Engineering topics

Ignatiev, Alex

Publications and source records attributed to Ignatiev, Alex.

18 records

NASA NTRS2010

Electrically Variable Resistive Memory Devices

Nonvolatile electronic memory devices that store data in the form of electrical- resistance values, and memory circuits based on such devices, have been invented. These devices and circuits exploit an electrically-variable-resistance phenomenon that occurs in thin films of certain oxides that exhibit the colossal magnetoresistive (CMR) effect. It is worth emphasizing that, as stated in the immediately preceding article, these devices function at room temperature and do not depend on externally applied magnetic fields. A device of this type is basically a thin film resistor: it consists of a thin film of a CMR material located between, and in contact with, two electrical conductors. The application of a short-duration, low-voltage current pulse via the terminals changes the electrical resistance of the film. The amount of the change in resistance depends on the size of the pulse. The direction of change (increase or decrease of resistance) depends on the polarity of the pulse. Hence, a datum can be written (or a prior datum overwritten) in the memory device by applying a pulse of size and polarity tailored to set the resistance at a value that represents a specific numerical value. To read the datum, one applies a smaller pulse - one that is large enough to enable accurate measurement of resistance, but small enough so as not to change the resistance. In writing, the resistance can be set to any value within the dynamic range of the CMR film. Typically, the value would be one of several discrete resistance values that represent logic levels or digits. Because the number of levels can exceed 2, a memory device of this type is not limited to binary data. Like other memory devices, devices of this type can be incorporated into a memory integrated circuit by laying them out on a substrate in rows and columns, along with row and column conductors for electrically addressing them individually or collectively.

Liu, Shangqing↗

NASA NTRS2010

Electrical Switching of Perovskite Thin-Film Resistors

Electronic devices that exploit electrical switching of physical properties of thin films of perovskite materials (especially colossal magnetoresistive materials) have been invented. Unlike some related prior devices, these devices function at room temperature and do not depend on externally applied magnetic fields. Devices of this type can be designed to function as sensors (exhibiting varying electrical resistance in response to varying temperature, magnetic field, electric field, and/or mechanical pressure) and as elements of electronic memories. The underlying principle is that the application of one or more short electrical pulse(s) can induce a reversible, irreversible, or partly reversible change in the electrical, thermal, mechanical, and magnetic properties of a thin perovskite film. The energy in the pulse must be large enough to induce the desired change but not so large as to destroy the film. Depending on the requirements of a specific application, the pulse(s) can have any of a large variety of waveforms (e.g., square, triangular, or sine) and be of positive, negative, or alternating polarity. In some applications, it could be necessary to use multiple pulses to induce successive incremental physical changes. In one class of applications, electrical pulses of suitable shapes, sizes, and polarities are applied to vary the detection sensitivities of sensors. Another class of applications arises in electronic circuits in which certain resistance values are required to be variable: Incorporating the affected resistors into devices of the present type makes it possible to control their resistances electrically over wide ranges, and the lifetimes of electrically variable resistors exceed those of conventional mechanically variable resistors. Another and potentially the most important class of applications is that of resistance-based nonvolatile-memory devices, such as a resistance random access memory (RRAM) described in the immediately following article, Electrically Variable Resistive Memory Devices (MFS-32511-1).

Liu, Shangqing↗

NASA NTRS2009

Apparatus and method to pulverize rock using a superconducting electromagnetic linear motor

A rock pulverizer device based on a superconducting linear motor. The superconducting electromagnetic rock pulverizer accelerates a projectile via a superconducting linear motor and directs the projectile at high speed toward a rock structure that is to be pulverized by collision of the speeding projectile with the rock structure. The rock pulverizer is comprised of a trapped field superconducting secondary magnet mounted on a movable car following a track, a wire wound series of primary magnets mounted on the track, and the complete magnet/track system mounted on a vehicle used for movement of the pulverizer through a mine as well as for momentum transfer during launch of the rock breaking projectile.

Ignatiev, Alex↗

NASA NTRS2009

Thin-Film Solid Oxide Fuel Cells

The development of thin-film solid oxide fuel cells (TFSOFCs) and a method of fabricating them have progressed to the prototype stage. This can result in the reduction of mass, volume, and the cost of materials for a given power level.

Chen, Xin↗

NASA NTRS2009

Quantum-Well Thermophotovoltaic Cells

Thermophotovoltaic cells containing multiple quantum wells have been invented as improved means of conversion of thermal to electrical energy. The semiconductor bandgaps of the quantum wells can be tailored to be narrower than those of prior thermophotovoltaic cells, thereby enabling the cells to convert energy from longer-wavelength photons that dominate the infrared-rich spectra of typical thermal sources with which these cells would be used. Moreover, in comparison with a conventional single-junction thermophotovoltaic cell, a cell containing multiple narrow-bandgap quantum wells according to the invention can convert energy from a wider range of wavelengths. Hence, the invention increases the achievable thermal-to-electrical energy-conversion efficiency. These thermophotovoltaic cells are expected to be especially useful for extracting electrical energy from combustion, waste-heat, and nuclear sources having temperatures in the approximate range from 1,000 to 1,500 C.

Freudlich, Alex↗

NASA NTRS2005

Manufacture of Solar Cells on the Moon

In support of the space exploration initiative a new architecture for the production of solar cells on the lunar surface is devised. The paper discusses experimental data on the fabrication and properties of lunar glass substrates, evaporated lunar regolith thin film (antireflect coatings and insulators), and preliminary attempts in the fabrication of thin film (silicon/II-VI) photovoltaic materials on lunar regolith substrates. A conceptual design for a solar powered robotic rover capable of fabricating solar cells directly on the lunar surface is provided. Technical challenges in the development of such a facility and strategies to alleviate perceived difficulties are discussed. Finally, preliminary cost benefit ratio analysis for different in situ solar cell production scenarios (using exclusively in-situ planetary resources or hybrid) are discussed.

Freundich, Alex↗

NASA NTRS1997

Solar Cells for Lunar Application

In this work a preliminary study of the vacuum evaporation of silicon extracted from the lunar regolith has been undertaken. An electron gun vacuum evaporation system has been adapted for this purpose. Following the calibration of the system using ultra high purity silicon deposited on Al coated glass substrates, thin films of lunar Si were evaporated on a variety of crystalline substrates as well as on glass and lightweight 1 mil (25 microns) Al foil. Extremely smooth and featureless films with essentially semiconducting properties were obtained. Optical absorption analysis sets the bandgap (about 1.1 eV) and the refractive index (n=3.5) of the deposited thin films close to that of crystalline silicon. Secondary ion mass spectroscopy and energy dispersive spectroscopy analysis indicated that these films are essentially comparable to high purity silicon and that the evaporation process resulted in a substantial reduction of impurity levels. All layers exhibited a p-type conductivity suggesting the presence of a p-type dopant in the fabricated layers. While the purity of the 'lunar waste material' is below that of the 'microelectronic-grade silicon', the vacuum evaporated material properties seems to be adequate for the fabrication of average performance Si-based devices such as thin film solar cells. Taking into account solar cell thickness requirements (greater than 10 microns) and the small quantities of lunar material available for this study, solar cell fabrication was not possible. However, the high quality of the optical and electronic properties of evaporated thin films was found to be similar to those obtained using ultra-high purity silicon suggest that thin film solar cell production on the lunar surface with in situ resource utilization may be a viable approach for electric power generation on the moon.

Freundlich, Alex↗

NASA NTRS1993

Return flux contamination of an outgassing spacecraft in low earth orbit

The recontamination of a spacecraft surface directly exposed to the ram flux is investigated. It is assumed that the surface has been contaminated by a rocket plume contact and that, subsequent to the exposure, the contaminated surface is placed in the ram flux. A BGK-simulation was compared to both a Direct Simulation Monte Carlo (DSMC) and a Full Flow Monte Carlo (FFMC) using sensitivity analysis. Results indicate that the BGK-based simulation underpredicted the return flux contamination as compared to both the DSMC and FFMC techniques. Results from the full flow model suggest that the BGK model is inadequate to represent this physical problem.

Justiz, Charles R.↗

NASA NTRS1992

Solar cells for lunar applications by vacuum evaporation of lunar regolith materials

The possibility of the direct fabrication of solar cells on the lunar surface by the vacuum evaporation of lunar regolith is examined as an alternative approach to electric power generation on the surface of the moon. The raw materials for large-scale solar cell growth could be available from the waste products generated in regolith processing for volatiles collection and oxygen extraction. The production of vast areas of solar cells can be implemented through a self-generation process whereby the power generated by grown cells is used to produce more cells.

Ignatiev, Alex↗

NASA NTRS1992

A hybrid flow model for charged and neutral particles around spacecraft in Low Earth Orbit

A flow simulation for charged and neutral particles around spacecraft is given that combines the fully coupled effects of neutral particle flow, plasma flow, electromagnetic field effects, and spacecraft charging. The simulation allows for chemically reacting flows (associative ionization, dissociation, and chain exchange) and for thermal accommodation at a spacecraft surface. The solution procedure was applied to several types of flows with orbital altitudes ranging from 250 km to 500 km. Excellent agreement with previously verified computational algorithms was obtained for both the neutral and charged particle cases. Results for the full flow simulation are presented for altitudes of 250 km and 500 km.

Justiz, Charles R.↗

NASA NTRS1991

Production of solar photovoltaic cells on the Moon

Solar energy is directly available on the sunward lunar surface. Most, if not all, the materials are available on the Moon to make silicon based solar photovoltaic cells. A few additional types are possible. There is a small but growing literature on production of lunar derived solar cells. This literature is reviewed. Topics explored include trade-offs of local production versus import of key materials, processing options, the scale and nature of production equipment, implications of storage requirements, and the end-uses of the energy. Directions for future research and demonstrations are indicated.

Criswell, David R.↗

NASA NTRS1991

Solar cells for lunar applications by vacuum evaporation of lunar regolith materials

The National Space Exploration Initiative, specifically the Lunar component, has major requirements for technology development of critical systems, one of which is electrical power. The availability of significant electrical power on the surface of the Moon is a principal driver defining the complexity of the lunar base. Proposals to generate power on the Moon include both nuclear and solar (photovoltaic) systems. A more efficient approach is to attempt utilization of the existing lunar resources to generate the power systems. Synergism may occur from the fact that there have already been lunar materials processing techniques proposed for the extraction of oxygen that would have, as by-products, materials that could be specifically used to generate solar cells. The lunar environment is a vacuum with pressures generally in the 1 x 10(exp -10) torr range. Such conditions provide an ideal environment for direct vacuum deposition of thin film solar cells using the waste silicon, iron, and TiO2 available from the lunar regolith processing meant to extract oxygen. It is proposed, therefore, to grow by vacuum deposition, thin film silicon solar cells from the improved regolith processing by-products.

Ignatiev, Alex↗

NASA NTRS1990

Applying CLIPS to control of molecular beam epitaxy processing

A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

Rabeau, Arthur A.↗

NASA NTRS1990

Particle radiation near the orbit of the Vacuum Wake Shield

The particle populations that are expected to inflict the most damage on thin film materials grown on the vacuum Wake Shield Facility (WSF) are ions and energetic neutral atoms with energies in the range of 100 eV to 20 keV. The production of films that have an order of magnitude fewer defects than are now available requires that the 1-keV particle flux be kept lower than 1000 particles/(sq cm s sr keV) (assuming a reasonable spectral shape). WSF will be flown on orbits with an inclination of 28 deg at altitudes of 300-700 km. Because of the background counting rate produced by the about 100 MeV trapped protons in the inner belt, obtaining accurate measurements of the particles of interest is very difficult. The quiet-time background fluxes of the relevant particles are not presently known. At times of magnetic activity, fluxes of 0.1-17 keV O(+) ions as great as 10 million ions/(sq cm s sr keV) have been observed flowing out of the ionosphere at these latitudes. It appears that instrumentation for detailed assessment is essential for the proof-of-concept flight(s) and that real-time monitoring of low-energy ion and energetic neutral radiation will be required for the production flights.

Bering, Edgar A., III↗

NASA NTRS1988

A proposal for epitaxial thin film growth in outer space

A new concept for materials processing in space exploits the ultravacuum component of space for thin film epitaxial growth. The unique low earth orbit space environment is expected to yield 10 to the -14th torr or better pressures, semiinfinite pumping speeds, and large ultravacuum volume without walls. These space ultravacuum properties promise major improvement in the quality, unique nature, and the throughput of epitaxially grown materials. Advanced thin film materials to be epitaxially grown in space include semiconductors, magnetic materials, and thin film high temperature superconductors.

Ignatiev, Alex↗

NASA NTRS1988

Commercial aspects of epitaxial thin film growth in outer space

A new concept for materials processing in space exploits the ultra vacuum component of space for thin film epitaxial growth. The unique low earth orbit space environment is expected to yield 10 to the -14th torr or better pressures, semiinfinite pumping speeds and large ultra vacuum volume (about 100 cu m) without walls. These space ultra vacuum properties promise major improvement in the quality, unique nature, and the throughput of epitaxially grown materials especially in the area of semiconductors for microelectronics use. For such thin film materials there is expected a very large value added from space ultra vacuum processing, and as a result the application of the epitaxial thin film growth technology to space could lead to major commercial efforts in space.

Ignatiev, Alex↗

NASA NTRS1988

Epitaxial thin film growth in outer space

A new concept for materials processing in space exploits the ultravacuum component of space for thin-film epitaxial growth. The unique LEO space environment is expected to yield 10-ftorr or better pressures, semiinfinite pumping speeds, and large ultravacuum volume (about 100 cu m) without walls. These space ultravacuum properties promise major improvement in the quality, unique nature, and throughput of epitaxially grown materials, including semiconductors, magnetic materials, and thin-film high-temperature superconductors.

Ignatiev, Alex↗

NASA NTRS1988

Future superconductivity applications in space - A review

High temperature superconductor (HISC) materials and devices can provide immediate applications for many space missions. The in-space thermal environment provides an opportunity to develop, test, and apply this technology to enhance performance and reliability for many applications of crucial importance to NASA. Specifically, the technology development areas include: (1) high current power transmission, (2) microwave components, devices, and antennas, (3) microwave, optical, and infrared sensors, (4) signal processors, (5) submillimeter wave components and systems, (6) ultra stable space clocks, (7) electromagnetic launch systems, and (8) accelerometers and position sensors for flight operations. HTSC is expected to impact NASA's Lunar Bases, Mars exploration, Mission to Earth, and Planetary exploration programs providing enabling and cost-effect technology. A review of the space applications of the HTSC technology is presented. Problem areas in technology development needing special attention are identified.

Krishen, Kumar↗