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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Double-Diffusive Convection During Growth of Halides and Selenides

Heavy metal halides and selenides have unique properties which make them excellent materials for chemical, biological and radiological sensors. Recently it has been shown that selenohalides are even better materials than halides or selenides for gamma-ray detection. These materials also meet the strong needs of a wide band imaging technology to cover ultra-violet (UV), midwave infrared wavelength (MWIR) to very long wavelength infrared (VLWIR) region for hyperspectral imager components such as etalon filters and acousto-optic tunable filters (AO). In fact AOTF based imagers based on these materials have some superiority than imagers based on liquid crystals, FTIR, Fabry-Perot, grating, etalon, electro-optic modulation, piezoelectric and several other concepts. For example, broadband spectral and imagers have problems of processing large amount of information during real-time observation. Acousto-Optic Tunable Filter (AOTF) imagers are being developed to fill the need of reducing processing time of data, low cost operation and key to achieving the goal of covering long-wave infrared (LWIR). At the present time spectral imaging systems are based on the use of diffraction gratings are typically used in a pushbroom or whiskbroom mode. They are mostly used in systems and acquire large amounts of hyperspectral data that is processed off-line later. In contrast, acousto-optic tunable filter spectral imagers require very little image processing, providing new strategies for object recognition and tracking. They are ideally suited for tactical situations requiring immediate real-time image processing. But the performance of these imagers depends on the quality and homogeneity of acousto-optic materials. In addition for many systems requirements are so demanding that crystals up to sizes of 10 cm length are desired. We have studied several selenides and halide crystals for laser and AO imagers for MWIR and LWIR wavelength regions. We have grown and fabricated crystals of several materials such as mercurous chloride, mercurous bromide, mercurous iodide, lead chloride lead bromide, lead iodide, thallium arsenic selenide, gallium selenide, zince sulfide zinc selenide and several crystals into devices. We have used both Bridgman and physical vapor transport (PVT) crystal growth methods. In the past have examined PVT growth numerically for conditions where the boundary of the enclosure is subjected to a nonlinear thermal profile. Since past few months we have been working on binary and ternary materials such as selenoiodides, doped zinc sulfides and mercurous chloro bromide and mercurous bromoiodides. In the doped and ternary materials thermal and solutal convection play extremely important role during the growth. Very commonly striations and banding is observed. Our experiments have indicated that even in highly purified source materials, homogeneity in 1-g environment is very difficult. Some of our previous numerical studies have indicated that gravity level less than 10-4 (-g) helps in controlling the thermosolutal convection. We will discuss the ground based growth results of HgClxBr(1-x) and ZnSe growth results for the mm thick to large cm size crystals. These results will be compared with our microgravity experiments performed with this class of materials. For both HgCl-HgBr and ZnS-ZnSe the lattice parameters of the mixtures obey Vagard's law in the studied composition range. The study demonstrates that properties are very anisotropic with crystal orientation, and performance achievement requires extremely careful fabrication to utilize highest figure of merit. In addition, some parameters such as crystal growth fabrication, processing time, resolution, field of view and efficiency will be described based on novel solid solution materials. It was predicted that very similar to the pure compounds solid solutions also have very large anisotropy, and very precise oriented and homogeneous bulk and thin film crystals is required to achieve maximum performance of laser or imagers. Some of the parameters controlling the homogeneity such as thermos-solutal convection driven forces can be controlled in microgravity environments to utilize the benefits of these unique materials.

Singh, N. B.↗
NASA NTRS2017

Design of Multifunctional Materials: Chalcogenides and Chalcopyrites

There is a strong need for developing multifunctional materials to reduce the cost of applied material without compromising the performance of the detectors, devices and sensors. The materials design, processing, growth and fabrication of bulk and nanocrystals and fabrication into devices and sensors involve huge cost and resources including a multidisciplinary team of experts. Because of this reason, prediction of multifunctionality of materials before design and development should be evaluated. Chalcogenides and chalcopyrites are a very exciting class of materials for developing multifunctionality. Materials such as Gallium selenide GaSe and zinc selenide ZnSe have been proven to be excellent examples. GaSe is a layered material and very difficult to grow in large crystal. However, it's ternary and quaternary analogs such as thallium gallium selenide TlGaSe2, thallium gallium selenide sulfide TlGaSe2-xSs, thallium arsenic selenide Tl3AsSe3, silver gallium selenide AgGaGe3Se8, AgGaGe5Se12 and several others have shown great promise for multifunctionality. Several of these materials have shown good efficiency for frequency conversion (nonlinear optical NLO), electro-optic modulation, and acousto-optic tunable filters and imagers suitable for the visible, near-infrared wavelength, mid wave infrared (MWIR), long wave infrared (LWIR) and even up to Tera hertz wavelength (THW) regions. In addition, this class of materials have demonstrated low absorption coefficients and power handling capability in the systems. Also, these crystals do not require post growth annealing, show very large transparency range and fabricability.

Singh, N. B.↗
NASA NTRS2023

Optical Characteristics of Radiated Multifunctional Optical Materials

The performance of optical and electronic materials, and devices are affected significantly in space due to exposure from high energy radiations. We have been investigating the effect of -ray radiations on multifunctional binary and ternary selenide and halide crystals. These materials have shown excellent performance for the wavelength conversion in MWIR and LWIR regions, acousto-optics, and great potential for radiation detection. Crystals with high Z materials such as thallium, mercury and lead based compounds have great potential for the development of a variety of devices and components suitable for space applications. We will report on the characteristics of several halides including mercurous halides (Hg2X2, X= Cl, Br, I), Thallium mercury iodide (Tl4HgI4) and thallium arsenic selenide and thallium gallium selenide, and ternary selenides. These crystals, synthesized with high purity source materials, will be evaluated by studying optical characteristics and measuring resistivity after exposure to a 137Cs -ray source.

Radiation↗
NASA NTRS1968

Guidance and control research

Guidance and control research - Josephson junction memory elements, frequency response of thin film thermal detectors, gallium selenide barrier gate, and photoconductor metal contacts

Source record↗
NASA NTRS1966

Cuprous selenide and sulfide form improved photovoltaic barriers

Photovoltaic barriers formed by depositing a layer of polycrystalline cuprous sulfide or cuprous selenide on gallium arsenide are chemically and electrically stable. The stability of these barrier materials is significantly greater than that of cuprous iodide.

Source record↗
NASA NTRS2021

Design of ZnSe QPM for Wide Transparency Sensing and Laser Applications

ZnSe has been a great choice for the rare-earth and transition metal doping to develop lasers. It is an excellent materialfor variety of optical applications due to wide transparency range, good fabricability and very low optical absorptionsimilar to other selenides. NASA Marshall Space Flight Center has developed large crystals using physical vapordeposition (PVD) doped with transition metals for lasing. GaAs based quasi-phase matched structures have a lot oflimitations including difficulty of frequency conversion from available high power lasers. We are developing Si- andGaAs- based templates and using microfabrication process to deposit ZnSe using physical vapor transport (PVT)method. Experimental results of the fabrication of templates and growth of ZnSe on templates will be presented.

Epitaxial↗
NASA NTRS1975

Electrical characterization of GaAs single crystal in direct support of M555 flight experiment

The exploration of several nondestructive methods of electrical characterization of semiconductor single crystals was carried out during the period ending May 1974. Two methods of obtaining the microwave skin depth, one for the mapping flat surfaces and the other for analyzing the whole surface of small single crystal wafers, were developed to the stage of working laboratory procedures. The preliminary 35 GHz data characterizing the two types of space-related single crystal surfaces, flat slices of gallium arsenide and small wafers of germanium selenide, are discussed. A third method of nondestructive mapping of donor impurity density in semiconductor surfaces by scanning with a light beam was developed for GaAs; its testing indicates reasonable precision at reasonable scan rates for GaAs surfaces at room temperature.

Castle, J. G.↗
NASA NTRS1975

Electrical characterization of GaAs single crystal in direct support of M555 flight experiment

An exploration of several nondestructive methods of electrical characterization of semiconductor single crystals was carried out. Two methods of obtaining the microwave skin depth, one for mapping flat surfaces and the other for analyzing the whole surface of small single crystal wafers, were developed to the stage of working laboratory procedures. The preliminary 35 GHz data characterizing the two types of space related single crystal surfaces, flat slices of gallium arsenide and small wafers of germanium selenide, are discussed. A third method of nondestructive mapping of donor impurity density in semiconductor surfaces by scanning with a light beam was developed for GaAs; its testing indicates reasonable precision at reasonable scan rates for GaAs surfaces at room temperature.

Castle, J. G.↗
NASA NTRS1986

Low-Resistivity Zinc Selenide for Heterojunctions

Magnetron reactive sputtering enables doping of this semiconductor. Proposed method of reactive sputtering combined with doping shows potential for yielding low-resistivity zinc selenide films. Zinc selenide attractive material for forming heterojunctions with other semiconductor compounds as zinc phosphide, cadmium telluride, and gallium arsenide. Semiconductor junctions promising for future optoelectronic devices, including solar cells and electroluminescent displays. Resistivities of zinc selenide layers deposited by evaporation or chemical vapor deposition too high to form practical heterojunctions.

Stirn, R. J.↗
NASA NTRS1987

ZnSe Films in GaAs Solar Cells

ZnSe increases efficiency and conserves material. Two proposed uses of zinc selenide films promise to boost performance and reduce cost of gallium arsenide solar cells. Accordingly ZnSe serves as surface-passivation layer and as sacrificial layer enabling repeated use of costly GaAs substrate in fabrication.

Kachare, Ram H.↗
NASA NTRS2005

Inorganic Photovoltaics Materials and Devices: Past, Present, and Future

This report describes recent aspects of advanced inorganic materials for photovoltaics or solar cell applications. Specific materials examined will be high-efficiency silicon, gallium arsenide and related materials, and thin-film materials, particularly amorphous silicon and (polycrystalline) copper indium selenide. Some of the advanced concepts discussed include multi-junction III-V (and thin-film) devices, utilization of nanotechnology, specifically quantum dots, low-temperature chemical processing, polymer substrates for lightweight and low-cost solar arrays, concentrator cells, and integrated power devices. While many of these technologies will eventually be used for utility and consumer applications, their genesis can be traced back to challenging problems related to power generation for aerospace and defense. Because this overview of inorganic materials is included in a monogram focused on organic photovoltaics, fundamental issues and metrics common to all solar cell devices (and arrays) will be addressed.

Hepp, Aloysius F.↗
NASA NTRS1974

Skylab experiments on semiconductors and alkali halides

The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.

Lundquist, C. A.↗