High-quality transparent and heat-reflecting Indium-Tin-Oxide films were prepared by reactive electron-beam evaporation. The complex dielectric function was evaluated from spectrophotometric measurements in the 0.25-50-pm range. The optical data are discussed from a theoretical model which encompasses the contributions from free carriers, valence electrons, and phonons. It is found that ionized impurity scattering is the main damping mechanism of the free electrons.

Energy consumption can be reduced from room heating using coated architectural glass panes. With a system oxide/metal/oxide high transmittance in the visible as well as high reflectance in the thermal infrared can be achieved^2-7. This heat mirrors can be deposited economically by diode- and high rate sputtering. Of most interest are heat mirrors based on Cu, Ag and Au coatings. In the visible Au and Cu show a remarkable amount of absorptance which leads to a clear decrease in visible light transmittance. Best results are obtained with Ag based coatings. Ag is still high reflective even at the near U-V region. This part of re-flected energy can be converted to transmittance by a properly designed optical interference stack of the type oxide/metal/oxide. For a single pane an average value of visible light transmittance between 380 nm and 780 nm of 81 % is possible without loss of infrared reflec-tance at 8 4m below 90 % which corresponds to a low-emittance of 0.1. For this high quality a smooth growth of the Ag layer is necessary. Experiments have shown that a bombardement of the Ag layer with high energetic ions must be avoided as far as possible.

Films of indium oxide and indium oxide doped with tin have been produced by reactive planar magnetron sputtering of the pure metal and the alloy and from two metal sources simultaneously. In each case the oxygen partial pressure was controlled to give the highest sheet resistance in the oxide film which was deposited onto a plastic sheet transferred over a drum at ambient temperature. Films prepared under these conditions with the best properties for heat reflecting and visible transparent filters were found to be the oxide of the pure metal. A radio frequency discharge used in conjunction with the magnetron allowed the operating pressure to be considerably reduced, which allowed the preparation of titanium nitride films from a titanium metal target and the construction of simple metal and dielectric-metal-dielectric filters, which match theoretical predictions. A sandwich filter could be made from one titanium target by varying the active gas between oxygen and nitrogen to give a structure of: TiO₂ - TiN - Ti0₂.

Unique d.c. reactive sputtering process using a very thin layer of In/Sn alloy(10 wt% Sn) target, at high power levels hasAbeen used to prepare transparent conducting films of ITO with low resistivity (1.17 x 10 ' ohm.m), high optical transmission ("› 95%) and of high infra-red reflectivity (e,J90%) for applications as transparent windows in electro-optical devices and solar energy systems. No post-deposition annealing is required. Substrate heating is accomplished entirely by the ion-bombardment intrinsic to DC sputtering, rather than by using an auxilliary resistance heater. Optical, electrical and structural proper-ties of the films have been studied. The characteristic features of the ITO films are very low resistivity, high carrier density, high mobility, low temperature coefficient of resistivity and smaller grain size in comparison with pure indium oxide films. It was concluded from the thermal stability test that the contribution to the carrier density by tin is only a few percent to that created by oxygen.

A thin film, which reflects infra-red ray while transmits visible light, is discussed in a background of energy saving incandescent lamps. The film which consists of multi-layer Ti0₂-Si0₂ film reflects infra-red ray effectively and has a high heat resistance. This film is formed from organometallic solutions by dipping method. In order to carry out multi-layer coatings, the organometallic solutions are improved. A film on a substrate turns into a metalic oxide film having desired optical thickness and refractive index. The optical properties of this film and its application to tubular tungsten halogen lamps are discussed in this paper.

We report on coatings which exhibit both spectral and angular selectivity. These coatings are prepared by oblique electron-beam or resistive heating evaporation of Ge and Cr onto glass substrates. Transmittance measurements in the 0.35 - 20 pm range showed a remarkably high absorption in the solar spectrum combined with transparency in the infrared region. Typical results for a 140 nm thick chromium film deposited on aluminium or chromium substrate gave a solar absorptance value higher than 0.90 and a normal emissivity value of 5 to 12 % depending on the type of metal backing. These coatings were found to be stable in air at 250°C, which make them satisfactory for both flat plate and low concen-tration collectors producing low and medium grade heat. Thin films (-70 - 100 nm) showed interesting features when transmission measurements were made at various angles of incidence. They showed high transmission when rotated in one direction but low when rotated in the opposite direction, hence exhibiting an angular selectivity.

Windows and building envelopes with an externally variable light transmission can be used to reduce significantly heating and cooling loads. Thin film, large area electrochromic structures are conceptualized which would permit reversible aperture control through applica-tion of small dc electrical currents. The structures have the generalized geometry TEC/EC₁/FIC/EC₂/TEC, where TEC is a thin transparent electrical conductor, EC₁. and EC₂ are complementary electrochromic layers, and FIC is a fast ion conductor. Measurements of the optical properties of the polycrystalline electrochromic oxide H_xWO₃ show large increases in reflectivity on increasing x, an effect not pronounced in the more frequently investigated amorphous material. The variation of the optical constants with x are used to demonstrate the dominance of free electron scattering in determining the optical properties. It is therefore concluded that electrochromic windows based on polycrystalline electrochromic layers may be operated in a reflectivity mode, which has several important advantages over variable absorption operation.

Electrochromic thin film devices are in advanced stage of development for display applications. Another field of interest is the large area energy efficient window shutter systems for control of transmission and reflectivity. The important desired characteristics for such systems include wide operating temperature range and fast speed of electro-optical response. The use of an "aprotic" electrolyte and "oblique" deposition of WO, improve the operational temperature range and the speed of these systems respectively. A systematic study of the response time with the angle of deposition of WO, reveals that there is an optimum angle for which the response time improves by a factor of three as compared to WO, films deposited normally. The difference in the response times of the normally and the obliquely deposited WO, films is attributed to the morphological differences as shown distinctly by the optical and electron microscopic observations. Use of an oxygen free Li+ based electrolyte increases the operational temperature range, electrochemical stability and lifetime of cycling of these systems.

Coloring / bleaching processes of LixWO3 electrochrothismwere examined by means of emf, chronoamperometry, voltammetry and ac impedance measurements. Current-potential relation was found to be ohmic in the short time region and expressed by i=(Eapp-emf(x))/ R. Satisfactory fittings were obtained for chronoamperometry and voltammetry measurements on the basis of the assumption of diffusion-limited process with above i-E relation. It was elucidated from the detailed analysis of impedance that R was given by the summation of the resistances of solution, electrode, charge transfer and material transfer. It was newly found that diffusion coefficients for several WO3 films were in the range of 1.5 X 10^-9 to 3 x 10_-12 cm²,sec at 20°C and they were strongly dependent on water content in the electrolyte solution.

Substances that undergo dramatic changes in optical properties when subjected to changes in temperature, pressure, or magnetic field are the subject of growing interest to both basic and applied scientists. Possible applications of such optical switching materials range from dense optical information storage to switchable filters to components of integrated optical circuitry. Some switching materials are found among rare-earth compounds; they are denoted as mixed-valence, mixed-configuration, or fluctuating-valence compounds. More than fifty mixed-valence compounds were known as of 1980, and many more, including a large number of alloys, have been discovered since (Varma, 1976; Kaldis, 1983).

The potential of the sun as an energy resource cannot be overstated. A minute fraction of the solar energy striking the earth's surface could supply our present energy needs indefinitely. It is clean, readily available, and inexhaustible. It is truly our best natural source of energy.

The physical properties of TiO2 rutile n-type semiconductor as anode in photoelectrolytical cells have been widely investigated from many authors in order to explain the exhibited photoresponces. In this paper the attention is focused in particular to characterize by backscattering,PIXE (proton induced X-rays emission) ad X-rays diffraction analysis titanium surfaces oxidized at different temperatures in oxygen flux. Using a Schottky barrier model for the surface of the semiconductor in contact with the electrolyte the meaningful physical quantities like minority carrier diffusion length, barrier width and the quantum efficiency of cells result strongly dependent on oxidation temperature of the TiO2 electrode. The behaviour of these quantities is interpreted in terms of structural properties of anode, analyzed with the above mentioned methods. The possibility of application of a thin film in quantum size effects regime on the semi-conducting electrode in photoelectrolytical cells, is discussed.

Fluorescent planar concentrators have been discussed in the literature for about five years. The advantages of the system are the ability to concentrate both direct and diffuse light, and variability in transparency which offers the possibility of a manifold of hybrid applications. The best total efficiency measured for electrical conversion with a stack of two plates is 4 %, the highest energy concentration factor at the output edge was ten. Theoretical calculations of the limitations on the concentration factor are presented. The life-time of the total system could be improved, so the first commercial applications are now being planned.

An optical scanner for on-line analysis of defects in solar cells is described. A micro-computer is used to scan a He-Ne laser spot (5 to 25 pm diameter) over the solar cell in both X and Y directions. It also acquires 'Sc or Voc signal at each point in the area scanned and presents a map on an oscilloscope/X-Y recorder. For detailed analysis of a defective region, a fine scan is made and such cell parameters as recombination velocity and diffusion length around the defect region are calculated. The scanner has been used to study the spatial variations in the performance of single crystal and polycrystalline Si solar cells and thin film CdS/Cu₂S solar cells.

When alkali-borosilicate glasses are heat treated, they can be caused to phase separate. The silica and non-silica constituents are separated on a sub-microscopic scale. This enables small amounts of the non-silica phase to be chemically leached from the surface, which results in a graded reduction in the index of refraction near the surface. The index gradient can be controlled so that it leads to the most effective broad band, anti-reflection (A.R.) films known. At normal incidence, average reflection per surface can be kept well below 1% in the spectral region from .35 microns to 2.5 microns. Further, films produced by this method maintain their effectiveness even at incident angles up to 70 degrees. All these aspects; i.e., manufacturing method, spectral response and angular response, combine to make the leached gradient index A.R. treatment ideally suited to enhance the efficiency of linear trough solar collector systems. Such systems typically use borosilicate glass cover tubes over the absorber tubes to cut heat losses, but in the absence of A.R. treatment, reflective losses from the cover tubes can cut system output by about 7-8%. The leached A.R. surface eliminates reflective losses almost entirely. Exposure to the elements in an industrial environment for five (5) years has resulted in no degradation of the effectiveness of the leached A.R. surfaces. While the surface is somewhat sensitive to contamination by body oils because of its porous nature, once installed, the inherent chemical durability of the nearly pure silica leads to excellent long-term performance.

The development of highly transparent insulation materials is an important step in raising the efficiency of flat plate collectors and for passive use of solar energy in buildings. The problem in combining selective absorbers and honeycomb structures is that the radiation losses due to thermal emission of the material of the structure may be larger than the losses due to convection which are present without the structure. Therefore a thorough analysis of the different loss mechanisms has been made. There are two possibilities for overcoming these difficulties. The first is the use of materials with low absorptance in the infrared or with selective surfaces for the honeycomb structure. The second possibility is the use of highly IR-absorbing materials. In the latter case a selective absorber is not needed. Results from both approaches will be presented.

The clear sky can act as a heat sink. Cooling to low temperatures is possible with materials which are strongly emitting in the 8-13-μm band and non-absorbing elsewhere. In this paper we discuss the resource for radiative cooling and its implementation with thin solid films (Si00.6N0.2 coatings on Al) and with slabs of certain gases (C₂H₄, C₂H₄0, and NH3 backed by Al). Results are given on spectrophotometric infrared reflectance and transmittance, computed parameters which govern the predicted cooling performance, and some preliminary field tests.

The technique of Fourier transform infrared reflection-absorption (FTIR-RA) spectroscopy has been successfully adapted to studying bulk and interfacially activated photodegradation of several types of polymers on various metallic substrates. The technique enables quali-tative and quantitative study of photochemical reaction mechanisms and rates. A Controlled Environmental Exposure Chamber (CEEC), which permits collection of IR-RA spectra of the polymer/metal samples during their exposure to controlled spectral distributions of UV, temperatures, and gas mixtures, was built into the sample compartment of a Nicolet 7199 FTIR spectrophotometer. Surface analysis, gel permeation chromatography (GPC), UV spectro-scopy, and UV spectroradiometry were used to complement the FTIR-RA results.

This paper covers some preliminary results of research on the environmental responses of solar reflective surfaces. Although this paper provides information for the selection and evaluation of solar reflective surfaces in general, the work was performed for dish concentrator applications. Over a dozen types of glass, metallic and polymeric reflective surfaces have been exposed to the environment in Southern California. Data fran three locations were obtained: two sites at Pasadena and one site at Goldstone, near Barstow. Qualitative effects of contamination buildup are described. Evaluation of clean surfaces of the same three types of surfaces was performed under a separate program. Modeling of dust buildup and removal of worst-case data based upon six nationwide sites is presented and compared to Albuquerque, New Mexico soiling data. These data are useful in providing insight to determine the effects of soiling buildup to be expected in the design of concentrators at various geographical locations. They are also used to determine the method and frequency of washing requirements for optimum reflector performance.

The general design requirements of a portable reflectometer which can determine the specular reflectance properties of solar mirror materials is presented. Based on these considerations a prototype instrument was developed at Sandia National Labs. Because of the interest in this instrument, a competitive contract was placed with Devices and Services Company, Dallas, TX for the development of a commercial instrument based on the Sandia design. The operation and performance of this instrument are discussed, including the ac-curacy, stability, reproducibility, temperature response, and outdoor performance. Finally, limitations of this instrument and future developments in this area are briefly discussed.

We discuss and compare several photometric methods for the evaluation of optical constants of thin absorbing films. Optical constants of such films are frequently troublesome to assess with conventional photometric techniques. For the commonly used (T,R) method, where near normal transmittance T and reflectance R of a thin film on a transparent sub-strate are measured, specific problems occur when the real part n of the refractive index is of the same order of magnitude as the imaginary part k. By combining instead T and Rm, where Rm is the reflectance of the film on a metallized part of the substrate, we obtain the (T,Rm) method, which has a greatly increased sensitivity. It is further shown that the (T,Rmb) combination, where Rmb is the substrate side reflectance of the thin film with an optically thick metal overcoating, yields additional advantages. A detailed evaluation of the accuracy obtained for the (T,R), (T,R_m) and (T,R_mb) methods is presented.

Accepted limits of a/E for high temperature selective surfaces may be too pessimistic, primarily because absorptance has been over-emphasised from the point of view of low concentration optical collectors. Careful positioning of the exponential region of a modelled semiconductor-insular-metal (SIM) surface indicates values of a/E which are 3-5 times previous estimates.

An optical laminar composite is defined and a method for calculating its complex index of refraction is determined. This type of composite, along with composites of the mosaic type (Bruggeman composites) and the included-grain type (Maxwell Garnett composites), are then used to model the optical properties of graded cermets (metal/insulator composites) of platinum/alumina. The results of the modelling are compared to recent experimental data obtained in a selective absorber study, where the graded cermets were produced by alternating sputter-deposition of platinum and alumina. The comparison suggests that the intrinsic structural nature of the sputtered cermets cannot be described by a single com-posite model. The intrinsic structure appears to depend on position within the coating; that is, on proximity to the underlying substrate.

Conventional coloured stainless steel selective absorbing surfaces produced by the chemical oxidation of stainless steel in acidic solutions deteriorate at temperatures in excess of 250°C. The as-produced surface is porous and is normally sealed with an oxide of matching refractive index. The paper compared the optical properties of these surfaces with those where the sealing process has been replaced by a metal plating process. Attention has focussed on nickel and palladium filled surfaces. The variation of optical properties with process parameters is described. The thermal stability of conventional coloured stainless steel is compared with the palladium and nickel filled surfaces.

We discuss the importance of low emittance and temperature stability for solar-selective high-temperature coatings. We show experimentally that high stagnation temperatures can be achieved by reducing the coating emissivity below previously-obtained values. We have investigated amorphous hydrogenated carbon (a-C:H) and silicon-carbon alloy (a-Si_xCi_-x:H) films prepared by magnetically-enhanced glow discharge decomposition. In the latter case, we have prepared alloys from acetylene, ethylene and methane mixed with silane. We have shown by electron microprobe analysis that the atomic C/Si ratio in the film is the same as that in the gas. We show that both the emittance of a-C:H films and their high temperature stability can be enhanced by annealing in vacuum. The film properties change substantially in the first hour of heat treatment at 500°C, before stabilizing after about 24 hours. Thereafter, the properties do not change during a further 300 hours of heat treatment. The heat -stabilized films, when placed on copper substrates and used in non-concentrating systems, have been shown to yield stagnation temperatures up to 459°C in preliminary experiments. The a-Si_xC_1-x :H films investigated have the potential to provide lower emittance coatings than the a-C:H alloys which are currently employed in composite metal-amorphous semiconductor films. The use of silicon/carbon alloys also provides greater flexibility in grading profiles for the composite films, permitting greater control in the trade-off between high solar absorptance and low emissivity.

Oxidized copper surfaces have been prepared by chemical oxidation and their thermal stability has been investigated. Auger Electron Spectroscopy and optical reflectance measurements have been used to verify that the reduced solar absorption, that is the result of annealing, is due to a smoothing of the interface between the oxide layer and the base metal.

Molybdenum black solar selective absorbers have been deposited on galvanized steel and zinc-plated mild steel sheet by chemical conversion process. The high solar absorptance ( 0.88 ) and low thermal emittance ( 0.20 ) have been achieved for molybdenum films deposited on galvanized steel sheet at room temperature. In this paper we discuss the stability and dependence of selective properties on elevated temperature, temperature cycling and highly humid atmosphere. It is observed that the coatings do not degrade on annealing at 250°C in air upto 800 hours constantly. The selective properties remain almost constant on thermal cycling ( 600 times at 150°C ) and 98% humidity. The heat loss factor of the molybdenum black film coated absorbing surface has been calculated from the stagnation temperature measurements. The molybdenum black film coated absorbers achieve 141° C as compared to black painted absorber temperature 124°C under identical condition.s. It is concluded that the coatings produced by chemical conversion process are of appropriate quality for applications in solar appliances.

The conversion of radiation into heat is significantly improved by selective solar absorbers. When the only losses are radiative, the selectivity determines the stagnation temperature. Low emissivity and stability of the selective surface is a problem in high temperature applications. A new type of selective absorber in com-bination with the fluorescent concentrator is presented. Thin coatings working as interference layers on highly polished metal substrates give a high absorbtivity for the emitted fluorescent light, which has a high intensity over a narrow wavelength range. The very thin coating (< 500 nm) does not increase the emissivity of the metal substrate. Therefore the temperature dependence of the emissivity is determined by the metal alone. With a test collector, stagnation temperatures of 808 K were reached. Theoretical calculations and experimental results are given.