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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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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Optical Properties of Ar Ions Irradiated Nanocrystalline ZrC and ZrN Thin Films

Thin nanocrystalline ZrC and ZrN films (less than 400 nanometers), grown on (100) Si substrates at a substrate temperature of 500 degrees Centigrade by the pulsed laser deposition (PLD) technique, were irradiated by 800 kiloelectronvolts Ar ion irradiation with fluences from 1 times 10(sup 14) atoms per square centimeter up to 2 times 10(sup 15) atoms per square centimeter. Optical reflectance data, acquired from as-deposited and irradiated films, in the range of 500-50000 per centimeter (0.06–6 electronvolts), was used to assess the effect of irradiation on the optical and electronic properties. Both in ZrC and ZrN films we observed that irradiation affects the optical properties of the films mostly at low frequencies, which is dominated by the free carriers response. In both materials, we found a significant reduction in the free carriers scattering rate, i.e. possible increase in mobility, at higher irradiation flux. This is consistent with our previous findings that irradiation affects the crystallite size and the micro-strain, but it does not induce major structural changes.

ZrN↗
NASA NTRS1981

Defect chemistry and characterization of (Hg, Cd)Te

Single crystal samples of phosphorus doped Hg sub 0.8 Cd sub 0.2 Te were anneald at temperatures varying from 450 C to 600 C in various Hg atmospheres. The samples were quenched to room temperature from the annealing temperatures. Hall effect and mobility measurements were performed at 77 K on all these samples. The results indicate the crystals to be p type for a total phosphorus concentration of 10 to the 19th power/cu cm in all the samples. The hole concentration at 77 K increases with increasing Hg pressures at 450 C and 500 C contrary to the observation in undoped crystals. Also, at low Hg pressures the concentration of holes in the phosphorus doped crystals is lower than in the undoped crystals. The hole concentration in all the samples is lower than the intrinsic carrier concentration at the annealing temperatures. The hole mobility in the doped crystals is similar to that in the undoped crystals. A defect model according to which phosphorus behaves as a single acceptor interstitially, occupying Te lattice sites while it acts as a single donor occupying Hg lattice sites was established. Equilibrum constants established for the incorporation of all the phosphorus species explain the experimental results

Vydyanath, H. R.↗
NASA NTRS1986

Model verifies design of mobile data modem

It has been proposed to use differential minimum shift keying (DMSK) modems in spacecraft-based mobile communications systems. For an employment of these modems, it is necessary that the transmitted carrier frequency be known prior to signal detection. In addition, the time needed by the receiver to lock onto the carrier frequency must be minimized. The present article is concerned with a DMSK modem developed for the Mobile Satellite Service. This device demonstrated fast acquisition time and good performance in the presence of fading. However, certain problems arose in initial attempts to study the acquisition behavior of the AFC loop through breadboard techniques. The development of a software model of the AFC loop is discussed, taking into account two cases which were plotted using the model. Attention is given to a demonstration of the viability of the modem by an approach involving modeling and analysis of the frequency synchronizer.

Davarian, F.↗
NASA NTRS1990

Dissociation and recombination of positive holes in minerals

The formation mechanisms are described of positive holes - electronic defects in the O2 sublattice - with attention given to detecting the positive surface charge of minerals with these holes. Charge distribution analysis (CDA) is presented which measures dielectric polarization in an inhomogeneous field. CDA can be applied to the detection of the peroxide/superoxide functionality caused by positive holes on the surface. It is demonstrated with obsidian that the measurements provide data on O(-) mobility as a function of surface-charge carrier density and on O(-) generation as a function of temperature.

Freund, Friedemann↗
NASA NTRS2005

Impurity Studies of Cd(0.8)Zn(0.2)Te Crystals Using Photoluminescence and Glow Discharge Mass Spectroscopy

Cd(1-x)Zn(x)Te semiconductor crystal is a highly promising material for room temperature x- and gamma-ray detector applications because of its high resistivity, long carrier lifetime, and relatively high hole and electron mobilities. This paper reports the investigation of the impurities in several Cd(1-x)Zn(x)Te (x = 0.20) crystals grown using the vertical Bridgman method under a Cd overpressure. The impurity concentrations were measured using glow discharge mass spectroscopy (GDMS). The energy states of the impurities were studied using photoluminescence (PL) spectroscopy at liquid helium temperature. The PL spectra showed a series of sharp high energy lines which are associated with free excitons and excitons bound to impurities as donors and acceptors in the crystals. The impurities also contributed to donor-acceptor pair recombination. The correlation between the GDMS and PL results will be reported.

Su, Ching-Hua↗
NASA NTRS2011

Assessment of Durable SiC JFET Technology for +600 C to -125 C Integrated Circuit Operation

Electrical characteristics and circuit design considerations for prototype 6H-SiC JFET integrated circuits (ICs) operating over the broad temperature range of -125 C to +600 C are described. Strategic implementation of circuits with transistors and resistors in the same 6H-SiC n-channel layer enabled ICs with nearly temperature-independent functionality to be achieved. The frequency performance of the circuits declined at temperatures increasingly below or above room temperature, roughly corresponding to the change in 6H-SiC n-channel resistance arising from incomplete carrier ionization at low temperature and decreased electron mobility at high temperature. In addition to very broad temperature functionality, these simple digital and analog demonstration integrated circuits successfully operated with little change in functional characteristics over the course of thousands of hours at 500 C before experiencing interconnect-related failures. With appropriate further development, these initial results establish a new technology foundation for realizing durable 500 C ICs for combustion engine sensing and control, deep-well drilling, and other harsh-environment applications.

Neudeck, P. G.↗
NASA NTRS2003

High Electron Mobility in SiGe/Si n-MODFET Structures on Sapphire Substrates

For the first time, SiGe/Si n-Modulation Doped Field Effect Transistors (n-MODFET) structures have been grown on sapphire substrates. Room temperature electron mobility value of 1271 square centimeters N-sec at an electron carrier density (n(sub e) = 1.33x10(exp 12) per square centimeter)) of 1.6 x 10(exp 12) per square centimeter was obtained. At 250 mK, the mobility increases to 13,313 square centimeters/V-sec (n(sub e)=1.33x10(exp 12) per square centimeter)) and Shubnikov-de Haas oscillations appear, showing excellent confinement of the two-dimensional electron gas.

Mueller, Carl H.↗
NASA NTRS1989

Digital 8-DPSK Modem For Trellis-Coded Communication

Digital real-time modem processes octuple differential-phase-shift-keyed trellis-coded modulation. Intended for use in communicating data at rate up to 4.8 kb/s in land-mobile satellite channel (Rician fading) of 5-kHz bandwidth at carrier frequency of 1 to 2 GHz. Modulator and demodulator contain digital signal processors performing modem functions. Design flexible in that functions altered via software. Modem successfully tested and evaluated in both laboratory and field experiments, including recent full-scale satellite experiment. In all cases, modem performed within 1 dB of theory. Other communication systems benefitting from this type of modem include land mobile (without satellites), paging, digitized voice, and frequency-modulation subcarrier data broadcasting.

Jedrey, T. C.↗
NASA NTRS1978

A study and experiment plan for digital mobile communication via satellite

The viability of mobile communications is examined within the context of a frequency division multiple access, single channel per carrier satellite system emphasizing digital techniques to serve a large population of users. The intent is to provide the mobile users with a grade of service consistant with the requirements for remote, rural (perhaps emergency) voice communications, but which approaches toll quality speech. A traffic model is derived on which to base the determination of the required maximum number of satellite channels to provide the anticipated level of service. Various voice digitalization and digital modulation schemes are reviewed along with a general link analysis of the mobile system. Demand assignment multiple access considerations and analysis tradeoffs are presented. Finally, a completed configuration is described.

Jones, J. J.↗
NASA NTRS1972

Proposed semiconductor film improvement

Film grown in inert carriers (A, He, or N) displays low impurity, high mobility, and improved crystal structure. Annealing steps used in growing process improves film quality and allows utilization of film for Gunn and LSA devices.

Manasevit, H. M.↗
NASA NTRS2004

Stimulated Mid-Infrared Luminescence Experiment: Contribution to the Study of Pre-Earthquake Phenomena and UV Absorption by Interstellar Dust

The work performed under this proposal is based on the experimentally supported observation - or inference - that a small fraction of the oxygen anions in silicate minerals in igneous and high-grade metamorphic rocks on Earth may not be in the usual 2- oxidation state, O(sup 2-), but in a higher oxidation state, as O(sup -). If this is true, the same would likely apply to the fine dust that fills the diffuse interstellar medium. An (sup -) in a matrix of O(sup 2-) represents a defect electron in the valence band, also known as positive hole or p-hole for short. When two O(sup -) combine, they undergo spin-pairing and form a positive hole pair, PHP. Chemically speaking a PHP is a peroxy bond. In an oxide matrix a peroxy bond takes the form of a peroxy anion, O2(sup 2-). In a silicate matrix it probably exists in the form of peroxy links between adjacent [SiO4] tetrahedral, O3Si00\SiO3. From a physics perspective a PHP is an electrically inactive point defect, which contains dormant electronic charge carriers. When the peroxy bond breaks, p-hole charge carriers are released. These p-holes are diffusively mobile and spread through the O 2p-dominated valence band of the otherwise insulating mineral matrix.

Freund, Friedemann↗
NASA NTRS2019

Molten Target Sputtering: Non-Conventional Method for High Mobility Si0.15Ge0.85 Growth at 500°C

Since electrons travel over 100 times faster in Silicon-Germanium (SiGe) than in pure Si due to the low effective masses associated with Ge and SiGe-based devices continue to replace Si-based solid-state electronic devices. SiGe thin film on sapphire was successfully grown at 890°C, using a magnetron sputtering system within heteroepitaxial framework. However, SiGe growth at 890oC is a costly and difficult process to produce as a uniform wafer for semiconductor device manufacturing due to thermal soak times, and geometric thermal shadowing from the wafer holder. To leverage the semiconducting capabilities of SiGe, novel processing techniques for SiGe film growth with decreased thermal loading are required. This paper introduces the Molten Target Sputtering (MTS) method that produces high mobility SiGe on sapphire below 500°C. This non-conventional method has the advantage of high kinetic energy, high-energy latency, and high flux density of sputtered atoms by combining benefits of both magnetron sputtering and thermal evaporation. For the MTS method, a 1~2 mm (depth and width) ring-shaped groove was cut between the center magnet and surrounded by electromagnets creating a circular cavity between the copper plate and source target materials that melt the target material. The SiGe grown from the MTS shows continuous morphology and 99.7% single crystal Si0.15Ge0.85 films. The Hall electron mobilities of the Si0.15Ge0.85 are 456 sq. cmV(exp -1)s(exp -1) and 123.9 sq. cmV(exp -1)s(exp -1) at 5.59 x 10(exp 18) cubic cm and 3.5 x 10(exp 20) cubic cm carrier concentration at 22.38°C, respectively. This is approximately 5.5 times higher than that of Si and similar to the Ge value at equivalent carrier concentrations and temperatures.

High mobility SiGe↗
NASA NTRS1988

A study on the co- and adjacent channel protection requirements for mobile satellite ACSSB modulation

Samples of speech modulated by narrowband frequency modulation (NBFM) (cellular) and amplitude companded single sideband (ACSSB) radios were subjected to simulated co- and adjacent channel interference environments typical of proposed frequency division multiple access (FDMA) mobile satellite systems. These samples were then listened to by a group of evaluators whose subjective responses to the samples were used to produce a series of graphs showing the relationship between subjective acceptability, carrier to noise density (C/No), carrier to interference ratio (C/I), and frequency offset. The results show that in a mobile satellite environment, ACSSB deteriorates more slowly than NBFM. The co- and adjacent channel protection ratios for both modulation techniques were roughly the same, even though the mechanism for signal deterioration is different.

Sydor, John T.↗
NASA NTRS2024

MAGIK Animation of Robotic Operations for Flight SpaceX-31 to ISS

The MAGIK Robotics analysis team provides kinematic feasibility assessments for the ISS and has produced an animation to showcase Extravehicular Robotics (EVR) activities for Flight SpaceX (SpX)-31. Shown EVR activities were developed by Flight Operations Directorate (FOD) Robotics (ROBO). The animation also displays the current ISS configuration at the time of the flight in Increment 72. Flight SpX-31 includes a SpaceX Cargo Dragon vehicle docked to Node 2 Forward (N2F) and consists of the delivery of the Coronal Observation Experiment (CODEX) payload. Robotic operations shown include utilization the Special Purpose Dexterous Manipulator (SPDM) based on the Space Station Remote Manipulator System (SSRMS), survey of the cargo trunk, extraction of CODEX from the trunk, stow of SPDM, SSRMS walkoff to the Mobile Remote Servicer (MRS) Base System (MBS), SSRMS grapple of SPDM, translate of the Mobile Transporter (MT), and install of CODEX to Express Logistics Carrier 3 (ELC-3) Site 3. There is no disposal payload for this flight.

ISS↗
NASA NTRS1993

Mobilesat (tm): A world first

Mobilesat will be the world's first truly mobile satellite telephony service to be offered in the land mobile market. Essentially a car phone which will be offered as a fixed service at a later date, mobilesat will bring circuit switched voice communications to remote and rural areas of Australia. This paper outlines where mobilesat fits as part of Optus, Australia's new telecommunications carrier, and briefly discuss the mobilesat system, its market, and the future of mobile communications in Australia.

Cooper, Paul↗
NASA NTRS2007

Potential for Measurement of Trace Volatile Organic Compounds in Closed Environments Using Gas Chromatograph/Differential Mobility Spectrometer

For nearly 3.5 years, the Volatile Organic Analyzer (VOA) has routinely analyzed the International Space Station (ISS) atmosphere for a target list of approximately 20 volatile organic compounds (VOCs). Additionally, an early prototype of the VOA collected data aboard submarines in two separate trials. Comparison of the data collected on ISS and submarines showed a surprising similarity in the atmospheres of the two environments. Furthermore, in both cases it was demonstrated that the VOA data can detect hardware issues unrelated to crew health. Finally, it was also clear in both operations that the VOA s size and resource consumption were major disadvantages that would restrict its use in the future. The VOA showed the value of measuring VOCs in closed environments, but it had to be shrunk if it was to be considered for future operations in these environments that are characterized by cramped spaces and limited resources. The Sionex Microanalyzer is a fraction of the VOA s size and this instrument seems capable of maintaining or improving upon the analytical performance of the VOA. The two design improvements that led to a smaller, less complex instrument are the Microanalyzer s use of recirculated air as the gas chromatograph s carrier gas and a micromachined detector. Although the VOA s ion mobility spectrometer and the Microanalyzer s differential mobility spectrometer (DMS) are related detector technologies, the DMS was more amenable to micromachining. This paper will present data from the initial assessment of the Microanalyzer. The instrument was challenged with mixtures that simulated the VOCs typically detected in closed-environment atmospheres.

Limero, Thomas↗
NASA NTRS1986

Growth of high-quality thin-film Ge single crystals by plasma-enhanced chemical vapor deposition

Thin-film Ge single crystals (approx. 10 microns) have been epitaxially grown on polished NaCl(100) substrates at 450C by using plasma-enhanced chemical vapor deposition. Films on approximately 1 sq cm and larger were separated from the NaCl by either melting the salt or by differential shear stress upon cooling to room temperature. The ordered growth of the Ge was found to be most sensitive to the initial plasma power and to the continuum flow dynamics within the carbon susceptor. The films were visually specular and exhibited a high degree of crysalline order when examined by X-ray diffraction. The films were found to be p-type with a carrier concentration of approximately 3 x 10 to the 16th power/cu cm, a resistivity of 0.11 ohm-cm, and a Hall hole mobility of 1820 sq cm/v/s at room temperature. Vacuum firing minimized the primary contaminant, Na, and corresponding lowered the carrier concentration to 4 x 10 to the 14th power/cu cm.

Outlaw, R. A.↗