A dual-ion-beam-sputtering (DIBS) deposition system is used to deposit doped vanadium dioxide (V_1-xM_x0₂), where M is a dopant that decreases the transition temperature (T_t) from that of stoichiometric V0₂. The objective is to synthesize a material that will passively switch between a heat- transmitting-and a heat-reflecting-state at specific design temperatures. The technique is reactive ion beam sputtering of vanadium and a dopant (separate beams) in a well controlled atmosphere of Ar with a partial pressure of O₂. The films are deposited at elevated temperature (>700K) onto glass and sapphire substrates for spectrophotometric evaluation above and below T_t. The longer range goals of this research are to develop the material for: (1) thin film application to building glazings and (2) pigments for opaque wall coatings. The glazings will transmit and the walls will absorb solar energy when the V_1-xM_xO₂ temperature (T) is low (T<T_t). At T>T_t, both glazings and walls will reflect the solar infrared.

Spiroindolinonaphthoxazine compounds exhibit good photochromic effect and excellent light fatigue resistance in organic solvents as well as in plastics. Further improvement in the light fatigue resistance can be achieved by organo-nickel light stabilizers without impairing the photocolorability of the photochromic compound. The photochromic performance of a spiroindolinonaphthoxazine derivative in CAB including darkening and fading kinetics, temperature dependence, and fatigue characteristics is presented in detail.

Liquid crystal window has been considered as an optical shutter to control the solar energy. Investigation of various types of liquid crystal cells show that the phase change guest host (PCGH) type would be better to fabricate large size LC-cell. PCGH-cell with black dye has anormalous transmission dip near the threshold voltage for incoherent light in the range of 400 to 500nm. The anomalous dip is shown to come from scattering of incident light by the voltage induced inhomogeneities created during the phase transformation. 6μm thick 12.5cm x 12.5 cm LC-window has been fabricated using PCGH-LC mixture. The transmittance of the window could be controlled to an accuracy of less than 1% using IBM-PC computer.

Thin films of nickel oxide-nickel hydroxide are investigated to determine electrochromic switching properties. Crystalline nickel oxide films are synthesized by electrochemical deposition and by anodization of nickel electrodes. Electrochemical deposition using nickel sulfate-based chemistry is used to deposit films directly on doped tin oxide-coated glass. Spectral solar transmittance is obtained for films switched in liquid cells containing a KOH electrolyte. The solar transmittance (T_s) can be switched from T_s (bleached) = 0.73 to T_s (colored)= 0.35 for films with thickness of about 500 Å. Voltammetric data is correlated to known electrochemical processes for nickel electrodes. The nickel oxide films are chemically analyzed using a sputter-Auger microprobe and x-ray photoelectron spectroscopy. As a result of combined analysis, it was determined that these films transform from uncolored to colored states by the reversible transformation of nickel hydroxide Ni(OH)₂ to nickel oxyhydroxide NiOOH and that dehydrated films correspond chemically to NiO.

Windows with switchable electrochromic glazings are potentially useful for regulating solar input to building interiors. In this article, we describe the structure and operation of a proposed solid-state electrochromic glazing based on crystalline LixWO₃ (c-LiXWO₃) and a low coloration efficiency counter electrode material such as amorphous Nb₂O₅ (a-Nb₂O₅). The importance of reversibility in electrochromic glazing operation is emphasized, and optical switching experiments that demonstrate reversible lithium insertion/extraction in c-Li_xW0₃, a-Li_xWO₃, and a-Li_xNb₂O₅ are described. Additional optical switching experiments in tandem electrochromic cells comprised of c-Li_xWO₃/a-Nb₂O₅ and a-Li_xWO₃/a-Nb₂O₅ demonstrated the proposed design, indicating reversible optical switching over 500 and 200 complete cycles, respectively, without degradation. Optical data on the evolution of reflective and absorp-tive modulation in c-Li_xWO₃ are presented and solar attenuation results are used to demon-strate the advantage of using crystalline electrochromics to conserve daylighting during electrochromic window operation.

The results of recent research on each of the layers of a solid-state multilayer structure for electrochromic windows are reviewed. This includes a review of the requirements of the multilayer structure for building windows and especially the need to have an electrochemically balanced system. The results indicate that excess free electron scattering in polycrystalline W0₃ films (the electrochromic layer) is not only the source of lower than desired reflectivity modulation, but it is also the major source of higher than desired absorptivity modulation. Research on LiAlF₄ indicatesthat it is a viable candidate for the ionic conducting layer, being a good lithium ion conductor and a good electronic insulator. Finally, we have recently discovered that tin-doped and undoped In ₂0₃ films are mixed conductors, exhibiting lithium ion injection/ extraction. This is significant since such films could possibly serve in the dual capacity of counterelectrode and transparent conductor, thereby reducing the complexity, the technical problems, and the cost of electrochromic window assemblies.

This paper describes the fundamental properties of the transmissive electrochromic device. The device comprises of a semi-solid electrolyte and a WO₃ film sandwiched by a pair of electroconductive sheet glasses. The transmittance of the device can be arbitrarily controlled within the range from 80% to 10%. The response time was found to be greatly dependent on the size of device and the applied DC voltage. The life time for the repetitive operations is more than 10⁵ cycles. The devices have fairly good durability against the outdoor conditions. Based on the kinetic study on tungsten bronze and the analysis of equivalent circuit, the effects of the rate determining factors are discussed.

Multilayer, solid-state electrochromic coatings based on "amorphous" tungsten oxide (a-W03) are being evaluated for control of solar gain through windows. This paper summarizes recent progress at SERI in this effort. A typical electrochromic coating consists of indium-tin oxide (520 nm), a-W0₃ (410 nm), MgF, (170 nm) and gold (15 nm) all applied by vacuum deposition. Transmission electron diffraction of the a-WO₃ shows a very fine structure with short range order and an ill-defined grain structure on the order of 8 nm diameter. Optical measurements show two electrochromically active absorption bands in the coating, at least one of which can be attributed to small polaron absorption quite similar to that observed in crystalline WO₃ at low temperatures. Methods were developed for depositing electrochromic a-W0₃ by plasma enhanced, chemical vapor deposition. Apparatus for testing the cyclic durability of solid state electrochromic coatings has been designed and constructed.

Solid state electrochromic (EC) structure Au/W0₃/LiF/Au has been studied with different thicknesses of LiF electrolyte. The results indicate a dependence of EC behavior on humidity and electrolyte thickness. A simple theoretical model has been proposed to explain the coloration process.

This paper shows that brightness theorem and the various parameters influencing the holographic solar concentrator's efficiency request a perfect knowledge of the use of the H.S.C. in view to optimize the system.

In this report, we present the experience gained up-to-date in the development of holographic solar concentrators. The techniques used in the generation of high efficiency dielectric volume-holograms of the transmission type are presented in detail. These techniques facilitate the manufacturing of holographic lenses with diffraction efficiency in the order of 97%. In order to achieve the high efficiency, the research team has developed sensitizing and film development procedures for dichromated layers whose scattering losses are comparable to those of the unexposed gelatin layer. The manufacturing of the dichromated gelatin layers is performed in-house (30 x 40 cm²) and can easily be extended to large apertures. The layering procedure is a continuous process and is limited at present only by the travel of the motor-driven table top. The reproducibility of the film-thickness for a batch of manufactured 30 x 40 cm² holographic plates is better than ± 1 μm. The film-thickness variation of the gelatin film averaged over the entire surface of a holographic plate is in the order of 0.2 Pm/cm. Theoretical and experimental results are presented for some relevant parameters that control the diffraction efficiency of the concentrator. Emphasis is placed on the problems encountered when a multiple lens-system (stack) is generated in a single gelatin layer or in an integrated multi-layer hologram.

Tunable Lippmann Holowindows have been developed by NTS as a particular application for Broad-Band Lippmann Holograms investigated within Super High Efficiency (SHE) Holographic Technology. Those holograms can be tuned to be highly reflective (above 99%) in any part of the near UV, Visible and near IR. In particular, they can reflect all direct solar heat radiation and additionally, the near UV part of the solar spectrum that cannot be blocked by glass or acrylic. Additionally, they can be combined with conductive adhesives to create ideal cooling mirrors, with parameters much better than those of existing products. Therefore, they can create a new generation of high efficiency solar heat control windows whose rejection of adjusted parts of the solar spectrum still preserve high visible transmission (up to 87% for single glazing), and the near perfect (close to 100%) reflection of IR direct solar component. In the case of Tunable Lippmann Holowindows, it is possible to adjust independently the U-value, emittance and shading coefficient by the number of glazings, conductive adhesive thickness and hologram reflection, respectively. In other words, SHE Holographic Technology introduces to heat mirror engineering a new degree of freedom - separate near IR reflection coefficient.

Silvered polymers have been studied for possible mirror applications in concentrators for solar thermal systems. The polymeric mirrors were prepared by vacuum evaporating or dc-sputtering silver onto several candidate polymers for use as second surface mirrors. Specularities were measured at 7 and 15 mrad acceptance angles at 660 nm. The specularity of silvered polymers depends strongly on the topography and bulk properties of the polymer used. It is independent both of the deposition rate from 0.1 to 7 nm/s and from thermal evaporation and dc-sputtering processes. Silvered glass specularities are also independent of deposition rates from 0.1 to 45 nm/s and are typically 93% at 7 mrad. The specularity does not depend on the substrate temperatures during depositions for the range of 5° to about 100°C. In some cases, a metallic film was deposited onto the silver before mounting onto a Corning 7809 glass substrate. Inconel backing of films from 35 to 150 nm thick does not reduce the specularity of silvered polymers at 15 mrad, but does accelerate the degradation of the multilayer combination during accelerated or real-time weathering. After measuring the solar-weighted hemispherical reflectance and the second surface specularity at 660 nm for acceptance angles of 15 and 7 mrad, the silvered polymeric specimens were subjected to accelerated testing in a Weather-Ometer at 60°C, 80% relative humidity, and UV irradiation, or in a QUV at 40°C, UV irradiation, and condensation cycles. Real-time testing has also been carried out in the suburban Denver atmosphere. With exposure, all mirrors prepared show evidence for some or extensive optical and/or visual degradation. The relative durabilities of the various combinations studied are discussed in terms of the silvering method, polymer used, metallic backing for the silver, and adhesive used for mounting the silvered polymer onto a test substrate.

Fourier transform infrared (FT-IR) reflection-absorbance (RA) measurements have been used to characterize Ag-backed polyacrylonitrile (PAN) films and to study their photodegradation. The optical constants n and k for the polymers are determined in the mid-IR region, and the dependence of RA values on polymer functionality concentration as a function of film thickness calculated. The IR-RA values are nearly linear with the concentration of functionalities for PAN films of thicknesses up to 0.1 μm. Some oxidative photodegradation pathways have been proposed; with radiation of λ ≥ 250 nm, a polyimine structure is generated. A combination of 1.0% wt of Irganox 1010 and 0.5% wt of Irgastab 2002 in PAN films was found to significantly retard the photodegradation of the polymer without affecting the specularity of the PAN/Ag surface.

This paper reports on our evaluation and modification of polymeric glazings to protect silver mirrors. The mirrors were made using Corning 7809 glass as a substrate onto which a thin silver film is deposited. The modified polymeric films are then cast from solution onto the silver. The mirrors were characterized by measuring the hemispherical reflectance and the specular reflectance at 660 nm and selected acceptance angles (7.5 mrad or 3.5 mrad). The mirrors were exposed to environmental degradation using accelerated weathering devices and outdoor exposure. Empirical evidence has demonstrated that poly-methylmethacrylate is a stable polymer in a terrestrial environment, but the polymer does not provide adequate protection for the silver reflector. The crucial role in degradation played by ultraviolet (UV) light is shown by several experimental results. We have demonstrated that UV stabilizers added to the polymer improve the weatherability of mirrors. The relative effectiveness of different stabilizers will be discussed in terms of the weathering modes, retention of optical properties, and effectiveness of the additives. The process for silver deposition influences the reflectance of silver mirrors, and the optical properties depend on subtle relationships between the metallization and the dielectric (polymeric) films that are in contact with the silver.

Very thin gold layers were produced on glass by evaporation with and without simultaneous ion bombardment. Electron microscopy showed that films with thicknesses below a certain magnitude - which decreased with increasing ion flux - had a non-uniform (network) structure. Optical properties were measured by spectrophotometry in the 0.3-50-μm range. w Uniform films were consistent with the Drude theory with an anomalously large frequency dependence of the relaxation energy. Non-uniform films displayed characteristic plateaus in the near-infrared transmittance. This feature, which is conducive to high solar transmittance, can be explained from effective medium theories based on the film structure. Our results are important for the development of improved noble-metal-based infrared-reflectors for energy efficient windows.

Electrical and optical measurements on r.f. sputtered cdIn₂O₄ films show that this compound is a wide-band-gap semiconductor. Coatings have been prepared which have high visible transmission and high infrared reflectivity. The optical properties of these samples come close to those of the best known semiconductor heat mirror materials.

We prepared In₂O₃:Sn coatings by reactive dc magnetron sputtering. At a substrate tem-perature of 300-400°C and a deposition rate of ~ 0.8 nm/s we could obtain transparent films with - 4% normal luminous absorptance, - 88% normal thermal reflectance, and - 3 x 10^-4 Ωcm electrical dc resistivity. Spectrophotometric measurements were used to evaluate the complex dynamic resistivity. It could be reconciled with the Gerlach-Grosse theory for a gas of free electrons damped by ionized impurity scattering.

We formulate a detailed theoretical model for the optical properties of heavily dopQd oxide semiconductors. The complex dielectric function is expressed as ε = 1+χ^VE+χ^FC+χ^PH, where the χs are susceptibilities due to valence electrons (VE), free carriers (FC), and polar optical phonons (PH). We obtained χ^VE by including a wavelength-shifted Urbach tail of the direct semiconductor transition. χ^FC was calculated from the Gerlach-Grosse theory and accounting for screening of point-like ions within the Random Phase Approximation. Pseudo-potential scattering as well as exchange and correlation effects in the electron gas were considered. χ^PH was specified through emipirically determined damped Lorentz oscillators. The model was applied to In₂0₃:Sn coatings and used to compute their integrated luminous, solar and thermal properties. Optimization of thickness and electron density yielded single coatings on glass with 78% normal solar transmittance and 20% hemispherical thermal emittance.

The efficiency of conversion of concentrated solar energy can be improved by separating the solar spectrum into portions matched to specific photoquantum processes and the balance used for photothermal conversion. The basic approaches of spectrally selective beam splitters are presented. A detailed simulation analysis using TRNSYS is developed for a spectrally selective hybrid photovoltaic/photothermal concentrating system. The analysis shows definite benefits to a spectrally selective approach.

The efficiency of hybrid photothermal/photovoltaic energy conversion can be increased by separating the solar spectrum into portions matched to the photothermal and photovoltaic processes. Thin-film multilayer filters can implement this concept; five such filters consisting of all-dielectric or metal-dielectric layers have been designed. The transmission profile of each design is calculated by computer, considering dispersion, absorption, and angle of incidence effects. These profiles are compared and evaluated with respect to the desired spectral performance. The most successful candidate design is an optical minus filter consisting of Ti0₂, Zr0₂, and Si0₂. Results show very sharp selection of the targeted photovoltaic spectral region and low ripple in the transmission region outside the bandstop.

Various techniques have been proposed to convert solar energy to both electric power and heat in hybrid systems. Many of these approaches are designed to utilize spectral selectivity to improve the overall conversion efficiency. Examples include spectrally selective beamsplitters and arrangements of long-wave or short-wave-pass glass filters that divide the spectrum so that photon energies are roughly matched to the energies corresponding to the solar-cell bandgaps or to efficient photothermal convertors. This paper describes the analysis of liquid optical filters that have high transmittance in the visible spectrum and high absorptance in the infrared. These qualities make it possible to capture that portion of the spectrum useful to a quantum convertor, such as a photovoltaic cell, while channeling the "excess heat" of the photons with energies below the bandgap to a thermal convertor, thereby enhancing the overall conversion efficiency of the system. The preliminary studies show that spectral responses of the tested solutions (salts in water) are primarily influenced by the cation component of the salt solution. By changing the solutions and concentrations, a variety of spectrally selective filters can be tailored to match system requirements.

A new type of concentrating photovoltaic-photothermal solar conversion system with output cogeneration is presented. This technique, called total solar cogeneration (TSC), converts the total solar spectrum directly and cogenerates the output into three energy components: high-temperature heat (HT), photovoltaic electricity (PV), and low-temperature heat (LT). A specially designed heat-mirror with a beam-splitting technique is used to direct a selected portion of the solar spectrum to a HT evacuated-tube receiver. This high-grade heat transfer is optimized, while effectively maintaining the integrity of the photovoltaic conversion efficiency. High-current A.S.E.C. silicon solar cells (nominally 18.3% efficient at 28°C and 35x) are used. An analysis of heat-mirror transmittance profiles has led to an optimized theoretical parametric model profile, that in a TSC system is capable of delivering HT heat with 39% efficiency, while reducing PV efficiency by only 3.4%. In an experimental TSC concentrating module using a dielectric-Au-dielectric multilayer heat-mirror with optical losses, the projected output is HT heat (150°-250°C) at 17.8% efficiency, 12 V d.c. PV electricity at 9.5%, and LT heat (50°-70°C) at 41.9%, with a total cogenerated output efficiency of 69%.

N-silicon photoanodes have been protected against photocorrosion, for use in photo-assisted water electrolysis photoelectrochemical cells, by chemically depositing a thin film of manganese oxide on the surface. Current-potential characteristics of the electrodes have been measured in 0.5 M K₂SO₄ solution and in 0.2 M NaOH solutions. The onset potential for photocurrent in these electrolytes occur at + 1.1 V and + 0.56 V (vs NHE), respectively. The occurrence of photocurrent due to the photoevolution of oxygen was confirmed by pH dependence of onset potential and the appearance of gas bubbles on the electrode surface. When used in 0.5 M K₂SO₄ solution, at ~ 1.1 mA.cm^-2 photocurrent density, the electrode has shown complete stability, for continuous illumination of ~ 650 hours. The surface analysis of the electrode surface shows that manganese in the manganese oxide is present in + 3 state. The use of electrode for oxygen evolution in aqueous solution changes the Mn₂0₃ to MnO (OH) on the surface without affecting the bulk composition.

The thermal oxidation of Titanium foils is one of the most used techniques for the prepation of TiO₂ - rutile polycrystalline films, exhibiting a good quantum efficiency when used as photosensitive electrodes in photoelectrolytical cells (PEC). Such technique offers several advantages among which the economicity of the process and the possibility to control the uniformity and the thickness of the oxidized layer, even when large surfaces are treated. Since in the current literature different indications are given on the parameters relative to the Titanium thermal treatment, to get the semiconducting oxide, the aim of the present work was to carry out a systematic experimental investigation on the photoelectrochemical behaviour of Titanium surfaces oxidized at different temperatures and for different periods of oxidation^1÷6. In particular the spectral quantum yield exhibited by photoelectrolytical cells has been studied in correlation with the oxidation process parameters of the anode.

Thin films of indium doped CdS have been deposited by spray pyrolysis on Sn0₂-coated and plain glass substrates. The films on Sn0₂-coated substrates showed lower sheet resistances than those deposited on plain glass substrates. Photoelectrochemical studies with annealed Sn0₂-coated CdS films in 1M NaOH-0.1M Na₂S-0.1M S electrolyte showed an open-circuit voltage V_oc = 0.51 V and short-circuit current density, J_sc= 0.82 mA.cm^-2. The forward dark J-V characteristic showed Jo = 4.4 x 10^-6A.cm^-2 and ideality factor, n = 3.25. Mott-Schottky plots revealed a flat-band potential, V_fb = 1.7 V (SCE) and a donor density, N_D = 9.68 x 10¹⁸ cm^-3. The spectral response of photocurrent indicated a peak response at a wavelength of 500 nm. Intensity dependence of Voc showed a (log I_L)² dependence in conformity with Reiss theory, while Jsc varied linearly with intensity with a slope of 0.8. Surface modification with Zn²⁺ions resulted in enhancement of both V_oc and J_sc from 0.47 V and 0.37 mA. cm^-2 before modification to 0.61 V and 0.63 mA.cm^-2 after modification respectively.

Double Surface Solar Cell has a potential performance to reduce cost per watt for photovoltaic application. Pre-experiment by using two solar cells with back-to-back configuration was investigated. With combination of reflecting mirrors and tracking mechanism, the output gain of 1.8 was measured. The symmetrical structure of Double Surface Solar Cells is proposed and designed withiti the technical limitation of our facilities.

Bulk intrinsically selective absorbers are interesting for solar energy applications as a replacement for more complex thickness sensitive coatings. However, research in this field has not been very fruitful so far. Only ZrB₂ has proven to be a good candidate material. For this reason, the development of bulk intrinsic absorbers has received relatively little attention during the last decade. Materials which have hardly been studied so far in relation to solar energy conversion are the transition metal (TM) alloys. In this paper, we will show that some of these alloys have interesting optical properties, which makes them potential candidates for application as intrinsic absorbers.

The reflectivity spectra of sputtered zirconium nitride, carbide and carbonitride thin films have been studied. The data are interpreted by means of their electronic structure and by the nature of the bonding. The influence of nitrogen and carbon concentrations on the materials is qualitatively understood. Auger electron spectroscopy has been made on the carbide films. The KLL carbon Auger transitions show structures characteristic of the nature of the bonding : carbide or graphite-like. Although no good solar absorber is reported here, these studies show that, by adjusting the carbon and nitrogen contents, the optical profile of ternary compounds of transition metal can be tailored in a wide range between those of the binary compounds, so that the elaboration of a material for photothermal conversion of solar energy is not an impossible challenge.

Recent solar central receiver designs emphasize direct absorption receiver. (DAR) concepts primarily because of their ability to absorb high flux densities. An attractive design utilizes molten salt as the transport/storage fluid, which is pumped to the receiver and allowed to flow over a high-temperature absorber surface. As the salt runs down the absorber surface in a thin film, concentrated solar flux heats the salt to 9000C, either directly (blackened fluid) or by convective heat transfer with the irradiated absorber (clear fluid). The feasibility of such a design depends on the optical efficiency of the absorber/fluid combination. The optical properties of candidate absorber materials and transport fluids are therefore required at appropriate elevated temperatures. Because such salts can be extremely reactive at high temperatures, it is important to measure optical properties as a function of exposure history of the salt/absorber. Optical characterization of a clear molten carbonate salt (Li₂CO₃-Na₂CO₃-K₂CO₃ ternary eutectic) and a high-temperature metal alloy (Inconel 600) has been carried out at elevated temperatures using a recently developed integrating sphere solar spectrometer. Reflectance measurements of oxidized Inconel 600 alone and covered with several thicknesses of molten salt have been made. Measurements were also made of the reflectance of Inconel 600 samples that had been exposed to molten salt under high cyclic temperatures.

As part of the Solar Thermal Technology Program, the direct absorption of sunlight by free-falling particles inside a cavity receiver is being evaluated. The objective of the on-going optical properties measurement program is to obtain information to be used as input to radiation transfer models for prediction of receiver performance. Instrumenta tion and data analysis techniques have been developed to determine both the angular scattering properties and the scattering and absorption components of the extinction coefficient of candidate materials. This report summarizes the measurement procedures and presents data for an ion-doped alumina spheroid, Masterbeads®, manufactured by Norton Chemical Company. This material exhibits good optical absorption properties over the solar insolation spectrum and favorable thermal and mechanical properties for temperatures up to 1000°C. Scattering and extinction measurements were performed at 632.8 nm in a falling curtain geometry of one-particle nominal thickness. Data were obtained over a range of mass flow rates and particle areal densities. Photographic documentation of curtain particle density enabled calculation of mean particle scattering and absorption loss components in the absence of multiple-particle optical interactions. Prediction of optical extinction properties at other wavelengths is anticipated to be straightforward using spectral hemispherical reflectance measurements on bulk samples. Additional scattering and extinction data were obtained on transparent glass microspheres for comparison and as a verification of the measurement apparatus and procedures.

An experimental system to measure the diffuse reflectance of a particulate sample over the wavelength range of 300 to 2500 nm at elevated temperatures up to 1000°C has been developed and implemented. A description of the experimental apparatus and measurement procedures, as well as optical reflectance data for the Masterbeadse, are presented. Using the high temperature measurement system, the diffuse reflectance of Masterbeads® changed by less than 1% for sample temperatures from 150°C to 930°C. However, after heating a sample for three hours at 1000°C in air, the solar absorptance measured at room temperature decreased from an initial value of 0.93 to 0.89.

The Solid State Radiative Heat Pump (SSRHP) concept is introduced. It offers the potential to pump infrared radiation--for heating and cooling--with high second law efficiency. In particular, some of the limitations of Peltier-effect heat pumps can be circumvented. Two approaches for constructing SSRHP devices are described. In one approach the device is a large-area p-n junction, similar to an IR (light) emitting diode. In the second approach one uses orthogonal electric and magnetic fields to alter equilibrium carrier concentrations of electrons and holes near the crystal surface, altering the IR emission due to electron-hole recombination radiation. This phenomenon is usually termed galvanomagnetic luminescence (GML). Either approach can be used to make radiative heat pumps. Materials suitable for SSRHP devices are narrow-bandgap semiconduc-tors with direct bandgaps in the range of 0.03-0.3 eV for room temperature operation.

The design and fabrication of a highly insulating window glazing is being studied at SERI. Computer aided design analyses indicate that an all glass, edge sealed vacuum window with spherical glass interpane spacers and a low emittance, coating,on one internal surface could exhibit a thermal conductance of less than 0.6 W/m²K (thermal resistance, R > 10°F ft h/Btu). Cost effective means of mass-producing such a glazing have been explored. A CO₂ laser has been used to produce a continuous, leak tight welded glass perimeter at 580°C, and this process appears to be a promising approach. However, at this temperature in vacuum, few low-emissivity coatings retain their desirable properties. Systemmatic measurements were made on tin oxide (fluorine doped) and indium-tin oxide low-e coatings. The indium-tin oxide was shown to be improved by vacuum heating. The ratio of solar weighted transmittance to emittance (313 K black-body weighted), a measure of performance in this application, is shown to have a sharply defined maximum at a coating sheet resistance of approximately 5 ohms per square in both of these oxide semiconductor coatings.

The sol-gel process uses metal alkoxides of network forming cations, such as Si, B, or Al, in alcohol/water solutions to form glass-like, polymeric networks in liquid solution. Thin films are formed by depositing the solution on a substrate by spinning, dipping or spraying. When the film is then heated to moderate temperatures (400-500°C), dense glass films or stable porous films are obtained.

A Post Magnetron Sputter concept employing a cylindrical internally cooled target (cathode) is described. The use of an internal, rotating, permanent magnetic field resulting in 360° utilisation of the target material is outlined. Computer controlled horizontal and vertical movement of the cathode assembly facilitates the coating of contoured substrates which may be glass, acrylic or polycarbonate. Deposition of different metals is easily achieved by changing the cathode or covering it with a suitable sheath material. The design of the cathode results in economic utilisation of the target material, which is particularly important when sputtering expensive metals such as gold. In addition to the deposition of metallic films, such as stainless steel or chrome, reactive sputtering may be undertaken by the introduction of a reactive gas into the vacuum chamber. In this way metal oxide, sulphide or nitride layers may be deposited according to the requirements of the layer structure. Specific optically-active oxides such as indium tin oxide are easily deposited in a uniform film and the formation of multilayer coatings for sun protective and heat rejecting applications is practicable. Indeed, a complete process may be undertaken without removing the substrate from the chamber; merely by adding or changing the reactive gas present.

A state-of-the-art, high-temperature integrating sphere spectrometer has been fabricated and characterized. The liquid-cooled sphere is combined with a furnace designed for a maximum specimen temperature of 1200°C. The spectrometer is capable of measuring the spectral, diffuse, and hemispherical reflectance and transmittance over the wavelength range of 0.35-2.5 micrometers. Chopped white light from a high pressure xenon arc-lamp is introduced into the sphere, alternately reflected from the sphere wall and reflected from or transmitted through the specimen, spectrally resolved by a monochromator, and focused onto a two-color Si/PbS detector. Data are sampled at wavelengths corresponding to equal energy bands of the terrestrial solar distribution and are graphically displayed. Data acquisition and hardware module commands are computer controlled. The sphere and light collecting optics can be rotated about the horizontal optical axis of the monochromator so that the specimen port is at the top (0°), side (90°), or bottom (180°) of the sphere. This allows optical characterization of a variety of materials relevant to high-temperature solar energy applications to be carried out by rotating the instrument into a desired orientation. For example, in the 0° ("look up" at the sample) position, reflectance and transmittance of molten salt in a furnace-heated cell can be measured without salt vapor entering the sphere. At 90°, a vertical wall of falling sand particles can be characterized. In the 180° ("look down") position, the optical properties of solids such as ceramics, metal alloys, or powders can be ascertained.