric core are presented both inside the particle and outside. The dependence of the near-field strength and extent on shell thickness and total particle size is discussed qualitatively. Although the internal fields inside the shell and in the core are larger than for homogeneous particles, for not too thick shells, this does not translate into a stronger near-field away from the surface of the shell. The fields inside the shell, at the low energy resonance and close to it, are rotated by ?/2 with respect to fields inside homogeneous particles, which means that the maximum field strengths in the shell are perpendicular to the incident polarisation. This follows from the fact that the low energy resonance for a shell is for the largest dipole moment of the whole system, which compensates the incident field. The largest moment is created when the same charges are collected at both interfaces (shell/medium and core/shell) along the incident polarisation. This creates regions of low field densities at the poles along the incident polarisation, because same charge fields repel each other. Following from that, the field lines are bunched up at the perpendicular poles, creating large field line densities and hence large fields at these points. The case for opposite charges across the interfaces creates the high energy, antisymmetric resonance.
Deller, C.A., Smith, G.B. & Franklin, J.B. 2004, 'Uniform white light distribution with low loss from coloured LEDs using polymer doped polymer mixing rods', Proceedings of SPIE - The International Society for Optical Engineering, pp. 231-240.
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Colour mixing of red, green and blue (RGB) LEDs is demonstrated for a 6 cm long PMMA cylindrical rod with a transparent refractive index matched micro particle (TRIMM) diffuser sheet at the output end. Ray tracing simulations have been performed, and the output light distributions, transmittances and losses modelled and compared with experiment. Photographed and modelled colour mixing results are presented for rods with and without TRIMM sheet mixers. The TRIMM particles homogenize the light output of plain PMMA rods to form white light, with negligible backscattering. A simple method for measuring the concentration of the particles in the diffuser sheet is described, and computer modeling and analysis of TRIMM particle systems is discussed.
Schelm, S., Smith, G.B., Wei, G., Vella, A., Wieczorek, L., Müller, K.H. & Raguse, B. 2003, 'Optical properties of dense self-assembled gold nanoparticle layers with organic linker molecules', Proceedings of SPIE - The International Society for Optical Engineering, pp. 59-65.
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Films consisting of self-assembled gold nanoparticles cross-linked with alkane-dithiols were prepared by a filtration method and studied with scanning electron microscopy to determine the structure of the films and spectrophotometry and ellipsometry to ascertain their optical properties. The structural characterization showed the existence of nanometer-sized voids within the films. This previously unmentioned feature is responsible for the previous difficulties in modelling the optical properties with effective medium models. This can be remedied, using a two-tiered hierarchical effective medium model, which takes into account the existence of the voids. Using this model we were able to fit the experimental data, with only the void volume fraction to be determined by the overall fit, while the gold volume fraction in the linker medium is fixed by the wavelength of the resonance peak. Our model should be applicable to all such films, when the deposition method, which determines the microstructure, is properly taken into account.
Jonsson, J.C., Roos, A. & Smith, G.B. 2003, 'Light trapping in translucent samples and its effect on the hemispherical transmittance obtained by an integrating sphere', Proceedings of SPIE - The International Society for Optical Engineering, pp. 91-100.
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When a beam of light is incident on a translucent sample, a significant fraction of the light is scattered at high angles. Some of this scattered light may be trapped inside the substrate through multiple reflections and total internal reflection, similar to light coupling into an optical fiber. The trapping depends on factors such as the surface roughness of the external surfaces and/or the size and distribution of scattering particles inside the sample. The scattered light may thus escape out of the sample at a shifted position relative to the incident beam. This leads to port losses in an integrating sphere. The detected signal from the light entering the sphere then underestimates the hemispherical transmittance. In this paper the signal versus lateral position has been measured in an attempt to estimate the error and to find an extrapolation procedure for the correct transmittance value. The lateral measurements were carried out by moving a detector behind the sample, a procedure carried out at several angles of incidence. Different illumination methods have also been studied both theoretically and experimentally to further investigate what effect light trapping can have when characterising scattering samples.
Tomkin, D.F., Muir, J.G., Cortie, M.B., Masens, C. & Smith, G. 2003, 'The Nanohouse- Australian initiative to develop the home of the future', Nanotechnology, Nanotechnology, Nanotechnology, Scotland.
Conference presentation
Deller, C.A., Smith, G., Franklin, J. & Joseph, E.K. 2002, 'The integration of forward light transport and lateral illumination of polymer optical fibre', Proceedings of the Australian Institute of Physics 15th Biennial Congress 2002., Congress of the Australian Institute of Physics, Causal Productions Pty Ltd, Sydney, Australia, pp. 307-309.
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Smith, G.B. 2002, 'Nanostructured thin films - A critical review', Proceedings of SPIE - The International Society for Optical Engineering, pp. 207-221.
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Nanostructured thin films containing metal or conducting oxides underpin some existing technologies. Based on recent advances they will also enable many emerging opportunities. The optical properties from different nanostructures are linked to examples including, spectrally selective solar absorbers, solar control glazing, angular selective filters, optical bio-sensors, and decorative paints. This review will cover studies of various film and coating morphologies including cermets, and polymers containing metal or oxide conductor nanoparticles, oblique nano-metal columns in oxide, clusters and arrays of conducting nanoparticles, nanoholes in metal, granular metal networks and thin metal layers on nanostructures. Situations where quasi-static effective medium theories of optical response can be used and those where they are inadequate due to surface plasmon polariton effects will be compared. The latter includes very fine scale nano-features. Coupling between surface plasmons to form new modes is an important consideration. A brief look will also be given into an important new field - very thin metal films on nanoparticles which allow broad band tuning as thickness changes. The nanostructure within such films is quite influential.
Smith, G.B., Gerritsen, S., Hossain, A.K.M. & McCredie, G. 2001, 'Plasmon mediated visible and near infra red transmission through sub-30 nm holes in metal films: Potential in solar energy applications', Proceedings of SPIE - The International Society for Optical Engineering, pp. 29-37.
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The recent discovery that electromagnetic radiation can transmit super-efficiently through sub-wavelength holes in metal films and thin metal foils has implications for solar energy and energy efficiency technologies, especially thin metal films and metal particle arrays. The effect involves light induced surface plasmons coupling through the holes to form new states which can resonantly absorb and re-emit photons. They are a "virtual bound state" for photons. The material must have a dielectric constant below - 1, and for noble metals enhancement is strong beyond ? ? 0.7 ?m, with a long wavelength limit set by absorption losses, well into the black body spectral range. In aluminium the strong onset is in the visible. Thus control of solar heat gain and thermal radiation can utilize this effect. Broad band or narrow band spectral selectivity are possible, depending on metal thickness and how the holes are arranged with respect to each other. Very interesting effects occur in multilayers, with standard multilayer thin film optics not applying when this phenomena is present. An admittance approach to handling thin film optics in the presence of surface plasmon coupling is addressed.
Smith, G.B., Earp, A., Franklin, J. & McCredie, G. 2001, 'Novel high performance scattering materials for use in energy saving light fittings and skylights based on polymer pigmented with polymer', Proceedings of SPIE - The International Society for Optical Engineering, pp. 10-18.
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Simple quantitative performance criteria are developed for translucent materials in terms of hemispherical visible transmittance, and angular spread of transmitted luminance using a half angle. Criteria are linked to applications in luminaires and skylights with emphasis on maximising visible throughput while minimising glare. These basic criteria are also extended to angle of incidence changes which are substantial. Example data is provided showing that acrylic pigmented with spherical polymer particles can have total hemispherical transmittance with weak thickness dependence which is better than clear sheet, while the spread of transmitted light is quite thickness sensitive and occurs over wider angles than inorganic pigments. This combination means significantly fewer lamps can achieve specified lux levels with low glare, and smaller skylights can provide higher more uniform daylight illuminance.
Swift, P.D., Smith, G.B. & Franklin, J.B. 1999, 'Light to light efficiencies in luminescent solar concentrators', Proceedings of SPIE - The International Society for Optical Engineering, pp. 21-28.
Luminescent Solar Concentrators (LSC's) were thoroughly explored over a decade ago for use with photovoltaic cells. However LSC's as a source for lighting have received less attention than is deserved. To evaluate the lumens supplied by a LSC lighting source over the course of a year and in a fixed orientation it is necessary to know the light-to-light conversion efficiency. We present a model for this and examine its sensitivity to the geometry of the LSC and light transport losses for light guided within the LSC. The latter depends on dye concentration due to spectral overlaps of the absorption and emission bands and to bulk and surface losses due to defects. As a result of these effects the spectral distribution of the emitted light, and hence the colour rendering properties, depend on the size of the LSC. Calculated spectra are compared with those measured in the laboratory for full scale LSC's. Results for calculated efficiency as a function of length and dye concentration are given. It is found that properly orientated compact LSC's can provide enough lumens under moderate external illuminance to illuminate a typical room in a house.
Hossain, A.K.M.M. & Smith, G.B. 1999, 'Production of angular selective films by inter-diffusion for novel spectral responses', Proceedings of SPIE - The International Society for Optical Engineering, pp. 58-65.
Aluminium is a good candidate for both solar and visible angular selectivity if used in metal/high refractive index insulator combinations, but angular selectivity was not observed in Al/TiO 2 films prepared in traditional co-deposition techniques. A new approach, deposition of a thin oblique Al layer, then oblique TiO 2, and later annealing in vacuum, was attempted and good angular selectivity observed in this material combination. In contrast to other angular selective films, these films showed angular selectivity in s-polarised light for the plane of incidence parallel to the TiO 2 columns. Spectral transmittance plots show the effects of Al content and annealing temperature on angular selectivity. SEM micrographs confirm the oblique columnar structure of the annealed complex, and inter-diffusion of Al through the TiO 2 columns.
Xue, Y.L., Smith, G.B. & Baker, A.T. 1996, 'Collective effects, nonlinear response, and critical switching intensity in densely doped composite materials', Proceedings of SPIE - The International Society for Optical Engineering, pp. 296-307.
We have performed a study of the population dynamics in a composite, in which the active-medium is densely doped, by considering the near dipole-dipole interaction between nearest neighboring active particles. A model is presented to describe the particle-particle collective effects on the response time of the nonlinear refractive index in such a densely doped composite to an input optical signal. The results show that collective effects greatly enhance the magnitude of the nonlinear refractive index without changing the transient response time. This is expected to have potential in lowering the critical switching intensity of bistable switching devices without sacrificing switching speed. We examined two typical composites: rare-earth densely doped silica and perylimide-dye densely doped polymer/glass composites. It is found that perylimide-dye densely doped polymer/glass composite is more suitable for the switching application due to its large nonlinear refractive index and fast response time at relatively low optical intensity.
Smith, G.B., Dligatch, S. & Ng, M.W. 1995, 'Low-emittance angular selective window systems', Proceedings of SPIE - The International Society for Optical Engineering, pp. 317-325.
The issue of low emittance in angular selective window systems is discussed in the context of the overall aims of controlling glare and lowering solar gains while maintaining a clear view. Low e adds considerably to the overall performance of the window. The spectral dependence of both angular selectivity and overall transmittance in single layer anisotropic metal-insulator films needed to be improved. While these have excellent visible properties, they have high infrared transmittance and hence the window has high emittance. Results on coatings and systems set up to give the glazing a low e are examined. It is found that the visible performance is not impaired but the solar and thermal performance are improved substantially. Two methods of achieving a low emittance are discussed.
Paley, A.V., Radchik, A.V. & Smith, G.B. 1995, 'Anomalous optical scattering from intersecting fine particles', Proceedings of SPIE - The International Society for Optical Engineering, pp. 80-90.
There are many areas of science and technology where the scattering of electromagnetic waves by clusters or merging particles are of interest. The merging particles under study might be inclusions in high-density composites, liquid drops, biological cells, macroscopic ceramic particles, etc. As intersecting particles are bounded by a complex physical surface, the problem of scattering from these particles valid for any degree of merging, including touching, and for arbitrary materials of the constituents, has received limited attention. Here we present solutions which are valid and exact in the long wavelength limit compared with the size of intersecting spherical particles and cardioidal particles of similar dimensions. Both shapes are almost coincident everywhere except in the region of intersection. We treat the case when the waves are polarized along the common axis (longitudinal field). The solutions of Laplace's equation are integrals (spheres) or sums (cardioids) over continuous or discrete eigenvalue spectra respectively. The spectral dependencies of the resulting extinction coefficients and the scattering for the spherical and cardioidal particles are quite distinct. There is an enormous difference in the magnitude of absorption responses. Overall the cardioidal particle behaves as if it is almost invisible in terms of effects on the external field for a very broad band of optical frequencies. THe latter result was checked for a number of dielectric permittivities and seems to be universal. It scatters far more weakly than the isolated sphere. In constrast the intersecting sphere has an extinction band which is broad and is much enhanced at longer wavelegnths relative to the simple sphere. This result has significant implications for the design of surfaces with minimum scattering.
Bell, J.M., Barczynska, J., Evans, L.A., MacDonald, K.A., Wang, J., Green, D.C. & Smith, G.B. 1994, 'Electrochromism in sol-gel deposited TiO2 films', Proceedings of SPIE - The International Society for Optical Engineering, pp. 324-331.
Electrochromism is sol-gel deposited TiO2 films and films containing TiO2 and WO 3 has been observed. The films are deposited by dip-coating from a precursor containing titanium isopropoxide in ethanol or titanium propoxide in ethanol, and after deposition the films are heat treated to between 250&deg;C and 300&deg;C. The films do not show any signs of crystallinity. However substantial coloration is observed using Li+ ions in a non-aqueous electrolyte, both in pure TiO2 films and in mixed metal oxide films (WO 3:TiO2), although the voltage required to produce coloration is different in the two cases. Results will be presented detailing the optical switching and charge transport properties of the films during cyclic voltammetry. These results will be used to compare the performance of the TiO2 films with other electrochromics. The TiO2 and mixed metal films all color cathodically, and the colored state is a neutral greyish color for TiO2, while the bleached state is transparent and colorless, Results on coloration efficiency and the stability under repeated electrochemical cycling will also be presented. The neutral color of the TiO 2 films and mixed-metal films means that electrochromic windows based on TiO2 may have significant advantages over WO3-based windows. A detailed analysis of the optical properties of the colored state of the films will be presented. The dynamics of coloration for these films is also under investigation, and preliminary results will be presented.
Smith, G.B., Ng, M.W., Reuben, A.J., Radchik, A.V. & Dligatch, S. 1993, 'Fine tuning the spectral response of metal insulator composites for specific solar applications', Proceedings of SPIE - The International Society for Optical Engineering, pp. 58-67.
Theories developed to understand angular selective films, recent new deposition procedures , the structural information on the resulting films, and new advances in effective medium theories have together provided the insights into controlling the spectral optical response of cermets to a degree not previously realized. The key is understanding the resonance characteristics of cermets. Several factors play a role, but three have a prime influence. They are the spatial distribution of the metal particles (even more important than total content), the dielectric constant of the host material and the metal itself.
Cochrane, G., Zheng, Z. & Smith, G.B. 1993, 'Optimization of the electrical and optical properties of ITO layers deposited by magnetron sputtering', Proceedings of SPIE - The International Society for Optical Engineering, pp. 68-74.
A comprehensive investigation of the deposition parameters of In2O3:Sn films on Corning 7059 glass substrates using r.f. planar magnetron sputtering has lead to the production of films with sheet resistance < 1.5 ohms per square, an integrated luminous transmittance of approximately 77% and an integrated solar transmittance of approximately 54%. Films characterized by measurement of their resistivity and Hall coefficient show a distinct minimum in film resistivity with deposition rate, substrate temperature, oxygen partial pressure, total deposition pressure and target composition. Results are presented showing the variation in carrier concentration and carrier mobility as a function of the deposition parameters together with the optical properties and microstructure of films with a resistivity approaching 10-4 approximately egacm. Potentially, films with these properties can be used for energy efficient window applications. The results indicate that it should be possible to industrially produce large area ITO for electrochromic windows with sufficiently low sheet resistance coupled with high visible transmittance.
Bell, J.M., Smith, G.B., Green, D.C., Barczynska, J., Evans, L., MacDonald, K.A., Voelkel, G., West, B.O. & Spiccia, L. 1993, 'Assessment of electrochromic devices based on sol-gel deposited films', Proceedings of SPIE - The International Society for Optical Engineering, pp. 132-142.
We discuss the preparation and performance of various electrochromic devices based on sol-gel deposited thin films. The films are deposited by dip-coating from alcohol-based sol-gel precursor solutions and the process is well suited to scaling up to large areas for window production. The coloration and bleaching performance of the devices is compared with the performance of individual films colored in liquid electrolytes, as well as with devices deposited using sputtered and evaporated films. Devices are based on sol-gel deposited tungsten oxide thin films which forms the active electrode. A range of counter-electrode materials have been tested, including sol-gel deposited vanadium pentoxide and titania films. Various ion conductors have been tested with these films, including simple, doped PEO and hartolyte, as well as a range of other polymers and inorganic ion conductors. Results will be presented showing the optical switching performance of the devices and comparing the performance of the devices with other device configurations. Initial results show that the sol-gel-based devices exhibit good switching performance, but the devices are sensitive to the details of the precursor solution used. Long term switching performance is an important issue in window applications, and the behavior of the sol-gel deposited films under repeated cycling will also be discussed, in particular a significant difference between the performance in liquid electrolytes and solid-state devices.
Green, D.C., Bell, J.M. & Smith, G.B. 1992, 'Microstructure and stoichiometry effects in electrochromic sol-gel deposited tungsten oxide films', Proceedings of SPIE - The International Society for Optical Engineering, pp. 26-30.
Thin films produced by dip-coating from tungsten alkoxide solutions are of interest for large area electrochromic (switchable) window coatings. The window systems consist, in part, of a layer of tungsten oxide (WO3) on a layer of indium tin oxide (ITO) on glass substrate. Sol-gel processing has several advantages over other preparation techniques. However, there is the possibility of hydrocarbon residue within the films. Such carbon may restrict the electrochromic performance of the films. Rutherford backscattering spectroscopy (RBS) has been used for determining elemental composition and depth profiles in these film structures. The spectra confirm that sol-gel samples contain a substantial level of a light element, such as carbon. Auger electron spectroscopy supports the estimate obtained for the carbon content. The residual carbon can, however, be burnt out by firing at > 500&deg;C. Under certain conditions, a sub-layering is seen in the depth profiles.
Smith, G.B., Niklasson, G.A., Svensson, J.S.E.M. & Granqvist, C.G. 1985, 'NOBLE-METAL-BASED TRANSPARENT INFRARED-REFLECTORS: PREPARATION AND ANALYSIS OF THIN GOLD FILMS.', Proceedings of SPIE - The International Society for Optical Engineering, pp. 116-123.
Very thin gold layers were produced on glass by evaporation with and without simultaneous ion bombardment. Electron microscopy showed that films with thicknesses below a certain magnitude - which decreased with increasing ion flux - has a non-uniform (network) structure. Optical properties were measured by spectrophotometry in the 0. 3-50- mu m range. Uniform films were consistent with the Drude theory with an anomalously large frequency dependence of the relaxation energy. Non-uniform films displayed characteristic plateaus in the near-infrared transmittance. This feature, which is conducive to high solar transmittance, can be explained from effective medium theories based on the film structure. Our results are important for the development of improved noble-metal-based infrared-reflectors for energy efficient windows.
Smith, G.B., Hillery, P. & Teytz, K. 1984, 'ABSORBER COATINGS FOR CONCENTRATING COLLECTORS.', pp. 1914-1918.
Ignatiev, A., Zajac, G. & Smith, G.B. 1982, 'SOLAR ABSORBER MATERIAL STABILITY UNDER HIGH SOLAR FLUX.', Proceedings of SPIE - The International Society for Optical Engineering, pp. 170-175.

Journal articles

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.
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&copy; 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Flexible multilayer electrodes that combine high transparency, high conductivity, and efficient charge extraction have been deposited, characterised and used as the anode in organic solar cells. The anode consists of an AZO/Ag/AZO stack plus a very thin oxide interlayer whose ionization potential is fine-tuned by manipulating its gap state density to optimise charge transfer with the bulk heterojunction active layer consisting of poly(n-3- hexylthiophene-2,5-diyl) and phenyl-C61-butyric acid methyl ester (P3HT:BC61BM). The deposition method for the stack was compatible with the low temperatures required for polymer substrates. Optimisation of the electrode stack was achieved by modelling the optical and electrical properties of the device and a power conversion efficiency of 2.9% under AM1.5 illumination compared to 3.0% with an ITO-only anode and 3.5% for an ITO:PEDOT electrode. Dark I-V reverse bias characteristics indicate very low densities of occupied buffer states close to the HOMO level of the hole conductor, despite observed ionization potential being high enough. Their elimination should raise efficiency to that with ITO:PEDOT.
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.
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&copy; 2014 Elsevier Ltd. 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. & Smith, G.B. 2015, 'A Subambient Open Roof Surface under the Mid-Summer Sun', Advanced Science, vol. 2, no. 9, pp. n/a-n/a.
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Arnold, M., Blaber, M. & Ford, M. 2014, 'Local plasmon resonances of metal-in-metal core-shells', Optics Express, vol. 22, no. 3, pp. 3186-3198.
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We investigate the tunability and strength of the localized surface plasmons of binary metal-in-metal core-shells. Ellipsoids are used as an analytical model to show how the fill factor continuously tunes a hybridized mode between those of the constituents, suggesting the use of metal combinations with widely differing plasma frequencies for broad tunability. A quasistatic eigenmode method is used separate geometric and material parameters to facilitate prediction of hybridized dipole modes in arbitrary shapes. A modified ellipsoid model is found to adequately describe the symmetric dipole-dipole resonance of well-rounded cuboids. &copy; 2014 Optical Society of America.
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. 7157-7167.
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&copy; 2014 Optical Society of America Accurate solar and visual transmittances of materials in which surfaces or internal structures are complex are often not easily amenable to standard procedures with laboratory-based spectrophotometers and integr ting spheres. Localized "hot spots" of intensity are common in such materials, so data on smallsamples is unreliable. A novel device and simple protocols have been developed and undergone validation testing. Simultaneous solar and visible transmittance and reflectance data have been acquired for skylight components and multilayer polycarbonate roof panels. The pyranometer and lux sensor setups also directly yield "light coolness" in lumens/watt. Sample areas must be large, and, although mainly in sheet form, some testing has been done on curved panels. The instrument, its operation, and the simple calculations used are described. Results on a subset of diffuse and partially diffuse materials with no hot spots have been cross checked using 150 mm integrating spheres with a spectrophotometer and the Air Mass 1.5 spectrum. Indications are that results are as good or better than with such spheres for transmittance, but reflectance techniques need refinement for some sample types.
Gentle, A.R., Dybdal, K.L. & Smith, G.B. 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, pp. 79-85.
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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. &copy; 2013 Elsevier B.V. All rights reserved.
Gentle, A.R., Smith, G.B. & Watkins, S.E. 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. PARTB, pp. 110-114.
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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 multilayer transparent conducting electrodes for organic solar cells and OLED's. Work function in most traditional transparent electrodes has to be raised to maximise charge transfer while high transmittance and high conductance must be retained. Results are presented for a range of metal oxide buffers, which achieve this goal. This compact photo-yield spectroscopy tool with its fast turn-around has been a valuable development aid since ionisation potential can vary significantly as deposition conditions change slightly, and as ultra-thin films grow. It has also been useful in tracking the impact of different post deposition cleaning treatments along with some storage and transport protocols, which can adversely reduce ionisation potential and hence subsequent device performance. &copy; 2013 Elsevier B.V. All rights reserved.
Smith, G.B., Golestan, D. & Gentle, A.R. 2013, 'The insulator to correlated metal phase transition in molybdenum oxides', Applied Physics Letters, vol. 103, no. 5.
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In sub-stoichiometric MoO3, electrical and optical responses across the solar spectrum are tunable and manifest a sharp phase transition in thin films at a specific oxygen content. Models of optical response in insulating and conducting regimes have been developed. Oxygen vacancies induce semiconducting response exactly proportional to the observed concentration of gap d-states until the transition. Ionization potential is thus tunable. Metallic thin films are never plasmonic at any stoichiometry and their conductivity, Hall mobility, carrier density, and plasma frequency are consistent, but either loss rate or effective mass mean metallic conduction is correlated rather than classical. &copy; 2013 AIP Publishing LLC.
Smith, G.B. 2012, 'Green nanophotonics', Journal of Nanophotonics, vol. 6, no. 1.
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Nanotechnology, in particular nanophotonics, is proving essential to achieving green outcomes of sustainability and renewable energy at the production scales needed. Nanomaterials enable optimization of optical, opto-electrical, and thermal responses. Optical harmonization of material responses to environmental energy flows involves large changes in spectral response over limited wavelength bands and tailoring to environmental dynamics. The latter includes engineering angle of incidence dependencies and switchable (or chromogenic) responses. Nanomaterials can be made at sufficient scale and low enough cost to be economical and have high impact on a short time scale. Issues to be addressed include human safety and property changes induced during manufacture, handling, and outdoor use. Unexpected advantages have arisen in this work such as the savings and environmental benefits of cool roofs extending beyond the more obvious benefit of reduced heat flows from the roof into the building. We explore some of the likely elements involved in harmonizing nature and technology with applications of nanophotonics to reduce the use of energy in buildings. &copy; 2012 Society of Photo-Optical Instrumentation Engineers.
Smith, G.B., Aguilar, J.L.C., 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, pp. 668-673.
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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 could be beneficial in one season while reducing performance or neutral in the other. In doing so it is important in this multi-parameter design space to consider impact of changes in each parameter when other variables also change. Such 2-variable up to n-variable correlation is called factorial analysis. The methodology is introduced using three variables (roof solar absorptance, air exchange rates, and sub-roof R-value) in a simple structure with all other parameters fixed. Sensitivity is via impact of changes on each of heating load, cooling load and annual total. Knowledge of factorial effects is shown to be important and lead to simple strategies that provide large benefits in both seasons. They also show that some standard approaches to saving energy (e.g. raising R significantly), while useful are often unnecessary, unless poor settings are made in other parameters. &copy; 2012 Elsevier B.V. All rights reserved.
Edmonds, I. & Smith, G. 2011, 'Surface reflectance and conversion efficiency dependence of technologies for mitigating global warming', Renewable Energy, vol. 36, no. 5, pp. 1343-1351.
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A means of assessing the relative impact of different renewable energy technologies on global warming has been developed. All power plants emit thermal energy to the atmosphere. Fossil fuel power plants also emit CO2 which accumulates in the atmosphere and provides an indirect increase in global warming via the greenhouse effect. A fossil fuel power plant may operate for some time before the global warming due to its CO2 emission exceeds the warming due to its direct heat emission. When a renewable energy power plant is deployed instead of a fossil fuel power plant there may be a significant time delay before the direct global warming effect is less than the combined direct and indirect global warming effect from an equivalent output coal fired plant - the " business as usual" case. Simple expressions are derived to calculate global temperature change as a function of ground reflectance and conversion efficiency for various types of fossil fuelled and renewable energy power plants. These expressions are used to assess the global warming mitigation potential of some proposed Australian renewable energy projects. The application of the expressions is extended to evaluate the deployment in Australia of current and new geo-engineering and carbon sequestration solutions to mitigate global warming. Principal findings are that warming mitigation depends strongly on the solar to electric conversion efficiency of renewable technologies, geo-engineering projects may offer more economic mitigation than renewable energy projects and the mitigation potential of reforestation projects depends strongly on the location of the projects. &copy; 2010 Elsevier Ltd.
Gentle, A.R., Aguilar, J.L.C. & Smith, G.B. 2011, 'Optimized cool roofs: Integrating albedo and thermal emittance with R-value', Solar Energy Materials and Solar Cells, vol. 95, no. 12, pp. 3207-3215.
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For cool roofs the combined effect of the three parameters that define heat gain and loss from a roof, namely solar albedo ?, 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 (?,E,R) demonstrate the over-riding importance of a high ?, 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?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. &copy; 2011 Elsevier B.V. All rights reserved.
Earp, A.A., Franklin, J.B. & Smith, G.B. 2011, 'Absorption tails and extinction in luminescent solar concentrators', Solar Energy Materials and Solar Cells, vol. 95, no. 4, pp. 1157-1162.
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Non-ultraviolet (UV) photoexposure of luminescent solar concentrators (LSCs) can produce photoproducts that cause additional extinction at wavelengths somewhat longer than the main dye absorption peak. This photo-induced 'tails' extinction is deleterious to luminous output in collectors of useful lengths. An experimental method that enables the subdivision of tails extinction in an LSC into absorbed and scattered components is described. The relevant theory is outlined, and experimental results are presented for a polymethyl methacrylate (PMMA) LSC containing Lumogen F083 dye. For this sample, tails absorption increased significantly with outdoor exposure, while tails scattering remained constant. Further measurements indicate that LSC luminous output is around five times more sensitive to tails absorption than to fluorescence quenching. This work also indicates that merely checking for dye quenching, as is often done, can be a misleading indicator of long-term LSC output. &copy; 2010 Elsevier B.V. All rights reserved.
Earp, A.A. & Smith, G.B. 2011, 'Evolution of plasmonic response in growing silver thin films with pre-percolation non-local conduction and emittance drop', Journal of Physics D: Applied Physics, vol. 44, no. 25.
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The optical response of growing silver thin films undergoes a transition dominated by three distinct plasmonic modes, two localized and one delocalized. Their admix as a function of added mass is analysed. The onset of the delocalized or Drude mode occurs before the sharp electrical percolation transition so optically the full insulator-metal transition is broadened. A scaling explanation supported by images shows Ag islands only have to link up over 200-300 nm to yield partial delocalization. The localized modes are (i) from silver nano-islands and (ii) a transitional anomalous mode, peaking near the dc critical percolation point, from islands surrounded by network. Growing silver within a multilayer oxide stack is compared with that on glass. The transition in thermal emittance matches that in the delocalized mode. Its broadening enables practical tuning of intermediate emittance by varying mass. &copy; 2011 IOP Publishing Ltd.
Smith, G.B. 2011, 'Commentary: Environmental nanophotonics and energy', Journal of Nanophotonics, vol. 5, no. 1.
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The reasons nanophotonics is proving central to meeting the need for large gains in energy efficiency and renewable energy supply are analyzed. It enables optimum management and use of environmental energy flows at low cost and on a sufficient scale by providing spectral, directional and temporal control in tune with radiant flows from the sun, and the local atmosphere. Benefits and problems involved in large scale manufacture and deployment are discussed including how managing and avoiding safety issues in some nanosystems will occur, a process long established in nature. &copy; 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).
Earp, A.A., Rawling, T., Franklin, J.B. & Smith, G.B. 2010, 'Perylene dye photodegradation due to ketones and singlet oxygen', Dyes and Pigments, vol. 84, no. 1, pp. 59-61.
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The photodegradation rate of a perylene dye (Lumogen F Yellow 083) in methyl isobutyrate was found to increase with ketone concentration for two different ketones. Of the ketones employed, methyl pyruvate, an impurity in methyl methacrylate, was found to be particularly deleterious to dye stability. In agreement with other published studies, the addition of the anti-oxidant DABCO (1,4-diazabicyclo-[2.2.2] octane) to the dye matrix was found to increase dye stability; however when ketones were present, DABCO lead to increased photodegradation. These results highlight the importance of removing ketone impurities from dye matrices during production of Luminescent Solar Concentrators (LSCs). &copy; 2009 Elsevier Ltd. All rights reserved.
Gentle, A.R. & Smith, G.B. 2010, 'Radiative heat pumping from the Earth using surface phonon resonant nanoparticles', Nano Letters, vol. 10, no. 2, pp. 373-379.
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Nanoparticles that have narrow absorption bands that lie entirely within the atmosphere's 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. &copy; 2010 American Chemical Society.
Earp, A.A. & Smith, G.B. 2010, 'Metal nanoparticle plasmonics inside reflecting metal films', Applied Physics Letters, vol. 96, no. 24.
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Oxide coated metal nanoparticles buried within a thin metal layer support a surface plasmon resonance. A local dip occurs in spectral reflectance along with a switching off of the film's plasmonic response. Models are introduced in which these resonances are tunable by altering the ratio of oxide thickness to core particle radius. The optical response of two experimental examples is presented and modeled using effective medium theory. Beyond the resonance zone the doped layer switches back to the plasmonic response of a nanoporous version of the host metal whose effective plasma frequency arises only from the percolating component. &copy; 2010 American Institute of Physics.
Smith, G.B. & Earp, A.A. 2010, 'Metal-in-metal localized surface plasmon resonance', Nanotechnology, vol. 21, no. 1.
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Anomalous strong resonances in silver and gold nanoporous thin films which conduct are found to arise from isolated metal nano-islands separated from the surrounding percolating metal network by a thin loop of insulator. This observed resonant optical response is modelled. The observed peak position is in agreement with the observed average dimensions of the silver core and insulator shell. As the insulating ring thickness shrinks, the resonance moves to longer wavelengths and strengthens. This structure is the Babinet's principle counterpart of dielectric core-metal shell nanoparticles embedded in dielectric. Like for the latter, tuning of resonant absorption is possible, but here the matrix reflects rather than transmits, and tuning to longer wavelengths is more practical. A new class of metal mirror occurring as a single thin layer is identified using the same resonances in dense metal mirrors. Narrow band deep localized dips in reflectance result. &copy; 2010 IOP Publishing Ltd.
Gentle, A.R., Smith, G.B. & 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. 1.
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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. T c 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 T c values. &copy; 2009 Society of Photo-Optical Instrumentation Engineers.
Smith, G.B. 2009, 'Guest editorial: Nanostructured thin films', Journal of Nanophotonics, vol. 3, no. 1.
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Smith, G.B. 2009, 'Amplified radiative cooling via optimised combinations of aperture geometry and spectral emittance profiles of surfaces and the atmosphere', Solar Energy Materials and Solar Cells, vol. 93, no. 9, pp. 1696-1701.
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Net thermal radiation cooling, from surfaces at sub-ambient temperatures, to the night sky is amplified if the aperture to the sky is partially blocked with heat mirrors. The temperature at which radiation loss stagnates (the effective sky temperature) falls continuously as the aperture closes and is derived in terms of the aperture size and the spectral properties and temperatures of the atmosphere and of the emitting surface. Cooling surfaces must have high absorptance between 7.9 ?m and 13 ?m where the atmosphere is most transparent. The best response for the remainder of the Planck radiation spectrum surprisingly switches between two spectral extremes at a temperature which falls as the aperture gets smaller. A perfect absorber is best above this switch, while surfaces which reflect all of this radiation are best below it. A simple formula is presented for the cross-over temperature as a function of aperture size. With known material properties plus representative non-radiative heat gains a high emittance surface is generally better except when heat mirrors are not used. A known high emittance roof paint at 10&deg; C below ambient, under a 45&deg; aperture lined with shiny aluminium, can achieve a net output power near 135 W m-2 under a clear sky. &copy; 2009 Elsevier B.V. All rights reserved.
Bai, H., Cortie, M.B., Maaroof, A.I., Dowd, A., Kealley, C. & Smith, G.B. 2009, 'The preparation of a plasmonically resonant VO2 thermochromic pigment', Nanotechnology, vol. 20, no. 8.
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Vanadium dioxide (VO2) undergoes a reversible metal-insulator transition, normally at ?68 &deg;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 VO 2 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. &copy; 2009 IOP Publishing Ltd.
Gentle, A.R. & Smith, G.B. 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.
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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 anti-reflection band where reflectance can be very close to zero and transmittance is close to 70%. In addition these properties are combined with IR reflectance approaching 99% for a very small thermal signature. Spatial variation of narrow band colour is easily achieved and is demonstrated with production of a simple wedge filter covering the full visible spectrum. Measured CIE colour contours in transmittance and reflectance are presented and spectral data on experimental films is compared with ideal models. Potential sources of small departures from ideal models are examined to assess the scope for future improvements. &copy; 2008 Springer-Verlag.
Gentle, A. & Smith, G.B. 2008, 'Dual metal-insulator and insulator-insulator switching in nanoscale and Al doped VO2', Journal of Physics D: Applied Physics, vol. 41, no. 1.
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Thin films of VO2 doped with aluminium, or with nanoscale grain sizes, have been produced. They display semiconductor resistive behaviour above the transition temperature Tc, but a metallic and plasmonic optical response. All samples optically switch over almost identical large ranges at the transition, but have quite variable resistive switching. At fixed grain size a rigorous new quantitative correlation is found between semiconductor resistivity below Tc and the activation energy above Tc as Al doping level varies. Large crystals doped with Al also display this dual behaviour. A possible mechanism is discussed involving fast local fluctuations on neighbouring V4+ ions involving transient dimers with no net spin. Such fluctuations would then need to interact and correlate their motion over the scale of a nanograin within the lifetime of the dimer excitation. &copy; 2008 IOP Publishing Ltd.
Swift, P.D., Lawlor, R., Smith, G.B. & Gentle, A. 2008, 'Rectangular-section mirror light pipes', Solar Energy Materials and Solar Cells, vol. 92, no. 8, pp. 969-975.
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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 rectangular-section MLPs have been measured experimentally and calculated theoretically for the case of collimated light input. The results presented extend the description of MLPs from the cylindrical case. Measured and calculated transmittances and irradiance distributions are in good agreement. &copy; 2008 Elsevier B.V. All rights reserved.
Gentle, A., Maaroof, A. & 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.
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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 &deg;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. &copy; 2007 Elsevier B.V. All rights reserved.
Smith, G.B., Maaroof, A.I. & Cortie, M.B. 2008, 'Percolation in nanoporous gold and the principle of universality for two-dimensional to hyperdimensional networks', Physical Review B - Condensed Matter and Materials Physics, vol. 78, no. 16.
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Percolation in nanoporous gold can be achieved with as little as 8% by volume of gold. Samples of nanoporous gold of various morphologies are analyzed with a combination of electrical and optical data. Growing thin films and complex multiply connected three-dimensional networks both display nonuniversal character. Growing films have two-dimensional morphology but a three-dimensional percolation threshold and nonuniversal critical coefficients, yet similar silver films percolate as expected with universal coefficients. Growing gold however regresses to two-dimensional resistive behavior between 65% to 100% gold, and this regime lies along a single power-law curve shared by the hyperdimensional networks of gold, suggesting underlying symmetry governed by diffusion-limited aggregation. Models of data imply either hyperdimensionality or major internal property changes as density shifts. The distinctive flat spectral signature found near the percolation threshold is common to all highly porous samples and is explained quantitatively in terms of effective plasmonic response. Parameters from fits of effective medium models to optical and resistivity data are in close agreement, especially at the highest porosities. They imply an effective dimension which increases continuously as porosity grows via the increased branching needed for structural integrity. &copy; 2008 The American Physical Society.
Maaroof, A.I., Gentle, A., Smith, G.B. & 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.
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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 for a conductor at their thicknesses 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 4 ?m 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 tailor the onset of effective plasmonic response across a wide range from 0.8 to 4 ?m and emittance from around 0.9 down to low values. An effective uniform metal response is thus found in the presence of surface nanostructure without the interface absorption found in dense gold layers with structured surfaces. &copy; 2007 IOP Publishing Ltd.
Maaroof, A.I., Cortie, M.B., Gentle, A. & Smith, G.B. 2007, 'Mesoporous gold sponge as a prototype 'metamaterial'', Physica B: Condensed Matter, vol. 394, no. 2, pp. 167-170.
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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 behavior. We found that it was necessary to include an additional special oscillator centered at 1.4 eV in order to model the unusual spectral response. This is quite unlike bulk gold, which can be modeled using a standard two-oscillator LD model. &copy; 2007 Elsevier B.V. All rights reserved.
Earp, A., Smith, G. & Franklin, J. 2007, 'Simplified BRDF of a non-Lambertian diffuse surface', Lighting Research and Technology, vol. 39, no. 3, pp. 265-281.
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For real diffuse surfaces, the bi-directional reflectance distribution function (BRDF) is non-Lambertian, and may require a more complex model in ray tracing simulations. The BRDF of a diffuse white surface is studied at multiple angles of incidence, and an additional reflectance component is observed, which becomes more specular as the angle of incidence increases. For angles of incidence >85&deg;, the BRDF may be regarded as specular. In this article, a two-part model is proposed in which the BRDF of a diffuse surface consists of a Lambertian diffuse component and a Lorentzian pseudo-specular component - both of which vary with angle of incidence. This model may be used to reduce computation times for ray tracing simulations, as an alternative to large three-dimensional BRDF datasets. &copy; The Chartered Institution of Building Services Engineers 2007.
Gentle, A., Maaroof, A.I. & Smith, G.B. 2007, 'Nanograin VO2 in the metal phase: A plasmonic system with falling dc resistivity as temperature rises', Nanotechnology, vol. 18, no. 2.
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Thin films of vanadium dioxide with grain sizes smaller than 60nm have a metallic phase with excellent plasmonic response, but their dc resistivity falls as temperature rises to values well 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 found in large grain films. Conductivity rises with thermal activation energy of 108meV, which is well below that in the 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. &copy; IOP Publishing Ltd.
Smith, G.B., Maaroof, A.I. & Gentle, A. 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.
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Nanoporous gold 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 homogeneous Lorentz-Drude metal with a unique plasma frequency ?p * and an inter-band transition energy unchanged from that of dense gold. The link between ?p * and ?p in dense gold is found using a simplification of the Bergman expansion for permittivity valid at infra-red wavelengths. The carrier relaxation time of the "effective metal" becomes the actual relaxation time in the Au network 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 ?p * / ?p 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-NIR spectral response, giving excellent agreement with data. A range of films with these properties are presented. &copy; 2006 Elsevier B.V. All rights reserved.
Smith, G.B., Gentle, A.R. & Maaroof, A.I. 2007, 'Metal-insulator nanocomposites which act optically like homogeneous conductors', Journal of Nanophotonics, vol. 1, no. 1.
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Conductor-insulator nanocomposites in which the conductor percolates can have optical responses at longer wavelengths like dense conductors with an effective plasma frequency ?p*. This applies at wavelengths where the Bergman spectral function F for permittivity varies sufficiently slowly with wavelength. ?p* can be engineered by varying the components, the nanostructure's topology, or the dielectric volume fraction f. The homogenized conductor acts like a dense conductor whose charge carriers have effective mass meff*. Results are presented for ?p*(f) and m eff*(f) using the Maxwell Garnett (MG) and Bruggeman (BR) models for spheres and aligned ellipsoids. In the BR case meff* (f) at the percolation concentration is singular. Example ? p* data for spheres and ellipsoids are given which match predictions. Anisotropy in effective mass is considered, such that effective plasma frequency can depend strongly on polarization direction of incident light. &copy; 2007 Society of Photo-Optical Instrumentation Engineers.
Swift, P.D., Smith, G.B., Franklin, J., Edmonds, I.R. & Carter, D.J. 2006, 'Hotspots in cylindrical mirror light pipes: Description and removal', Lighting Research and Technology, vol. 38, no. 1, pp. 19-31.
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The transmittance and irradiance distribution at the exit aperture of a cylindrical mirror light pipe (MLP) have been measured and calculated for the cases of collimated and diffuse inputs. MLPs are an example of a nonimaging optical system that can concentrate light, which may give rise to problematic hotspots and glare either on any diffuser used at the exit aperture or in the illuminated room. It is shown in this work that use of a diffuser at the entrance aperture overcomes these problems without a marked reduction in transmission of a typical MLP. &copy; The Chartered Institute of Building Services Engineers 2006.
Cortie, M.B., Maaroof, A., Smith, G.B. & Ngoepe, P. 2006, 'Nanoscale coatings of AuAlx and PtAlx and their mesoporous elemental derivatives', Current Applied Physics, vol. 6, no. 3, pp. 440-443.
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A method to produce nanoscale films of AuAlx and PtAlx, and their mesoporous elemental derivatives is described, and the morphology and optical properties of these coatings explored. The color of the AuAlx film is bright purple, in agreement with ab initio calculations and experimental observations for the compound AuAl2, but becomes black after de-alloying with NaOH. The film of PtAlx is silver-grey and changes to grey after being converted to mesoporous Pt by de-alloying. Both mesoporous coatings exhibit a very rough surface, with pores of between 2 and 20 nm in diameter, and display a significantly more absorptive optical characteristic compared to their ordinary elemental counterparts. &copy; 2005 Elsevier B.V. All rights reserved.
Deller, C.A., Franklin, J. & Smith, G.B. 2006, 'Monte Carlo ray-tracing in particle-doped light guides', Lighting Research and Technology, vol. 38, no. 2, pp. 95-108.
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A general Monte Carlo ray-tracing method for light guides with particles randomly dispersed in a matrix material is presented. Previous ray-tracing approaches have been designed for undoped cylindrical light guides, where a propagating ray is deviated by total internal reflection only. These geometrical principles are extended and further developed into a method of ray-tracing suitable for particle-doped systems. Redefining ray direction after deviation by a particle, obtaining ray/ wall intercept points and angles, and calculation of ray reflection angles from a cylindrical surface are described. Simulations of light from a source LED traced through TRIMM-doped (Transparent Refractive Index Matched Micro-Particle) polymethyl methacrylate (PMMA) light guides have been performed. Distributions of the light exiting the walls of two concentrations of TRIMM-doped light guides are given, as an example of an application of the described ray-tracing method.
Maaroof, A.I., Cortie, M.B. & Smith, G.B. 2005, 'Optical properties of mesoporous gold films', Journal of Optics A: Pure and Applied Optics, vol. 7, no. 7, pp. 303-309.
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Mesoporous gold thin films on glass substrates were fabricated by sputtering of AuAl2 precursor films followed by a de-alloying etch. The resulting sponge-like Au films have very high internal surface area due to nanoscale pores and channels. Scattering is not significant and the optical properties for such nanostructured films were examined using ellipsometry and spectrophotometry. The complex refractive indices of the optically equivalent uniform smooth layer satisfy Kramers-Kronig (KK) self-consistency but have unusual dispersion relations and magnitudes for a film containing the amount of noble metal present. The reflectance at infrared wavelengths is neither metal-nor insulator-like, and the indices have unique dispersion curves. &copy; 2005 IOP Publishing Ltd.
Maaroof, A.I. & Smith, G.B. 2005, 'Effective optical constants of nanostructured thin silver films and impact of an insulator coating', Thin Solid Films, vol. 485, no. 1-2, pp. 198-206.
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Two distinct electrically percolated types of nanostructured silver (n-Ag) films on glass substrates have been optically and structurally studied and effective refractive indices determined. The first though well above the percolation threshold contains networks of elongated nano-voids over ?15% of the film area. The second is at a thickness where the film is almost void free. A surprising qualitative shift in spectral response to Drude like behaviour in the n-Ag film with many voids has been found after overcoating with oxide dielectric (Al2O3). With no overcoat much incident light is being shunted through the voids and does not see the metal while with the overcoat the reverse occurs and light passes mainly through the metal. A recent effective medium model for a pair and chain of cylindrical voids is used to explore if quasistatic models can describe these resonant features. It is concluded that induced surface current related dynamic effects are present and impact strongly on effective indices in n-Ag containing nano-voids. &copy; 2005 Elsevier B.V. All rights reserved.
Cortie, M.B., Maaroof, A.I. & Smith, G.B. 2005, 'Electrochemical capacitance of mesoporous gold', Gold Bulletin, vol. 38, no. 1, pp. 14-22.
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The surfaces of nanoscale gold particles and components are oxide-free under normal ambient conditions. This unusual attribute permits the exploration of microstructures and functionalities that would not be feasible for less noble metals. Here we consider the electrochemical properties of mesoporous gold sponges, prepared by de-alloying an AuAl2 precursor. The sponges have a high specific surface area, with an average pore diameter of 12 nm, but are prone to sinter. They may be prepared in bulk, or, more usefully, as coatings. Their electrochemical capacitance divided by their nominal surface area is high and, at a cell voltage of 0.6 V, reaches 100 mF/cm2 for bulk samples and 2 mF/cm2 for coatings. This is up to a thousand times greater than the 50 to 100 ?F/cm2 exhibited by a planar gold surface.
Schelm, S. & Smith, G.B. 2005, 'Evaluation of the limits of resonance tunability in metallic nanoshells with a spectral averaging method', Journal of the Optical Society of America A: Optics and Image Science, and Vision, vol. 22, no. 7, pp. 1288-1292.
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Spectral selectivity based on tuning the surface plasmon resonance in metallic nanoshells by variation of the relative shell thickness is shown to be limited by the interplay between scattering and absorption. To achieve resonance energies in the near infrared and infrared, relatively large cores are needed, which lead to strong and broad scattering bands and multipolar contributions in the visible. The scattering contribution to extinction is described with a new parameter S<inf>?</inf>, which is defined for a wavelength range of interest ?. This parameter can help in designing materials for specific applications where scattering is either hindering, as in near-infrared absorbers for visually clear windows, or actually desired, such as in particle-array-based sensors. &copy; 2005 Optical Society of America.
Schelm, S. & Smith, G.B. 2005, 'Internal electric field densities of metal nanoshells', Journal of Physical Chemistry B, vol. 109, no. 5, pp. 1689-1694.
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The internal field patterns for gold shells filled with the same material as the surrounding medium are calculated with Mie theory and in the quasistatic approximation and their properties compared to the response of homogeneous spheres and metallic rings. One major difference between the sphere and shell case is that the areas of highest field enhancement in metallic shells are located perpendicular to the incident polarization, whereas for metallic spheres they are along the polarization direction. Recent results based on the discrete dipole approximation (DDA) are shown to be misleading, which might be due to the use of a too coarse grid size. We also show that the type of resonance and the associated internal field pattern (low or high energy) has a strong impact on the external fields.
Jonsson, J.C., Smith, G.B., Deller, C. & Roos, A. 2005, 'Directional and angle-resolved optical scattering of high-performance translucent polymer sheets for energy-efficient lighting and skylights', Applied Optics, vol. 44, no. 14, pp. 2745-2753.
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Transparent refractive-index matched micro (TRIMM) particles have proved to be an excellent scattering component for use in translucent sheets. Measurements of hemispheric transmittance and reflectance versus angle of incidence, as well as angle-resolved studies of such translucent sheets, have been carried out to complement earlier published hemispheric reflectance and transmittance spectral measurements carried out at normal angle of incidence. Hemispheric values relative to angle of incidence are of interest for daylighting applications and building simulations, and angle-resolved measurements are vital for verifying that our modeling tools are reliable. Ray-tracing simulations based on Mie scattering for the individual TRIMM particles and angle-resolved measurements are in good agreement, indicating that the simulation method used is practical for the design of new scattering profiles by varying particle concentration or refractive index. &copy; 2005 Optical Society of America.
Schelm, S., Smith, G.B., Garrett, P.D. & Fisher, W.K. 2005, 'Tuning the surface-plasmon resonance in nanoparticles for glazing applications', Journal of Applied Physics, vol. 97, no. 12.
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Issues affecting the performance of polymers doped with conducting nanoparticles for use with windows are examined in terms of impact on visible and solar transmittance, solar heat gain, and residual scattering. Emphasis is on visible transmittance fixed in the range of 30%-75%, combined with maximal blocking of the near-infrared (NIR) component of solar energy in the wavelength range of 750-1300 nm. Spectral data and surface-plasmon resonance (SPR) models of absorbance for La B6 and indium tin oxide nanoparticles embedded in polymer are quite distinct from each other, but both can be used and each material has its advantages and disadvantages. The SPR of La B6 nanoparticles is very efficient at NIR blocking, as it lies near 1000 nm, but as a result its tail overlaps the visible. In contrast the SPR of ITO lies well beyond 1000 nm and is thus far less efficient, only relying on its SPR tail. However, this means it only weakly affects the visible. Results of a quasistatic model for the optical properties are presented, along with comparisons to full Mie scattering calculations. It is found that ellipsoidal particles are required to explain the properties of the studied La B6 particles, and that scattering can be significant in the NIR while weak in the visible. Furthermore, the forward-to-backward-scattering ratio is different for Rayleigh scattering in the visible and scattering near the SPR. The latter is much more isotropic, even for larger particles. &copy; 2005 American Institute of Physics.
Schelm, S., Smith, G.B., Wei, G., Vella, A., Wieczorek, L., Muller, K.H. & Raguse, B. 2004, 'Double Effective Medium Model for the Optical Properties of Self-Assembled Gold Nanoparticle Films Cross-Linked with Alkane Dithiols', Nano Letters, vol. 4, no. 2, pp. 335-339.
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We present a comprehensive and structurally correct optical model for layers of nanometer sized gold particles, cross-linked with ?,?- alkane dithiol molecules, HS-(CH2)n-SH with n = 2, 8, 15. The solution requires a two-stage, three-phase effective medium model based on the observed nanostructure of the three constituents, gold, thiol, and voids. Voids and their topology, which were neglected in previous models, prove to be crucial in the explanation of the optical properties.
Jonsson, J.C., Smith, G.B. & Niklasson, G.A. 2004, 'Experimental and Monte Carlo analysis of isotropic multiple Mie scattering', Optics Communications, vol. 240, no. 1-3, pp. 9-17.
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This paper demonstrates patterns in the multiple scattering behavior of three test cases, of which one is verified experimentally. Mie scattering patterns are known to emerge when the scattering angle is plotted versus the dimensionless parameter qR, where q is the scattering wave vector for a single particle, and R is the radius of the scattering particle. The power-law behavior of single scattering is modified, but not completely destroyed, when translated to multiple scattering situations. The predicted behavior is seen in translucent sheets, where transparent refractive index matched micro (TRIMM) particles scatter light, a case which is ideal to model with Mie scattering. &copy; 2004 Elsevier B.V. All rights reserved.
Earp, A.A., Smith, G.B., Swift, P.D. & Franklin, J. 2004, 'Maximising the light output of a Luminescent Solar Concentrator', Solar Energy, vol. 76, no. 6, pp. 655-667.
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Luminescent Solar Concentrators (LSC's) are currently being developed so that sunlight may be more fully utilised in place of conventional lighting sources. In order to optimise the light output of an LSC, various collector properties including fluorescent dye concentration, collector dimensions and matrix quality have been investigated. This study, involving measurement and computer modelling of the light transport in a single colour LSC, shows that luminous output is highly sensitive to weak extinction processes in the emission spectral band. These fine details in the loss spectrum play a key role in determining the output and efficiency of an LSC system. The separation of dye and matrix losses enables a quantitative study of the effect of matrix optical quality on performance. &copy; 2004 Elsevier Ltd. All rights reserved.
Smith, G.B., Ford, M.J., Masens, C. & Muir, J. 2004, 'Energy-efficient coatings in the Nanohouse™ Initiative', Current Applied Physics, vol. 4, no. 2-4, pp. 381-384.
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The University of Technology Sydney (UTS), in collaboration with CSIRO has created the Nanohouse&#8482; Initiative, a concept that serves as the conceptual framework for various pedagogical, scientific, architectural and engineering activities at the University. Housing is a significant item in both personal and regional budgets, and the Nanohouse&#8482; therefore serves as a powerful vehicle for demonstrating nanotechnologies. One of the major energy-efficient components of the Nanohouse&#8482; are nanoengineered coatings and films for transparent and translucent surfaces that modify their optical properties. These nanostructured materials can provide wavelength-selective control of reflection, absorption and transmission of light as well as angular selectivity for directional control, making it possible to design houses that have very large windows and skylights, but which nevertheless remain cool in summer and warm in winter. We have already made significant progress towards the development of these nanotechnologies. In this paper will be discuss the design and performance of these optically controllable nanocoatings and their application to the Nanohouse&#8482;. &copy; 2003 Elsevier B.V. All rights reserved.
Earp, A.A., Smith, G.B., Franklin, J. & Swift, P. 2004, 'Optimisation of a three-colour luminescent solar concentrator daylighting system', Solar Energy Materials and Solar Cells, vol. 84, no. 1-4, pp. 411-426.
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Electrical power consumption in buildings may be reduced considerably by more efficient use of sunlight for indoor lighting. A stack of luminescent solar concentrator sheets has been developed, which utilises three different coloured fluorescent dyes to produce a concentrated near-white light source to be coupled into flexible polymer sheets and transported up to 10m. Thus in clear sky conditions a remote room with neither walls nor roof in direct contact with the sun, can be illuminated by over 1000lm of natural light with a luminous efficacy of over 300lm/W, regardless of the sun's position. &copy; 2004 Elsevier B.V. All rights reserved.
Smith, G.B. & Maaroof, A.I. 2004, 'Optical response in nanostructured thin metal films with dielectric over-layers', Optics Communications, vol. 242, no. 4-6, pp. 383-392.
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Thin metal films which contain nano-size pores yield higher than expected transmittance and larger than expected times for transmission of near infra red radiation. An optically equivalent layer with complex refractive index (n*, k*) can model measured specular transmittance and reflectance, when scattering is weak. The way surface plasmon effects impact on these measured indices is considered. A strongly elevated n* is linked to t rad the time for a surface plasmon to re-radiate and hence delay transmission times, and reduced imaginary part k*, to resonant channelling via voids. Measurement of n* thus allows an estimate of t rad. The sensitivity of (n*, k*) to surface effects is illustrated using an insulating overlayer to modify the surface states. Resultant measured changes in n*, k* are substantial. Results are for two nanostructured metal systems characterised with 400,000 scanning electron microscopy. &copy; 2004 Elsevier B.V. All rights reserved.
Smith, G.B. 2004, 'Materials and systems for efficient lighting and delivery of daylight', Solar Energy Materials and Solar Cells, vol. 84, no. 1-4, pp. 395-409.
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Materials advances which enable improved lighting and daylighting performance in terms of luminous efficacy (energy efficient lighting), visual comfort and colour management are reviewed. Spectral and angular selective glazing, energy efficient translucent polymers, light piping and complete colour mixing of discrete sources are covered. The underlying science is given along with descriptions for key examples which include solar control windows utilising nanoparticles, diffusers of clear polymer doped with clear polymer for lamps and skylights, solid flexible light guides with controlled continuous emission, luminescent solar collectors coupled to light pipes for daylighting provision to any interior spaces, and uniform high efficacy white light lamps using three colour LED arrays. Greater use of daylight and of PV powered lighting is enabled by these advances which are all affordable, along with exciting new aesthetic, safety, display and artistic possibilities. &copy; 2004 Elsevier B.V. All rights reserved.
Deller, C., Smith, G. & Franklin, J. 2004, 'Colour mixing LEDs with short microsphere doped acrylic rods', Optics Express, vol. 12, no. 15, pp. 3327-3333.
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The output colour distributions from red, green and blue (RGB) LEDs mixed with cross linked PMMA micro particle doped PMMA mixing rods is compared to output from a plain PMMA mixing rod. Distinctive patterns with clear colour separation result with the undoped rod. These are homogenised by our mixers, resulting in white light. Light output has been photographed, measured and computer simulated at a distance of 10 cm from the output end of the rods. &copy; 2004 Optical Society of America.
Jonsson, J.C., Karlsson, L., Nostell, P., Niklasson, G.A. & Smith, G.B. 2004, 'Angle-dependent light scattering in materials with controlled diffuse solar optical properties', Solar Energy Materials and Solar Cells, vol. 84, no. 1-4, pp. 427-439.
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Light scattering plays a prominent role in a wide range of energy-efficient materials and solar applications. Some examples are materials for daylighting, diffusely reflecting sunscreens, foils for radiative cooling and nanocrystalline solar cells. Measurements of the angular profile of light scattering are very useful for obtaining a detailed characterization of the light scattering mechanisms. We review recent theoretical results on the forward and backward light scattering profiles. Forward scattering is of major importance for novel pigmented polymeric daylighting materials. Measurements of scattering profiles are in good agreement with Mie theory. Backscattering profiles from highly diffusely reflecting paints containing titanium oxide-based pigments have also been measured. It seems that scattering from the paint surface dominates at low pigment volume fractions. Results for paints with high pigment volume fractions are interpreted in terms of coherent backscattering effects from the pigment particles. &copy; 2004 Elsevier B.V. All rights reserved.
Swift, P.D. & Smith, G.B. 2003, 'Color considerations in fluorescent solar concentrator stacks', Applied Optics, vol. 42, no. 25, pp. 5112-5117.
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We present modeled results of the luminous and color outputs of a three-layer stack of fluorescent planar concentrators (FPCs). FPCs have the potential to provide sufficient luminous output to illuminate moderate-sized rooms for reasonably-sized collecting areas. It is of course necessary not only that the lumens be sufficient, but also that the light be sufficiently white as to be comfortable. Modeling shows that by use of a stack of three FPCs, one each of violet, green, and red, it is possible to achieve good color rendering and sufficient lighting levels for room illumination. &copy; 2003 Optical Society of America.
Smith, G.B., Gentle, A., Swift, P.D., Earp, 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.
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Energy efficient coloured paint coatings utilising flaky aluminium pigment with either single layer (Fe2O3) or double layer (Fe 2O3 on SiO2) interference coatings are optically and thermally characterised. Similar pigments with coatings on flaky dielectric particles and standard paints of similar colour are compared. Data presented includes hemispherical and specular reflectance spectra across visible and infra red wavelengths, thermal emittance from an emissometer and light spreading data from a photogoniometer. Solar absorptance, and colour show that, as theoretically predicted, and provided flaky metal pigments are used, a wide range of colours combined with a much lower solar absorptance than traditional paints of similar colour is achieved. Superior thermal performance to ordinary paints with similar colour is thus possible and is demonstrated for two such coloured layers via controlled heating-cooling studies under both an indoor lamp and outdoor clear sky solar illumination. It is seen that heat gains from the sun and associated cooling loads can be reduced by up to 50% for most colours, which is of some benefit for cars and metal roofs in hot climates. &copy; 2002 Elsevier Science B.V. All rights reserved.
Schelm, S. & Smith, G.B. 2003, 'Dilute LaB6 nanoparticles in polymer as optimized clear solar control glazing', Applied Physics Letters, vol. 82, no. 24, pp. 4346-4348.
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The performance of window samples with a LaB6 nanoparticle-doped polymer laminate in the reduction of solar heat gain was studied. The reason behind the near-infrared absorption was the excitation of surface plasmons. Windows, considered suitable for solar control glazing, transmitted visible radiation but blocked the near infrared (NIR) between 750 and 2500 nm.
Smith, G.B., Jonsson, J.C. & Franklin, J. 2003, 'Spectral and global diffuse properties of high-performance translucent polymer sheets for energy efficient lighting and skylights', Applied Optics, vol. 42, no. 19, pp. 3981-3991.
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A visible and near-IR spectral study is presented for a translucent smooth polymer sheet in which dopant particles are clear polymer with a refractive index close to that of the clear polymer host. Diffuse, specular, and total reflectance and transmittance and absorptance as a function of sheet thickness and dopant levels approach ideal behavior for lighting applications. A fourth optical parameter, side loss ST, is introduced to fully account for the measured data. This covers radiation that is trapped by total internal reflection (TIR) and travels sideways sufficiently far, including to the sheet's edges, to miss detection on exit. ST has a strong spectral character, whereas total T and R spectra closely follow the spectrally flat wavelength dependence of the undoped clear sheet. Three distinct regimes are identified for the behavior with wavelength of the specular and diffuse components and are linked to rear surface TIR and side loss. &copy; 2003 Optical Society of America.
Smith, G.B., Gentle, A., Swift, P., Earp, 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.
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Flakes of metal coated with thin dielectric films, when used as various coloured paint pigments, can reflect much more of the near infra red component of solar radiation than standard paints of equivalent colour, which makes them attractive for reducing cooling loads in cars and under metal roofs, while maintaining a wide range of decorative options. Spectral responses, solar absorptance and CIE colour co-ordinates are explored theoretically for a single layer, and two layers of different refractive index, on smooth aluminium flakes. Results in air, and in a clear matrix of refractive index close to that of the paint binder, are presented to highlight the colour shifts that are observed in a matrix when colour is due to interference. Thin film models show that the single layers have weak angle of incidence dependence while double layers have attractive variations in reflected colour while retaining their high NIR reflectance. This adds to decorative appeal. The origins and impact of diffuseness are briefly discussed. &copy; 2002 Elsevier Science B.V. All rights reserved.
Smith, G. 2002, 'Nanoparticle physics for energy, lighting and environmental control technologies', Materials Forum, vol. 26, pp. 20-28.
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Performance of everyday systems such as windows, skylights, painted car panels, roofs and walls and lighting installations, can be improved markedly using nanoparticles, nanocoated micro-particles and nanocomposites. Additional functionality such as self cleaning and power generation is also possible. Properties and applications using polymer and conductor nano- and micro-particles, metal coated particles and nano-voids in metals are covered. Engineering of novel optical and thermal properties based on surface plasmons and surface plasmon polaritons is outlined. The diversity of responses and technical opportunities demands modelling. Empirical exploration by itself is time consuming and risky. Representing an inhomogeneous nanocomposite optically by an "effective" homogeneous medium is shown to be useful when correctly applied, but is seen to be prone to misuse. The current controversy about negative refractive index nanostructures is a recent example. Opportunities in solar cells, thermal-to-electric conversion and refrigeration, separation, energy storage and power management systems are outlined, along with new decorative and display options.
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.
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Smith, G.B. & Pustovit, V.N. 2002, 'Coupled multipolar interactions in clusters of nanoparticles with metal shells', Optics Communications, vol. 211, no. 1-6, pp. 197-204.
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Coupled multipolar interactions between spherical nanoparticles coated with metal nanoshells are shown to yield very different optical behaviour to those between all metal nanoparticles in the same configurations. Controlled spectral tuning of absorption bands in metal shell nano-systems is shown to be easier than with all metal particles because strong localised fields between particles and the associated high order multipoles are much weaker. In the touching limit differences in field distributions mean that whereas all metal clusters are far from convergent when 300 pole-terms are included in the calculation, the metal nanoshells give full convergence after less than 10 poles, even for metal volume fractions over 50%. Extinction bands are also far less sensitive to particle spacing in the shell case. &copy; 2002 Elsevier Science B.V. All rights reserved.
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.
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Since nanoparticles can provide spectrally selective absorption without scattering they can be used to dope polymers for use in windows, to provide a clear view while strongly attenuating both solar heat gain and UV, at lower cost than alternative technologies. The underlying physics and how it influences the choice and concentration of nanoparticle materials is outlined. Spectral data, visible and solar transmittance, and solar heat gain coefficient are measured for clear polymers and some laminated glass, in which the polymer layer is doped with conducting oxide nanoparticles. Simple models are shown to apply making general optical design straightforward. Use with clear glass and tinted glass is considered and performance shown to match existing solar control alternatives. A potential for widespread adoption in buildings and cars is clearly demonstrated, and scopes for further improvements are identified, so that ultimately both cost and performance are superior.
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.
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Smith, G.B., Ben-David, A. & Swift, P.D. 2001, 'New type of TiN coating combining broad band visible transparency and solar control', Renewable energy, vol. 22, no. 1, pp. 79-84.
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Production of thin films of Titanium nitride (TiN) with N/Ti ratios as high as 1.3 has been achieved without destroying the metallic properties characteristic of stoichiometric TiN. The resultant change in mobile electron density shows that by depositing thin films the onset of a rise in reflection can be pushed out almost into the near infra red. It then becomes possible to produce films which transmit daylight neutrally at reasonably high levels, while still maintaining solar control in the NIR and a low emittance. Nitrogen ion assisted cathodic arc deposition has been used to achieve these results. Both the additional impacting and implanting nitrogen ions raise stoichiometry and help to reduce disorder so as to maintain good metallic character.
Smith, G.B., Green, D.C., McCredie, G., Hossain, M., Swift, P.D. & Luther, M.B. 2001, 'Optical characterisation of materials and systems for daylighting', Renewable energy, vol. 22, no. 1, pp. 85-90.
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The measurement of BRTF (Bi-directional reflectance and transmittance function) is described using a new instrument which is capable of supplying BRTF data and algorithms for use in computer simulations directly on diffuse materials and indirectly on large samples and sub-systems. A high sensitivity and dynamic range is needed to achieve low minimum observable BRTF and the role of angular resolution are discussed with examples. Forward scattering with extended tails is found to dominate pigmented polycarbonate. Slatted blinds are discussed as examples of systems where azimuth is important.
Smith, G.B., Hossain, A.K.M. & Gentle, A. 2001, 'Near infra-red radiation squeezing through 20 nm voids in obliquely deposited metal films', Applied Physics Letters, vol. 78, no. 15, pp. 2143-2144.
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Obliquely deposited metal films which are nearly continuous, displaying several unexpected solar optical properties. Transmittance intensity, spectral character, preferred direction of incidence, and polarization sensitivity, infer processes which effective-medium models based solely on "interior" properties cannot describe. Amplified transmittance through voids around 20 nm wide involving near surface excitations can explain the data. &copy; 2001 American Institute of Physics.
Smith, G., Earp, A.A., Stevens, J., Swift, P.D., McCredie, G. & Franklin, J. 2000, 'Materials Properties for Advanced Daylighting in Buildings', Sayish AAM, vol. 6, no. 1, pp. 201-206.
Some recent developments in materials used to illuminate interior and exterior spaces with daylight, and mathematical modelling of their interaction with light for design purposes are presented. The Sydney 2000 Olympic Stadium roof and a new solid light guide system are two examples. Emphasis is on making full use of the daylight resource, not just the diffuse component, while controlling the associated solar heat gain. Sensitivity to glare is essential if materials capabilities are to be realised.
Smith, G.B. & Reuben, A.J. 1999, 'Normal mode analysis of optical polarisation response in nanocomposite particles', Nanostructured Materials, vol. 12, no. 1, pp. 353-356.
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A new technique for establishing the spectral density and resonance positions of normal optical modes in fine particle systems is outlined and applied to finite chains of closely spaced aluminium cylinders. The method uses multiple conformal frames and a new type of structure factor. Finite chain results are compared to those of the pair and infinite chain on a per particle basis. One key result is the dominance and strong red shift of the fundamental mode as chain length increases beyond a few cylinders. Another is that this fundamental mode is largely isolated in the long UV, visible and NIR wavelength range. Surprisingly long chains (typically > 100 cylinders) are needed to give results resembling the infinite chain, unless gaps are large.
Smith, G.B. & Dligatch, S. 1999, 'Ellipsometric studies of nanocomposite cermets', Nanostructured Materials, vol. 12, no. 1, pp. 535-538.
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The three pairs of complex refractive indices and the direction of the optical axis for metal insulator thin film composites in which the very small metal particles form narrow tilted columns which are arranged asymmetrically have been found using a combination of ellipsometry and spectrophotometry. Results have been used to theoretically model transmittance which depends on the two angles defining incident direction in these films. Insights into the unusual optical response of the nano-size silver particles are also given.
Smith, G.B., Swift, P.D. & Bendavid, A. 1999, 'TiNx films with metallic behavior at high N/Ti ratios for better solar control windows', Applied Physics Letters, vol. 75, no. 5, pp. 630-632.
The ability of thin TiNx films to retain metallic properties at N/Ti ratios as high as 1.3 was studied with ion assisted cathodic arc deposition. Results showed that the optical response was dominated by intraband absorption which can be modeled well with a classical Drude model. The films can give more desirable visible window properties without a significant sacrifice in solar control or insulating performance.
Martin, P.J., Bendavid, A., Netterfield, R.P., Kinder, T.J., Jahan, F. & Smith, G. 1999, 'Plasma deposition of tribological and optical thin film materials with a filtered cathodic arc source', Surface and Coatings Technology, vol. 112, no. 1-3, pp. 257-260.
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The recent development of the filtered arc deposition method (FAD) has shown that hard, wear-resistant materials can be deposited free of cathode microdroplets and with exceptional smoothness and reproducible properties. The microhardness and stress of TiN films are determined by the bias applied to the substrate during growth. Microhardness values have been measured over the range of 2000-3000 Hv. The absence of particulates in the deposited films renders the technique suitable for the preparation of high-quality optical dielectric oxide and metallic films on to ambient temperature substrates. Films of amorphous TiO2 with refractive indices of 2.45 at a wavelength of 600 nm can be easily prepared with a very low absorption. Optical-quality films of Nb2O5 and Al2O3 have also been prepared similarly by reactive deposition from pure Nb and Al cathodes. Smooth Au films with a high reflectivity are also deposited by the FAD process. | The recent development of the filtered arc deposition method (FAD) has shown that hard, wear-resistant materials can be deposited free of cathode microdroplets and with exceptional smoothness and reproducible properties. The microhardness and stress of TiN films are determined by the bias applied to the substrate during growth. Microhardness values have been measured over the range of 2000-3000 Hv. The absence of particulates in the deposited films renders the technique suitable for the preparation of high-quality optical dielectric oxide and metallic films on to ambient temperature substrates. Films of amorphous TiO2 with refractive indices of 2.45 at a wavelength of 600 nm can be easily prepared with a very low absorption. Optical-quality films of Nb2O5 and Al2O3 have also been prepared similarly by reactive deposition from pure Nb and Al cathodes. Smooth Au films with a high reflectivity are also deposited by the FAD process.
Jahan, F. & Smith, G.B. 1998, 'Investigation of angular selective optical properties of silver/titanium oxide cermet thin films', Thin Solid Films, vol. 333, no. 1-2, pp. 185-190.
Thin films of silver-titanium oxide cermet were prepared with angular and spectral selectivity of optical transmittance. Titanium oxide was deposited reactively by d.c. magnetron sputtering and in a filtered cathodic arc system. Metallic silver was co-deposited by thermal evaporation. Deposition parameters were varied to get optimum angular selective properties. The films have inclined columnar microstructure as studied by atomic force microscopy. The study of optical properties shows that the filtered arc film performs better than the sputtered film. Unlike most of the angular selective films reported to date, the angular selectivity of this film is large in the near infrared region. Spectral switching of the preferred transmission direction at a particular visible wavelength was observed, resulting in 'reverse angular selectivity', where for visible radiation the high transmission direction of incidence lies on the opposite side of the normal to that in the near infra-red range. The angle of incidence dependence of solar and luminous transmittance of each film was analyzed. &copy; 1998 Elsevier Science S.A. All rights reserved.
Smith, G.B., Yan, W., Hossain, M. & McCredie, G. 1998, 'Science of daylighting in buildings', Renewable Energy, vol. 15, no. 1-4, pp. 325-330.
The materials characterisation requirements for accurate yet practical simulation of daylighting in buildings is examined for a range of emerging and existing technologies which seek to raise the contribution of daylighting to overall lighting requirements. Algorithms based on underlying physical models can be established from analysis of data on bi-directional transmission and reflection. Demonstrations of effects in simulation relevant to glare, view and illuminance are given. &copy; 1998 Published by Elsevier Science Ltd. All rights reserved.
Reuben, A.J. & Smith, G.B. 1998, 'Normal-mode decomposition for the optical response of cylinder clusters', Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, vol. 58, no. 1, pp. 1101-1111.
We present a powerful technique that generates the complete normal-mode representation for the two-dimensional quasistatic response of any finite cluster of nonintersecting cylinders. We initially study two particular structures, a rectangular and then a triangular arrangement of cylinders. In each case a superposition technique involving two coordinate frames is used to obtain eigenfunction expansions for the induced electrostatic potential. Imposition of boundary conditions at each cylinder surface generates a system of equations for the expansion coefficients in which optical and geometric factors can be trivially separated. This produces a so-called structure matrix whose eigenvalues determine the resonance positions for the total response. The weights for these uncoupled and independent resonances are also readily calculated. Predicted results for the two chosen arrangements are then given. We conclude by showing how the technique is extended to cover general finite clusters of nonintersecting cylinders.
Radchik, A.V., Moses, P., Skryabin, I.L. & Smith, G.B. 1998, 'New effective medium approach to optical response in non-random arrays', Thin Solid Films, vol. 317, no. 1-2, pp. 446-448.
The existing modifications of Effective Medium theories (EM), such as Maxwell-Garnett (MG) or Bruggemann are established for essentially random structures and could be highly inaccurate for regular or partly ordered arrays. We have obtained from first principles a generalised EM Eq. (1) of a Maxwell-Garnett type: ?* - ?h/?* + ?h = f* (?) ?g - ?h/?g + ?h where ?*, ?h and ?g are effective, host and guest dielectric constants respectively. An exact expression for effective fill-factor f* was derived from a conformal transformation which describes periodical properties of an ordered array of cylindrical particles. f* is a complex wavelength dependent variable. The difference between the real fill-factor and f* found for a number of metal-insulator composites, is an indication of screening. Weak wavelength dependence of f* allows it's approximation as a real constant. Therefore it could be used as a fitting parameter in ellipsometric routines, but the interpretation of a fill-factor there must be reviewed. &copy; 1998 Elsevier Science S.A.
Smith, G.B., Dligatch, S., Sullivan, R. & Hutchins, M.G. 1998, 'Thin film angular selective glazing', Solar Energy, vol. 62, no. 3, pp. 229-244.
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Angular selective glazing based on special obliquely deposited thin films, has considerable potential for optimizing the overall performance of a window in temperate to hot climates. In contrast to most currently used glazings for these environments it has the ability to control solar heat gain and glare while providing a clear view through the window and considerable but not excessive light gain. Various deposition techniques and film materials will be discussed and the spectral and integrated optical performance of single and double-layered systems presented for various directions of incidence. Full optical characterisation requires measurements for incidence directions over half a hemisphere. Some of this is presented but most data is confined to planes of incidence where angular selectivity is greatest as determined by deposition geometry. Two layer systems are designed to provide a low emittance and better solar control than the single layer systems while retaining good visible angular selectivity. The single layers are primarily to provide angular selective control of the visual radiation since they have moderately high transmittance in the near infrared and a high emittance. Theoretical models used to extract structural information and model the complex optical properties are introduced and their predictions assessed. Preliminary results on simulation of the performance of full size angular selective windows in comparison to other types of solar control glazing such as low e heavily tinted windows are discussed in terms of their relative impact on cooling load, lighting contribution, glare control and total energy savings. | Angular selective glazing based on special obliquely deposited thin films, has considerable potential for optimizing the overall performance of a window in temperate to hot climates. In contrast to most currently used glazings for these environments it has the ability to control solar heat gain and glare while providing a clear view th...
Dligatch, S., Cheary, R.W. & Smith, G.B. 1998, 'An analysis of Ag/Al2O3 angular selective films by X-ray reflectivity', Thin Solid Films, vol. 312, no. 1-2, pp. 4-6.
X-ray reflectivity measurements using a conventional X-ray diffractometer have been carried out on Ag/Al2O3 films prepared by simultaneous bi-oblique deposition of Ag and Al2O3. The results show that this technique is a sensitive way of identifying the presence of a discontinuous 1 nm Ag layer on the surface of the Ag/Al2O3 composite film. &copy; 1998 Elsevier Science S.A.
Smith, G.B., Dligatch, S. & Jahan, F. 1998, 'Angular selective thin film glazing', Renewable Energy, vol. 15, no. 1-4, pp. 183-188.
Angular selective control of daylight, solar heat gain and visual performance is the aim of a variety of emerging technologies for windows, roof and wall glazing. Certain oblique thin metal and metal/insulator films on glass have transmittance as a unique function of direction of incidence and they are also spectrally selective. A variety of angular selective control options result according to choice of film materials covering one or a combination of (i) light and glare from high angles (ii) solar heat gain (iii) visual amenity (iv) glare from lower angles (iv) emittance control. They are thus able to be adapted by materials choice to the needs of different latitudes and window orientations. A new and simple way of categorizing performance will be presented. &copy; 1998 Published by Elsevier Science Ltd. All rights reserved.
Smith, G.B., Radchik, A.V., Reuben, A.J., Moses, P., Skryabin, I. & Dligatch, S. 1998, 'Columnar cermet structures in solar energy materials: Can one model spectral response with simple effective medium theories', Solar Energy Materials and Solar Cells, vol. 54, no. 1-4, pp. 387-396.
Selective absorbers and angular selective windows use cermets and many of these surfaces have columnar features, for example, Ni pigmented aluminium oxide, many types of black chrome and silver/aluminium oxide angular selective films. There are numerous examples where optical properties in these films have been modelled with quite simple effective medium theories. Extension to optimise film designs prior to production is then assumed possible. Recent work on effective medium models has indicated why the simple models often appear to give good fits to cermet data for solar materials. Visible and near infra-red data with fitting parameters, fill factor and depolarisation factors of the variables, may need to be reevaluated. More rigorous theories show a good fit with an equation of the same mathematical form as the Maxwell-Garnett model is often expected and that parameters used to obtain these fits are not those of the simple models. Relatively simple mathematical equations for modelling is useful but compositions and particle shapes noticeably different from those assuming the conventional dipole models are possible. We use a normal polarisation modal analysis which allows us to introduce by analogy with the conventional models an "apparent fill factor". This is less than the real fill factor as a result of interparticle interactions which effectively diminish the impact of individual particles. &copy; 1998 Published by Elsevier Science B.V. All rights reserved.
Xue, Y.L., Smith, G.B. & Baker, A.T. 1998, 'Large Refractive Index and Interparticle-Interaction-Induced Nonlinear Modulation in Densely Doped Composite Materials', IEEE Journal of Quantum Electronics, vol. 34, no. 8, pp. 1380-1389.
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We have performed a study of the population dynamics in a composite, in which the active medium is densely doped, by considering the interparticle interaction between the nearest neighboring active particles. A model is presented to describe the nonlinear modulation induced by interparticle collective effects and upconversion in the resonantly enhanced nonlinearity and its response to an input optical signal in such a densely doped composite. The results show that the nonlinear refractive index can be greatly increased with unchanged or slightly reduced transient response time. This is expected to have potential in lowering the critical switching intensity of bistable switching devices without sacrificing switching speed. We examined two typical composites: rare-earth densely doped silica and perylimide-dye densely doped polymer/glass composites. It is found that perylimide-dye densely doped polymer/glass composite is more suitable for the switching application due to its large nonlinear refractive index and fast response time at relatively low optical intensity.
Skryabin, I.L., Radchik, A.V., Moses, P. & Smith, G.B. 1997, 'The consistent application of Maxwell-Garnett effective medium theory to anisotropic composites', Applied Physics Letters, vol. 70, no. 17, pp. 2221-2223.
The Maxwell-Garnett class of effective medium model applies if a representative cell can be found whose polarization vanishes upon insertion in the effective medium. For an anisotropic composite with randomly distributed ellipsoidal particles aligned along the principal axis, this leads to electrostatic restraints on the shape of such cells. It is shown that the cell boundary must have different depolarization factors to the inclusion within the cell. Practice is to equate them. A new physically correct ellipsometric modeling routine still with only two fitting parameters is demonstrated. &copy; 1997 American Institute of Physics.
Reuben, A.J., Smith, G.B., Moses, P., Vagov, A.V., Woods, M.D., Gordon, D.B. & Munn, R.W. 1996, 'Ion trajectories in exactly determined quadrupole fields', International Journal of Mass Spectrometry and Ion Processes, vol. 154, no. 1-2, pp. 43-59.
The use of multi-electrode structures as mass analysers is now very widespread. These devices are employed as partial pressure analysers, mass filters and ion traps. The first of these devices to utilise an electric quadrupole field for separating ions according to their mass-to-charge ratio was introduced in the 1950s. The operation of these devices is based on the nature of particle trajectories between the electrode rods. The lack of an exact theory up to now has precluded full exploitation of the device. In the quadrupole mass filter the relevant stability theory depends directly on the precise structure of the multipole potential expansion. The exact coefficients in this expansion have been determined. A number of trajectory simulations are performed using these coefficients. In addition a simple relationship is found for which certain key coefficients vanish. A set of scaling rules has also been discovered which enables immediate calculation of each higher order coefficient from a fixed set of values for the corresponding scaled coefficients. &copy; 1996 Elsevier Science B.V. All rights reserved.
Kempej, J., Radchik, A.V. & Smith, G.B. 1996, 'New transform techniques applied to anomolous absorption in the dense chain of metal cylinders', Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 452, no. 1951, pp. 1845-1856.
The quasi-static absorption response, at optical and infrared frequencies, of an infinite chain of circular metal cylinders has been modelled in a new way for arbitrarily small separations between the particles. A number of novel features are predicted. The starting point is a solution of the Laplace equation in a conformai frame with correct chain symmetry, not a solution for an isolated cylinder, as is usual. Boundary equations based on Fourier analysis lead to a matrix equation for polarization. Convergence as a function of matrix dimensions is rapid, even at almost touching separations. The absorption modal characteristics of a chain emerge naturally in this model. For the same small separations, these characteristics are very different for the pair and extremely different for the single cylinder. In the chain, most of the spectral weight is in the fundamental mode which is strongly red shifted and intense. In contrast, weak higher-order modes combine to dominate (at shorter wavelengths) in the component pair by itself. Long-range effects are thus very important. This fundamental mode in a dense chain appears to be responsible for the well-known infrared anomaly experimentally observed in collections of fine metal particles. &copy; 1996 The Royal Society.
Radchik, A.V., Paley, A.V. & Smith, G.B. 1996, '"Invisibility" in certain intersecting particles and arrays of such particles in a solid host', Journal of Applied Physics, vol. 79, no. 5, pp. 2613-2621.
Theoretical results recently obtained for polarizability of intersecting spherical particles have been compared with those for polarizability of intersecting cardioidal particles resembling the spherical shape. Calculations based on a modified Parseval Rule have been performed for a number of metals in a dielectric matrix in a quasistatic approximation. A large difference in the polarizabilities has been found in spite of a striking similarity in their shapes. An unexpected small value for both the real and the imaginary part of the polarizability of cardioidal shaped metal particles occurs at wavelengths where simple metal spheres absorb strongly. A Maxwell-Garnett model has been used to compare the optical properties of composite materials containing the cardioidal and intersecting spherical particles of interest. It has been found that a composite containing cardioid shaped particles in a dielectric matrix can have an unusual response. Its absorption is very close to zero, while the refractive index is close to that of the fully dense host. &copy; 1996 American Institute of Physics.
Bendavid, A., Martin, P.J., Smith, G.B., Wielunski, L. & Kinder, T.J. 1996, 'The mechanical and structural properties of Ti films prepared by filtered arc deposition', Vacuum, vol. 47, no. 10, pp. 1179-1188.
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In this study the development of residual stress of arc deposited Ti films as a function of the energy of deposited atoms was investigated. A comparison with the momentum transfer model for Ti films deposited under substrate bias indicate that the films are in a region characterised by momentum values of 50-150 amu1/2 eV1/2. The compressive stress was found to vary from 1.1 GPa to 0.1 GPa and the range of Ti microhardness was measured to be 6.7-8.7 GPa. The microchardness varied with grain size according the Hall-Petch relationship. The substrate bias was varied and the influence on residual stress, microhardness, preferred orientation, density, surface roughness and topography of the deposited films was investigated. Copyright &copy; 1996 Elsevier Science Ltd.
Reuben, A.J., Smith, G.B. & Radchik, A.V. 1995, 'The Polarisability of Cylinder Arrays in Two Dimensions', Annals of Physics, vol. 242, no. 1, pp. 52-76.
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The technique of solving the two-dimensional Laplace equation by means of conformal transformations is a very useful one. Here we develop this method into one which is applicable to chains and lattices in which the fundamental unit is a cylinder pair. An exact closed form expression for the polarisability with explicit spectral weights is immediate once the appropriate transformation for the given cylinder arrangement is determined. The present formalism provides simple derivations of certain results, among which is a proof of Keller?s theorem. We derive the polarisability formulae for a pair of separate cylinders and then determine the corresponding results for chains and lattices of cylinder pairs. &copy; 1995 Academic Press. All rights reserved.
Dligatch, S., Ng, M.W., Smith, G.B., Reuben, A.J., Radchik, A.V. & Vagov, A.V. 1995, 'New effective medium models and their applications', Vacuum, vol. 46, no. 8-10, pp. 935-938.
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Thin films and many surfaces often have complex structures which are conveniently analysed for overall optical response by effective medium models. Examples from new deposition techniques and new exact theory are presented that highlight effects that are not predictable by many of the widely used simple effective medium models. High order multipoles and associated multiple resonances play a key role and alter spectral response and transport properties markedly. The new theories can discriminate the short range forces between neighbouring pairs and longer range forces in chains and arrays. Experimental data on composite films show how changes in component distribution can strongly effect spectral absorptance in ways that are not predictable by standard dipole theories. &copy; 1995.
Swift, P.D. & Smith, G.B. 1995, 'Cylindrical mirror light pipes', Solar Energy Materials and Solar Cells, vol. 36, no. 2, pp. 159-168.
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The interplays between design and material parameters in a cylindrical mirror light pipe are discussed. The transmission is calculated exactly using a ray optics method. The result is an integral equation involving the mirror light pipe parameters, reflectivity and aspect ratio, and the angle of incidence of the incident radiation. The calculations of transmission are found to be in good agreement with experimental results. The specular reflectivity is the key parameter so that the wall material determines colour rendering properties of the transmitted light. &copy; 1995.
Ng, M.W., Smith, G.B. & Dligatch, S. 1995, 'Spectral switching of the preferred transmission direction in absorbing anisotropic composites', Journal of Physics D: Applied Physics, vol. 28, no. 12, pp. 2578-2584.
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Transmittance in inhomogeneous composite structures in which the arrangement or shape of an absorbing component is anisotropic, depends on the incident direction in relation to the axes that define the anisotropy. There are easily distinguished preferred transmittance directions in a given plane of incidence. However a complete reversal in the preferred direction, which is at first sight counter intuitive, has been observed in several anisotropic thin films containing small quantities of silver inclusions in partially ordered arrays. This switching occurs at a particular wavelength and is studied in terms of transmittance at equal angles of incidence either side of the normal. A filter which is low pass or high pass depending on direction of incidence may be possible based on this phenomenon. A theoretical explanation is given in terms of a two-component effective dielectric response of the composite. In the samples studied the splitting of the resonant absorption spectra for the two principal directions is seen to be the underlying cause of switching in the preferred transmittance direction. The experimentally observed optical data, and the observed microstructures, demand the use of advanced effective medium models which incorporate strong interaction effects.
Smith, G.B., Vargas, W.E., Niklasson, G.A., Sotelo, J.A., Paley, A.V. & Radchik, A.V. 1995, 'Optical properties of a pair of spheres: comparison of different theories', Optics Communications, vol. 115, no. 1-2, pp. 8-12.
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We compare the optical absorption of two touching and non-touching spheres, as calculated by different approaches. In the quasistatic limit, an exact treatment based on the conformal transformation of coordinate frames has recently been developed. On the other hand, a multipolar expansion of the rigorous solution of Maxwells equations can in principle be used for arbitrary aggregates and beyond the quasistatic limit. Our aim is to study the convergence and ascertain the accuracy of the low multipolar orders of the latter theory. Calculations were carried out for gold particles in air. A comparison of the exact theory and the dipolar approximation shows a very good agreement for spheres that are one half to one radius apart. In the case of touching spheres the convergence of the multipolar expansion is very slow and there are considerable quantitative discrepancies between the theories. &copy; 1995.
Vagov, A., Radchik, A. & Smith, G. 1995, 'Vagov, Radchik, and Smith reply [2]', Physical Review Letters, vol. 75, no. 23, p. 4333.
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Radchik, A.V., Paley, A.V., Smith, G.B. & Vagov, A.V. 1994, 'Polarization and resonant absorption in intersecting cylinders and spheres', Journal of Applied Physics, vol. 76, no. 8, pp. 4827-4835.
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The polarization of a pair of merging spheres and merging cylinders of any complex dielectric constant immersed in an external electric field has been solved. Any degree of intersection, including touching, is covered by the result. The method for cylinders is based on the solution of Laplace's equation with boundary conditions on the conjugate surfaces in a modified bicylindrical frame. The result is presented as an integral over a continuum of eigenstates. For merging spherical particles solving the boundary problem requires a Miller-Fok integral transformation. Imaginary parts of polarizabilities were calculated for aluminum cylinders and spheres to assess the spectral absorption response of small merging particles. The relative spacing has a significant influence on optical response.
Sloggett, G., McKenzie, D., Cockayne, D., Smith, G., Jenkins, B., Foley, C., Takano, Y., Studer, A., Haub, J. & Orr, B. 1994, 'In situ deposition of high Tc materials using vacuum arc ablation with macroparticle filter', Physica B: Physics of Condensed Matter, vol. 194-196, no. PART 2, pp. 2353-2354.
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Vacuum arc ablation is shown to be a new deposition technique for depositing YBCO thin films in situ with zero resistance below 85 K. A high deposition rate was achieved from small specimens. The size of macroparticles is larger than for laser ablation for the same target material, but a curved solenoidal filter was used to reduce the macroparticle content. &copy; 1994.
Vagov, A.V., Radchik, A. & Smith, G.B. 1994, 'Optical response of arrays of spheres from the theory of hypercomplex variables', Physical Review Letters, vol. 73, no. 7, pp. 1035-1038.
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Transformation from the three-dimensional hypercomplex X(x,y,z) frame to another which has infinite dimensions but has the symmetry properties of an array built in allows the Laplace equation to be solved in structures for which it is nonseparable. The power and practicality of this technique is demonstrated on pairs and chains of spheres of arbitrary complex permittivity in a quasiconstant electric field. New results include strong absorption enhancement at long wavelengths in high density chains due to structurally induced resonances. &copy; 1994 The American Physical Society.
Paley, A.V., Radchik, A.V., Smith, G.B. & Vagov, A.V. 1994, 'Polarization of intersecting particles', Applied Physics Letters, vol. 64, no. 23, pp. 3187-3189.
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An exact expression for the polarizability of intersecting circular cylinders has been derived covering all degrees of intersection and arbitrary complex dielectric constants for the particle material. This enables a comparison between the induced dipole moment on two particles of almost identical shape; a cardioid and a particular pair of overlapping cylinders. The absorption spectra in the small particle limit are extremely sensitive to the detailed shape of the surfaces near the point of intersection.
Paley, A.V., Radchik, A.V. & Smith, G.B. 1993, 'Quasistatic optical response of pairs of touching spheres with arbitrary dielectric permeability', Journal of Applied Physics, vol. 73, no. 7, pp. 3446-3453.
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The problem of polarization of two touching spherical particles, of any complex dielectric constant, immersed in a uniform external electric field is solved exactly in the tangent-sphere frame. A straightforward integral over the continuum of eigenstates yields the dipole moment for fields parallel and perpendicular to the line joining the centers. Predictions are compared to those from a recent approximate model based on the method of images. A modified Clausius-Mossotti formalism is used to assess the impact on absorption and refraction at optical frequencies (in the quasistatic limit). Actual composite materials containing small touching sphere pairs are considered.
Reuben, A.J., Radchik, A.V. & Smith, G.B. 1993, 'The polarizability of chains of touching cylinder pairs', Journal of Physics A: Mathematical and General, vol. 26, no. 8, pp. 2021-2036.
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By solving the Laplace equation in an appropriate coordinate frame, simple expressions have been derived for the polarizability per unit area of infinitely long chains of touching pairs of cylinders. The method used presupposes no restrictions on the value of the dielectric constant of the cylindrical particles and yields an exact analytic solution incorporating all multipoles. The results offer an insight into the effect of long range interactions between particle pairs. Moreover the technique can be extended to the study of arrays generally. Comparisons are made between the induced dipole moment on pairs within a chain and the moment on an isolated touching pair in the case of aluminium columns in air. A quasistatic assumption is used at optical frequencies.
Radchik, A.V., Smith, G.B. & Reuben, A.J. 1993, 'Erratum: Quasistatic optical response of separate, touching, and intersecting cylinder pairs', Physical Review B, vol. 47, no. 5, p. 2952.
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Studer, A.J., McKenzie, D.R., Cockayne, D.J.H., Smith, G.B. & Brown, I.G. 1992, 'Cathodic arc ablation as a new method of high-Tc superconductor deposition', Physica C: Superconductivity and its applications, vol. 197, no. 1-2, pp. 147-150.
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A process has been developed in which a pulsed cathodic arc is used to deposit thin films of YBa2Cu3O7-? superconductor. After post-deposition annealing, the films are found to be metallic with a superconducting transition at 85 K, and are highly oriented perpendicular to the c-axis. Microstructure analysis shows that macroscopic particles produced in the ablation process are recrystallized by the annealing procedure. &copy; 1992.
Smith, G.B., Ng, M.W., Ditchburn, R.J., Martin, P.J. & Netterfield, R.P. 1992, 'Cermets for angular selective transmittance', Solar Energy Materials and Solar Cells, vol. 25, no. 1-2, pp. 149-167.
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Cermets have been reactively deposited at an oblique angle onto transparent glass substrates at ambient temperature by thermal and cathodic arc evaporation. They have been found to display angular selective transmittance that is in general better than that found in oblique columnar films which are predominantly metallic. The structure and optical properties of Al/Al2O3 and Ag/Al2O3 films are discussed including the angle of incidence dependence, over a 120&deg; range, of the integrated solar and photoptic transmittance. The spectral characteristics of these films can vary continously with angle of incidence with large differences possible between spectral properties at the same angle of incidence on opposite sides of the normal. Results indicate that those surfaces can provide the basis for applications including automobile and building glazing. The cathodic arc samples have the advantage of being very durable, which is essential for such applications. &copy; 1992.
Ditchburn, R.J. & Smith, G.B. 1992, 'Model for the optical response of obliquely deposited thin films', Journal of Physics D: Applied Physics, vol. 25, no. 2, pp. 334-337.
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An effective medium model, capable of explaining both the unusual transmittance characteristics and the pronounced biaxial response observed in obliquely deposited metal and metal-insulator composites, is used to model experimental data. Short-range interactions between neighbouring columns dominate the response. This in turn leads to biaxial behaviour, provided the columns are packed anisotropically.
Radchik, A.V., Smith, G.B. & Reuben, A.J. 1992, 'Quasistatic optical response of separate, touching, and intersecting cylinder pairs', Physical Review B, vol. 46, no. 10, pp. 6115-6125.
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By use of a unified approach involving conformal transformations, useful expressions have been derived for the dipole moment induced on cylinder pairs in a uniform electric field when the pairs are separate, touching, and intersecting. The results involve no restrictions on the dielectric constants of the particles and can be used in studies of arrays. A major advantage of the technique over previous work using the method of images is its ability to handle a close approach between more complex particles such as coated cylinders. Examples of optical property modeling are given for arrays of aluminum columns along with an example of their application to coated cylinders. A sharp enhancement in response is found as the particles approach the touching limit, while once they intersect there is an even sharper falloff in polarizability. The results clearly show that once multipolar effects become important the structural arrangement of the absorbing material, rather than its quantity, dominates the dielectric response. &copy; 1992 The American Physical Society.
Kirkup, L., Bell, J.M., Green, D.C., Smith, G.B. & MacDonald, K.A. 1992, 'Simple computer-controlled potentiostat for the characterization of electrochromic films', Review of Scientific Instruments, vol. 63, no. 4, pp. 2328-2329.
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We describe a simple and inexpensive potentiostat, incorporating current boosting and filtering circuitry for use in the study of coloration and bleaching in electrochromic thin films. The system is sufficiently flexible to permit utilization in other electrochemical applications.
Smith, G.B., McKenzie, D.R., Puchert, M., Filipczuk, S.W. & Cockayne, D.J.H. 1991, 'Anomalous voltage-current characteristics in the sputtering of YBaCuO', Physica C: Superconductivity and its applications, vol. 183, no. 1-3, pp. 172-176.
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The I-V characteristics of magnetron glow discharges with a Y1Ba2Cu3O7-? superconductor cathode are studied and found to have anomalously low operating voltage, negative resistance and strong hysteresis effects. The energy dependence of the ion induced secondary electron and secondary ion emission coefficient of Y1Ba2Cu3O7-? was measured and found to have a minimum at 350 V, a strong increase below this value and a steady increase above this value. The characteristics of the discharge are explained in terms of the secondary species emission coefficient. &copy; 1991.
Ditchburn, R.J. & Smith, G.B. 1991, 'Useful angular selectivity in oblique columnar aluminum', Journal of Applied Physics, vol. 69, no. 6, pp. 3769-3771.
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A useful magnitude of angular selective transmittance of incident unpolarized light is demonstrated in obliquely deposited aluminum. Required deposition procedures and anisotropic optical properties are discussed. Angular selectivity is very strong at visible wavelengths but both experiment and theory indicate that a single oblique layer with well defined columns gives high transmittance at near-infrared wavelengths compared with normal films. There are ways of reducing this to enhance the energy control capability. Both solar and luminous angular selectivity are reported.
Turner, G.M., Sikorski, A., McKenzie, D.R., Smith, G.B., Ng, K. & Cockayne, D.J.H. 1990, 'Spatial variations in the stoichiometry of sputtered YBaCuO thin films: theory and experiment', Physica C: Superconductivity and its applications, vol. 170, no. 5-6, pp. 473-480.
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A Monte Carlo simulation of the sputtering process is applied to the problem of the thickness and stoichiometry variations in the sputtering of YBaCuO superconducting targets. The theory predicts no strong spatial variations in stoichiometry due to the different scattering behaviour of the various constituents of the superconductor. The theory is compared with a systematic experimental study using both RF and DC sputtering in either argon or oxygen gases. The ratios Ba: Y and Cu: Y were determined as a function of radial distance by inductively coupled plasma analysis (ICP). In argon, both DC and RF sputtering gave a thickness distribution in reasonable agreement with theory. In oxygen, RF sputtering gave a thickness distribution very different to theory and gave no net deposition in an annular central region. Stoichiometry variations are interpreted in terms of etching processes. The role of oxygen ions in etching is discussed and a case made for the importance of oxygen positive ions in RF sputtering in oxygen. &copy; 1990.
Smith, G.B., Müller, K.H., Andrikidis, C., Filipczuk, S.W., Bell, J.M. & Ricketts, B.W. 1990, 'Phase slippage in a magnetic field at intra- and intergranular Josephson junctions in high-Tc superconductors', Physica C: Superconductivity and its applications, vol. 170, no. 3-4, pp. 222-230.
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The intra- and intergranular components of resistance in high-Tc superconductors are modelled, after configurational averaging, as due to a single resistively shunted Josephson junction in each case. They are combined in series. A voltage develops across each junction due to thermally activated phase slippage. In the presence of a magnetic field slippage occurs at a faster rate and is accompanied by motion of the entire flux bundle in the junction. Data on thin films is fitted well by the model over a wide temperature range. The model predicts that in a flux density B the critical currents and activation energies at higher fields fall off as (&oslash;0/B) 1 2/[D+(&oslash;0/B) 1 2] with D the junction width. Experimental data on thin films of YBa2Cu3O 7 agrees with this prediction for both types of junction. It also shows that neither the intra- nor the intergranular components of resistance are sensitive to the relative direction of macroscopic current and field down to low temperatures. Differences between the roles of the Lorentz force in flux creep and phase slippage models are discussed. &copy; 1990.
Filipczuk, S.W., Driver, R. & Smith, G.B. 1990, 'Aspects of annealing and free surface crystallization of YBCO thin films', Physica C: Superconductivity and its applications, vol. 170, no. 5-6, pp. 457-468.
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We describe a method of high temperature annealing in which the control of oxygen partial pressure is the principal experimental determinant in obtaining highly c? oriented thin films of YBa2Cu3O7 - ? on YSZ. Film crystallization, morphology and substrate interactions are discussed with detailed reference to the equilibria existing in the YBCO system. A model based on the melt-assisted crystallization of the precursor tetragonal compound, beginning at the free film surface, is used to explain the observed c? texturing. Excellent Josephson coupling between grains of YBa2Cu3O7 - ? in our films is related to melt-assisted growth. We discuss the adverse effects of annealing in pure oxygen at high temperatures. &copy; 1990.
Lake, M.R., Smith, G.B., McKenzie, D.R. & Dzurak, A.S. 1989, 'Properties of powders deposited by silane/hydrogen and silane/methane plasmas', Journal of Non-Crystalline Solids, vol. 109, no. 2-3, pp. 318-326.
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Particulate matter is often produced by the glow discharge decomposition of silane/hydrogen and silane/methane mixtures during the production of amorphous thin films. This material, produced in two forms of rf-excited reactors, has been studied by electron microscopy and diffraction and thermomanometric analysis. The latter material is produced under conditions in which physical vapour deposition processes dominate, i.e. high plasma current density and high reactive gas pressure. The material produced in a silane/hydrogen plasma has an average size of 20 nm while that from the silane/methane plasma has an average size of 100 nm. Material deposited on the walls of the chamber is amorphous with a high hydrogen content while material deposited on the central electrode is partly crystalline. The former material produces columnar structures which reflect, on a large scale, the structures formed in thin film deposits. The latter material has a lower hydrogen content due to densification and bond reconstruction caused by ion bombardment. The two distinct processes by which hydrogen evolves from the amorphous powder were modelled by simple second-order equations with activation energies of 1.3 and 2.5 eV. &copy; 1989.
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Smith, G.B., Bell, J.M., Filipczuk, S.W. & Andrikidis, C. 1989, 'Temperature, field and grain size dependence of flux pinning in high Tc superconductors', Physica C: Superconductivity and its applications, vol. 160, no. 3-4, pp. 333-340.
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Three models of flux pinning are discussed in terms of their basic geometric characteristics. The models are distinguished by their predictions of the field, temperature and sample size dependence of resistivity in an applied magnetic field below Tc. Field dependent resistance data below Tc from several good quality thin film samples and a single crystal are examined to extract activation energies and the resistivity pre-factor. A universal correlation between the latter two quantities and evidence that activation energies scale with sample thickness point strongly to a model involving flux pinning along a line as the most appropriate to describe thermally activated flux creep behaviour. These data also indicate that vortex lines are straight and the vortex lattice ordered for fields along the c-axis and for sample thickness up to at least {reversed tilde} 20 ?m provided one is not too close to Tc. &copy; 1989.
Smith, G.B. & McKenzie, D.R. 1989, 'Optical properties of chemically ordered a-Si1-xCx', Journal of Applied Physics, vol. 65, no. 4, pp. 1694-1698.
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The optical properties (n,k,?,neff) of chemically ordered a-Si1-xCx@B: H alloys have been measured and then analyzed with the effective-medium theory. Included is the first experimental result for an amorphous binary semiconductor that is known to be almost fully chemically ordered, and represented by the formula a-SiC0.64@B: H. Chemical order is induced by heavy dilution of the plasma with hydrogen. Chemical ordering shifts absorption to shorter wavelengths. Analysis using a scaling theory to define optical constants of different tetrahedron components leads to serious errors in the a-Si1-xCx@B: H series.
Smith, G.B. 1989, 'Effective medium theory and angular dispersion of optical constants in films with oblique columnar structure', Optics Communications, vol. 71, no. 5, pp. 279-284.
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The optical properties of thin films, containing metal and voids in an oblique columnar structure, are modelled in the quasi-static limit. The complex dielectric function is shown to be strongly dependent on the angle of incidence and on the columnar orientation for p-polarised light. Effects of morphology, type of metal, and wavelength are ilucidated. &copy; 1989.
Mbise, G., Smith, G.B. & Granqvist, C.G. 1989, 'High resolution studies of columnar growth in obliquely deposited metal films on glass', Thin Solid Films, vol. 173, no. 2, pp. L123-L127.
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Mbise, G., Smith, G.B., Niklasson, G.A. & Granqvist, C.G. 1989, 'Angular-selective optical properties of Cr films made by oblique-angle evaporation', Applied Physics Letters, vol. 54, no. 11, pp. 987-989.
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Thin Cr films were made by oblique-angle evaporation onto glass. Electron microscopy showed an inclined columnar microstructure. Spectrophotometry yielded a strongly angular-selective p-polarized transmittance, consistent with recent theoretical notions, of potential interest for energy-efficient windows.
McKenzie, D.R., Bruley, J. & Smith, G.B. 1988, 'Electron energy-loss study of bonding in amorphous silicon-carbon alloy films prepared with hydrogen dilution', Applied Physics Letters, vol. 53, no. 23, pp. 2284-2286.
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Electron energy-loss spectroscopy was used to study the nature of chemical bonding in a-Si1-xCx:H films produced by rf glow discharge decomposition of SiH4/CH4 mixtures with hydrogen dilution. The low-loss region, the Si L edge, and the C K edge were studied. It was found that near stoichiometric films have a high degree of Si to C bonding and that substoichiometric films show some C to C sp2 bonding. A free-electron model was used to interpret the variation of plasmon energy of these films with composition.
McKenzie, D.R., Smith, G.B. & Liu, Z.Q. 1988, 'Electron-diffraction study of chemical ordering in glow-discharge a-Si1-xCx:H', Physical Review B, vol. 37, no. 15, pp. 8875-8881.
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Energy-filtered electron-diffraction data were collected from a range of plasma-deposited amorphous hydrogenated silicon-carbon alloy films at high and low substrate temperature with and without hydrogen dilution of the active gases (silane and methane). The data were Fourier transformed to a reduced density function which was compared with the predictions of three versions of a recently published tetrahedron model of the structure of tetrahedrally bonded amorphous binary alloys. For nearly equiatomic material prepared at 300&deg;C with hydrogen dilution a completely chemically ordered structure was obtained, described as amorphous tetrahedral silicon carbide. Films prepared under other conditions were described as partially chemically ordered. Substrate heating and hydrogen dilution of the plasma both tend to promote order and result in a reduced carbon content. &copy; 1988 The American Physical Society.
Smith, G.B. 1987, 'Photoresponse in amorphous semiconductors as dark conductivity varies', Journal of Applied Physics, vol. 62, no. 8, pp. 3380-3387.
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The variations in conductivity, under illumination of amorphous semiconductors, is examined as a function of the dark Fermi level (E F) using a simple, generally accurate approach which eliminates the need for a complete numerical solution of equations covering generation, recombination, and trapping. The enhanced photoconduction on doping is readily quantified along with the reduced photosensitivity (total to dark conductivity ratio). Various models can be more readily assessed. Predictions are examined in detail for the often used exponential gap state model. The associated Rose model result for the intensity dependence is seen to be an asymptotic limit which becomes less applicable as dark conductivity increases. Temperature dependence is also examined. Emphasis is on doping, but contrasts are also drawn between the effects of a homogeneous and inhomogeneous shift in dark activation energy. The reduction in the exponent ? for the intensity dependence is far more pronounced when external fields modify the dark conductivity.
Smith, G.B. & McKenzie, D.R. 1986, 'STEADY-STATE PHOTOCONDUCTIVITY IN a-Si:H PREPARED BY d. c. MAGNETRON METHODS.', Philosophical Magazine B: Physics of Condensed Matter; Electronic, Optical and Magnetic Properties, vol. 54, no. 4, pp. 255-272.
The steady-state photoconductivity of amorphous silicon produced from glow discharge in a d. c. magnetron has been studied. Cylindrical and planar magnetrons were used. Measurements were made over a range of temperatures and illumination intensities. Recombination models involving traps, alone, and combined with deep-level defects, are analysed and applied to our data. The exponent gamma in the intensity dependence depends on temperature in the usual Rose model format. However, the characteristic temperature depends not just on the steepness of the tail states but on the positions of the dark and quasi-Fermi levels. Values of gamma below one-half are then allowed.
Sie, S.H., McKenzie, D.R., Smith, G.B. & Ryan, C.G. 1986, 'Depth profiles of hydrogen and oxygen in hydrogenated amorphous silicon thin films', Nuclear Inst. and Methods in Physics Research, B, vol. 15, no. 1-6, pp. 525-529.
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Detailed depth profiles of hydrogen and oxygen have been measured in samples of thin films of a-Si: H produced by dc magnetron glow discharge techniques. The resonant capture reaction 1H(19F, ??)16O at E19v = 6.417 MeV was used for hydrogen profile measurements, and resonant ? scattering at E? = 3.0359 MeV was used for oxygen. Contrasting results reflecting the different fabrication conditions were obtained and these were correlated with measured electrical properties. &copy; 1986.
Sie, S.H., McKenzie, D.R., Smith, G.B. & Ryan, C.G. 1986, 'Analysis of carbon content and distribution in a-Si1-xCx:H films by resonant scattering', Nuclear Inst. and Methods in Physics Research, B, vol. 15, no. 1-6, pp. 632-635.
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Resonant alpha scattering has been used to determine detailed depth profiles of carbon in amorphous silicon carbon alloys produced by glow discharge decomposition. The carbon profiles exhibit a two layer structure similar to that indicated by hydrogen profiles in a-Si: H films. By comparison electron probe analysis seems to considerably overestimate average carbon content while electron energy loss measurements on very thin specimens agree with the surface layer content in the resonance profiles of thicker films. The bulk content is, however, still lower. &copy; 1986.
Smith, G.B., Niklasson, G.A., Svensson, J.S.E.M. & Granqvist, C.G. 1986, 'Noble-metal-based transparent infrared reflectors: Experiments and theoretical analyses for very thin gold films', Journal of Applied Physics, vol. 59, no. 2, pp. 571-581.
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Very thin gold films were prepared on glass by ion plating (IP) and by conventional evaporation (CE). Below a certain thickness - ?9 nm for IP and ?15 nm for CE - the films comprised a metal network; above this thickness we found uniform films. Optical properties were recorded by spectrophotometry. Conspicuous near-infrared transmittance plateaus were seen in network films. This effect is conducive to high solar transmission. The spectral features were explained from effective medium theories based on the film structure. The uniform films were consistent with the Drude theory, provided that an anomalously large frequency dependence of the relaxation energy was invoked. Significant induced transmission was found in calculations on dielectric/gold/dielectric coatings. Our results lead to improved noble-metal-based transparent infrared reflectors for potential use on energy efficient windows.
Smith, G.B., Niklasson, G.A., Svensson, J.S.E.M. & Granqvist, C.G. 1986, 'Noble-metal-based transparent infrared-reflectors. Preparation and analysis of thin gold films', Solar Energy Materials, vol. 14, no. 3-5, pp. 257-268.
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Very thin gold layers were produced on glass by evaporation with and without simultaneous ion bombardment. Electron microscopy showed that films with thicknesses below a certain magnitude - which decreased with increasing ion flux - had a nonuniform (network) structure. Optical properties were measured by spectrophotometry in the 0.3-50 ?m range. Uniform films were consistent with the Drude theory with an anomalously large frequency dependdence of the relaxation energy. Nonuniform films displayed characteristic plateaus in the near-infrared transmittance. This feature, which is conducive to high solar transmittance, can be explained from effective medium theories based on the film structure. Our results are important for the development of improved noble-metal-based infrared-reflectors for energy efficient windows. &copy; 1986.
Smith, G.B., McPhedran, R.C. & Derrick, G.H. 1985, 'Surface structure and the optical properties of black chrome', Applied Physics A Solids and Surfaces, vol. 36, no. 4, pp. 193-204.
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A new optical model is presented for solar-selective black chrome. Surface texture is shown to be the primary factor which gives thin films of black chrome a uniformly high absorptance in the visible and near-infrared regions. Internal composition of the films is a secondary influence on their optical properties. We present results consistent with experimental data obtained from films having widely varying structures and compositions, both before and after heat treatment. Our optical model does not rely on the quasistatic approximation, hitherto universally employed in theoretical studies of solar-selective black chrome. Instead, we use a rigorous diffraction formulation for doubly-periodic surfaces (bigratings). The key parameters of the surface morphology are determined from stereo-pair electronmicrographs, and are used in the bigrating model. We present the predicted variation of spectral absorptance with wavelength, as well as integrated absorptance and thermal emittance, for roughened chromium. We give results both for bare metal, and for the metal conformally overcoated either with a thin layer of Cr2O3 or with a Cr/Cr2O3 cermet. Various shapes of surface features are examined, and surface profile is shown not to be crucial in determining optical properties. &copy; 1985 Springer-Verlag.
Smith, G., Derrick, G. & McPhedran, R.C. 1985, 'A Rigorous Diffraction Theory For The Optical-properties Of Black Chrome', Applied Surface Science, vol. 0, no. MAY, pp. 813-819.
McKenzie, D.R. & Smith, G. 1985, 'Amorphous-silicon Solar-cells Produced By A Dc Magnetron Glow-discharge Technique', Applied Surface Science, vol. 0, no. MAY, pp. 891-898.
Sie, S., McKenzie, D.R. & Smith, G. 1985, 'Profiling Of Hydrogen In A-si-h By The H(f-19,alpha-gamma)o-16star Reaction', Applied Surface Science, vol. 0, no. MAY, pp. 908-915.
McKenzie, D.R. & Smith, G.B. 1985, 'Amorphous silicon solar cells produced by a DC magnetron glow discharge technique', Applied Surface Science, vol. 22-23, no. PART 2, pp. 891-898.
The production of amorphous silicon solar cells using deposition from a DC magnetron glow discharge is described. The cells have the p-i-n structure with indium tin oxide front contacts. Fill factors of 40% and overall solar efficiencies of around 1.2% were obtained. Investigations were carried out to determine the reasons for deficiencies in the carrier collection efficiency. The cell efficiency was increased by increasing the ?? product of the i-layer. The spectral dependences of carrier collection efficiency, open circuit voltage and fill factors were determined. Comparison with published theoretical models of similar cells showed that for the best cells, surface recombination effects limited the efficiency. Argon used in the p-layer deposition was the most likely cause of these effects. &copy; 1985.
Smith, G.B., Derrick, G.H. & McPhedran, R.C. 1985, 'A rigorous diffraction theory for the optical properties of black chrome', Applied Surface Science, vol. 22-23, no. PART 2, pp. 813-819.
Quantitative three-dimensional studies of morphology together with analysis of the validity of quasistatic effective medium theories show the need for a diffraction treatment of the optical properties of solar selective black chrome. The spectral absorptance A(?) is calculated for a doubly periodic modulation of chrome overcoated with Cr2O3 or a cermet of Cr2O3 and Cr metal. Various profiles, depths and coating thicknesses are used. Diffraction caused by the surface morphology explains the major features of A(?) for black chrome. Internal structure is of secondary importance. &copy; 1985.
Willis, G.L. & Smith, G.C. 1985, 'Amine accumulation in behavioural pathology', Brain Research Reviews, vol. 9, no. 2, pp. 109-132.
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When nigro-striatal and meso-cortical neurons degenerate there is a loss of dopamine in the terminal fields and an accumulation of amines in the axons of these systems as they traverse the hypothalamus through the medial forebrain bundle. Traditional lines of thought have attributed the occurrence of motor and consummatory deficits which occur after dopamine neuron degeneration to the loss of functional dopamine neurotransmitter in the terminal fields. However we have hypothesized that hypothalamic amine accumulation represents an area of brain tissue where processes such as neurotransmitter release ephaptic transmission or local axon swelling may be affecting adjacent neurons and may thereby participate in the production of behavioural deficits. There is a considerable amount of evidence from studies on both peripheral and central catecholamine-containing neurons indicating that when their axons degenerate a release of functional neurotransmitter can occur. Information from neuropharmacological studies indicates that several drugs which facilitate behavioural recovery from dopamine-depleting lesions may do so by affecting amine release or receptor sensitivity near areas of accumulation rather than depleted terminal fields. We conclude that amine accumulation is a component of dopamine neuron degeneration which should be considered when assessing the role of the central catecholamine systems in the control of various behavioural and physiological processes. &copy; 1985.
Smith, G.B. 1985, 'Very thin gold films produced with ion plating for improved transparent infrared reflectors', Applied Physics Letters, vol. 46, no. 8, pp. 716-718.
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Semitransparent gold films under 10 nm thick were produced with ion plating onto glass and were shown to give improvements, depending on thickness, for either solar control or transparent heat-mirror applications relative to conventional deposits. Film inhomogeneities, modified gold optical constants, and ion-beam assisted onset of film coalescence all play an important role. An anomalously large frequency dependence of conduction electron relaxation time was identified in a continuous film from a Drude analysis.
Sie, S.H., McKenzie, D.R. & Smith, G.B. 1985, 'Profiling of hydrogen in a-Si:H by the H(19F, ??)16O* reaction', Applied Surface Science, vol. 22-23, no. PART 2, pp. 908-915.
The resonant reaction H(19F, ??)16O* was used to study the hydrogen content and distribution with depth in a-Si: H films. The films were prepared in a DC magnetron by glow discharge decomposition of silane at a pressure of 1 Pa. The results showed that a surface hydrogen peak was present for a film prepared at 310&deg;C but disappeared when the films were prepared at 370&deg;C. The total hydrogen content was one half of that calculated using infrared absorption spectroscopy. RBS was used to determine the film density and scanning electron microscopy was used to investigate microstructure. &copy; 1985.
Smith, G.B. & Teytz, K. 1984, 'An immersion coated molybdenum based selective absorber', Solar Energy Materials, vol. 9, no. 4, pp. 449-458.
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A new selective surface has been developed using an immersion process. It works for certain metals using hot acidic molybdate based bath. Detailed analysis is confined to cobalt conversion because it gives good high temperature stability. Absorptance and emittance versus pH, and bath composition are analysed. Spectral reflectance is studied for films of varying thickness. Composition profiles from GDOS and AES show the surface to be a mixed hydrated oxide with some grading in stoichiometry. &copy; 1984.
Smith, G.B. & McKenzie, D.R. 1984, 'DC magnetron glow discharge amorphous silicon', Solar Energy Materials, vol. 11, no. 1-2, pp. 45-56.
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The preparation of amorphous hydrogenated silicon (a-Si:H) by glow discharge decomposition of pure monosilane in a cylindrical dc magnetron has been studied. Deposition parameters cover pressured from 1 to 8 Pa, magnetic fields from 0.008 to 0.05 T, power dissipation from 5 to 200 W and substrate temperatures of 260, 310 and 370&deg;C. Deposition rates to 60 nm/min, approximate to a universal function of power. Properties investigated, for these conditions, were photoconductivity, dark conductivity, infrared absorption (hydrogen content and bonding) and refractive index. Electron diffraction showed the films to be amorphous under all conditions. Properties are dependent on pressure and deposition rate with photoconductivity increasing with increases in both parameters. Magnetic field in this axial configuration had no direct effect on film properties. It is concluded that thismethod has potential for large scale commercial applications. &copy; 1984.
Smith, G.B., Ignatiev, A. & Bacon, D. 1983, 'An introduction and overview of two studies of substrate influence on selective absorber structure and stability', Solar Energy Materials, vol. 9, no. 1, pp. 1-2.
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The following two papers on the selective absorber black chrome represent independent analyses of substrate effects on absorber stability. The studies are complementary and taken together they reveal a much clearer picture not only of the potential role of the substrate in high temperature degradation but of the way the structure and composition of black chrome is affected by plating conditions. This note was deemed appropriate to put each study in context of an overall picture of absorber stability and to pin-point the way in which the studies differ and hence how their findings complement each other. &copy; 1983.
Bird, J.R., Duerden, P., Cohen, D.D., Smith, G.B. & Hillery, P. 1983, 'Depth profiles and microtopology', Nuclear Instruments and Methods In Physics Research, vol. 218, no. 1-3, pp. 53-56.
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Depth profiling by ion beam techniques, including Rutherford backscattering and nuclear reaction methods, is affected by the presence of surface microtopology. This is especially true in glancing angle measurements which involve enhanced depth resolution. Such effects have been previously investigated for samples of uniform composition but basic ambiguities appear in the interpretation of measurements of non-uniform depth profiles when roughness is present. Measurements at a number of angles can provide information on the influence of both these uniformity and roughness factors on observed energy spectra. &copy; 1983.
Smith, G.B., Teytz, K. & Hillery, P. 1983, 'The substrate impact on the structure and thermal stability of solar selective black chrome', Solar Energy Materials, vol. 9, no. 1, pp. 21-41.
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The role of the substrate in the structure and thermal stability of several types of black chrome has been examined by comparison of optical and structural results on fourteen substrate systems at temperatures up to 450&deg;C. The main feature is the spread in behaviour with substrate for each of three sets of plating conditions used. Each set gave progressive improvements in overall stability coupled with diminishing sensitivity to the substrate. Porosity levels appear to be responsible. Oxide to metal ratios are shown to be a poor guide, by themselves, to absorber quality. Oxide percentage always increases at higher temperatures but associated ? shifts vary with substrate. Other important factors discussed are diffusion through intermediate layers in multilayer substrates, the level of substrate oxidation, the influence of substrate on film structure and film thickness versus stability. &copy; 1983.
Smith, G.B., Hillery, P. & Teytz, K. 1983, 'Ranking solar absorber structural parameters in terms of impact on performance and stability', Thin Solid Films, vol. 108, no. 3, pp. 239-245.
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For electrochemically produced solar-selective surfaces the size and spacing of surface features, independently of their shape, is shown to be the most important contribution to high absorptance. The composition and composition gradients can aid absorption but are not critical. Data from optical measurements, surface profiles derived with a stereo digitizer and scanning electron microscopy stereo pairs, surface analysis and thermal degradation studies are used to rank parameters. &copy; 1983.
Smith, G.B., Zajac, G., Ignatiev, A. & Rabalais, J.W. 1982, 'Surface composition of solar selective black chrome films as determined by SIMS', Surface Science, vol. 114, no. 2-3, pp. 614-626.
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The composition of electro-deposited black chrome solar absorbing films has been investigated via secondary ion mass spectrometry (SIMS). Positive and negative SIMS show a number of (OH)- bearing ions which have been related to a near-surface region dominated by CrO(OH) and Cr(OH)3 compounds. Depth concentration profiles indicate that the hydroxide content decreases and the metallic chromium fraction increases with depth into the film. The studies further refine the chemical and microstructural model for the black chrome coating from which its solar selective optical properties can be derived. &copy; 1982.
Smith, G.B., Zajac, G. & Ignatiev, A. 1982, 'High flux photochemical changes in Black Chrome solar absorbing coatings', Solar Energy, vol. 29, no. 4, pp. 279-289.
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Black Chrome samples have been exposed to concentrated solar radiation (350kW m-2-2.5 MW m-2) at elevated temperatures (250-500&deg;C) over limited periods of time with the resultant observation that the coatings degrade less optically than equivalent coatings heated by IR radiation. The decreased degradation is a result of decreased oxidation of the Black Chrome coating under solar heating as compared to oven heating. This is proposed to be due to photo-desorption of gaseous oxygen bearing species from the surface of the film. &copy; 1982.
Smith, G.B. & Ignatiev, A. 1981, 'Black chromium-molybdenum: A new stable solar absorber', Solar Energy Materials, vol. 4, no. 2, pp. 119-133.
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A new solar selective black which is more stable at high temperatures in air than standard black chrome has been electrodeposited. It is based on two refractory metals and their oxides, chromium and molybdenum. Their micromorphology is the same as found in black chrome and the solar absorption mechanisms are similar. Plating mechanisms are discussed and related to film structure. Chemical structure via X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) as a function of depth reveal important differences to the structure of standard black chrome which affect stability but not optical response before heating. Absorptance is stable at a value of 0.95 to at least 425&deg;C in air in the best composites which have Mo/Cr ratios of about 0.05. The molybdenum is not present as metal and the total metallic Cr content decreases as the Mo content increases. The Mo percentage is very high near the surface of the film. &copy; 1981.
Smith, G.B. & Ignatiev, A. 1980, 'The relative merits of black cobalt and black chrome as high temperature selective absorbers', Solar Energy Materials, vol. 2, no. 4, pp. 461-467.
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Solar selectivity, with emphasis on high solar absorptance (?), has been measured in three distinct classes of black cobalt before and after long term exposure to high temperatures (300 to 500&deg;C) in air. Absorption processes in black cobalt and black chrome are quite different, although surface morphology reduces front surface reflections in both systems. However, the thermal stability of the solar absorptance are comparable to black chrome for black cobalt coatings composed of cobalt oxides but not for those composed of cobalt sulphides which are found to be unsuitable at T > 300&deg;C in air. None of the coatings on nickel substrates are suitable for applications at T > 450&deg;C where high absorptance (?{greater-than or approximate}0.95) is needed. &copy; 1980.
Willrath, H. & Smith, G.B. 1980, 'A new transient temperature emissometer', Solar Energy Materials, vol. 4, no. 1, pp. 31-46.
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An emissometer is described which measures the temperature dependent total hemispherical emittance of flat samples coated with a selective surface. The construction of the instrument is such that heat losses occur only through radiation and then only from the surface under investigation. The emittances of several selective surfaces are measured and compared with other results on the same, or similar surfaces. These are measured in both other calorimeters and in instruments using reflectance methods. It is found that different calorimetric methods give close agreement, as do different reflectance methods. However, reflectance results tend to be about one third lower than those obtained through calorimetry. This seems to indicate that normal emittance and hemispherical emittance should not be equated for selective surfaces. There also appears to be a marked difference in the temperature dependence of emittance, depending on whether the measurements are made in a calorimeter or calculated from theoretical black body shifts applied to spectral reflectance curves. &copy; 1980.
Smith, G.B., Ignatiev, A. & Zajac, G. 1980, 'Solar selective black cobalt: Preparation, structure, and thermal stability', Journal of Applied Physics, vol. 51, no. 8, pp. 4186-4196.
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In the quest for an electroplated selective black coating stable to 500&deg;C in air, black cobalts have been prepared by three techniques to yield (a) plated cobalt sulphides, (b) plated cobalt oxide-hydroxide, and (c) cobalt oxide prepared by thermal oxidation of electropolated cobalt metal. The optical properties of the various coatings are analyzed before and after exposure to air for extended periods of time at temperatures in the 300&deg;-500&deg;C range. The sulfide black cobalt is not acceptable as a high-temperature selective absorber due to severe thermal degradation. The plated oxide is a good selective absorber to about 400&deg;C, and the thermally oxidized black to a slightly higher temperature, but degrades at 500&deg;C. Structure studies via scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and x-ray photoemission spectroscopy (XPS) are reported which yield a full account of the coating chemistry before and after heating. The studies reveal that the high solar absorptance of the acceptable black cobalt coatings is due to a continuation of a porous outer layer grading into nondense oxides of cobalt; either CoO or Co3O4, depending on the film. Absorption is intrinsic but not due to metal particles as in black chrome. A limited amount of optical degradation occurs upon heating the oxide black cobalt in air due to oxidation of hydroxide. However, the major degradation problem is shown to be substrate oxidation in contrast to black chrome where film oxidation is the principal problem.
Zajac, G., Smith, G.B. & Ignatiev, A. 1980, 'Refinement of solar absorbing black chrome microstructure and its relationship to optical degradation mechanisms', Journal of Applied Physics, vol. 51, no. 10, pp. 5544-5554.
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An in depth characterization of the electrodeposited solar absorber black chrome resulting in refinement of the microstructural model of the coating is presented in light of current studies in valence band Auger electron spectroscopy, x-ray photoelectron spectroscopy, thermal desorption spectroscopy, secondary ion mass spectroscopy, and the chromium electrodeposition mechanism. Through the presented model, the structural and chemical parameters of the coating are linked to its optical response with the degradation of the optical response at elevated temperatures related to changes in these parameters. The degradation process is divided into two distinct phases. First, upon heating to low temperatures (?300&deg;C) the chromium hydroxide localized on the surface and within the microstructure of the film decomposes producing H 2O and chromium oxide leaving an expected microvoid-metallic particle structure. Heating to temperatures in excess of 300&deg;C leads to the second degradation phase. The fine chromium crystallites comprising the film undergo oxidation and the metallic chromium component, responsible for the intrinsic optical absorption, is diminished. The optical model of the solar absorbing film has been refined within the effective medium approach to account for the flat response in the visible part of the spectrum.
Zajac, G., Ignatiev, A. & Smith, G.B. 1980, 'PHOTODESORPTION STUDIES OF CO AND CO//2 FROM THE SOLAR ABSORBER BLACK CHROME.', Journal of vacuum science & technology, vol. 18, no. 2, pp. 379-381.
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Photodesorption of CO and CO//2 were studied on black chrome solar absorbing coatings. It is shown that the desorption is a quantum effect with possible basis in the photo-hole model applicable to semiconductor surfaces, but with yields similar to that reported for photodesorption for metals.
Smith, G.B. 1979, 'The scope of effective medium theory for fine metal particle solar absorbers', Applied Physics Letters, vol. 35, no. 9, pp. 668-670.
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The treatment of an array of small metal particles as a continuous effective medium is shown to be possible for visible and near infrared frequencies at much larger particle sizes and separations than often supposed. Specific upper limits are evaluated for chromium. Results are based on the strongly correlated model. For this, the usual topology, variation, and attenuation of the field strength over average unit cell dimensions are permissible, provided such variations are characteristic of the effective medium as a whole. As wavelength decreases, the leading contribution to diffuse scattering off such composite films should come from terms proportional to ?-8 not the Rayleigh term.
Smith, G.B. 1979, 'The effect of a self consistent effective ambient temperature on collector efficiency parameters', Solar Energy, vol. 23, no. 6, pp. 541-542.
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Smith, G.B. & Willrath, H. 1979, 'Calorimetric emissivities for solar-selective coatings on flat sheet', Journal of Physics E: Scientific Instruments 89, vol. 12, no. 9, pp. 813-814.
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A calorimeter designed for measuring the hemispherical emissivity of flat sheet, coated on one side only, is described. Prime interest is in solar-selective coatings. A novel technique is used to ensure negligible heat losses from all but the coated surface. Results indicate that the selective coatings hemispherical emissivity is always significantly larger than normal emissivity, as found from spectral reflectance.
Hogg, S.W. & Smith, G.B. 1977, 'The unusual and useful optical properties of electrodeposited chrome-black films', Journal of Physics D: Applied Physics, vol. 10, no. 13, pp. 1863-1869.
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Visible and infrared reflectance of various electrodeposited chrome-black films is unusual. A theoretical model explaining this behaviour is presented. It appears that a graded volume density of Cr metal across the film is required to produce the observed effects. The substrate's role is examined. Its direct influence is minor, because of the film's effective skin depth even at moderate metallic densities and in the infrared (for all films over about 0.15 mu m thick). The substrate must have a major indirect influence, though, by determining film structure. These systems make excellent solar selective absorbers.
Smith, G.B. 1977, 'Dielectric constants for mixed media', Journal of Physics D: Applied Physics, vol. 10, no. 4, pp. L39-L42.
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A new approach to deriving effective dielectric constants for two-component systems is developed. For metal-dielectric mixtures three classes of problem are discussed: two where one constituent exists as particles embedded in the other, and the third where both are in particle form.
Sabine, T.M., Smith, G.B. & Reeve, K.D. 1974, 'CRITICAL CONCENTRATION FOR MAGNETIC ORDER IN SOLID SOLUTIONS OF UO//2 WITH ThO//2 AND ZrO//2.', J Phys C (Solid State Phys), vol. 7, no. 24, pp. 4513-4521.
Changes in Neel temperature and the changes in the localized magnetic moment on the uranium ion in solid solutions of UO//2 with ZrO//2 and ThO//2 have been measured by neutron diffraction methods. The localized magnetic moment per uranium atom falls immediately UO//2 is diluted and vanishes well before the expected critical concentration for the breakdown of long-range order. These observations are shown to be consistent with spin - lattice interaction effects.
Smith, G.B. 1972, 'Magnetization of nearly magnetic dilute alloys', Journal of Physics F: Metal Physics, vol. 2, no. 3, pp. L55-L59.
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The magnetization of nearly magnetic dilute alloys is examined in and beyond the linear response region. Explanation of existing data using a localized enhancement model is shown to be impossible without the condition of charge neutrality on the impurity. A field dependent impurity-host coupling is found which also considerably affects the observed field dependence, mainly because the host susceptibility is exchange enhanced.
Smith, D.A. & Smith, G.B. 1971, 's-d exchange integrals obtained from experiment in Cu:Mn, Ag:Mn, and Au:Mn', Physical Review B, vol. 4, no. 1, pp. 191-196.
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s-d exchange integrals are estimated (i) from the energies of virtual bound states appearing in the optical absorption and (ii) from susceptibility, specific-heat, and resistivity measurements above TK, using the high-temperature results of the s-d exchange model. The resistivity gives values which are much too low; it is suggested that this arises from neglecting nonlogarithmic terms especially important in the theory of transport properties. &copy; 1971 The American Physical Society.
Smith, D.A. & Smith, G.B. 1970, 'The high temperature properties of transition metal alloys', Journal of Physics C: Solid State Physics, vol. 3, no. 1 S, pp. S69-S80.
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A treatment of Anderson's model for dilute alloys of the (orbitally degenerate) 3d transition elements dissolved in simple hosts is given, applicable in the strong-coupling (atomic) limit and at temperatures well above the Kondo temperature. The theory is applied to the impurity susceptibility and resistivity to obtain spectroscopic information on the impurity atom. Experimental magneton numbers from the high temperature susceptibility are used to label the atomic states of the impurity. Residual resistivities are then used to obtain the energy spacing | T - ? | between the virtual bound state T and the Fermi level ? . Given this information, the sign of T - ? is fixed by calculating the magneton number and comparing with experiment. In most cases good agreement can be obtained: the comparison serves as an internal check between theory and observation.