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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
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 NTRSDate not supplied

Space-qualified Chalcogenide Materials through ISS MISSE Exposure —From Property to Application

In March 2021, twenty-four samples of various phase change materials (PCMs - Ge2Sb2Te5, Ge2Sb2Se4Te1, and Sb2Se3) along with metasurface optical components comprised of these PCMs, were delivered to the International Space Station (ISS) as part of the Materials International Space Station Experiment (MISSE-14) test campaign [1]. Although PCMs have previously been noted for their resilience to various forms of radiation [2], they had not been tested in a realistic space environment until this exposure campaign with joint NASA and MIT collaboration. During the six-month total open exposure time in low earth orbit (LEO), high-resolution cameras scanned and captured photographs of the samples to detect changes as a function of time along with on-orbit measured temperature, UV radiation, total atomic oxygen fluence, and total ionizing radiation doses. The samples were returned to NASA Langley Research Center in March 2022 for post-flight characterization. This duplicated the preflight characterization (i.e., material composition and crystallinity that limits switching speed, index contrast, loss, etc.) conducted before launch. The space sector has witnessed tremendous growth within the past decade—not only from government agencies but also entrants from the private sector. Future growth in the capabilities of Earth observation, deep space, and planetary surface missions using miniaturized spacecraft platforms can only be sustained by innovations in the design of remote sensors and other sub-systems. Active metasurface optics with enhanced tunability and reconfigurability continues to redefine the boundaries of optical science [3]. The introduction of PCM technology and associated optical devices will help to accelerate the adoption of new architectures for reduced size, weight, power, and cost (SWaP-C) platforms in space.Here we introduce results obtained from the MISSE-14 mission related to space qualification of PCM-based optic devices and constituent materials. We then discuss our recent work developing active integrated photonic devices and metasurface optics based on PCMs for space applications. This includes tunable and reconfigurable optical metasurface devices to support NASA space communication and LIDAR applications. PCMs are quickly becoming interesting photonics materials but questions related to mission suitability remain, particularly in regard to key properties like figures-of-merit (FOM, Δn/Δk), glass forming temperatures, and phase transition speeds. This talk will describe efforts to afford researchers the ability to have access to cost-effective data on exposure-induced changes to PCM fundamental physical and optical properties to assess their utility for space applications. The MISSE-14 sample exposure campaign allows a complete understanding of the limitations of the PCMs for various space-based electronic and optoelectronic applications.

Chalcogenide Phase change material↗
NASA NTRS1982

Design, fabrication and evaluation of chalcogenide glass Luneburg lenses for LiNbO3 integrated optical devices

Optical waveguide Luneburg lenses of arsenic trisulfide glass are described. The lenses are formed by thermal evaporation of As2S3 through suitably placed masks onto the surface of LiNbO3:Ti indiffused waveguides. The lenses are designed for input apertures up to 1 cm and for speeds of f/5 or better. They are designed to focus the TM sub 0 guided mode of a beam of wavelength, external to the guide, of 633 nm. The refractive index of the As2S3 films and the changes induced in the refractive index by exposure to short wavelength light were measured. Some correlation between film thickness and optical properties was noted. The short wavelength photosensitivity was used to shorten the lens focal length from the as deposited value. Lenses of rectangular shape, as viewed from above the guide, as well as conventional circular Luneburg lenses, were made. Measurements made on the lenses include thickness profile, general optical quality, focal length, quality of focal spot, and effect of ultraviolet irradiation on optical properties.

Wood, V. E.↗
NASA NTRS1986

Vapor transport processes of Ge-chalcogenides under normal and reduced gravity conditions

Experimental and theoretical studies of the GeSe-GeI4 system revealed the multicomponent, multireaction nature of this system and the existence of a diffusion boundary layer; they also yielded equations for the prediction of diffusion limited mass transport rates. Vapor transport and crystal growth experiments of the GeSe-GeI4 and GeSe-Xe systems on earth and in a microgravity environment demonstrated the effects of convection and of microgravity on mass flux and crystal morphology. The surface and bulk morphology of GeSe crystals obtained for both systems in microgravity is considerably improved relative to ground-based specimens. Unexpected crystal growth phenomena were observed for the GeSe-Xenon system on recent Shuttle flights.

Wiedemeier, H.↗
NASA NTRS1987

Effect of the microstructure on the thermoelectric properties of polycrystalline lanthanum chalcogenides

Small amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline gamma-La(3-x)X4 (X-S, Te; X in the range of 0 to 1/3). Microscopic examination by SEM of hot pressed La(3-x)Te4 samples has revealed from 1-5 vol. pct of La2O2Te, an amount which is not detected by X-ray powder diffraction measurements. This amount of La2O2Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10 to 75 percent below the electron concentration calculated for single phase La(3-x)Te4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons. These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.

Lockwood, A.↗
NASA NTRS2001

Vapor Growth of Binary and Ternary Chalcogenides in Preparation for Microgravity Experiments

In the bulk crystal growth of some technologically important semiconducting chalcopyrites, such as ZnTe, CdS, ZnSe and ZnS, vapor growth techniques have significant advantages over melt growth techniques due to the high melting points of these materials. The realization of routine production of high-quality single crystals of these semiconductors requires a fundamental, systematic and in-depth study on the PVT growth process and crystal growth by vapor transport in low gravity offers a set of unique conditions for this study. Previously, two reasons have been put forward to account for this. The first is weight-related reductions in crystal strain and defects. These are thought to be caused by the weight of the crystals during processing at elevated temperatures and retained on cooling, particularly for materials with a low yield strength. The second, and more general, reason is related to the reduction in density-gradient driven convection. The PVT crystal growth process consists of essentially three processes: sublimation of the source material, transport of the vapor species and condensation of the vapor species to form the crystal. The latter two processes can be affected by the convection caused by gravitational accelerations on Earth. Reductions in such convection in low gravity is expected to yield a nearly diffusion-limited growth condition which results in more uniform growth rates (on the microscopic scale) and hence greater crystalline perfection and compositional homogeneity. The reduction of convective contamination by performing flight experiments in a reduced gravity environment will help to understand the relation between fluid phase processes (growth parameters) and defect and impurity incorporation in grown crystals.

Su, C.↗
NASA NTRS2001

Vapor Growth of Binary and Ternary Chalcogenides in Preparation for Microgravity Experiments

In the bulk crystal growth of some technologically important semiconducting chalcopyrites, such as ZnTe, CdS, ZnSe and ZnS, vapor growth techniques have significant advantages over melt growth techniques due to the high melting points of these materials. The realization of routine production of high-quality single crystals of these semiconductors requires a fundamental, systematic and in-depth study on the PVT growth process and crystal growth by vapor transport in low gravity offers a set of unique conditions for this study. Previously, two reasons have been put forward to account for this. The first is weight-related reductions in crystal strain and defects. These are thought to be caused by the weight of the crystals during processing at elevated temperatures and retained on cooling, particularly for materials with a low yield strength. The second, and more general, reason is related to the reduction in density-gradient driven convection. The PVT crystal growth process consists of essentially three processes: sublimation of the source material, transport of the vapor species and condensation of the vapor species to form the crystal. The latter two processes can be affected by the convection caused by gravitational accelerations on Earth. Reductions in such convection in low gravity is expected to yield a nearly diffusion-limited growth condition which results in more uniform growth rates (on the microscopic scale) and hence greater crystalline perfection and compositional homogeneity. The reduction of convective contamination by performing flight experiments in a reduced gravity environment will help to understand the relation between fluid phase processes (growth parameters) and defect and impurity incorporation in grown crystals.

Su, Ching-Hua↗
NASA NTRS2002

Development of Chemically and Thermally Robust Lithium Fast Ion Conducting Chalcogenide Glasses

In this project, a new research thrust into the development of an entirely new class of FIC glasses has begun that may lead to a new set of optimized thin-film lithium ion conducting materials. New chemically robust FIC glasses are being prepared that are expected to exhibit unusually high chemical and electrochemical stability. New thermally robust FIC glasses are being prepared that exhibit softening points in excess of 500 C which will dramatically expand the usable operating temperature range of batteries, fuel-cells, and sensors using such electrolytes. Glasses are being explored in the general compositional series xLi2S+ yGa2S3 + (1-x-y)GeS2. Li2S is added as the source of the conductive lithium ions. GeS2 is the base glass-forming phase and the trivalent sulfides, Ga2S3, is added to increase the "refractoniness" of the glass, that is to significantly increase the softening point of the glass as well as its chemical stability. By optimizing the composition of the glass, new glasses and glass-ceramic FIC materials have been prepared with softening points in excess of 500 C and conductivities above 10(exp -3)/Ohm cm at room temperature. These latter attributes are currently not available in any FIC glasses to date.

Martin, Steve W.↗
NASA NTRS2016

Growth Mechanism of Nanowires: Binary and Ternary Chalcogenides

Semiconductor nanowires exhibit very exciting optical and electrical properties including high transparency and a several order of magnitude better photocurrent than thin film and bulk materials. We present here the mechanism of nanowire growth from the melt-liquid-vapor medium. We describe preliminary results of binary and ternary selenide materials in light of recent theories. Experiments were performed with lead selenide and thallium arsenic selenide systems which are multifunctional material and have been used for detectors, acousto-optical, nonlinear and radiation detection applications. We observed that small units of nanocubes and elongated nanoparticles arrange and rearrange at moderate melt undercooling to form the building block of a nanowire. Since we avoided the catalyst, we observed self-nucleation and uncontrolled growth of wires from different places. Growth of lead selenide nanowires was performed by physical vapor transport method and thallium arsenic selenide nanowire by vapor-liquid-solid (VLS) method. In some cases very long wires (>mm) are formed. To achieve this goal experiments were performed to create situation where nanowires grew on the surface of solid thallium arsenic selenide itself.

Singh, N. B.↗
NASA NTRS2016

Growth Mechanism of Nanowires: Ternary Chalcogenides

In the past two decades there has been a large rise in the investment and expectations for nanotechnology use. Almost every area of research has projected improvements in sensors, or even a promise for the emergence of some novel device technologies. For these applications major focuses of research are in the areas of nanoparticles and graphene. Although there are some near term applications with nanowires in photodetectors and other low light detectors, there are few papers on the growth mechanism and fabrication of nanowire-based devices. Semiconductor nanowires exhibit very favorable and promising optical properties, including high transparency and a several order of magnitude better photocurrent than thin film and bulk materials. We present here an overview of the mechanism of nanowire growth from the melt, and some preliminary results for the thallium arsenic selenide material system. Thallium arsenic selenide (TAS) is a multifunctional material combining excellent acousto-optical, nonlinear and radiation detection properties. We observed that small units of (TAS) nanocubes arrange and rearrange at moderate melt undercooling to form the building block of a nanowire. In some cases very long wires (less than mm) are formed. Since we avoided the catalyst, we observed self-nucleation and uncontrolled growth of wires from different places.

Singh, N. B.↗
NASA NTRS2018

Electrostatic Levitation of ZBLAN and Chalcogenide Glasses

Heavy Metal Fluoride Glasses have been studied for approximately 35 years. ZrF4-BaF BaF2-LaF3-AlF3-NaF (ZBLAN) showed the most promise as an optical fiber. It transmits IR out to approximately 5 microns. Applications: fiber amplifiers, lasers and nuclear radiation resistant links. Intrinsic and Extrinsic processes limit light propagation; Intrinsic: band gap absorption, Rayleigh scatter and multiphonon absorption; Extrinsic: impurities such as rare-earth ions and crystallite formation. Theoretical loss coefficient is 0.001 dB/km. This loss has not been achieved to date due to intrinsic and extrinsic processes. ZBLAN fibers obtained from Infrared Focal Systems, Inc. and Bell Laboratories. Fibers were stripped of coating and placed in evacuated quartz ampoules. These fibers were first flown on NASA’s KC135 Reduced Gravity Aircraft. KC135 produces approximately 25 sec. of reduced gravity per parabola. One week of flights led to approximately 200 total parabolas. Fibers were heated to the crystallization temperature during reduced gravity and compared to unit gravity for the same amount of time. Fibers were also flown on board the Conquest sub-orbital rocket. This flight gave approximately 6.5 minutes of reduced gravity.

Tucker, Dennis S.↗
NASA NTRS2011

Nanoscale Deformable Optics

Several missions and instruments in the conceptual design phase rely on the technique of interferometry to create detectable fringe patterns. The intimate emplacement of reflective material upon electron device cells based upon chalcogenide material technology permits high-speed, predictable deformation of the reflective surface to a subnanometer or finer resolution with a very high degree of accuracy. In this innovation, a layer of reflective material is deposited upon a wafer containing (perhaps in the millions) chalcogenic memory cells with the reflective material becoming the front surface of a mirror and the chalcogenic material becoming a means of selectively deforming the mirror by the application of heat to the chalcogenic material. By doing so, the mirror surface can deform anywhere from nil to nanometers in spots the size of a modern day memory cell, thereby permitting realtime tuning of mirror focus and reflectivity to mitigate aberrations caused elsewhere in the optical system. Modern foundry methods permit the design and manufacture of individual memory cells having an area of or equal to the Feature (F) size of the design (assume 65 nm). Fabrication rules and restraints generally require the instantiation of one memory cell to another no closer than 1.5 F, or, for this innovation, 90 nm from its neighbor in any direction. Chalcogenide is a semiconducting glass compound consisting of a combination of chalcogen ions, the ratios of which vary according to properties desired. It has been shown that the application of heat to cells of chalcogenic material cause a large alteration in resistance to the range of 4 orders of magnitude. It is this effect upon which chalcogenidebased commercial memories rely. Upon removal of the heat source, the chalcogenide rapidly cools and remains frozen in the excited state. It has also been shown that the chalcogenide expands in volume because of the applied heat, meaning that the coefficient of expansion of chalcogenic materials is larger than 1. In this innovation, chalcogenidebased cells are addressed (as though they are a memory), and heated and cooled according to well-established criteria. In doing so, the exact size of chalcogenide cell deformation is known and predictable; therefore, the deformation of the reflective surface is, likewise, known and predictable. Control electronics can also be implemented so that a closed-loop feedback can be maintained. Changing the contents of the chalcogenide memory cells can compensate for any change in environmental effects that might cause a change in optical path. This real-time control provides significant control and stability in use conditions.

Strauss, Karl F.↗
NASA NTRS1995

Preparation of Thermoelectric Materials From Melts

A review of melt preparation techniques is presented covering necessary phase relationships, synthesis/alloying and crystal growth of thermoelectric materials. The processes described require the knowledge of composition-temperature or composition- temperature-pressure phase diagrams. This knowledge enables the selection of the appropriate method of preparation, apparatus design and processing. The materials, from a technological point of view, will be roughly divided into three categories: low temperature materials (group V chalcogenides based on Bi2Te3), middle temperature materials (group IV chalcogenides based on PbTe) and high temperature materials (Si-Ge solid solutions). All known methods of preparation from melts are described, and a comparative analysis is given. (complete abstract)

thermoelectrics↗
NASA NTRS1984

Infrared-Responsive Monolithic MOS Circuit

Lead chalcogenide photoresistors integrated with FET amplifiers. Circuit combines voltage divider containing lead chalcogenide photoresistor with FET source follower. Source and drain of FET p-doped regions in underlying n-type silicon wafer. All other structures formed at or deposited above original surface plane of wafer.

Jhabvala, Muzban D.↗
NASA NTRS1984

High Temperature Thermoelectric Energy Conversion

The electronic and thermal transport properties of the most promising material systems for high temperature thermoelectric energy conversion are discussed from a theoretical and experimental viewpoint. Rare earth chalcogenides and boron-rich borides are considered in terms of thermal conductivity and transport mechanisms. Rare earth chalcogenides are generally n-type semiconductors and boron-rich borides are generally p-type semiconductors.

Wood, C.↗
NASA NTRS1984

High-temperature thermoelectric energy conversion. II - Materials survey

The current status of materials research for high-temperature thermoelectric energy conversion is reviewed. Two general classes of materials show promise for high temperature figure of merit (Z) values, viz, the rare-earth chalcogenides and the boron-rich borides. The electronic transport properties of the rare-earth chalcogenides are explicable on the basis of degenerate or partially degenerate n-type semiconductors. Boron and boron-rich borides exhibit p-type hopping conductivity, with detailed explanations proposed for the transport differing from compound to compound. Some discussion is presented on the reasons for the low thermal conductivities in these materials. Also, ZTs greater than one appear to have been realized at high temperature in many of these compounds.

Wood, C.↗