Surface Deposition Rate Research Articles

Laser ablation induced surface modification of NdBa2Cu3O7−δ single crystal target in pulsed laser deposition

The surface modification of both morphology and composition of a single crystal NdBa2Cu3O7−δ (NBCO) target induced by laser ablation has been studied by scanning electron microscopy with x-ray energy dispersive spectroscopy. After a long period of laser ablation, the sintered target displays a cone-shaped columnar surface morphology. However, the single crystal target exhibits a continuous and smooth undulating morphology with ridges and grooves. This cone-free surface morphology is thought to inhibit the ejection of droplets from the target surface and thus lead to NBCO films with excellent surface morphology. After a large number of laser shots per site on the single crystal target, both the surface composition and deposition rate remain unchanged. Our experimental results prove that the observed results for the sintered target are in agreement with the erosion model, while the laser ablation induced surface modification for the single crystal target is dominated by the melt–resolidification process.

Influence of deposition parameters on diamond thermal plasma chemical vapor deposition with liquid feedstock injection

Abstract A global three-dimensional two-phase model for thermal plasma chemical vapor deposition with liquid feedstock injection developed in our group [1,2] has been used for a simulation of diamond production from acetone, ethanol and methane in argon-hydrogen plasmas. In this study, the influence of precursor type, gas and liquid flow rates, atomizing probe location and characteristics, and catalytic reactor chamber is discussed. The main finding is that deposition utilizing liquid precursors offers a distinct new deposition mechanism—liquid droplet penetration of the substrate boundary layer followed by a rapid droplet evaporation and a local increase in the surface deposition rates. Although the overall deposition rate does not exceed that of gasphase precursors, it is believed that further optimization will lead to a deposition rate increase.

Structures on Si(100) 2 × 1 at the Initial Stages of Homoepitaxy by SiH 4 Decomposition

The initial stages of homoepitaxial island formation on Si(100)2×1 by SiH4 decomposition under ultra high vacuum chemical vapor deposition conditions are studied by scanning tunneling microscopy and kinetic model calculations. The concentrations of the intermediate species formed on the surface during SiH4 decomposition are calculated from the kinetic parameters of the dissociation cascade leading to Si film growth in the temperature regime of 500 to 800 K and for SiH4 pressures in the range of 2×10-7 to 2×10-5 mbar. Experimental results showing the surface topography after interaction with SiH4 at various surface temperatures and deposition rates are presented, and the observed surface structures are related to the different surface conditions, i.e., deposition flux and sample temperature, under which islands are formed.

Single Wafer Amorphous Silicon Process Evaluation

ABSTRACTSingle wafer amorphous silicon deposition was characterized through process modeling and film characterization for application in semiconductor production. DOE methodology was used to determine the main deposition parameters, and the responses were limited to device production requirement properties of surface roughness, deposition rate and degree of crystallinity of the as-deposited film. The data trends and models show that deposition temperature and silane flow are the main factors. Increasing either or both factor increases the deposition rate and the surface roughness. The surface morphology, evaluated by AFM, SEM and TEM, was found to be rougher at extreme growth conditions than the poly crystalline film formed after anneal. The as-deposited surface morphology was not a result of pre-anneal crystal formations as determined by TEM cross sections of samples before and after anneal. Lack of crystalinity is important for impurity diffusion considerations. Device application of the single wafer a-Si process will be a compromise between growth rate (and associated throughput) and surface roughness that can be tolerated.

Thermal Stability of Jet-A Fuel Blends

The thermal stability of a high-quality hydrotreated Jet-A fuel, an average-quality straight-run Jet-A fuel, and several blends of each fuel has been studied during flow through a single-pass tubular heat exchanger at 185 °C. The goal was to obtain fundamental information concerning the thermal stability of fuel blends using dynamic isothermal methods. Autoxidation was tracked as a function of stress duration by measurements of dissolved oxygen and hydroperoxides; insoluble formation was determined by measurements of the average surface deposition rate and the total quantity of bulk insolubles collected on in-line filters. On the basis of several thermooxidative stability criteria, some of the blends were found to be less stable than either neat fuel. Furthermore, benefits of blending were not realized until the lesser-quality fuel had been diluted more than 8-fold. The implications of blending high- and lesser-quality fuels are discussed in the context of autoxidation and insoluble formation.

High 222Rn levels, enhanced surface deposition, increased diffusion coefficient, humidity, and air change effects.

Measurements have been made of surface deposition rates for 218Po radon decay products in a small (0.283m3) aluminum test chamber for 222Rn levels from 1 to 1,600 kBq m-3. an increase in macroscopic surface deposition rate has been found to be induced by the high 222Rn concentrations. A distinct 222Rn level threshold has been found below which plateout is constant at the normal rate for ambient residential conditions. Above the threshold, an increase in plateout is observed and the transition quickly reaches a constant, higher plateout. With all environmental conditions remaining constant and varying humidity, the threshold 222Rn level decreases with increasing relative humidity. The rate of rise to the new plateau is found to increase with increasing humidity. For the constant air change rate of ACH = 0.2 h-1, the fraction of airborne 218Po lost by the enhanced plateout was consistently 0.4 +or- 0.25 for seven values of humidity from 8 to 54% RH. For a fixed RH = 40 +or- 2%, it was found that the threshold increases from 5 to 58 kBq m-3 for a change in ACH from 0 1.06 h-1. In converting the deposition data to values of diffusion coefficient D, using Crump and Seinfeld's theory, a very high D of 0.18 cm2s-1 is assumed for ambient air conditions. Results indicate an ambient D = 0.027 cm2s-1. The results may impact on research utilizing high levels in test chambers and diffusion coefficients and attached and unattached fractions, and also for cancer studies using animals with 222Rn levels as much as 10(4) times greater than ambient residential levels.

Modeling of the formation of RuO2 thin film from Ru(C5H5)2 by metal-organic chemical vapor decomposition

A modeling technique based on bond graph methods is used to analyze the mechanism of metal-organic chemical vapor deposition processes of RuO2 by Ru(C5H5)2. Theoretical models are considered and compared with experimental data. The most suitable model, which incorporates both the homogeneous gas-phase reactions and the heterogeneous surface processes, is constructed. The proposed model agreed well with the experimental data. The model indicates that besides a single-surface reaction there exists a gas-phase reaction which is the rate-controlling step. The surface deposition rate constant as well as the forward and backward reaction rate constants for the gas-phase reversible reaction of Ru(C5H5)2 are also determined.

Degradation of a Jet A Fuel in a Single-Pass Heat Exchanger

The formation of bulk and surface insolubles in a Jet A fuel during a single pass through heated stainless-steel tubes has been studied. Low temperature and low flow rates were utilized to produce near-isothermal conditions. In a second series of experiments, depletion of oxygen in the fuel saturated with respect to room-temperature air was measured under identical isothermal conditions. At a wall/bulk-fuel temperature of 185°C, rates of surface deposition and oxygen depletion were correlated; the maximum in the surface-deposition rate was found to occur after the Jet A fuel was stressed sufficiently that the dissolved oxygen was totally consumed. Results are discussed in terms of the autoxidation of the Jet A fuel and the concurrent production of deleterious bulk and surface insolubles.

Surface roughness scaling of plasma polymer films.

Atomic force microscopy data reveal self-affine scaling of plasma polymer films. The rms surface roughness $\ensuremath{\sigma}$ increases with film thickness $\ensuremath{\tau}$ as $\ensuremath{\sigma}(fl{\ensuremath{\xi}}^{\ensuremath{-}1})\ensuremath{\sim}{\ensuremath{\tau}}^{\ensuremath{\beta}}$, and with measurement length $L$ as $\ensuremath{\sigma}(fg{L}^{\ensuremath{-}1}g{\ensuremath{\xi}}^{\ensuremath{-}1})\ensuremath{\sim}{L}^{\ensuremath{\alpha}}$, where $\ensuremath{\xi}$ is the surface roughness correlation length. At the deposition rate $R=2 \frac{\ensuremath{\mu}m}{h}$, the scaling exponents $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ are 0.9 and 0.7, both increasing to 1 at $R=2 \frac{\ensuremath{\mu}m}{h}$. A competition between surface relaxation and deposition rate determine $\ensuremath{\alpha}$ and $\ensuremath{\xi}$, which increase rapidly with $R$ or inverse temperature.

Measured Effects of Reduced Flow Velocity in a Laminar Flow Cleanroom

Vertical laminar flow (VLF) cleanrooms generally operate with airflows between 60 feet per minute (fpm) and 110 fpm. Tests were performed to evaluate the effects on particle contamination levels when the airflow velocity in a FED-STD-209 Class 1 VLF cleanroom was reduced. The cleanroom normally operates at 90 fpm. Measurements of surface particle concentrations were made on settling monitor wafers and on wafers carried in an open cassette. Optical particle counters measured the airborne particle concentrations at several locations. Results at 100 fpm and 50 fpm, respectively, for particles larger than or equal to 0.3 μm in optical equivalent diameter were −0.0002 and +0.0029 particles/sq cm/hr for the settling wafers and 0.009 and 0.024/sq cm total for the wafers carried for 5 hr in the open cassettes. Summary statistics are provided for the airborne and surface particle counts. Deposition velocity is the ratio of surface deposition rate to airborne concentration. For the monitor wafers at the lower flow, the calculated particle deposition velocities were near 0.003 cm/sec, which is within the range expected from theory and experiments in the literature.

A Monte-Carlo simulation of the electrodeposition process

Nucleation, grain growth, texture formation, and porosity formation in the electro-deposition process has been simulated with a Monte-Carlo method. In the simulation, a two-dimensional hexagonal lattice containing 12000 lattice sites are used to map the microstructure at the cross section of deposit. The criterion for grain growth is based on the energy state of the lattice site which is set by counting the interactions between the site and its nearest neighbors. This model can be used to obtain information of how the deposition rate affects the microstructure and porosity. The texture formation during the deposition process is modeled by taking surface energy anisotropy and deposition rate into account.

Coating of titanium carbide films on stainless steel by chemical vapour deposition and their corrosion behaviour in a Br2-O2-Ar atmosphere

Stainless steel (SUS304) plates were coated with TiC films using chemical vapour deposition (CVD) as a candidate material for “UT-3” which is a promising process of hydrogen production through the thermal decomposition of water. The corrosion behaviour of the TiC film-coated SUS304 plates was examined in a Br2-O2-Ar atmosphere. The effects of CVD conditions on the surface texture, deposition rates and preferred orientation of the TiC films were investigated, and the optimum CVD conditions determined. Corrosion of the TiC film-coated SUS304 plates in the Br2-O2-Ar atmosphere was mainly caused by oxidation of the TiC film and SUS304 substrate. Microcracks in the TiC films lead to corrosion of the SUS304 substrate. At oxygen partial pressures below 0.1 kPa, weight loss was observed due to the formation of volatile titanium and iron bromides. At oxygen partial pressures greater 0.1 kPa, the time dependence of weight increase was parabolic due to the formation of oxide scale. The oxide scales were mixtures of TiO2, Fe2O3 and Fe3O4. The corrosion mechanism is discussed thermodynamically.

The effect of processing parameters on the microstructure and erosion resistance of NiCr3C2 coatings

NiCr3C2 coatings have been applied to Ti-6Al-4V and Inconel 718 substrates using direct current magnetron sputtering. The substrate surface finish, bias voltage, percentage bias and deposition rates were varied systematically. The effect of changing sputtering parameters on the resultant microstructure was characterized using scanning electron microscopy and microhardness measurements. The erosion resistance of the coatings to an Al2O3 abrasive stream was determined at 30° and 90° impingement angles and related to the process parameters. The dominant erosion mechanisms at the two impingement angles were determined using scanning electron microscopy.

Overbank Sedimentation Rates of Fine Grained Sediments. A Study of the Recent Deposition in the Lower River Fyrisån

ABSTRACTRecent overbank deposition of fine grained sediments along Swedish rivers is a rare process. Favourable conditions for overbank deposition exist, however, near the base level of low gradient rivers on the central Swedish plains. Lack of sedimentation data has inspired us to make this study which aims to estimate the present sedimentation rate and to test a field method to observe the spatial variation in deposition, by using simple sediment traps. The study area lies within the River Fyrisan drainage basin, previously investigated in several studies of fluvial geomorphology and sedimentology. The suspended sediment transport was calculated from actual discharge figures and from concentration figures obtained by water sampling and by using a “Surface Scatter Turbidimeter”. The total sedimentation in the deposition area was estimated in three ways, i.e. from actual figures on sediment transport, by a sedimentation formula and by using the results from the sediment traps. The surface deposition rates...

Vacuum-lamination process for metallized polymer films

A process is described whereby polymer films are laminated using vacuum-deposited aluminium as an adhesive. Only modest pressures are needed to produce a pressure weld between the freshly deposited metal coatings. The influence of various process parameters on the metal–metal bonding is explored, with particular reference to surface contamination and deposition rate. In addition to their commercial potential, the laminates are particularly useful as test specimens for measuring metal–polymer adhesion.MST/178

Control of respirable particles in indoor air with portable air cleaners

Eleven portable air cleaning devices have been evaluated for control of indoor concentrations of respirable particles using in situ chamber decay tests. Following injection of cigarette smoke in a room-size chamber, decay rates for particle concentrations were obtained for total number concentration and for number concentration by particle size with and without air cleaner operation. The size distribution of the tobacco smoke particles was log normal with a count median diameter of 0.15 μm and a geometric standard deviation of 2.0. Without air cleaner operation, the natural mass-averaged surface deposition rate of particles was observed to be 0.1 h −1. Air cleaning rates for particles were found to be negligible for several small panel-filter devices, a residential-sized ion-generator, and a pair of mixing fans. Electrostatic precipitators and extended surface filters removed particles at substantial rates, and a HEPA-type filter was most efficient air cleaner studied.

Preparation of thin polymer films of predictable chemical functionality using plasma chemistry

Plasma-polymerized vinyldimethylethoxysilane (PP VDMES) and plasma-copolymerized styrene-vinyldimethylethoxysilane (PC St-VDMES) thin films were prepared in a tubular reactor capacitively coupled to an r.f. power supply. The surface polymer structure as determined by X-ray photoelectron spectroscopy was correlated with the controllable discharge parameters of power, pressure and feed gas composition. PP VDMES films show carbon enrichment and concomitant loss of the ethoxy group (via cleavage of the C-O bond) as the power per molecule ratio P/M is increased during the deposition reaction. The rate of deposition of PP VDMES was also found to be a strong function of P/M. The PC St-VDMES surface chemical structure and deposition rate are complicated functions of the feed gas composition (styrene and VDMES). In both systems it is found that the chemical functionalities of the monomers (ethoxy group for VDMES and phenyl ring for styrene) are retained and incorporated into the plasma-deposited films under low P/M discharge conditions.

Radon Daughter Deposition Velocities Estimated from Field Measurements

The surface deposition rate (plateout) of unattached radon daughters was estimated from simple surface activity measurements in a number of occupied buildings, and found to be about one third of the lowest value measured in diffusion tube experiments. This low value was confirmed by surface deposition and activity measurements made in a commercial building with high radon levels, which also showed that the deposition rate was higher on walls than on floors or tables. Predictions of the ratio between airborne and surface-deposited radon daughter activity using the estimated surface deposition rate were close to the ratios observed in occupied homes. Refinements to existing models are required to explain the variability of deposition rate with surface orientation.

Possible oxidant sources in the atmosphere and surface of Mars

Photolysis of H2O in the atmosphere near the surface is a copious source of OH, HO2, and probably superoxides, some of which are likely to condense on the surface and migrate through the pores. The processes have been modeled in detail for their atmospheric interest. The models successfully account for the rarity of CO and O2, the notable variability of ozone, and the escape flux of hydrogen. Though only qualitative estimates can be made of surface deposition rates and lifetimes, the suggested amounts are in the range inferred by Viking. The OH rapidly destroys any organic molecules that are present as vapors.

Structure of Silicon Films Evaporated onto a Clean NaCl Substrate

Silicon films, 30–300 Å in thickness, evaporated (using an electron beam evaporation technique) onto NaCl substrates cleaved in ultrahigh vacuum and held at 25–500 °C at various deposition rates (0.1–8 Å/sec) have been investigated by reflection electron diffraction and transmission electron microscopy. It was found that the structure and epitaxy of films were markedly influenced by the purity of the Si source, ambient pressure during evaporation, substrate surface condition, deposition rate, and substrate temperature. Decoration of imperfections of the substrate surface was obtained with Si deposited at relatively slow rate (0.1–0.3 Å/sec). Films produced on the substrates at 25–300 °C were amorphous. The amorphous to crystalline transition temperature was in the range of 300–400 °C. Epitaxial orientation of films (001)Si‖(001)NaCl with [100]Si‖ [100]NaCl was observed on the substrates at 400 °C at the slow deposition rate. The epitaxial films included microtwins with the twinning planes of {111}. The growth and structure of films were also influenced considerably by an electron beam bombardment applied to the substrate during evaporation.