Showing papers on "Deposition (chemistry) published in 1992"
TL;DR: The role of nitric acid in surface water acidification in the Catskill Mountains of New York has been investigated in this article, showing that during high-flow periods, Nitrate increases with increased stream flow throughout the year except during the late summer when biological activity and its attendant nitrogen uptake are greatest.
Abstract: Research on the effects of acidic deposition in the United States has focused largely on the role of sulfur deposition in the acidification of surface waters. Results from both long-term (up to 70 years) and recent monitoring of stream chemistry in the Catskill Mountains of New York indicate, however, that nitric acid has a significant and increasing role in surface water acidification that, during high-flow periods, rivals the role of sulfuric acid. Nitrate increases with increased stream flow throughout the year except during the late summer, when biological activity and its attendant nitrogen uptake are greatest; peak concentrations as high as 128 micrograms/l have been recorded during spring snowmelt. In contrast, sulfate concentrations decrease with increased flow.
223 citations
TL;DR: In this article, a steady state soil chemistry model was used to calculate the critical load of acidity for forest soils and surface waters at Lake GArdsjon in S.W. Sweden.
Abstract: A steady state soil chemistry model was used to calculate the critical load of acidity for forest soils and surface waters at Lake GArdsjon in S.W. Sweden. The critical load of all acid precursors (potential acidity) for the forest soil is 1.64 kmolc ha−1 yr−1, and 1.225 kmolc ha−1 yr−1 for surface waters. For the most sensitive receptor, the critical load is exceeded by 1.0 kmolc ha−1 yr−1, and a 80% reduction in S deposition is required, if N deposition remains unchanged. The critical load is largely affected by the present immobilization of N in the terrestrial ecosystem which is higher than the base cation uptake. The model, PROFILE, is based on mass balance calculations for the different soil layers. From measurable soil properties, PROFILE reproduces the present stream water composition as well as present soil solution chemistry. The model calculates the weathering rate from independent geophysical properties such as soil texture and mineral composition.
213 citations
TL;DR: In this article, the first season of the deep drill operation (GRIP) at Summit, Central Greenland (72° 34' N, 37° 38'W) continuous ammonium (NH4+) measurements were performed between 100 and 600 m depth covering the time period from 330 to 2500 years BP.
Abstract: Biomass burning is influencing the atmospheric chemistry by emitting large amounts of reactive species such as hydrocarbons, organic acids and nitrogen compounds [Andreae et al, 1988] Polar ice cores provide a unique record of precipitation whose chemistry reflects the atmospheric composition at the time of deposition The analysis of such ice samples therefore allows an estimate to be made of the concentration of atmospheric impurities in the past During the first season of the deep drill operation (GRIP) at Summit, Central Greenland (72° 34' N, 37° 38'W) continuous ammonium (NH4+) measurements were performed between 100 and 600 m depth covering the time period from 330 to 2500 years BP The NH4+ concentrations show seasonal variations between 1–20 ngg−1 with some sporadic high values up to 600 ngg−1 in narrow layers The chemical fingerprint points to biomass burning causing the high ammonium peaks
155 citations
TL;DR: In this paper, the authors examined the mechanism of film deposition in a planar rf CH4 discharge plasma and made measurements of the spatial distributions of the deposition rate and optical emission intensity along the discharge axis between parallel electrodes.
Abstract: To examine the mechanism of film deposition in a planar rf CH4 discharge plasma, measurements were made of the spatial distributions of the deposition rate and optical emission intensity along the discharge axis between parallel electrodes. Optical‐absorption properties of the deposited carbon films were also measured over both the infrared and visible regions. To measure the spatial deposition rates, the substrate surface was elevated from the cathode electrode with the use of quartz glass plates. It was found that the spatial properties of films, which were deposited in both the ion‐sheath and bulk‐plasma regions, differ markedly from each other. The carbon films obtained from within the ion‐sheath region were found to be extremely hard, while those obtained in the bulk‐plasma region were polymerlike soft films. This disparity was thought to be due to the difference in the kinetic energy of the ions bombarding the substrate surface; that is, the substrate surface potential could be changed by elevating the substrate surface. These results were incorporated in the discussion of the deposition mechanism, with emphasis on the contribution of ion bombardment to the film‐deposition process. It was tentatively concluded that the film‐deposition rate was predominantly dependent on the product of the ion kinetic energy and ion flux density that reached the substrate surface.
149 citations
TL;DR: A wide variety of techniques for growing diamond at low pressure and low temperature have emerged from laboratories all over the world as discussed by the authors, and the state-of-the-art of the major techniques is summarized.
115 citations
TL;DR: In this paper, the authors considered the presence or absence of volcanic rocks is not a clear indication of whether sedimentary manganese deposits, particularly in the ancient geologic record, are the result of a totally terrigenous or a totally volcanogenic source.
Abstract: Concentration of manganese in solution and its deposition takes place by redox-controlled processes in a variety of modern and ancient geologic and geochemical environments. Modern Mn deposition occurs predominantly in deep-sea areas rather than shallow-water domains. Although deep-sea sedimentary deposits dominate, hydrothermal contribution of Mn to the ocean system may be substantial. Mn deposition from hydrothermal solutions at or near sea-floor-spreading centers and less commonly in island-arc areas is known. In addition, near- and far-field dispersion of Mn from vent sites is also substantial. Such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of Mn in seawater. Thus, even in sedimentary deposit domains, at least partial derivation of Mn from a hydrothermal source is possible. Sedimentary Fe-Mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid-water column, oxygen-minimum zones. Thus, the presence or absence of volcanic rocks is not a clear indication of whether sedimentary Mn deposits, particularly in the ancient geologic record, are the result of a totally terrigenous or a totally volcanogenic source. Abyssal Fe-Mn nodules are considered to form from a basin water (hydrogenous) and/or pore water (early diagenetic) supply of metals, but in most cases the extent of supply from either of the sources is unknown. The metal incorporation mechanisms of free-moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition. Therefore, no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition. The determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules. Biological participation, directly or indirectly, controls Mn deposition. The stratified Black Sea demonstrates the concentration of Mn in solution in an anoxic zone, its advection toward the redox interface, and its precipitation in an oxygenated condition. Similar stratified basins are contemplated for ancient Mn deposition in shallow-water basin-margin areas. Geologic and geochemical signatures indicate that during sea-level highstands, stratified basins formed in which Mn was concentrated in solution in the anoxic part. Corresponding transgression led to the impingement of the redox interface on the continental shelf, and precipitation of Mn oxides could take place across the interface during transgression-regression cycles. Offshore, in anoxic or dysaerobic conditions,Mn carbonate could form by early diagenetic reaction of Mn (super +2) with CO 2 or HCO 3 (super -) produced by organic carbon oxidation. Critical Mn deposits occurring in transgressive, glaciogenic, and black shale-bearing ancient sequences support this paleoenvironmental model for Mn deposition.
114 citations
TL;DR: In this paper, a 3-yr period of 1986-89 at Strengbach, a small granitic basin in the Vosges mountains (north-eastern France), was studied.
Abstract: Hydrochemical budgets have been obtained for the 3-yr period 1986–89 at Strengbach, a small granitic basin in the Vosges mountains (north-eastern France). Here, the spruce forest shows both yellowing and crown thinning, symptoms of forest decline. Water amount and surface water chemistry were monitored in each ecosystem compartment. Bulk precipitation is acidic. Some pollution episodes occur in winter and early spring, but the annual bulk deposition acidity is rather low. Throughfall however, is much more concentrated, particularly for H+ and associated strong acid anions. These inputs come as occult deposits which comprise major ecosystem inputs, as confirmed by the chloride balance for the catchment. Input-output budgets for the catchment indicate a net deficit of base cations, especially calcium. Sulfate also shows a net loss while N budget is well balanced. As the soil exchange capacity is nearly exhausted for base cations, and dominated by H+ and Al, the neutralization of incident acid inputs occurs mainly in the weathered bedrock. Silicate weathering processes lead to high losses of cations and of silica. Aluminium hydroxide is precipitated; however, bicarbonate remains very low indicating poorly-buffered surface water.
109 citations
Journal Article•
108 citations
TL;DR: As a consequence of decreases in the emission rate of sulphur in eastern North America in the late 1970s and early 1980s, sulphate deposition in central Ontario declined by about 40%, but has remained constant for about six years.
98 citations
TL;DR: In this paper, a simple bulk plasma chemistry model combined with an analytical sheath model was developed to qualitatively explain the experimental findings, suggesting that the ionenhanced deposition rate is directly proportional to oxygen ion flux, with a reactive sticking coefficient approaching unity.
Abstract: The deposition rate of silicon dioxide from tetraethylorthosilicate/O2 capacitively coupled plasmas increases with increasing applied rf power, increasing total pressure and decreasing wafer temperature. These measured deposition rate dependences can be explained by a simple plasma deposition model in which deposition occurs through both an ion‐assisted and an oxygen atom initiated pathway. The relative contributions of these pathways were roughly isolated using limiting step coverage measurements on low aspect ratio trenches. Limiting step coverages decreased, and hence directionality increased, with increasing rf power density, decreasing total pressure, and increasing wafer temperature. A simple bulk plasma chemistry model combined with an analytical sheath model was developed to qualitatively explain our experimental findings. The model suggests that the ion‐enhanced deposition rate is directly proportional to oxygen ion flux, with a reactive sticking coefficient approaching unity. Using literature va...
TL;DR: Paleomagnetic results from 182 cores sampled at 15 sites in Pliocene and Pleistocene clayey units in the Sant'Arcangelo basin (southern Italy) and its surroundings are presented in this paper.
Abstract: New paleomagnetic results from 182 cores sampled at 15 sites in Pliocene and Pleistocene clayey units in the Sant'Arcangelo basin (southern Italy) and its surroundings are presented. They indicate that this area underwent a counterclockwise rotation of 22° after the deposition of the Lower Pleistocene clays.
TL;DR: The kinetics of selective deposition of epitaxial Si1−xGex layers in an atmospheric pressure reactor have been examined in this article, showing that the Si component of the deposition rate more than the Ge component, increasing the Ge fraction in the deposited layer.
Abstract: The kinetics of selective deposition of epitaxial Si1−xGex layers in an atmospheric‐pressure reactor have been examined. Adding HCl to the SiH2Cl2/GeH4/H2 system decreases the Si component of the deposition rate more than the Ge component, increasing the Ge fraction in the deposited layer. HCl addition also decreases boron incorporation. When deposited selectively on oxide‐patterned wafers, lateral transport of the depositing materials causes the deposition rate and the Ge fraction to be higher in small patterns than in large patterns and also to be higher near the edges of patterns than at their centers.
TL;DR: To investigate the belowground effects of a cloud water deposition gradient between two mature red spruce stands on the summit of Whitetop Mountain, Virginia, the chemistries of precipitation, throughfall, and soil solution were monitored over a 2-year period, and fine-root distributions were characterized.
Abstract: The decline of red spruce (Picearubens Sarg.) at high elevations in eastern North America has been linked in time and space with exposure to acidic cloud water. To investigate the belowground effects of a cloud water deposition gradient between two mature red spruce stands on the summit of Whitetop Mountain, Virginia, the chemistries of precipitation, throughfall, and soil solution were monitored over a 2-year period, and fine-root distributions were characterized. Deposition of water, sulfate, nitrate, and ammonium in throughfall and stemflow was from 15 to 55% greater at the site with greater exposure to cloud water deposition (high cloud site), depending upon the particular ion and year. Soil solution nitrate concentrations were highly variable over time, and base cation, Al, and H ion concentrations were highly correlated with nitrate in both organic and mineral horizons at both sites. Soil solution nitrate, base cation, Al, and H ion concentrations were two to six times greater during periods of low ...
TL;DR: In this article, the composition of pulsed-ultraviolet-laser-deposited Y-Ba-Cu-O films was examined as a function of position across the substrate, laser fluence, laser spot size, substrate temperature, target conditioning, oxygen pressure and target-substrate distance.
Abstract: The composition of pulsed-ultraviolet-laser-deposited Y-Ba-Cu-O films was examined as a function of position across the substrate, laser fluence, laser spot size, substrate temperature, target conditioning, oxygen pressure and target-substrate distance. Laser fluence, laser spot size, and substrate temperature were found to have little effect on composition within the range investigated. Ablation from a fresh target surface results in films enriched in copper and barium, both of which decrease in concentration until a steady state condition is achieved. Oxygen pressure and target-substrate distance have a significant effect on film composition. In vacuum, copper and barium are slightly concentrated at the center of deposition. With the introduction of an oxygen background pressure, scattering results in copper and barium depletion in the deposition center, an effect which increases with increasing target-substrate distance. A balancing of these two effects results in stoichiometric deposition.
01 Jan 1992
TL;DR: In this article, the structure of erbium films of 600 nm thickness on molybdenum substrates of different surface roughness (Rq=151, 500 and 850 nm), glass substrates, and amourphous carbon substrates was investigated by electron microscopy and X-ray diffraction.
TL;DR: In this paper, the influence of current density on the coulometric efficiency of β-PbO2 deposition in 0.5 M cM lead nitrate, the nonstoichiometry, impurity of α-PBO2 and voltammetric double layer capacitance have been studied.
Abstract: The influence of current density on the coulometric efficiency of β-PbO2 deposition in 0.5 M cM lead nitrate, the nonstoichiometry, impurity of α-PbO2 and voltammetric double layer capacitance have been studied. While the coulometric efficiency is about 95% at current densities less than 30 mA cm−2, it decreases at higher current densities. The oxygen deficiency, δ, in β-PbO2-δ has been found to be invariant with the current density. X-ray diffraction studies provide a linear decrease in the weight percent of α-PbO2 as an impurity in the β-PbO2 with increase in current density, and the α-PbO2 is found to be absent at 100mA cm−2 or higher. The estimated double layer capacitance from the cyclic voltammograms recorded in the potential range 0.70–1.10V, increases with deposition current density, indicating enhanced surface area.
01 Jan 1992
TL;DR: In this article, the authors measured concentrations of major ions in nine sections of a central Greenland ice core and found that concentrations of both SO 4 2− and NO 3 − have increased dramatically over the last 250 years, up to three to four times the 18th century levels.
Journal Article•
TL;DR: The mapping of steady-state stream chemistry indicates that streams in Maryland are still acidfying under the present deposition load, and land-use seems to play an important role in maintaining neutral pH in many of the streams of Maryland.
TL;DR: In this paper, a remarkable ambient effect on the resistance of CVD diamond during cooling after deposition has been observed, where the diamond films that were cooled slowly down to room temperature (RT) in the 10-3 Torr range after deposition showed relatively low resistances in the range of 106~107 Ω.
Abstract: A remarkable ambient effect on the resistance of CVD diamond during cooling after deposition has been observed. The diamond films that were cooled slowly down to room temperature (RT) in the 10-3 Torr range after deposition showed relatively low resistances in the range of 106~107 Ω. On the other hand, high resistances over 1013 Ω were observed for diamond films that were cooled down to RT in an oxygen or an air ambient and at atmospheric pressure. Among these surfaces a substantial difference was observed in the electronic structure as studied by electron energy loss spectroscopy.
TL;DR: In this paper, the authors surveyed four study areas along a wet sulfate deposition gradient in north-central Pennsylvania and found that species richness was significantly less in high sulfate-deposition areas than in low sulfate areas.
Abstract: Lichens were surveyed at four study areas along a wet sulfate deposition gradient in north-central Pennsylvania. Species richness was significantly less in high sulfate deposition areas than in low sulfate deposition areas. Although the causal agents for these differences are not known, it is hypothesized that SO, is responsible at least in part.
Journal Article•
TL;DR: The Integrated Forest Study (IFS) was a long-term research project designed to determine the effects of atmospheric deposition on forest nutrient cycles as mentioned in this paper, which was used for several years at 13 research forests in North America and Europe using a standard set of protocols.
TL;DR: In this paper, the dependence of the deposition rate on gas pressure, RF bias power, and substrate temperature was measured at a temperature between -120°C and 150°C in CH2F2, CHF3, CF4, and CHClF2 gas plasmas.
Abstract: Polymer deposition on Si and SiO2 surfaces has been investigated in CH2F2, CHF3, CF4, and CHClF2 gas plasmas, using a microwave plasma etching system. The dependence of the deposition rate on gas pressure, RF bias power, and substrate temperature was measured at a temperature between -120°C and 150°C. The deposition rate increased with decreasing temperature in CH2F2, CHF3, and CHClF2 plasmas. The deposition of polymers occured only below -60°C in the CF4 plasma. The obtained dependence of the deposition rate on gas pressure was examined in terms of the volume of adsorbed particles. X-ray photoelectron spectroscopy measurement showed that the number of bondings between C and F atoms in deposited polymers increases with decreasing temperature and RF power, and increasing gas pressure.