Decrease In Deposition Rate Research Articles

Current pulse with reverse plating of nickel-iron alloys in a sulphate bath

Ni-Fe alloys were galvanostatically pulse plated on copper rotating disk electrodes in sulphate solutions. Using a reverse current during the pulse relaxation period causes the dissolution of both iron and nickel. Anodic passivation of pure nickel was not observed in the binary Ni-Fe alloys since nickel dissolves during the period of reverse current. Boric acid increases the selectivity of iron in the current-controlled process. Higher solution pH enhances both nickel and iron reductions. Higher pulse frequency induces a decrease of average nickel deposition rate, and as a result, iron composition in the alloy is increased. Raising temperature causes the increase of iron contents in the alloys.

Prolonged laser ablation effects of YBCO ceramic targets during thin film deposition: Influence of processing parameters

Cumulative laser irradiation during high-Tc superconducting thin film pulsed laser deposition (PLD) may have a detrimental effect on film characteristics. Initial decrease of deposition rate and gradual shift of the center of the deposited material spot towards the incoming laser beam were registered on cold glass substrates. Their absorbance was used for evaluation of the film thickness distribution over the substrate area. At the initial stage, two components of the spot could be distinguished along its short axis: central (∼cosn θ, n≫1) and peripherial (∼cos θ), while with cumulative irradiation the thickness followed an overall cosm θ (m<n) angular distribution. Two stages of the laser-induced plasma optical emission evolution were observed, according to target surface morphology modification. Compositional and morphology changes of the ceramic YBCO target under prolonged XeCl laser irradiation were studied by EDAX and SEM for different processing parameters — laser fluence and oxygen environment. The results can be consistently explained suggesting the existence of an additional effective ablation threshold imposed by the modified surface relief.

Large-scale spatial trends in recent firn chemistry along an east-west transect through central Greenland

Seventeen shallow firn cores drilled along an ∼ 1000-km-long east-west traverse through central Greenland (EGIG-line) and dated by annual δ 18 O H 2 O 2 stratigraphy have been evaluated in seasonal resolution for their nitrate, sulphate, chloride, sodium and calcium content covering the time span ∼ 1982–1992. Each component showed a geographically uniform seasonal input pattern along the EGIG-line corresponding to what is observed at other sites over the central Greenland Ice Sheet. Going across the main ice divide from west to east, the strong decline in the mean snow accumulation rate (associated with precipitating air masses advected from the west) causes a linear decrease in the average deposition rates of nitrate, sulphate and calcium with longitude. Sea-salt components, however, exhibit an exponential decline (scale length ∼ 320 km) from the west to the ice divide but constant rates in the eastern part. The mean firn concentrations of all ions show a systematic increase from west to east related to the concurrent snow accumulation decline. Only exceptionally high sea-salt concentrations at the western-most positions deviate from this picture. Including results from other drill sites all over the Greenland Ice Sheet, a geographically uniform linear relationship of accumulation and deposition rates for the non-sea-salt components is observed. For nitrate, sulfate and calcium average dry deposition fluxes of 1080, 610 and 156 ng cm −1a −1, respectively, are inferred which, depending on the local accumlation rate, may explain 20–40% of the total nitrate and sulphate but 40–80% of the total calcium deposition flux

Electrodeposition of low tin content zinc-tin alloys

ZnSn alloy coatings containing 10%–20% tin with good appearance were deposited from slightly acidic sulphate electrolytes. The effect of the concentration of tin sulphate and the cathodic current density on the composition and the structure of the alloy deposits was investigated. The partial deposition rates for Zn and Sn from electrolytes containing various brightener concentrations at a definite potential were determined. An increase in the concentration of organic additive from 1 to 5 ml 1 −1 leads to an abrupt decrease in zinc deposition rate, while the tin deposition rate decreases slowly. A further increase in brightener (organic additive) concentration does not affect particularly the deposition rate of either metal. The protective properties of ZnSn coatings were investigated by means of the Paatsch test. It is established that the corrosion resistance of ZnSn alloy deposits is better than the corrosion resistance of Zn and ZnCo (0.3%–1.3% Co) coatings.

Effect of N 2O/SiH 4 ratio on the properties of low-temperature silicon oxide films from remote plasma chemical vapour deposition

Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 °C) from SiH 4N 2O. The effect of a gas-phase reaction on the SiO 2 film properties and Si/SiO 2 interface was investigated. As the partial pressure ratio was increased above N 2O/SiH 4 = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N 2O/SiH 4 <4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (SiOH and SiH) but when N 2O/SiH 4 >4, the incorporation of SiOH bond became significant and Si 1+, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C V and I V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO 2 interface.

A theory for the formation of tetrahedral amorphous carbon including deposition rate effects

A theoretical model is presented to describe the effect of ion beam bombardment rate on the formation of tetrahedral amorphous carbon (ta-C) films. The critical ion energy, E c, corresponding to a 50% sp 3 content in the films, is found to be dependent on both the effective thermal resistance and the ion beam bombardment rate. In the model, the ‘window’ width in the ion energy scale for the formation of ta-C material increases with decreasing deposition rate and with a reduction in the effective thermal resistance, until limited by lower and upper boundary thresholds. Experimental data are reproduced by the model. The plasmon energy, which correlates with sp 3 fraction, is found experimentally of be higher for lower deposition rate and smaller effective thermal resistance. Data points for high sp 3 content ta-C films deposited on silicon substrates at room temperature occupy a region in the ion energy-deposition rate ( E- r) diagram similar to that predicated from the theory.

Deposition of polydisperse particles in a Falkner-Skan wedge flow

Deposition of silica particles onto a target is utilized for studying the performance of optical fiber fabrication processes. The particles are synthesized from a flame due to chemical reactions, grow by collision and coalescence to become aggregates of approximately 0.2 μm in effective hydrodynamic diameter while they follow gas stream, and are deposited onto the target. Typically, the particles are polydisperse in size and follow a lognormal size distribution. For analysis, Falkner-Skan wedge flow was chosenk as the particle laden flow. Brownian diffusion, thermophoresis, and coagulation of the particles were considered and effects of these phenomena on particle deposition were studied. A moment model was developed in order to predict distribution of particle number density and particle size simultaneously. Particle deposition with various wedge configurations was examined for conditions selected for a typical VAD process. When coagulation was considered, the geometric mean particle size and its geometric standard deviation increased and the particle number density decreased, compared to the case without coagulation. These results proved the fact that coagulation effect expands particle size distribution. The results were discussed with characteristics of thermal and diffusion boundary layers. As the boundary layers grew in thickness, overall temperature and concentration gradient decreased, resulting in decrease of deposition rate and increase of particle residence time in the flow and thus coagulation effect. Effect of wedge configuration on particle deposition efficiency was studied and discussed also with the characteristics of boundary layers.

Tissue deposition rates in relation to muscle fibre and fat cell characteristics in lean female pigs ( Sus scrofa) following treatment with porcine growth hormone (pGH)

Two experiments were conducted to examine the effect of porcine growth hormone (pGH) on performance, carcase composition, muscle and fat deposition rates, muscle fibre characteristics, and fat cell volume in pigs. In the first experiment, ten pairs of littermates were treated with vehicle (saline buffer) or 80 μg pGH per kg live weight per day for 42 days starting at 50 kg live weight. In the second experiment, twelve pairs of littermates were untreated or treated with 3 mg pGH per day from approximately 56 kg live weight to slaughter at approximately 103 kg live weight. All pigs were fed ad libitum. In Experiments 1 and 2, respectively, feed intake decreased (10 and 11%) and the feed/gain ratio improved (8 and 13%), while daily gain was unaltered. There was an increase in deposition rates of muscle (11 and 22%), skin (27 and 23%), and bone (15% in both), and a decrease in deposition rates of intermuscular (48 and 24%) and subcutaneous (82 and 50%) fat. This resulted in a change in carcase composition towards more muscle (5 and 9%), bone (6 and 4%), and skin (18 and 12%), and less intermuscular (30 and 16%) and subcutaneous fat (51 and 32%). The increased muscle mass was due to enhanced hypertrophy of all muscle fibre types, while pGH did not affect the frequency of the different muscle fibre types. The reduction in subcutaneous fat was reflected in a similar reduction in fat cell volume. In contrast to the majority of pigs used in pGH experiments, the genotype used in the present experiments did not respond with respect to daily gain following pGH treatment. Furthermore, the increase in muscle deposition was rather low compared to results reported in pigs of other genotypes. These data together with published data on the cross-sectional area of muscle fibres indicate that genotypes with relatively large muscle fibres are less responsive to pGH treatment than genotypes with relatively small muscle fibres.

Low temperature growth of diamond-like films by cathodic arc plasma deposition

Diamond-like films with electrical resistivity exceeding 10 8 Ω·cm are grown successfully on silicon substrates at 40°C in a cathodic arc plasma deposition system with a steered-arc source. The substrate is placed in an atmosphere of argon/oxygen mixture and RF-bias is applied. Low density graphite serves as a cathode target and a carbon source. The magnetic field due to magnets behind the graphite target makes the arc spot move. The observed speed of the steered-arc spot is strongly dependent on the magnitude of the applied arc current and the intensity of the radial magnetic field at the surface of the target. Addition of O 2 to the system tends to improve the quality of the diamond-like films by increasing the sp 3-C sp 2-C ratio and reducing the number and size of graphite microparticles with decreased deposition rate of the films. The application of RF-bias also appears to have a similar beneficial effect on the quality of the films.

Inert Gas Dilution and Ion Bombardment Effects in Room Temperature (35°C) Plasma Deposition of a-Si:H

AbstractPlasma enhanced chemical vapor deposition (PECVD) of a-Si:H with silane or silane and hydrogen at temperatures lower than 200°C commonly results in films with significant dihydride bonding and a high defect density. In this paper, we demonstrate the formation of monohydride dominant a-Si:H films using rf parallel plate PECVD at 35°C at deposition rates greater than 100 Å/min. In the as-deposited state, these films have low dark conductivity (∼10−9 S/cm) and low photoconductivity. Annealing the films at 150°C caused the monohydride dominant films to show photo to dark conductivity ratio near 105. Our results also indicate that an increase in monohydride fraction is not linked with a decrease in deposition rate.

New Interpretation of the Effect of Hydrogen Dilution of Silane on Glow-Discharged Hydrogenated Amorphous Silicon for Stable Solar Cells

The effect of hydrogen dilution on glow-discharged hydrogenated amorphous silicon (a-Si:H) is investigated at substrate temperatures of 100–200° C. The dependence of the properties of a-Si:H on the hydrogen dilution ratio γ (γ=[ H2 gas flow rate]/[ SiH4 gas flow rate]) can be explained in terms of two different effects: i.e., decrease of the film deposition rate at a low γ and implantation of hydrogen atoms into a-Si:H during and after film deposition at a high γ. The latter effect, which is similar to that of hydrogen plasma post-treatment, increases the hydrogen content (C H) and optical gap (E opt) of a-Si:H with no significant deterioration in photoconductivity or SiH2/SiH ratio estimated from infrared absorption. It is found that the electric conductivity and defect density of a-Si:H, both in the annealed state and light-soaked state, have a better correlation with the hydrogen content with SiH2 bond configurations (C SiH2 ) than with C H or E opt. A conversion efficiency of 8.8% is achieved after light soaking (1.25 sun, AM-1.5, 48° C, open load, 310 h) for a single-junction a-Si:H solar cell using an a-Si:H i-layer with reduced C SiH2 .

On the electrical and optical properties of CdS films thermally deposited by a modified source

CdS films were prepared by a physical vacuum deposition technique on an amorphous (glass) substrate using a modified evaporation source. The effect of the processing conditions (the film thickness, substrate temperature and the deposition rate) were considered in comparison with the normal evaporation source. A van der Pauw four-probe arrangement was used for measuring the electrical resistivity, which varies between 0.1 × 104 and 8.18 × 104Ωcm. It decreases with increasing film thickness, and decreasing deposition rate and substrate temperature. This was attributed to the effect of crystallite size, the degree of preferred orientation, internal microstrain and the stoichiometry. From spectrophotometric measuring and using an approximate formula, the optical parameters (n,k, α) were evaluated. The values of the refractive indices and the energy gaps were evaluated and correlated with the preparation parameters.

Influences of the deposition rate on the microstructure and hardness of composite films prepared by reactive ion-assisted coevaporation

The influence of the deposition rate on the microstructure and hardness of TiO2-SiO2 and TiO2-MgF2 composites and their single component films prepared by reactive ion-assisted coevaporation in the deposition rate range 0.14 to 2 nm/s are investigated using an x-ray diffractometer, a transmission electron microscope, and a microhardness tester. It is found that the hardness of the composite films and their single components increase with a decreasing deposition rate. However, the hardnesses of TiO2-SiO2 and TiO2-MgF2 composite films were generally lower than that of pure SiO2 and MgF2, respectively, at the same component deposition rate. This indicates that the addition of TiO2 reduces the hardness of Si02 and MgF2 films. The ultrahigh hardness of pure MgF2 films deposited by ion assistance at the deposition rate of 0.14 nm/s probably results from the high packing density, low lattice defects, and the small grain size (<20 nm) with the preferred orientation of [110]. Furthermore, the homogeneous dispersion of these hard nanoscale MgF2 grains within the amorphous TiO2 matrix causes the hardening of the composite film.

Heavy Metal Concentrations in Plants in Relation to Atmospheric Heavy Metal Deposition

AbstractZinc, Cu, Pb, and Cd concentrations were examined in several plant species and corresponding organic topsoil collected in forest and on ombrotrophic bogs along a temporal (1982–1992) and a spatial (Southern Norway‐Central Norway) heavy metal deposition gradient. This allowed relations between metal concentrations in plants, soil/peat, and spatial and temporal changes in atmospheric deposition of heavy metals to be studied. Lead concentrations in plants decreased significantly from 1982 to 1992 both in Southern and Central Norway, while stable levels were observed in surface soil. These observations together with a decrease in atmospheric Pb deposition rates of about 70% both in Southern and Central Norway, suggests that direct atmospheric deposition strongly influenced Pb levels in vegetation. Lead concentrations in vegetation were significantly higher in Southern Norway than in Central Norway both in 1982 and 1992, evidently due to a more than 15 times higher Pb deposition in Southern Norway. Plant concentrations of Zn, Cu, and Cd were significantly higher in Southern Norway than in Central Norway, both in 1982 and 1992, most likely because of higher root uptake in Southern Norway due to distinctly higher surface soil levels of Zn, Cu, and Cd from air pollution in this region. No distinct changes in Zn, Cu, or Cd concentrations in plants, however, where observed from 1982 to 1992, even in Southern Norway where wet deposition of these elements decreased by about 26% (Zn), 40% (Cu), and 51% (Cd) during this period.

The Autocatalytic Deposition of Gold in Nonalkaline, Gold Thiosulfate Electroless Bath

The autocatalytic deposition of gold has been investigated in a novel, nonalkaline, noncyanide electroless gold plating bath. The bath consists of sodium L‐ascorbic acid as the reducing agent and sodium gold (I) thiosulfate as the gold complex. Ascorbic acid autocatalytically reduces gold thiosulfate at deposition rates of approximately 1 μm/h. The reaction sequence includes various side reactions responsible for consuming reactants and lowering the deposition rate. The rate of the electroless gold thiosulfate reduction is sensitive to the reactant concentration as well as the concentration of thiosulfate. The accumulation of thiosulfate and the depletion of the reactants explain the decreasing deposition rate with time. Periodic addition of hydrogen peroxide consumes the excess thiosulfate and increases the deposition rate and longevity of the bath.

Plasma enhanced deposition of a-Si-H: comparison of two reactor arrangements

Plasma deposition processes involve complex phenomena which render the design and optimization of industrial equipment difficult to perform. In the particular case of silane plasmas used to produce amorphous silicon, two flow arrangements were studied by numerical modeling of mass transport. The modeling of the first geometry, using inlet slit gas feed, showed a decrease of both silane concentration and deposition rate from inlet to outlet. The modeling of the second geometry, using a distributed gas feed by means of a porous electrode, showed more uniform concentration profiles and deposition rate. In large industrial plasma enhanced chemical vapor deposition machines, the choice of gas flow arrangement plays a particularly important role. However, this subject has seldom been treated in the literature [1,2], probably because an experimental approach would involve a high level of investment to build the necessary equipment. This paper suggests an alternative theoretical treatment, using modeling and numerical simulation. First, the principles and methods of a recently developed model [3,4] will be recalled. Then, numerical simulation will be used to compare two different gas flow arrangements and their consequences on the deposition rate profile.

Analysis and numerical modelling of silicon nitride deposition in a plasma-enhanced chemical vapour deposition reactor. I. Bidimensional modelling

A numerical model of silicon nitride deposition from an NH3-SiH4 mixture in a large-sized radiofrequency plasma reactor has been developed. A bidimensional treatment of transport phenomena, of major importance in this type of reactor, was used. Analysis of the modelling results showed that aminosilane radicals were the main deposition precursors. The steep decrease in deposition rate in the flow direction that was observed can be explained by examining the calculated concentration profiles.

Analytical model for chemical vapor deposition of SiO2 films using tetraethoxysilane and ozone

A theoretical model has been developed to analyze chemical vapor deposition (CVD) of SiO2 from tetraethoxysilane (TEOS) and ozone. The model incorporates both homogeneous gas phase reactions and heterogeneous surface reactions. Two new kinetic mechanisms which include parasitic gas phase reactions are proposed to explain the observed decrease in deposition rate of SiO2 films as the temperature is increased. The predicted values from the proposed model are found to agree well with all available experimental results over a wide range of experimental conditions. The effect of parasitic gas phase reactions becomes significantly more pronounced with increasing pressure and temperature. Correlations of experimental data on etch rate with surface concentrations predicted by the model at 60 Torr show that one can improve the film quality by increasing the ratio of O3 to TEOS at the wafer surface, (O3/TEOS)wafer, and the wafer temperature.

Deposition Characteristics and Properties of SiO2 Films Prepared by Reactive Sputtering in Hydrogen-, Oxygen- and Nitrogen-Argon Mixtures

Films are deposited by reactive sputtering in hydrogen-, oxygen- and nitrogen-argon mixtures from an SiO2 target in order to obtain device quality SiO2 films at low temperature. Deposition characteristics and film properties of SiO2 films sputtered in the mixtures are examined. Oxygen and nitrogen mixing with the sputtering gas leads to a large decrease in deposition rate compared with argon-only sputtering gas and hydrogen mixing. The SiO2 film properties of the etching rate in BHF solution, surface morphology and resistivity are found to be greatly affected by mixing these gases with sputtering gas. Mixing of oxygen and a small amount of hydrogen provides excellent SiO2 films, whose properties are superior to thermally grown films, even at low temperatures. These SiO2 films have been used to successfully fabricate silicon electronic devices. The effects of mixing the reactive gases with the sputtering gas are also discussed qualitatively through plasma-surface interaction on growing film surfaces.

Effect of deep-sea sedimentary calcite preservation on atmospheric CO2 concentration

DURING the last glaciation, the atmospheric carbon dioxide concentration was about 30% less than the Holocene pre-industrial value1. Although this change is thought to originate in oceanic processes2, the mechanism is still unclear. On timescales of thousands of years, the pH of the ocean (and hence the atmospheric CO2 concentration) is determined by a steady-state balance between the supply rate of calcium carbonate to the ocean from terrestrial weathering, and the alteration and removal of carbonate by burial in sediments2–4. Degradation of organic carbon in sediments promotes the dissolution of calcium carbonate in sedimentary pore water5,6, so that a change in the relative rates at which organic carbon and calcium carbonate are deposited on the sea floor should drive a compensating change in ocean pH. Here we use a model that combines ocean circulation, carbon cycling and other sedimentary processes to explore the relationship between deep-sea-sediment chemistry and atmospheric CO2 concentration. When we include organic-carbon-driven dissolution in our model, a 40% decrease in the calcite deposition rate is enough to decrease the atmospheric CO2 concentration to the glacial value.