Optical conductivity of amorphous Ta and beta-Ta films
(Previously announced in STAR as N82-23009)
Nestell, J. E., Jr.↗
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Results for “amorphization”
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Experimental studies of the vapor phase nucleation of refractory compounds. II - The condensation of an amorphous magnesium silicate
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Nuth, J. A.↗
Plasma Deposition of Doped Amorphous Silicon
Pair of reports present further experimental details of investigation of plasma deposition of films of phosphorous-doped amosphous silicon. Probe measurements of electrical resistance of deposited films indicated films not uniform. In general, it appeared that resistance decreased with film thickness.
Calcote, H. F.↗
Optical properties of hydrogenated amorphous carbon films grown from methane plasma
A 30 kHz ac glow discharge formed from methane gas was used to grow carbon films on InP substrates. Both the growth rate, and the realitive Ar ion sputtering rate at 3 keV varied monotonically with deposition power. Results from the N-15 nuclear reaction profile experiments indicated a slight drop in the hydrogen concentration as more energy was dissipated in the ac discharge. Values for the index of refraction and extinction coefficient ranged from 1.721 to 1.910 and 0 to -0.188, respectively. Optical bandgaps as high as 2.34 eV were determined.
Pouch, J. J.↗
Amorphous and porous ices in cometary nuclei
The heat flux into the cometary nucleus before and after perihelion and its influence on the nucleus are discussed. The surface temperature and the associated rate of evaporation are lower than usually calculated, and the effect is strongly dependent on the porosity of the nucleus. The surface temperature reaches a maximum after perihelion, in agreement with statistical studies of comae and tails. Delayed heating of the CO2-rich inclusions deep in the nucleus leads to outbursts and splittings as far as 9 AU after perihelion, also in agreement with observation. At sufficiently high temperatures, heat transport in porous cometary nuclei is controlled by vapor diffusion. The presence of CO2 vapor in the pores significantly increases the heat flow in mixed nuclei at temperatures above 140-150 C. Closed pores move up the radial thermal gradient so that the outside layer of a cometary nucleus should become denser.
Smoluchowski, R.↗
Accelerated stress testing of amorphous silicon solar cells
A technique for performing accelerated stress tests of large-area thin a-Si solar cells is presented. A computer-controlled short-interval test system employing low-cost ac-powered ELH illumination and a simulated a-Si reference cell (seven individually bandpass-filtered zero-biased crystalline PIN photodiodes) calibrated to the response of an a-Si control cell is described and illustrated with flow diagrams, drawings, and graphs. Preliminary results indicate that while most tests of a program developed for c-Si cells are applicable to a-Si cells, spurious degradation may appear in a-Si cells tested at temperatures above 130 C.
Stoddard, W. G.↗
Amorphous silicon deposition diagnostics using coherent anti-Stokes Raman spectroscopy
This paper reports on an in situ silicon deposition process diagnostics, using CARS performed at state-of-the-art a-Si:H film deposition conditions in a reactor designed for a-Si:H solar cell fabrication. The diagnostics procedure measures the silane depletion in an RF plasma as a function of the silane flow rate (where the relationship is linear between 50-percent depletion, at a flow rate of 5.6 sccm, and about 8-percent depletion, at 80 sccm) and the RF power (where the silane depletion is linearly dependent on the RF power in the region of 4 to 12 W). The linear RF power dependence of the silane depletion is considered to be consistent with the mechanism of silane decomposition primarily by electron impact dissociations, while the flow rate dependence is interpreted in terms of the residence time of the SiH4 molecules in the glow discharge region, where an increase of the residence time at a low flow rate results in a high depletion ratio.
Shing, Y. H.↗
Radiation-resistant, amorphous, all-aromatic poly(arylene ether sulfones) - Synthesis, physical behavior, and degradation characteristics
The effects of Co-60 gamma radiation on a series of poly(arylene ether sulfones) prepared by nucleophilic activated aromatic substitution are investigated experimentally. The preparation of the test compounds is described, and the test results are presented in extensive tables and graphs. Radiation-induced degradation, as measured by SO2 production, was found to be lowest in compounds based on biphenol rather than bisphenol A; these findings were also well correlated with ultimate-tensile-strain measurements.
Lewis, D. A.↗
Static compression of Ca(OH)2 at room temperature - Observations of amorphization and equation of state measurements to 10.7 GPa
X-ray diffraction measurements are reported for Ca(OH)2 portlandite as it is compressed to 37.6 GPa in the diamond cell at room temperature. Between 10.7 and 15.4 GPa crystalline Ca(OH)2 transforms to a glass, and on decompression the glass recrystallizes between 3.6 and 5.1 GPa. Below pressures of 10.7 GPa the elastic compression of crystalline Ca(OH)2 was measured. A finite strain analysis of these data shows that the isothermal bulk modulus and its pressure derivative are 37.8 + or - 1.8 GPa and 5.2 + or - 0.7 at zero pressure. The change in the unit cell dimensions indicates that the linear incompressibilities of Ca(OH)2 differ by a factor of three.
Meade, Charles↗
Annealing characteristics of irradiated hydrogenated amorphous silicon solar cells
It was shown that 1 MeV proton irradiation with fluences of 1.25E14 and 1.25E15/sq cm reduces the normalized I(sub SC) of a-Si:H solar cell. Solar cells recently fabricated showed superior radiation tolerance compared with cells fabricated four years ago; the improvement is probably due to the fact that the new cells are thinner and fabricated from improved materials. Room temperature annealing was observed for the first time in both new and old cells. New cells anneal at a faster rate than old cells for the same fluence. From the annealing work it is apparent that there are at least two types of defects and/or annealing mechanisms. One cell had improved I-V characteristics following irradiation as compared to the virgin cell. The work shows that the photothermal deflection spectroscopy (PDS) and annealing measurements may be used to predict the qualitative behavior of a-Si:H solar cells. It was anticipated that the modeling work will quantitatively link thin film measurements with solar cell properties. Quantitative predictions of the operation of a-Si:H solar cells in a space environment will require a knowledge of the defect creation mechanisms, defect structures, role of defects on degradation, and defect passivation and annealing mechanisms. The engineering data and knowledge base for justifying space flight testing of a-Si:H alloy based solar cells is being developed.
Payson, J. S.↗
A model for the spectral dependence of optically induced absorption in amorphous silicon
A model based on transitions from localized band tail states to states above the mobility edge is used to explain the broad band induced absorptions observed in recent pump-probe experiments. The model gives the observed decrease of absorption with frequency at subband gap photo energies and high carrier densities (of about 10 to the 20th/cu cm). At lower carrier densities, the absorption has a maximun which is sensitive to the spatial extent of the band tail states.
Lawandy, N. M.↗
Amorphization and recrystallization of epitaxial ReSi2 films grown on Si(100)
The effects of implantation damage and the chemical species of the implant on structural and electrical properties of epitaxial ReSi2 films on Si(100) implanted with Si-28 or Ar-40 ions, at doses ranging from 10 to the 13th/sq cm to 10 to the 15th/sq cm, were investigated using the backscattering spectrometry, XRD, and the van der Pauw techniques. Results showed that ion implantation produces damage in the film, which increases monotonically with dose; the resistivity of the film decreases monotonically with dose.
Kim, Kun HO↗
1.00 MeV proton radiation resistance studies of single-junction and single gap dual-junction amorphous-silicon alloy solar cells
A comparative study of the radiation resistance of a-Si:H and a-SiGe:H single-junction and a-Si:H dual-junction solar cells was conducted. The cells were irradiated with 1.00-MeV protons with fluences of 1.0 x 10 to the 14th, 5.0 x 10 to the 14th and 1.0 x 10 to the 15th/sq cm and characterized using I-V and quantum efficiency measurements. The radiation resistance of single-junction cells cannot be used to explain the behavior of dual-junction cells at a fluence of 1.0 x 10 to the 15th/sq cm. The a-Si H single-junction cells degraded the least of the three cells; a-SiGe:H single-junction cells showed the largest reduction in short-circuit current, while a-Si:H dual-junction cells exhibited the largest degradation in the open-circuit voltage. The quantum efficiency of the cells degraded more in the red part of the spectrum; the bottom junction degrades first in dual-junction cells.
Abdulaziz, Salman↗
Materials and characterization using acoustic nonlinearity parameters and harmonic generation - Effects of crystalline and amorphous structures
The effects of material structure on the nonlinearity parameters are reviewed. Problems discussed include definition of nonlinearity parameters, square-law nonlinearity and collinear beam-mixing, structure dependence of the nonlinearity parameters, negative nonlinearity parameters, and implications for materials characterization.
Cantrell, John H.↗
Growth and properties of amorphous silicon films grown using pulsed-flow reactive plasma beam epitaxy
The growth and properties of a-Si:H films grown using a novel deposition technique, reactive plasma beam epitaxy, are discussed. In this technique, a remote H plasma produced in a microwave-ECR reactor is used to grow a-Si:H films at low pressures. The H ions react with SiH4 introduced near the substrate to produce the film. The flow of SiH4 is pulsed on or off, thereby achieving in-situ annealing of the film during growth by H ions and radicals. The films produced by this technique appear to have good electronic quality, and are more stable than the standard glow discharge films.
Dalal, Vikram L.↗
Electrochemical patterning of amorphous carbon on diamond
The ability to pattern ion-implantation damaged or other nondiamond carbon on a diamond substrate is useful for fabricating a variety of devices. We accomplished such patterning by an unmasked implantation into a diamond substrate followed by photolithography and a selective electrochemical etch. The use of a high resistivity medium coupled with applied biases over 50 V permitted etching without requiring contact between the substrate and an electrode. Many electrolytes gave etches that exhibit high selectivity for nondiamond carbon over both diamond and dielectrics such as photoresist. Optical, electrical, and Raman spectroscopic measurements elucidate the effects of the etch on the implanted diamond surface.
Marchywka, Mike↗
Polyimide based amorphous silicon solar modules
Requirements for space power are increasingly emphasizing lower costs and higher specific powers. This results from new fiscal constraints, higher power requirements for larger applications, and the evolution toward longer distance missions such as a Lunar or Mars base. The polyimide based a-Si modules described are being developed to meet these needs. The modules consist of tandem a-Si solar cell material deposited directly on a roll of polyimide. A laser scribing/printing process subdivides the deposition into discrete cell strips which are series connected to produce the required voltage without cutting the polymer backing. The result is a large, monolithic, blanket type module approximately 30 cm wide and variable in length depending on demand. Current production modules have a specific power slightly over 500 W/Kg with room for significant improvement. Costs for the full blanket modules range from $30/Watt to $150/Watt depending on quantity and engineering requirements. Work to date focused on the modules themselves and adjusting them for the AMO spectrum. Work is needed yet to insure that the modules are suitable for the space environment.
Jeffrey, Frank R.↗
Mapping minerals, amorphous materials, environmental materials, vegetation, water, ice and snow, and other materials: The USGS tricorder algorithm
One of the challenges of Imaging Spectroscopy is the identification, mapping and abundance determination of materials, whether mineral, vegetable, or liquid, given enough spectral range, spectral resolution, signal to noise, and spatial resolution. Many materials show diagnostic absorption features in the visual and near infrared region (0.4 to 2.5 micrometers) of the spectrum. This region is covered by the modern imaging spectrometers such as AVIRIS. The challenge is to identify the materials from absorption bands in their spectra, and determine what specific analyses must be done to derive particular parameters of interest, ranging from simply identifying its presence to deriving its abundance, or determining specific chemistry of the material. Recently, a new analysis algorithm was developed that uses a digital spectral library of known materials and a fast, modified-least-squares method of determining if a single spectral feature for a given material is present. Clark et al. made another advance in the mapping algorithm: simultaneously mapping multiple minerals using multiple spectral features. This was done by a modified-least-squares fit of spectral features, from data in a digital spectral library, to corresponding spectral features in the image data. This version has now been superseded by a more comprehensive spectral analysis system called Tricorder.
Clark, Roger N.↗