Emeritus Professor Geoff Smith

Biography

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.

Professional

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 Physics and Advanced Materials
Core Member, Research Strength Materials and Technology for Energy Efficiency Member
Research Director, Institute for Nanoscale Technology
Senior Lecturer, School of Physics and Advanced Materials
Research Director, Institute for Nanoscale Technology
Core Member, Research Strength Materials and Technology for Energy Efficiency Member
BSc (UNE), PhD honoris causa (UU), PhD (Monash)
Member, Australian Optical Society
Fellow, Australian Institute of Physics
Fellow, Australian Institute of Energy
 
Phone
+61 2 9514 2224
Room
CB01.12.30

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
Applied
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

Book Chapters

Castro Aguilar, J.L., Smith, G.B., Gentle, A.R. & Chen, D. 2012, 'Making cool roofs compatible with low heating and cooling loads' in A. Mendez-Vilas, BrownWalker, Boca Raton (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. 2007, 'Combining energy efficiency with aesthetic appeal using advanced optical materials' in Choudhury PK; Singh ON (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.
Smith, G.B. 2003, 'Nanostructured Thin Films' in Wieglhofer WS, Lakhtakia A (eds), Introduction to Complex Mediums for Optics and Electromagnetics, International Society for Optical Engineering, Washington, USA, pp. 421-446.
Botten, L.C., McPhedran, R.C., Nicorovici, N.A., Asatryan, A.A., de Sterke, C.M., Robinson, P.A., Busch, K., Smith, G.B. & Langtry, T.N. 2003, 'Rayleigh multipole methods for photonic crystal calculations' in Priou A; Itoh T (eds), Electromagnetic applications of photonic band gap materials and structures, Massachusetts Institute of Technology, USA, pp. 21-60.

Books

Smith, G.B. & 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.

Conference Papers

Castro Aguilar, J.L., Smith, G.B., Gentle, A.R. & Chen, D. 2013, 'Optimum Integration of Albedo sub-roof r-value and phase change material for cool roofs', 13th International Conference of the International Building Performance Simulation Association, Chambery France, August 2013 in Proceedings of BS2013:13th International Conference of the International Building Performance Simulation Association, ed Smith, Geoff B, International Building Performance Simulation Association (IBPSA), France, pp. 1315-1321.
Franklin, J.B., Smith, G.B. & Earp, A.A. 2013, 'A critical hurdle to widespread use of polymer based luminescent solar concentrators', Reliability of Photovoltaic Cells, Modules, Components, and Systems, San Diego, USA, September 2013 in Proc. SPIE 8825, Reliability of Photovoltaic Cells, Modules, Components, and Systems VI,, ed Neelkanth G. Dhere; John H. Wohlgemuth; Kevin W. Lynn, SPIE, United States, pp. 1-9.
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Luminescent solar concentrators have been studied and improved for over 30 years.
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', anostructured Thin Films, San Diego. USA, August 2013 in Proc. SPIE 8818, Nanostructured Thin Films, ed Tom G. Mackay; Akhlesh Lakhtakia; Yi-Jun Jen; Motofumi Suzuki, SPIE, United States, pp. 1-10.
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The optical resonances that occur in nanostructured metal layers are modulated in thin film stacks if the nanostructured layer is separate from a reflecting conducting layer by various thickness of thin dielectric.
Smith, G.B. 2012, 'Green nanotechnology', Nanostructured Thin Films IV, San Diego, California United States, August 2011 in SPIE Proceedings, ed Raul J. Martin-Palma, Yi-Jun Jen, Tom G. Mackay, SPIE, United States, pp. 8104021-1-8104021-4.
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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.
Smith, G.B. 2011, 'Green nanotechnology', Nanostructured Thin Films IV, San Diego, California, USA, August 2011 in Proceedings of SPIE, ed Ral J. Martn-Palma; Yi-Jun Jen; Tom G. Mackay, The International Society for Optics and Photonics, United States, pp. 1-14.
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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.
Gentle, A.R. & Smith, G.B. 2011, 'Performance comparisons of sky window spectral selective and high emittance radiant cooling systems under varying atmospheric conditions', Solar2010, the 48th AuSES Annual Conference, Canberra, Australia, December 2010 in Solar 2010 : Proceedings of the 48th AuSES Annual Conference, ed Igor Skryabin, Australian Solar Energy Society, 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.B., Gentle, A.R. & Edmonds, I. 2011, 'Urban growth, albedo and global warming', Solar2010, the 48th AuSES Annual Conference, Canberra, December 2010 in Solar 2010 : Proceedings of the 48th AuSES Annual Conference, ed Igor Skryabin, Australian Solar Energy Society, Australia, 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', Photonics for Solar Energy Systems, Brussels, Belgium, May 2010 in Proceedings of SPIE - The International Society for Optical Engineering - Photonics for Solar Energy Systems III, ed Ralf B. Wehrspoh, SPIE, USA, pp. 77250Z-0.
The preferred surface spectral response for sub-ambient sky cooling varies according to the amount of water vapor in the atmosphere and the operating difference (Ta-Ts) between ambient and emitter surface temperatures. While all good candidates average h
Arnold, M.D. & Smith, G.B. 2009, 'Comparisons of enhanced absorption in closely-coupled grating-mirror and random particle-mirror systems', San Diego, USA, August 2009 in Proceeding of the SPIE 7404, ed Smith, GB; Lakhtakia, A; Lee, CC, SPIE, USA, pp. 1-8.
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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.
Dowd, A.R., Lewis, R.A., Maaroof, A.I., Gentle, A.R. & Smith, G.B. 2008, 'Temperature dependence of infrared optical properties of vanadium dioxide', Adelaide, SA, November 2008 in AIP 18th National Congress, ed R Clay, AIP, Parkville, VIC.
Tomkin, D.F., Thomas, L.E., Day, M.B., Burke, P.F., Franklin, J.B., Smith, G.B., Louviere, J.J. & Street, D. 2007, 'Solar Light for rooms without windows', Sustainable Innovation 07, Farnham, Surrey, UK, October 2007.
Maaroof, A.I., Gentle, A.R., Cortie, M.B. & Smith, G.B. 2007, 'Nanoporous plasmonic coatings', Inaugural SPIE proceedings on Nanocoatings, San Diego, California, USA, August 2007 in Nanocoatings: Proceeding for SPIE vol 6647, ed Smith, GB; Cortie, MB, The International Society for Optical Engineering, USA, pp. 6647OD-1-6647OD-10.
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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.
Gentle, A.R., Maaroof, A.I., Cortie, M.B. & Smith, G.B. 2007, 'Optical and electrical switching in nanostructured coatings of VO2', SPIE, San Diego, California, USA, August 2007 in Nanocoatings. Proceedings of SPIE vol 6647, ed Smith, GB; Cortie MB, SPIE, Washington, USA, pp. 1-8.
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Vanadium dioxide udergoes a reversible metal-insulator phase transition at about 68 degrees C. Cooatings iof this compound are reflective in the infrared above this temperature, and transmissive or absorptive below it, while resistivity changes by several orders of magnitude. We present a convenient methods for deposting films with nano-sized grains, which are then optically and electrically characterised. Emphasis in this study is the impact of aluminium doping and grain sturcture. The optical hysteresis is rpesnted and its switching range is not altered at different soping levels but he value of transition temperature Tc does shift. In contrast hysteresis in dc resistance does change with a strong correlation between the fall in resistance in the semiconductor state with doping, in the drop in Tc and the electrica properties in the metal state. For grain sizes under about 180 nm the conductivity in the mtal phase is not linear in temperature but is thermally activated, with activation enegies delta E dependent on both grain size G and doping level.
Gentle, A.R., Maaroof, A.I., Smith, G.B. & Cortie, M.B. 2006, 'Tuning plasma frequency for improved solar control glazing using mesoporous nanostructures - art. no. 61970T', Conference on Photonics for Solar Energy Systems, Strasbourg, France, April 2006 in Photonics For Solar Energy Systems, ed Gombert, A, Spie-Int Society Optical Engineering, Bellingham, USA, pp. T1970-T1970.
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The role of the plasma frequency omega(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, tra
Gentle, A.R., Maaroof, A.I., Smith, G.B. & Cortie, M.B. 2006, 'Optical properties and applications to production of plasmonic thin film nanostructures of self-ordered columnar alumina arrays on glass', Conference on Photonics - Design, Technology and Packaging II, Brisbane, Australia, December 2005 in Photonics: Design, Technology, And Packaging II, ed Abbott, D; Kivshar, YS; RubinszteinDunlop, HH; Fan, S, SPIE, Bellingham, USA, pp. 3816-3816.
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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
Cortie, M.B., Xu, X., Chowdhury, H.A., Zareie, H.M. & Smith, G.B. 2005, 'Plasmonic heating of gold nanoparticles and its exploitation', Conference on Smart Structures, Devices, and Systems II, Sydney, Australia, December 2004 in Smart Structures, Devices, and Systems II: Proceedings Of The Society Of Photo-Optical Instrumentation Engineers (SPIE) Volume 5649, ed AlSarawi, SF, SPIE, Washington, USA, 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. A
Smith, G.B., Cortie, M.B. & Maaroof, A.I. 2005, 'The apparent optical indices of spongy nanoporous gold', National Congress of the AIP, Canberra, January 2005 in Proceedings of the 16th National Congress of the Australian Institute of Physics, ed Colla, M., 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.B. & Smith, G.B. 2005, 'Extraction of trapped light from luminescent solar concentration', National Congress of the AIP, Canberra, Australia, January 2005 in Proceedings of the 16th National Congress of the Australian Institute of physics, ed Colla, M., 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', Complex Mediums V: Light & Complexity, Colorado, USA, August 2004 in Complex Mediums V: Light and Complexity: Proceedings of SPIE Vol 5508, ed McCall, M., International Society for Optical Engneering, USA, 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', SPIE Annual Meeting: Nanotechnology & Organic Materials, Denver, USA, August 2004 in SPIE Annual Meeting 2004: Nanotechnology and Organic Materials, ed McCall, M., SPIE, USA, pp. 160-169.
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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', SPIE Annual Meeting: Optical Systems Engineering, Denver, USA, August 2004 in SPIE Annual Meeting 2004: Optical systems engineering, ed McCall; M., SPIE, USA, pp. 231-239.
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Schelm, S., Smith, G.B., Wei, G., Vella, A., Wieczorek, L., Muller, K.H. & Raguse, B. 2003, 'Optical properties of DNCE self-assembled gold nanoparticle layers with organic linker molecules', Plasmonics: Metallic Nanostructures and their Optical Properties, San Diego CA, USA, August 2003 in Proceedings of the SPIE. Plasmonics: Metallic Nanostructures and Their Optical Properties, ed Halas NJ, Internationa Society for Optical Engineering, Washington, USA, pp. 59-65.
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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', Optical Diagnostic Methods for Inorganic Materials III, San Diego CA, USA, August 2003 in Proceedings of the SPIE. Optical Diagnostic Methods for Inorganic Meterials III, ed Hanssen, LM, International Society for Optical Engineering, Washington, USA, 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.B. 2003, 'The Nanohouse- Australian initiative to develop the home of the future', Nanotechnology, Scotland, February 2003 in Nanotechnology, Nanotechnology, Scotland.
Conference presentation
Deller, C.A., Smith, G.B., Franklin, J.B. & Joseph, E.K. 2002, 'The integration of forward light transport and lateral illumination of polymer optical fibre', Congress of the Australian Institute of Physics, Sydney, Australia, July 2002 in Proceedings of the Australian Institute of Physics 15th Biennial Congress 2002., ed Neilson D, Causal Productions Pty Ltd, Adelaide, pp. 307-309.
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Smith, G.B. 2002, 'Nanostructured thin films - a critical review', Complex Mediums III : Beyond Linear Isotropic Dielectrics, Seattle, USA, July 2002 in Proceedings of SPIE: Complex Mediums III: Beyond Linear Isotropic Dielectrics, ed Lakhatkia A; Dewar G; McCall M, SPIE, Bellingham, USA, pp. 207-221.
Smith, G.B., Earp, A.A., Franklin, J.B. & McCredie, G.M. 2001, 'Novel high-performance scattering materials for use in energy saving light fittings and skylights based on polymer pigmented with polymer', Solar and Switching Materials, San Diego, August 2001 in Solar and Switching Materials, ed Lampert, Granqvist, Lewis, SPIE, Bellingham WA USA, 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.
Smith, G.B., Gerritsen, S., Hossain, M. & McCredie, G.M. 2001, 'Plasmon-mediated visible and near infra red transmission through sub-30-nm holes in metal films: potential in solar energy applications', Solar and Switching Materials, San Diego, USA, August 2001 in Solar and Switching Materials, ed Lampert, Granqvist and Lewis, SPIE, Bellingham WA USA, pp. 29-38.
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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 (lambda) approximately 0.7 micrometers , 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.

Journal Articles

Smith, G.B., Gentle, A.R. & Dybdal, K.L. 2013, 'Polymeric Mesh For Durable Infra-red Transparent Convection Shields: Applications In Cool Roofs And Sky Cooling', Solar Energy Materials and Solar Cells, vol. 115, no. NA, pp. 79-85.
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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.
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, pp. 051119-1-051119-5.
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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
Smith, G.B. 2012, 'Green Nanophotonics', Journal of Nanophotonics, vol. 6, no. 1, pp. 1-19.
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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. Op
Smith, G.B., Castro Aguilar, J.L., Gentle, A.R. & Chen, D. 2012, 'Multi-parameter Sensitivity Analysis: A Design Methodology Applied To Energy Efficiency In Temperate Climate Houses', Energy And Buildings, vol. 55, no. NA, pp. 668-673.
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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
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 (LSC's) 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.
Gentle, A.R., Aguilar, J.L. & Smith, G.B. 2011, 'Optimized cool roofs: Integrating albedo and thermal emittance with R-value', Solar Energy Materials and Solar Cells, vol. 95, 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 a, thermal emittance E, and sub-roof R-value, must be considered. An accurate contribution of night sky cooling, and hence humidity and total down-welling atmospheric radiation is needed. A systematic analysis of the contribution of a roof to average cooling load per day and to peak load reductions is presented for a temperate climate zone over 6 cooling months using an hour-by-hour analysis. Eighteen 3-parameter sets (a,E,R) demonstrate the over-riding importance of a high a, while sensitivity to R-value and E drops away as albedo rises. Up-front cost per unit reductions in peak demand or average energy use per day always rises strongly as R rises unless albedo is low. A moderate R similar to 1.63 is superior to high R unless a roof is dark, or winter heating demand is high. We indicate briefly why the roof typically does not present a dominant influence on average winter heating needs in most temperate zones, enhancing the benefits of cool roofs.
Smith, G.B. 2011, 'Commentary: Environmental nanophotonics and energy', Journal of Nanophotonics, vol. 5, pp. 050301-1-050301-5.
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.
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, pp. 1-8.
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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.
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).
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.
Smith, G.B. & Earp, A.A. 2010, 'Metal-in-metal localised surface plasmon resonance', Nanotechnology, vol. 21, no. 1, pp. 1-8.
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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.
Earp, A.A. & Smith, G.B. 2010, 'Metal Nanoparticle Plasmonics Inside Reflecting Metal Films', Applied Physics Letters, vol. 96, no. 24, pp. 1-3.
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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
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 mu m and 13 mu 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 degrees C below ambient, under a 45 degrees aperture lined with shiny aluminium, can achieve a net output power near 135W m(-2) under a clear sky.
Bai, H., Cortie, M.B., Maaroof, A.I., Dowd, A.R., Kealley, C.S. & Smith, G.B. 2009, 'The preparation of a plasmonically resonant VO2 thermochromic pigment', Nanotechnology, vol. 20, no. 8, pp. 1-9.
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Vanadium dioxide (VO2) undergoes a reversible metal-insulator transition, normally at similar to 68 degrees C. While the properties of continuous semi-transparent coatings of VO2 are well known, there is far less information available concerning the potential use of discrete VO2 nanoparticles as a thermochromic pigment in opaque coatings. Individual VO2 nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO2 nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO2 powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties.
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. 031505, pp. 1-15.
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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. Tc drops as doping level increases, but does not depend on grain size. The observed phase transition undergoes a remarkable qualitative shift as the applied field goes from optical to low frequencies. The expected insulator to metal transition is found at optical frequencies, but at low frequencies an insulator-to-insulator transition occurs. Optical switching at both T < Tc and T > Tc is nearly independent of doping level and grain size. In contrast dc properties in both phases are sensitive to both factors. The band gaps from optical and dc data differ, and densities of states change with doping level. Such behaviour can arise if there is a transient phase change. The way doping and grain size can support such a phase is discussed. Only individual nanograins need to switch phases coherently to explain data, not the whole sample. Resistance as a function of composition across the transition was derived using effective medium compositional analysis of optical data in the hysteresis zone. The percolation thresholds are not at the usual Tc values.
Smith, G.B. 2009, 'Guest editorial, Nanostructured Thin Films', Journal of Nanophotonics, vol. 3, no. NA, pp. 1-4.
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Nanostructured thin films (NSTF) are providing enormous scope for advances in optical, electronic and optoelectronic engineering and underpinning key developments in nanoscience. From a scientific perspective they embody numerous challenges and opportunities: covering concepts, models, growth, structure and characterization. Emerging technologies which depend on NSTF include photonics and plasmonics for information processing and communications; semiconductor and molecular electronics; display and lighting; single molecule bio-sensing, proteomics, advanced medical therapies, diagnostics and imaging; large scale, low cost approaches to energy efficiency, renewable energy and energy storage; and material surfaces which are durable, self-repair, self-clean, and have the ability to sense, change color, and to modulate reflectance, transmittance or thermal emittance.
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
Gentle, A.R. & 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, pp. 1-5.
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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 T-c, but a metallic and plasmonic optical response. All samples optically switch ov
Swift, P.D., Lawlor, R., Smith, G.B. & Gentle, A.R. 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 rectangu
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, vol. 78, no. 16, pp. 1-1.
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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 th
Gentle, A.R., Maaroof, A.I. & Smith, G.B. 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 -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. - 2007 Elsevier B.V. All rights reserved.
Gentle, A.R., 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, pp. 025202-025209.
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Thin films of vanadium dioxide with grain size smaller than 60nm have a metallic phase with excellent plasmonic response,but their dc resistivity falls as temperature rises to values above the metal-insulator transition. At the transition optical switching is complete, but the switch in dc resistance is incomplete. In the metallic phase nanograin and large grain samples have similar values of both plasma frequency and relaxation rate. However, plasmonic response in nanograins is stronger due to the absence of a low energy interband transition foun din large grain fims. Conductivity rises with thermal activation energy of 108 meV, which is well below that in rthe semiconductor phase. Possible mechanisms for non-metal' like dc behaviour in this plasmonic system are briefly discussed. They include fluctuations which are coherent in nanograins but incoherent for larger grains. Nanoscale systems seem preferable for optical switching applications and large grain structures for dc switching work.
Smith, G.B., Maaroof, A.I. & Gentle, A.R. 2007, 'Homogenized Lorentz-Drude optical response in highly nanoporous conducting gold layers produced by de-alloying', Optics Communications, vol. 271, no. 1, pp. 263-268.
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Nanoporousgold films produced by de-alloying AuAl2 with void densities between 45% and 65% retain high infra-red reflectance and good conductivity. They act optically like a homogenous Lorentz-Drude metal with a unique wp and an inter-band transition energy unchanged from that of dense gold. The link between wp and wp in dense gold is found using a cimplification of the Bergmann expansio for permittivity valid at infra-red wavelengths. The carrier relaxation time of the effective metal becomes the actual relaxation time in the Au netowork and the complex refractive indices (n.k) found using normal incidence spectrophotometry and oblique incidence ellipsometry agree closely with each other. The single pole approximation for the ratio wp/wp in the infra-red allows estimates of void content and the apparent shift in carrier effective mass. It is then possible to model with no adjustable parameters, the full UV-visible-NR spectral response, giving excellent agreemtn with data. A range of films with these properties are presented.
Maaroof, A.I., Gentle, A.R., 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 fora conductor at their thickness and their flat spectral response at visible and near infrared wavelengths is not metal like. We derive effective optical constants which become plasmonic at wavelengths between 1.8 and 4um for f from 72 to 87%. This onset is much longer than that in bulk gold. For void densities below 70% the onset of plasmonic behaviour is much closer to the dense material. A simple test is implemented to test for surface plasmon polaritons (SPPs) under illumination. The more porous films show no evidence of SPP, while the less porous films display weak evidence. Thus by tailoring void content in these nanostructures we can taolor the onset of efefctive plasmonic response across a wide range from 0.8 to 4 um and emittance from around0.9 down to low values. An effective uniform metal response is this found in the presence o fsurface nanostructure without the interface absorption found in dense gold layers with sturctured surfaces.
Maaroof, A.I., Cortie, M.B., Gentle, A.R. & 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 behaviour. We found that it was necessary to include an additional special oscillator centered at 1.4eV in order to model the unusual spectral response. This is quite unlike bulk gold, which can be mideled using a standard two-oscillator LD model.
Earp, A.A., Smith, G.B. & Franklin, J.B. 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
Smith, G.B., Gentle, A.R. & Maaroof, A.I. 2007, 'Metal-Insulator nanocomposites which act optically like homogeneous conductors', Journal of Nanophotonics, vol. 1, pp. 013507-1-013507-15.
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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 wp*. This applies at wavelengths where the Bergman spectral function F for permittivity varies sufficiently slowly with wavelength. wp* 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 wp*(f) and meff*(f) using the Maxwell Garnett (MG) and Bruggemann (BR) models for spheres and aligned ellipsoids. In the BR case meff*(f) at the percolation concentration is singular. Example wp* 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 polarisation direction of incident light.
Cortie, M.B., Maaroof, A.I., 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 init
Deller, C.A., Franklin, J.B. & 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 is presentedd. Previous ray-tracing approaches have been designed for undoped cylindrical light guides, where a propagating ray is deviated bu total internal reflection only. These geometrical principles are extended and further developed into a method of ra-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 lgith guides are given, as an exampled of an application of the described ray-tracing method.
Swift, P.D., Smith, G.B. & Franklin, J.B. 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.
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
Jonsson, J.C., Smith, G.B., Deller, C.A. & 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
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
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 ring
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 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.
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, pp. 124314-1-124314-8.
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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
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, pp. 335-339.
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Deller, C.A., Smith, G.B. & Franklin, J.B. 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.
Jonsson, J.C., Smith, G.B. & Niklasson, G. 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.
Jonsson, J.C., Karlsson, L., Nostell, P., Niklasson, G. & 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.
Earp, A.A., Smith, G.B., Swift, P.D. & Franklin, J.B. 2004, 'Maximising the light output of a Luminescent Solar Concentrator', Solar Energy, vol. 76, pp. 655-667.
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Smith, G.B. 2004, 'Materials and systems for efficient lighting and delivery of daylight', Solar Energy Materials And Solar Cells, vol. 84, pp. 395-409.
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Smith, G.B., Ford, M.J., Masens, C.D. & Muir, J.G. 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 NanohouseTM 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 NanohouseTM therefore serves as a powerful vehicle for demonstrating nanotechnologies. One of the major energy-efficient components of the NanohouseTM 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
Earp, A.A., Smith, G.B., Franklin, J.B. & Swift, P.D. 2004, 'Optimisation of a three-colour luminescent solar concentrator daylighting system', Solar Energy Materials and Solar Cells, vol. 84, pp. 411-426.
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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 trad 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 trad. 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
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
Smith, G.B., Gentle, A.R., Swift, P.D., Earp, A.A. & Mronga, N. 2003, 'Coloured paints based on coated flakes of metal as the pigment, for enhanced solar reflectance and cooler interiors: description and theory', Solar Energy Materials And Solar Cells, vol. 79, no. 2, pp. 163-177.
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Smith, G.B., Gentle, A.R., Swift, P.D., Earp, A.A. & Mronga, N. 2003, 'Coloured paints based on iron oxide and silicon oxide coated flakes of aluminium as the pigment, for energy efficient paint: optical and thermal experiments', Solar Energy Materials And Solar Cells, vol. 79, no. 2, pp. 179-197.
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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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Window samples with a LaB6 nanoparticle-doped polymer laminate were tested for their performances in the reduction of solar heat gain. The near-infrared absorption, caused by the excitation of surface plasmons, was modeled using an average ellipsoid approach, including a size-induced broadening of the Drude part of the dielectric function. The resonance positions are well reproduced by this method and the size effect broadens the bulk resonance to an extent observed in the sample spectra. Additional broadening and spectral features observed in the absorption of the samples are attributed to shape and orientation effects.
Smith, G.B., Jonsson, J.C. & Franklin, J.B. 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
Smith, G.B. 2002, 'Nanoparticle physics for energy, lighting and environmental control technologies', Materials Forum, vol. 26, pp. 20-28.
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Smith, G.B., 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. N/A, 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.
Smith, G.B., 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, 'A New Type of TiN Coating Combining Broad Band Visible Transparency and Solar Control', Renewable Energy, vol. 22, pp. 79-84.
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Production of thin lms 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 lms the onset of a rise in reection can be pushed out almost into the near infra red. It then becomes possible to produce lms 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.M., Hossain, M., Swift, P.D. & Luther, M.B. 2001, 'Optical Characterisation of Materials and Systems for Daylighting', Renewable Energy, vol. 22, pp. 85-90.
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The measurement of BRTF (Bi-directional re Pectance 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 di use 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., Earp, A.A., Stevens, J., Swift, P.D., McCredie, G.M. & Franklin, J.B. 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.
Kirkup, L., Bell, J., 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 el
Ditchburn, R. & Smith, G.B. 1992, 'A 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 inte