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NASA NTRS1989

Plasma-deposited amorphous hydrogenated carbon films and their tribological properties

Recent work on the properties of diamondlike carbon films and their dependence on preparation conditions are reviewed. The results of the study indicate that plasma deposition enables one to deposit a variety of amorphous hydrogenated carbon (a-C:H) films exhibiting more diamondlike behavior to more graphitic behavior. The plasma-deposited a-C:H can be effectively used as hard, wear-resistant, and protective lubricating films on ceramic materials such as Si(sub 3)N(sub 4) under a variety of environmental conditions such as moist air, dry nitrogen, and vacuum.

Miyoshi, K.↗
NASA NTRS1989

VUV-visible measurements on different samples of amorphous carbon

Among various candidate materials for interstellar dust, amorphous carbon (AC) is playing an increasingly important role (Greenstein, 1981; Hecht et al., 1984; Jura, 1983, 1986). Furthermore, recent in situ measurements have clearly shown the presence of carbonaceous grains in the coma of comet Halley (Kissel et al., 1986). Laboratory investigations on AC grains may be very useful to better interpret observations and to support theoretical elaborations. Recently, the authors started an international research program which also includes UV extinction analyses on AC samples, by using synchrotron light. Preliminary results obtained in a first shift of measurements, last June, are given. At the present stage of the data analysis, the authors can only draw some preliminary considerations. A wide band falling at around 240 nm is detected in all the analyzed samples. It intensity seems to decrease with increasing the dust collecting distance. A peak at 150 nm decreases in intensity with increasing the collecting distance. The band seems absent in the samples characterized by a larger amount of dust. A feature at about 200 nm is detected in some samples. At the moment the authors tend to attribute it to the transmission properties of the LiF substrates at the wavelength and/or to some problems in the experimental setup. It is unclear if a hump at 120 nm is real or due to instrumental effects. The profile of the spectra does not show substantial changes when the samples are cooled down to about 100 K. The present results appear to be in general agreement with previous findings, but their analysis is in progress and the interpretation is still on the way.

Blanco, A.↗
NASA NTRS1989

Experimental evidence for amorphous carbon grains in comets

Amorphous carbon grains similar to those produced in the laboratory, but with a higher hydrogen content, appear to be good candidates to simulate both the IR continuum emission and the 3.4 micron band measured for P/Halley. The comparison of the cometary features with those detected in the laboratory for carbon grains characterized by various sp(exp 2)/sp(exp 3) ratios seems to indicate that a prevalent diamond-like (sp(exp 3)) structure should be present in cometary particles. These kinds of solid particles seem also suitable to explain the daily and monthly variations of the 3.4 micron band intensity, relative to the continuum, and, at the same time,- to fulfill the abundance constraints. The same grains appear to be able to reproduce the absorption bands detected in the IR galactic source IRS 7. This result may be considered as a first experimental evidence of a relation existing between interstellar dust and cometary materials.

Colangeli, Luigi↗
NASA NTRS1991

Integral bypass diodes in an amorphous silicon alloy photovoltaic module

Thin-film, tandem-junction, amorphous silicon (a-Si) photovoltaic modules were constructed in which a part of the a-Si alloy cell material is used to form bypass protection diodes. This integral design circumvents the need for incorporating external, conventional diodes, thus simplifying the manufacturing process and reducing module weight.

Hanak, J. J.↗
NASA NTRS1991

Low-pressure clathrate-hydrate formation in amorphous astrophysical ice analogs

In modeling cometary ice, the properties of clathrate hydrates were used to explain anomalous gas release at large radial distances from the Sun, and the retention of particular gas inventories at elevated temperatures. Clathrates may also have been important early in solar system history. However, there has never been a reasonable mechanism proposed for clathrate formation under the low pressures typical of these environments. For the first time, it was shown that clathrate hydrates can be formed by warming and annealing amorphous mixed molecular ices at low pressures. The complex microstructures which occur as a result of clathrate formation from the solid state may provide an explanation for a variety of unexplained phenomena. The vacuum and imaging systems of an Hitachi H-500H Analytical Electron Microscope was modified to study mixed molecular ices at temperatures between 12 and 373 K. The resulting ices are characterized by low-electron dose Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED). The implications of these results for the mechanical and gas release properties of comets are discussed. Laboratory IR data from similar ices are presented which suggest the possibility of remotely observing and identifying clathrates in astrophysical objects.

Blake, D. F.↗
NASA NTRS1991

The status of lightweight photovoltaic space array technology based on amorphous silicon solar cells

Ultralight, flexible photovoltaic (PV) array of amorphous silicon (a-Si) was identified as a potential low cost power source for small satellites. A survey was conducted of the status of the a-Si PV array technology with respect to present and future performance, availability, cost, and risks. For existing, experimental array blankets made of commercial cell material, utilizing metal foil substrates, the Beginning of Life (BOL) performance at Air Mass Zero (AM0) and 35 C includes total power up to 200 W, power per area of 64 W/sq m and power per weight of 258 W/kg. Doubling of power per weight occurs when polyimide substrates are used. Estimated End of Life (EOL) power output after 10 years in a nominal low earth orbit would be 80 pct. of BOL, the degradation being due to largely light induced effects (-10 to -15 pct.) and in part (-5 pct.) to space radiation. Predictions for the year 1995 for flexible PV arrays, made on the basis of published results for rigid a-Si modules, indicate EOL power output per area and per weight of 105 W/sq m and 400 W/kg, respectively, while predictions for the late 1990s based on existing U.S. national PV program goals indicate EOL values of 157 W/sq m and 600 W/kg. Cost estimates by vendors for 200 W ultralight arrays in volume of over 1000 units range from $100/watt to $125/watt. Identified risks include the lack of flexible, space compatible encapsulant, the lack of space qualification effort, recent partial or full acquisitions of US manufacturers of a-Si cells by foreign firms, and the absence of a national commitment for a long range development program toward developing of this important power source for space.

Hanak, Joseph J.↗
NASA NTRS1991

Comparison of high temperature, high frequency core loss and dynamic B-H loops of two 50 Ni-Fe crystalline alloys and an iron-based amorphous alloy

The availability of experimental data that characterizes the performance of soft magnetic materials for the combined conditions of high temperature and high frequency is almost nonexistent. An experimental investigation was conducted over the temperature range of 23 to 300 C and frequency range of 1 to 50 kHz to determine the effects of temperature and frequency on the core loss and dynamic B-H loops of three different soft magnetic materials; and oriented grain 50Ni-50Fe alloy, a nonoriented grain 50Ni-Fe alloy, and an iron based amorphous material (Metglas 2605SC). A comparison of these materials shows that the nonoriented grain 50Ni-50Fe alloy tends to have either the lowest or next lowest core loss for all temperatures and frequencies investigated.

Wieserman, W. R.↗
NASA NTRS1991

Effect of chromium and phosphorus on the physical properties of iron and titanium-based amorphous metallic alloy films

Amorphous iron and titanium-based alloys containing various amounts of chromium, phosphorus, and boron exhibit high corrosion resistance. Some physical properties of Fe and Ti-based metallic alloy films deposited on a glass substrate by a dc-magnetron sputtering technique are reported. The films were characterized using differential scanning calorimetry, stress analysis, SEM, XRD, SIMS, electron microprobe, and potentiodynamic polarization techniques.

Distefano, S.↗
NASA NTRS1991

Inelastic and reactive scattering of hyperthermal atomic oxygen from amorphous carbon

The reaction of hyperthermal oxygen atoms with an amorphous carbon-13 surface was studied using a modified universal crossed molecular beams apparatus. Time-of-flight distributions of inelastically scattered O-atoms and reactively scattered CO-13 and CO2-13 were measured with a rotatable mass spectrometer detector. Two inelastic scattering channels were observed, corresponding to a direct inelastic process in which the scattered O-atoms retain 20 to 30 percent of their initial kinetic energy and to a trapping desorption process whereby O-atoms emerge from the surface at thermal velocities. Reactive scattering data imply the formation of two kinds of CO products, slow products whose translational energies are determined by the surface temperature and hyperthermal (Approx. 3 eV) products with translational energies comprising roughly 30 percent of the total available energy (E sub avl), where E sub avl is the sum of the collision energy and the reaction exothermicity. Angular data show that the hyperthermal CO is scattered preferentially in the specular direction. CO2 product was also observed, but at much lower intensities than CO and with only thermal velocities.

Minton, Timothy K.↗
NASA NTRS1991

Coercivity of domain wall motion in thin films of amorphous rare earth-transition metal alloys

Computer simulations of a two dimensional lattice of magnetic dipoles are performed on the Connection Machine. The lattice is a discrete model for thin films of amorphous rare-earth transition metal alloys, which have application as the storage media in erasable optical data storage systems. In these simulations, the dipoles follow the dynamic Landau-Lifshitz-Gilbert equation under the influence of an effective field arising from local anisotropy, near-neighbor exchange, classical dipole-dipole interactions, and an externally applied field. Various sources of coercivity, such as defects and/or inhomogeneities in the lattice, are introduced and the subsequent motion of domain walls in response to external fields is investigated.

Mansuripur, M.↗
NASA NTRS1991

Effect of patch borders on coercivity in amorphous rare earth-transition metal thin films

The coercivity at the micron scale is a very important property of magneto-optical media. It is a key factor that determines the magnetic domain wall movement and domain reversal. How the coercivity is influenced by a special type of patch borders is discussed. Patch formation is a general phenomenon in growth processes of amorphous rare earth transition metal thin films. Different patches may stem from different seeds and the patch borders are formed when they merge. Though little is known about the exact properties of the borders, we may expect that the exchange interaction at the patch border is weaker than that within a patch, since there is usually a spatial gap between two patches. Computer simulations were performed on a 2-D hexagonal lattice consisting of 37 complete patches with random shape and size. From the series of simulations we may conclude that the domain in the patch with borders of 30 percent exchange strength can expand most easily to the whole lattice, because the exchange strength can expand most easily to the whole lattice, because the exchange strength of the border is not too high to prevent the domain from growing within the patch and it is not too low to prevent the domain from expanding beyond the patch.

Patterson, G.↗
NASA NTRS1991

Comparison of high temperature, high frequency core loss and dynamic B-H loops of two 50 Ni-Fe crystalline alloys and an iron-based amorphous alloy

The availability of experimental data that characterize the performance of soft magnetic materials for the combined conditions of high temperature and high frequency is almost nonexistent. An experimental investigation was conducted over the temperature range of 23 to 300 C and frequency range of 1 to 50 kHz to determine the effects of temperature and frequency on the core loss and dynamic B-H loops of three different soft magnetic materials: an oriented-grain 50Ni-50Fe alloy, a nonoriented-grain 50Ni-50Fe alloy, and an iron-based amorphous material (Metglas 2605SC). A comparison of these materials shows that the nonoriented-grain 50Ni-50Fe alloy tends to have either the lowest or the next lowest core loss for all temperatures and frequencies investigated.

Wieserman, W. R.↗
NASA NTRS1992

Properties Of Plasma-Deposited Amorphous Hydrogenated Carbon

Report reviews experimental research on plasma-deposited films of hydrogenated amorphous carbon. Such films exhibit electrical resistivity, semi-transparency, mechanical hardness, and chemical inertness. Useful as gate dielectrics and passivating layers in semiconductor devices, insulators for metal/insulator/metal devices, and masks in nanometer lithography. Show promise as wear-resistant, hard solid lubricating coats for bearings and optical components.

Miyoshi, Kazuhisa↗
NASA NTRS1991

Comparison of high frequency, high temperature core loss and B-H loop characteristics of an 80 Ni-Fe crystalline alloy and two iron-based amorphous alloys

Limited experimental data exists for the specific core loss and dynamic B-H loops for soft magnetic materials for the combined conditions of high frequency and high temperature. This experimental study investigates the specific core loss and dynamic B-H characteristics of a nickel-iron crystalline magnetic alloy (Supermalloy) and two iron-based amorphous magnetic materials (Metglas 2605S-3A and Metglas 2605SC) over the frequency range of 1-50 kHz and temperature range of 23-300 C under sinusoidal voltage excitation. The effects of maximum magnetic flux density, frequency, and temperature on the specific core loss and on the size and shape of the B-H loops are examined. The Supermalloy and Metglass 2605S-3A and 2605SC data are used to compare the core loss of transformers with identical kVA and voltage ratings.

Wieserman, William R.↗
NASA NTRS1992

Crystallization of amorphous ice as the cause of Comet P/Halley's outburst at 14 AU

An explanation is provided for the postperihelion eruption of Comet P/Halley, detected in February 1991 and believed to have started three months earlier, namely, the crystallization of amorphous ice taking place in the interior of the porous nucleus, at depths of a few tens of meters, accompanied by the release of trapped gases. Numerical calculations show that for a bulk density of 0.5 g/cu cm and a pore size of 1 micron crystallization occurs on the outbound leg of Comet P/Halley's orbit, at heliocentric distances between 5 AU and 17 AU. The trapped gas is released and flows to the surface through the porous medium. It may also open wider channels, as the internal pressures obtained surpass the tensile strength of cometary ice. The outflowing gas carries with it grains of ice and dust, and thus can explain the large amounts of dust observed in the coma at 14.3 AU and beyond.

Prialnik, D.↗
NASA NTRS1994

Amorphous silicon thin films: The ultimate lightweight space solar cell

Progress is reported with respect to the development of thin film amorphous (alpha-Si) terrestrial solar cells for space applications. Such devices promise to result in very lightweight, low cost, flexible arrays with superior end of life (EOL) performance. Each alpha-Si cell consists of a tandem arrangement of three very thin p-i-n junctions vapor deposited between film electrodes. The thickness of this entire stack is approximately 2.0 microns, resulting in a device of negligible weight, but one that must be mechanically supported for handling and fabrication into arrays. The stack is therefore presently deposited onto a large area (12 by 13 in), rigid, glass superstrate, 40 mil thick, and preliminary space qualification testing of modules so configured is underway. At the same time, a more advanced version is under development in which the thin film stack is transferred from the glass onto a thin (2.0 mil) polymer substrate to create large arrays that are truly flexible and significantly lighter than either the glassed alpha-Si version or present conventional crystalline technologies. In this paper the key processes for such effective transfer are described. In addition, both glassed (rigid) and unglassed (flexible) alpha-Si cells are studied when integrated with various advanced structures to form lightweight systems. EOL predictions are generated for the case of a 1000 W array in a standard, 10 year geosynchronous (GEO) orbit. Specific powers (W/kg), power densities (W/sq m) and total array costs ($/sq ft) are compared.

Vendura, G. J., Jr.↗
NASA NTRS1994

Investigation of the stability and 1.0 MeV proton radiation resistance of commercially produced hydrogenated amorphous silicon alloy solar cells

The radiation resistance of commercial solar cells fabricated from hydrogenated amorphous silicon alloys is reported. A number of different device structures were irradiated with 1.0 MeV protons. The cells were annealing at 200 C. The annealing time was dependent on proton fluence. Annealing devices for one hour restores cell parameters or fluences below 1(exp 14) cm(exp -2); fluences above 1(exp 14) cm(exp -2) require longer annealing times. A parametric fitting model was used to characterize current mechanisms observed in dark I-V measurements. The current mechanisms were explored with irradiation fluence, and voltage and light soaking times. The thermal generation current density and quality factor increased with proton fluence. Device simulation shows the degradation in cell characteristics may be explained by the reduction of the electric field in the intrinsic layer.

Lord, Kenneth R., II↗
NASA NTRS1994

Neutral hydrogen and optical properties of three amorphous galaxies

We present new interferometric H I and optical observations of three amorphous galaxies, systems with a smooth, high surface brightness but an asymmetrical distribution of light. All three galaxies are forming stars and have LMC-like emission-line ratios, low dust content, and high H I velocity dispersions. NGC 1140 has a boxy inner morphology with a hook off one corner. At low light levels unusual extensions of starlight are seen curving to the northwest and southeast. The galaxy contains a very luminous central star-forming region and a small chain of H II regions that coincide with the hook. The central H II region has broad H(alpha) velocity profiles full width at half maximum (FWHM) less than or equal to 140 km/s, and it is a radio continuum source. There is a rotating H I gas disk, 40 kpc in radius, at a position angle 51 deg from the optical major axis. The central gas ridge follows the chain of H II regions, and the H I peak is on the hook. The outer gas on the southeast side curves away from the H I major axis. The central gas density is high, and the surface density declines very slowly with radius. The rotation velocity yields a mass of 1 x 10(exp 11) solar mass at 3.3 Holmberg radii (R(sub H)). NGC 1800 has a hook that coincides with a large H II region, and an r(exp 1/4) luminosity distribution. There are numerous H II regions along the major axis and extraordinary filaments of ionized gas. Emanating from the major axis on either side of the galaxy are H(alpha) fingers approximately 750 pc long. About 2.3 kpc to the north is a web of filaments approximately 3 kpc in extent. H(alpha) profiles of H II regions and filaments are narrow. The H I gas disk has a position angle that is approximately 13 deg different from that of the optical axis. There are two peaks near the center, one of which is near the largest H II region. Beyond the Holmberg radius to the west is a 6 x 10(exp 6) solar mass H I cloud. Its velocity indicates a mass of approximately 6 x 10(exp 9) solar mass for NGC 1800 at 1.5 R(sub H). At approximately R(sub 25) to the east there is a large H I shell. Also at approximately R(sub 25) on both sides the velocity gradient switches by 90 deg, and in the interior the rotation is about the major axis. The central gas density is low and falls off slowly. In the inner regions NGC 4670 resembles an S0/a galaxy seen rather edge-on. It contains a central supergiant H II region with very high velocity widths (FWHM less than or equal to 180 km/s) and complex velocity structures. It is a radio continuum source as well. The H I gas is a single spherical cloud or a disk at low inclination centered on the galaxy with a slight elongation along the optical major axis and rotation about the minor axis. The central gas density is high, and there is a high degree of concentration. The rotation speed indicates a total mass of 5 x 10(exp 10) solar mass at 1.1 R(sub H). We compare these characteristics with properties of gas in the presence of stellar bar potentials, gas warps, and interacting and merging galaxy models. Although there are inconsistencies and uncertainties, we conclude that NGC 1140 is a spiral of low surface brightness that has undergone a merger, while NGC 1800 and NGC 4670 are, respectively, probably an Im system and a spiral that had an encounter of the Noguchi (1988a) kind.

Hunter, Deidre A.↗