Showing papers on "Deposition (chemistry) published in 2002"

A Global Analysis of Acidification and Eutrophication of Terrestrial Ecosystems

Abstract: This paper presents an explorative, quantitative analysis of acidification and eutrophication of natural terrestrial ecosystems caused by excess sulfur (S) and nitrogen (N) deposition. The analysis is based on a steady-state approach, involving the comparison of deposition fluxes with critical loads to identify areas where critical loads are exceeded. Deposition fields for sulfur and nitrogen were obtained from the STOCHEM global chemistry-transport model, and they were combined with estimated base cation deposition to derive net acid deposition fluxes. The results indicate that the critical loads for acidification are exceeded in 7–17% of the global area of natural ecosystems. In addition, comparison of nitrogen deposition with critical loads for eutrophication yielded an exceedance in 7–18% of the global natural ecosystems. Apart from serious problems in the heavily industrialized regions of eastern USA, Europe, the former Soviet Union, and large parts of Asia, risks are also found in parts of South America, and West, East and Southern Africa. Both acidification and eutrophication risks could significantly increase in Asia, Africa and South America in the near future, and decrease in North America and Western Europe. Accounting for the effects of N in the analysis of acidification significantly enlarges the potentially affected areas and moves them away from highly industrialized areas compared to studies considering S deposition alone. Major uncertainties in the approach followed are associated with upscaling, the estimates of S, N and base cation emission and deposition fluxes, the critical loads to describe ecosystem vulnerability and the treatment of soil N immobilization and denitrification.

The origin, composition and rates of organic nitrogen deposition: A missing piece of the nitrogen cycle?

Abstract: Organic forms of nitrogen are widespread in the atmosphere and their deposition may constitute a substantive input of atmospheric N to terrestrial and aquatic ecosystems. Recent studies have expanded the pool of available measurements and our awareness of their potential significance. Here, we use these measurements to provide a coherent picture of the processes that produce both oxidized and reduced forms of organic nitrogen in the atmosphere, examine how those processes are linked to human activity and how they may contribute to the N load from the atmosphere to ecosystems. We summarize and synthesize data from 41 measurements of the concentrations and fluxes of atmospheric organic nitrogen (AON). In addition, we examine the contribution of reduced organic nitrogen compounds such as amino acids, bacterial/particulate N, and oxidized compounds such as organic nitrates to deposition fluxes of AON. The percentage contribution of organic N to total N loading varies from site to site and with measurement methodology but is consistently around a third of the total N load with a median value of 30% (Standard Deviation of 16%). There are no indications that AON is a proportionally greater contributor to N deposition in unpolluted environments and there are not strong correlations between fluxes of nitrate and AON or ammonium and AON. Possible sources for AON include byproducts of reactions between NOx and hydrocarbons, marine and terrestrial sources of reduced (amino acid) N and the long-range transport of organic matter (dust, pollen etc.) and bacteria. Both dust and organic nitrates such as PAN appear to play an important role in the overall flux of AON to the surface of the earth. For estimates of organic nitrate deposition, we also use an atmospheric chemical transport model to evaluate the spatial distribution of fluxes and the globally integrated deposition values. Our preliminary estimate of the magnitude of global AON fluxes places the flux between 10 and 50 Tg of N per year with substantial unresolved uncertainties but clear indications that AON deposition is an important aspect of local and global atmospheric N budgets and deserves further consideration.

Ionized PVD with sequential deposition and etching

Abstract: An iPVD apparatus (20) is programmed to deposit material (10) into high aspect ratio submicron features (11) on semiconductor substrates (21) by cycling between deposition and etch modes within a vacuum chamber (30). The modes operate at different power and pressure parameters. Pressure of more than 50 mTorr, for example, is used for sputtering material from a target while pressure of less than a few mTorr, for example, is used to etch. Bias power on the substrate is an order of magnitude higher for etching, producing several hundred volt bias for etching, but only a few tens of volts for deposition. The alternating etching modes remove deposited material that overhangs edges of features on the substrate, removes some of the deposited material from the bottoms (15) of the features, and resputters the removed deposited material onto sidewalls (16) of the features. The substrate (21) is cooled during deposition and etching, and particularly during etching to substantially below 0°C. RF energy is coupled into the chamber (30) to form a high density plasma, with substantially higher RF power coupled during deposition than during etching. The substrate (21) is moved closer to the plasma source during etching than during deposition.

Spontaneous buildup of giant surface potential by vacuum deposition of Alq3 and its removal by visible light irradiation

Abstract: We observed high and persistent spontaneous buildup of the surface potential (SP) upon vacuum deposition of tris(8-hydroxyquinolinato) aluminum(III) (Alq3) on an Au substrate under dark conditions. SP determined by the Kelvin probe method reached 28 V at a thickness of 560 nm and the surface of the Alq3 film was positively charged. We propose a model in which preferential orientation of the dipole moments of Alq3 molecules is the origin of this buildup of the SP. The intensity of second-harmonic generation was also dramatically increased by the deposition of Alq3 under dark conditions, which supports the notion of a buildup of dipole layers. This giant surface potential was almost completely removed by irradiation of Alq3 molecules with visible light, and irradiation during deposition also prevented the buildup of SP.

CO and NO2 sensing properties of doped-Fe2O3 thin films prepared by LPD

Abstract: The CO and NO2 sensing properties of iron oxide thin films doped with Au and Zn and prepared by a liquid-phase deposition method (LPD) have been investigated. The undoped Fe2O3 sensor was found to be sensitive to NO2 but not to CO. The addition of Zn increases the sensitivity at low temperature towards NO2 and decreases strongly the intrinsic resistance of the iron oxide film. The addition of gold was necessary to obtain a detectable response to CO, the Au-doped ZnO sensor was found the most sensitive to CO. By operating at an appropriate temperature, these sensors could be able to detect selectively CO and NO2, with negligible humidity cross-sensitivity.

Deposition and Fate of Arsenic in Iron- and Arsenic-Enriched Reservoir Sediments

Abstract: Deposition of arsenic to the sediments of Haiwee Reservoir (Olancha, CA) has dramatically increased since March 1996 as a result of an interim strategy for arsenic management in the Los Angeles Aqueduct (LAA) water supply. Ferric chloride and cationic polymer are introduced into the Aqueduct at the Cottonwood treatment plant, 27 km north of the Haiwee Reservoir. This treatment decreases the average arsenic concentration from 25 μg/L above Cottonwood to 8.3 μg/L below Haiwee. Iron- and arsenic-rich flocculated solids are removed by deposition to the reservoir sediments. Analysis of sediments shows a pronounced signature of this deposition with elevated sediment concentrations of iron, arsenic, and manganese relative to a control site. Sediment concentrations of these elements remain elevated throughout the core length sampled (ca. 4% iron and 600 and 200 μg/g of manganese and arsenic, respectively, on a dry weight basis). A pore water profile revealed a strong redox gradient in the sediment. Manganese in the pore waters increased below 5 cm; iron and arsenic increased below 10 cm and were strongly correlated, consistent with reductive dissolution of iron oxyhydroxides and concurrent release of associated arsenic to solution. X-ray absorption near-edge spectroscopy revealed inorganic As(V) present only in the uppermost sediment (0-2.5 cm) in addition to inorganic As(III). In the deeper sediments (to 44 cm), only oxygen-coordinated As(III) was detected. Analysis of the extended X-ray absorption fine structure spectrum indicates that the As(III) at depth remains associated with iron oxyhydroxide. We hypothesize that this phase persists in the recently deposited sediment despite reducing conditions due to slow dissolution kinetics.

Effect of colloid characteristics on the fabrication of ZnO nanowire arrays by electrophoretic deposition

Abstract: In this study ZnO colloidal suspensions with varied characteristics were synthesized by varying the amount of added sodium hydroxide. The template-mediated preparation for nanosized ZnO arrays was conducted by electrophoretic deposition in the nanochannels of anodic alumina membranes. The effect of colloid characteristics on the deposition of ZnO nanowire arrays was investigated, and the related deposition mechanisms, morphologies and optical properties of the deposits were discussed. The deposited ZnO nanoarrays were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) studies. It was found that both the morphology and the deposition rate of ZnO nanowire arrays were influenced by the pH of the suspension and the applied voltage. The particle surface charge and size changed with the pH of the suspension, which in turn affected the deposition characteristics. The deposition rate of nanowire arrays was high at the initial stage and then approached a saturation value. The deposition rate also increased with increasing zeta potential of the particles and the applied voltage for EPD of ZnO nanowires. The photoluminescence properties of ZnO arrays were largely determined by particle size and surface properties of the nanoparticles comprising the nanowire arrays.

Controls on suppression of methane flux from a peat bog subjected to simulated acid rain sulfate deposition

Abstract: The effect of acid rain SO42− deposition on peatland CH4 emissions was examined by manipulating SO42− inputs to a pristine raised peat bog in northern Scotland. Weekly pulses of dissolved Na2SO4 were applied to the bog over two years in doses of 25, 50, and 100 kg S ha−1 yr−1, reflecting the range of pollutant S deposition loads experienced in acid rain-impacted regions of the world. CH4 fluxes were measured at regular intervals using a static chamber/gas chromatographic flame ionization detector method. Total emissions of CH4 were reduced by between 21 and 42% relative to controls, although no significant differences were observed between treatments. Estimated total annual fluxes during the second year of the experiment were 16.6 g m−2 from the controls and (in order of increasing SO42− dose size) 10.7, 13.2, and 9.8 g m−2 from the three SO42− treatments, respectively. The relative extent of CH4 flux suppression varied with changes in both peat temperature and peat water table with the largest suppression during cool periods and episodes of falling water table. Our findings suggest that low doses of SO42− at deposition rates commonly experienced in areas impacted by acid rain, may significantly affect CH4 emissions from wetlands in affected areas. We propose that SO42− from acid rain can stimulate sulfate-reducing bacteria into a population capable of outcompeting methanogens for substrates. We further propose that this microbially mediated interaction may have a significant current and future effect on the contribution of northern peatlands to the global methane budget.

Nitrogen deposition and extinction risk in the northern pitcher plant, sarracenia purpurea

Abstract: Chronic nitrogen deposition may affect the long-term survival of plant pop- ulations. The northern pitcher plant, Sarracenia purpurea, is a model system for forecasting extinction risk in the face of increasing nitrogen deposition. Uptake of N occurs directly from pitcher leaves, which fill with rainwater and prey, and accumulate nutrients. We monitored the demography of two populations of S. purpurea in ombrotrophic bogs of northern New England (USA) and described population growth with a four-stage matrix model. Growth, survivorship, and reproduction were in close balance, and the model pre- dicted population growth rates close to zero, with long doubling times. In a life-table response experiment, we manipulated in situ concentrations of nitrogen and phosphorus in pitcher plant leaves. At high levels of N and high N:P ratios, population growth rates were significantly depressed. Using local N-deposition records, we forecast different N-deposition scenarios and built a nonstationary population growth model, in which a different transition matrix at each time step reflected the current deposition regime. Autocorrelation in the time series of N deposition rates generated periodic increases in population size superimposed on long-term trends of exponential decline. For a 1% annual increase in N deposition rates, this model predicted a substantial risk of extinction at 100 yr (0.38-0.70), with an estimated population survival time of 160-180 yr. Although slow-growing populations of Sarracenia can buffer substantial environmental change, chronic increases in N deposition rate threaten population persistence.

Powder Preparation in Aerosol Deposition Method for Lead Zirconate Titanate Thick Films

Abstract: The influence of a pre-process for a starting powder in the deposition of ferroelectric thick films using the aerosol deposition method (ADM) was investigated. When a dry-milling procedure was introduced to the preparation of the ferroelectric powder, the deposition rate of ADM increased significantly up to 30-fold and reached 73 µm/min for a 5 mm2 area. However, density and electrical properties of the thick film decreased. If heat treatment at 800°C for 4 h was additionally introduced to the pre-process of the starting powder, the deposition rate increased up to 7–10-fold as compared with that for a starting powder and the electrical properties were improved from Pr=20 µC/cm2 at Ec=50 kV/cm to 32 µC/cm2 at Ec=45 kV/cm.

Potassium limits potential growth of bog vegetation under elevated atmospheric CO2 and N deposition

Abstract: Reference ECOS-ARTICLE-2006-011View record in Web of Science Record created on 2006-04-20, modified on 2016-08-08

Deposition Apparatus and Deposition Method

Abstract: A deposition apparatus is provided for manufacturing an organic compound layer having a plurality of function regions. The deposition apparatus includes a plurality of evaporation sources within a deposition chamber, for enabling continuous formation of respective function regions comprised of organic compounds and, further, formation of a mixed region at an interface between adjacent ones of the function regions. With the deposition apparatus having such fabrication chamber, it is possible to prevent impurity contamination between the functions regions and further possible to form an organic compound layer with an energy gap relaxed at the interface.

Effects of increased nitrogen deposition on the distribution of 15N-labeled nitrogen between Sphagnum and vascular plants

Abstract: To elucidate the sensitivity of bog ecosystems to high levels of nitrogen (N) deposition, we investigated the fate of 15N-labeled N deposition in bog vegetation in the Netherlands, both at ambient and increased N deposition. We doubled N deposition by adding 5 g N m−2 y−1 as dissolved NH4NO3 during three growing seasons to large peat monoliths (1.1 m diameter) with intact bog vegetation kept in large outdoor containers. A small amount of 15N tracer was applied at the start of the second growing season, and its distribution among Sphagnum, vascular plant species, and peat was determined at the end of the third growing season. The 15N tracer was also applied to additional plots at the untreated field site to check for initial distribution. One week after addition, 79% of the total amount of 15N retrieved was found in the living Sphagnum layer and less than 10% had been captured by vascular plants. Fifteen months later, 63% of the total amount of 15N retrieved was still present in the living Sphagnum layer at ambient N deposition. Increased N deposition significantly reduced the proportion of 15N in Sphagnum and increased the amount of 15N in vascular plants. Deep-rooting vascular plant species were significantly more 15N enriched, suggesting that at higher atmospheric inputs N penetrates deeper into the peat. Our results provide the first direct experimental evidence for that which has often been suggested: Increased atmospheric N deposition will lead to increased N availability for vascular plants in ombrotrophic mires.

Exchange fluxes of NO2 and O3 at soil and leaf surfaces in an Amazonian rain forest

Abstract: [1] Trace gas exchange of NO2 and O3 at the soil surface of the primary rain forest in Reserva Biologica Jaru (Rondonia, Brazil) was investigated by chamber and gradient methods. The ground resistance to NO2 and O3 deposition to soil was quantified for dry and wet surface conditions using dynamic chambers and was found to be fairly constant at 340 ± 110 and 190 ± 70 s m−1, respectively. For clear-sky conditions, the thermal stratification of the air in the first meter from the forest floor was stable during daytime and unstable during nighttime. The aerodynamic resistance to NO2 and O3 deposition to the ground in the first meter above the forest floor was determined by measurements of 220Rn and CO2 concentration gradients and CO2 surface fluxes. The aerodynamic resistance of the 1-m layer above the ground was 1700 s m−1 during daytime and 600 s m−1 during nighttime. The deposition flux of O3 and NO2 was quantified for clear-sky conditions from the measured concentrations and the quantified resistances. For both trace gases, deposition to the soil was generally observed. The O3 deposition flux to the soil was only significantly different from zero during daytime. The maximum of −1.2 nmol m−2 s−1 was observed at about 1800 and the mean daytime flux was −0.5 nmol m−2 s−1. The mean NO2 deposition flux during daytime was −1.6 ng N m−2 s−1 and during nighttime −2.2 ng N m−2 s−1. The NOx budget at the soil surface yielded net emission day and night. The NO2 deposition flux was 74% of the soil NO emission flux during nighttime and 34% during daytime. The plant uptake of NO2 and O3 by the leaves of Laetia corymbulosa and Pouteria glomerata, two typical plant species for the Amazon rain forest, was investigated in a greenhouse in Oldenburg (Germany) using branch cuvettes. The uptake of O3 was found to be completely under stomatal control. The uptake of NO2 was also controlled by the stomatal resistance but an additional mesophyll resistance of the same order of magnitude as the stomatal resistance was necessary to explain the observed uptake rate.

Influence of inert gas pressure on deposition rate during pulsed laser deposition

Abstract: The deposition rates of permalloy and Ag are monitored during pulsed laser deposition in different inert gas atmospheres. Under ultrahigh vacuum conditions, resputtering from the film surface occurs due to the presence of energetic particles in the plasma plume. With increasing gas pressure, a reduction of the particle energy is accompanied with a decrease of resputtering and a rise in the deposition rate for materials with high sputtering yield. In contrast, at higher gas pressures, scattering of ablated material out of the deposition path between target and substrate is observed, leading to a decrease in the deposition rate. While in the case of Xe and Ar these processes strongly overlap, they are best separated in He. A He pressure of about 0.4 mbar should be used to reduce the kinetic energy of the deposited particles, to reach the maximum deposition rate and to avoid implantation of the particles. This is helpful for the preparation of stoichiometric metallic alloy films and multilayers with sharp interfaces.

Anhydrous cosmetic compositions containing polyols

Abstract: Disclosed is anhydrous cosmetic compositions comprising:(a) a hydrophobic polyol; and(b) a hydrophilic polyol; which can provide improved conditioning benefits such as moisturizing benefit, and also can provide improved deposition of oily conditioning agents when included in the compositions.