Showing papers on "Deposition (chemistry) published in 1980"

Structure and Properties of LPCVD Silicon Films

Abstract: Silicon films deposited by low pressure chemical‐vapor deposition over the temperature range from 525° to 725°C were investigated. It was found that polycrystalline films are formed above 600°C and are more stable than the amorphous films deposited at lower temperatures. Their crystal structure is a strong function of the deposition temperature and a weaker function of the deposition rate. Either the {110} or the {100} texture may dominate the structure, depending primarily on the deposition temperature. The electrical resistance obtained on doping the LPCVD films that are polycrystalline as deposited is maximum for films deposited at the lower temperatures (near 600°C), although this dependence on deposition temperature decreases after annealing at higher temperatures. Dopant atoms reversibly segregate to the grain boundaries during lower temperature heat‐treatments subsequent to doping and are dispersed at higher temperatures, with corresponding changes in resistivity. The oxidation rate is only a weak function of the deposition temperature, although the initially amorphous films may oxidize somewhat more rapidly. The index of refraction of amorphous films is significantly higher than that of polycrystalline films.

Electrowinning of Silicon from K 2SiF6 ‐ Molten Fluoride Systems

Abstract: The electrowinning of silicon from solutions of in fluoride melts at 745°C has been achieved. Electrolysis close to the deposition potential gave dense, coherent, and well‐adherent deposits. Up to 3 mm thick films were grown using a concentration of 4–6 m/o. The polycrystalline silicon has a columnar structure with grain size up to 100 μm. The morphology of the electrodeposited silicon onto silver substrates and its dependence on the deposition parameters is discussed. The purity of the deposits is substantially higher than that previously reported for electrodeposited silicon.

Episodicity of Phosphate Deposition and Deep Ocean Circulation-a Hypothesis

Abstract: The geochemical cycle of phosphorus includes a cold deep ocean water phosphorus sink that recycles into the shallow water biosphere by vertical mixing At the present time water of this deep ocean sink is apparently undersaturated with respect to apatite even at shallow water temperatures and pressures In the present ocean in shallow water areas of upwelling ocean currents apatite probably is being precipitated diagenetieally within the marine sediments from interstitial waters but not at the sediment water interface In ancient oceans in shallow areas washed by upwelling ocean currents it probably at times was precipitated primarily at the sediment water interface This difference between the present and past oceans conforms with the empirically derived hypotheses of episodicity of phosphate deposition of earlier workers A general hypothesis of the episodicity of marine phosphate deposition caused by variations of deep ocean circulation is summarized as follows I episodes of phosphogenesis occur at the onset of episodes of oceanic vertical mixing after episodes of stability during which the phosphorus content of the deep ocean has built up to high levels 2 the major phosphogenic episodes of the Cretaceous to early Tertiary are due to phosphorus withdrawal from the deep ocean phosphorus sink primarily by equatorial upwelling at the time of high level warm seas and 3 the major phosphogenic episodes of the Cambrian Ordovician and Permian Periods and the Miocene Epoch are due to phosphorus withdrawals from the deep ocean phosphorus sink primarily by trade wind beIt upwelling at the time of transition from the high level warm oceans to low level cold oceans the transition relates to glacial episodes This general process of phosphogenesis began after the transition from the environment that existed 2 200 m y ago with an acidic ocean and oxygen free atmosphere to an environment of an alkaline ocean and an oxygen rich atmosphere

Glow discharge preparation of amorphous hydrogenated silicon from higher silanes

Abstract: Amorphous hydrogenated silicon has been deposited by plasma decomposition of Si2H6 and Si3H8. A major feature of the process is a deposition rate enhancement of over a factor of 20 compared to monosilane. The resulting films are compositionally similar to monosilane‐produced intrinsic a‐Si(H), but films deposited at 300 °C substrate temperature show greater photoconductivity. On the basis of our deposition experiments and the known thermolysis chemistry of the silanes, a conjectural model for the deposition process is presented.

Chemistry of precipitation at Gainesville, Florida

Abstract: Technical report: Rainwater collected in Gainesville, Fla., in 1976-77 was analyzed for chemical content. Analyses indicate that precipitation is the primary mechanism of deposition of sulfur oxides, ammonium, nitrogen oxides, magnesium, and potassium ions. Dry fallout is the primary means of deposition for ions of sodium, chlorine, and calcium. Heavy metals concentrations were variable for both rainfall and dry fallout. (6 graphs, 36 references, 2 tables)

Plasma spectroscopy control and analysis of a-Si:H deposition

Abstract: Plasma emission spectra have been measured for two different deposition methods, i. e., reactive sputtering of Si and glow discharge decomposition of SiH4. The possibility has been indicated that a-Si:H film can be prepared controllably by measuring the relative intensities of Ar, H2, H and SiH4 emission lines during deposition without disturbance to plasma. Some aspects in deposition kinetics have been discussed by comparing the emission lines during deposition with the properties of the deposited films.

Acid precipitation and sulfate deposition in Florida.

Abstract: The acidity of rainfall in Florida has increased markedly in the past 25 years, and the average sulfate and nitrate concentrations have increased by factors of 1.6 and 4.5, respectively, over the period. Annual average pH values below 4.7 now occur over the northern three quarters of the state. Summer rainfall has average pH values 0.2 to 0.3 unit lower than winter rainfall, and sulfate concentrations at most sites are higher in summer. The annual deposition of H+ (about 300 to 500 equivalents per hectare) in northern Florida is a third to a half of the deposition in the heavily impacted northeastern United States; comparable figures for excess sulfate (derived from sulfur dioxide) are 7 to 11 kilograms of sulfur per hectare or 50 to 90 percent of the sulfate deposition rates at Hubbard Brook, New Hampshire.

Mechanisms for intense relativistic electron precipitation

Abstract: From an indepth analysis of over fourteen months of data from the S3-3 satellite, 313 relativistic electron precipitation events have been detected with essentially isotropic flux over the upward looking hemisphere. The majority of events occur at night in a narrow latitudinal zone embedded within a broader region of intense energetic ion precipitation. Three distinct classes of precipitation have been identified each associated with strong diffusion resonant scattering by known magnetospheric plasma waves. The intense electron energy deposition Is a major source of middle atmospheric odd hydrogen and odd nitrogen molecules at sub-auroral latitudes; this can lead to observable catalytic destruction of mesospheric ozone.

Physics of airborne particles and their deposition in the lung.

Abstract: There have been a number of books and papers published on the physics of airborne particle^'.^ and a comparable number of expositions on particulate deposition in the airways and lungs of There is a large difference in the sophistication of these efforts. Often papers in both categories are by the same authors since it is well known that the respiratory deposition of particles is, to a considerable extent, described by the physical laws of particle behavior in the airborne state. In fact, it was the realization of this relationship that prompted W. Findeisen to accomplish his masterful work in Hamburg during 1931-2 described in his paper “Ober das Absetzen kleiner, in der Luft Suspendierter Teilchen in der Menschlichen Lunge bei der Atmung,”’ which was the starting point of many of the subsequent modeling efforts. Despite this rich background of information, the organizers of this conference have asked me to speak on the topic of aerosol physics and particulate deposition in the lungs. It must follow that they want a description that is uncomplicated and directed as much as possible toward airborne contagion. These will be my objectives.

Marine influence in the Triassic ‘uplands’

Abstract: Several authors1–4 have concluded that Mesozoic reptiles found in some fissures of the Bristol area belonged to a distinctive ‘upland’ fauna. We describe here a new fissure deposit recently found in the Carboniferous limestone near Thornbury which contains characteristic ‘upland’ reptiles associated with an assemblage of Rhaetian marine phytoplankton and land-derived palynomorphs. The marginal marine location of deposition deduced from the palynomorphs conflicts with the separation of late Triassic reptiles into ‘upland’ and ‘lowland’ regimens.

Energy costs of protein deposition

Abstract: Energy costs of protein deposition have been estimated directly from biochemical considerations. Maximum efficiencies of the utilization of the metabolizable energy for protein deposition of about 85% and 80% for monogastrics and ruminants, respectively, have been derived. Lower efficiencies, however, may very well occur in the animal body in view of our lack of precise knowledge on the biochemistry of protein deposition and on rate of protein turnover.

Present Day Dune Processes and Dune Morphology on the Łeba Barrier, Polish Coast of the Baltic

Abstract: Relations and interdependence between factors determining the processes of eolian transportation and deposition and results of these processes were studied in the area of the Łeba barrier on the Po...

Deposition of coatings from fine powder reactants

Abstract: A method and apparatus are disclosed for producing a film on a substrate surface from a cloud of dust-sized particles of a coating reactant.