Type Of Carrier Gas Research Articles

Large-Volume PTV injection: New results on direct injection of water samples in GC analysis

The elimination of water in large-volume PTV injection was investigated by means of a transparent model injector. Significant parameters were identified and suitable operating conditions for speed-controlled injection of water, such as maximum rate of injection or the type of carrier gas, were chosen. Furthermore, a simple back-flush device was installed; this prevented possible damage by water vapour without affecting the separation power.

Experimental and theoretical study of step coverage in metal-organic chemical vapor deposition of tantalum oxide thin films

The chemical vapor deposition of tantalum oxide thin films from pentaethoxy tantalum on to trench structures was conducted to investigate experimentally the step coverage and to compare these results with simulated findings. The dependence of the step coverage on the substrate temperature and the type of carrier gas was evaluated experimentally, and the sticking coefficient was determined from the comparison of the experimental results with the simulation. Deposition at low temperatures using He carrier gas gives better step coverage with the tantalum oxide thin film. A comparison of the activation energy associated with the sticking coefficient with the activation energy associated with the deposition rate on a blankwafer surface using He and Ar carrier gases was made. The step coverage with He was determined from the deposition rate, while the step coverage with Ar was determined using the Knudsen diffusion rate of reactant inside the trench.

Anesthetic and postanesthetic management of sea turtles

Objective To examine the physiologie effects of inhalation anesthesia in aquatic turtles to improve anesthetic techniques and postanesthetic monitoring. Design Retrospective case series. Animals 9 Kemp's ridley sea turtles. Procedure Isoflurane was used as the general anesthetic during 14 minor surgical procedures. Turtles were orotracheally intubated, and a surgical plane of anesthesia was maintained with 2.7 ± 0.4% (mean ± SE) isoflurane. The duration of anesthesia was 131 ± 12 minutes. Pulse rate, blood pressure, blood gases (PaO2 and PaCO2) and pH, blood lactic acid concentration, and capnography were used to evaluate the physiologic responses of sea turtles to isoflurane. Results An isoflurane concentration of 3.4 ± 0.3% provided anesthetic induction in 7 ± 1 minutes. The mean duration of the recovery phase was 241 ± 31 minutes. The duration of the recovery phase was not affected by the duration of anesthesia, type of carrier gas, method of ventilatory weaning, or use of selected pharmacologic agents. The recovery phase was characterized by hypoxemia, progressive acidemia, hypercapnia, and lactic acidosis. Awakening in the turtles was preceded by a characteristic tachycardia and tachypnea. All sea turtles recovered from isoflurane anesthesia without apparent adverse effects within 24 hours. Clinical Implications Isoflurane appears to be safe and effective in providing surgical anesthesia in turtles that require a timely return to an aquatic environment. This study should assist veterinarians in predicting the physiologic responses of aquatic turtles to inhalation agents. (J Am Vet Med Assoc 1996;208:720–726)

Growth and Resistivity Behavior of Copper Film by Chemical Vapor Deposition

The film growth of copper from Cu(hfac)VTMS by chemical vapor deposition is shown to be limited by the amount of the source transported to the substrate. The maximum possible growth rate under this transport‐limited condition is derived. An explanation is forwarded for a sudden increase in the growth rate between 175 and 200°C based on the deposition mechanism. Selective deposition is shown to take place between TiN and surfaces at temperatures below 175°C. The origin of the selectivity is attributed to a prohibitively high activation step on the surface. The resistivity of deposited copper is lower for higher temperature and is practically constant in the temperature range of 200 to 250°C. The resistivity is almost unaffected by the carrier gas flow rate. The effect of the type of carrier gas is such that a gas of a lower molecular weight gives a higher growth rate.

Ferroelectric Microdomains in Ti-diffused LiNbO3 Optical Devices

Etched hillock density on the -Z plane of a titanium-diffused LiNbO3 optical device was studied as a function of water vapor content in a diffusion atmosphere of oxygen and argon. It was found that the hillock formation depended greatly upon the water vapor content and the type of carrier gas. Furthermore, the shapes of the hillocks in the devices were observed on a microscopic scale. Scanning electron micrographs (SEM) clearly showed the crystallographic shape of steeple-crowned pyramidal hillocks. The shape of the steeple (i.e., the core) was compared with a cross-sectional view of an etched LiNbO3 single-crystal c-axis fiber, and it was revealed that the core was a microdomain whose polarization was opposite that of the outer matrix. The mechanisms which cause the microdomains to form during the Ti-diffusion process are also discussed.

MOCVD Route to Stable, Oxygen-Rich, Chromium Oxide Films and Their Conversion to Epitaxial Cr2O3

Using Cr(acac){sub 3} as a precursor, deposition of chromium oxide onto silicon and Al{sub 2}O{sub 3} by MOCVD produced 800 {angstrom} to 2 {mu}m thick films, which were characterized by IR, UV-vis spectroscopies, XPS, oxygen and carbon resonance RBS, and XRD, as well as optical and electron microscopies. Optimization of deposition conditions such as precursor temperature, carrier gas type and flow rate, substrate type and temperature, and postdeposition anneal yielded smooth, crystalline, epitaxially oriented films of Cr{sub 2}O{sub 3} on single crystalline Al{sub 2}O{sub 3} substrates. Deposition under flowing O{sub 2} at 400-900{degrees}C produced discontinuous Cr{sub 2}O{sub 3} films comprised of 1-20 {mu}m diameter crystallites the orientation of which was dependent on the substrate. Deposition at 300-350{degrees}C under O{sub 2} and at 300-500{degrees}C under N{sub 2} produced very smooth films of Cr{sub 2}O{sub x} (3.2 {le} x {le} 4.9); such films contained some crystalline Cr{sub 2}O{sub 3}. XPS analysis of these oxygen-rich films revealed the presence of chromium in oxidation states, III (major), IV, and VI. The Cr{sub 2}O{sub 3.5} films did not lose oxygen upon firing to 1100{degrees}C under argon, but were cleanly converted to smooth, epitaxial Cr{sub 2}O{sub 3} at 1300{degrees}C. 47 refs., 6 figs., 1 tab.

Synthesis and characterization of nanocrystalline powders of pure nickel and copper

Nanocrystalline particles of pure copper and nickel with a diameter of less than 0.1 μm have been produced by evaporating these metals into an inert gas atmosphere. A specific gas-evaporator apparatus was built to control the size of the nanocrystalline particles by adjusting the following factors: the evaporation rate of metals, the distance between the evaporation crucible and the collection cold trap (LN 2), the pressure, and the type of carrier gas. The results indicated that the mean particle size of Cu varied from 13 to 104 nm and that of Ni varied from 7 to 53 nm, with the absolute He pressure varying from 10 to 500 mbar. When the evaporation temperature increases, the evaporation rates rises and the particle size distribution becomes broader. Also, under a constant evaporation rate and absolute He pressure, varying the particle collection distance causes a change in the mean particle size. In the flowing helium process, the particles are more homogeneous and finer than those produced in the static process.

Solid silver particle production by spray pyrolysis

Solid, spherical, micron-sized silver metal particles were produced by spray pyrolysis from a silver nitrate solution. The effects of reaction temperature, carrier gas type, solution concentration, and aerosol droplet size on the characteristics of the resultant silver particles were examined. Pure, dense, unagglomerated particles were produced with an ultrasonic generator at and above 600° C using N 2 carrier gas, and at and above 900°C using air as the carrier gas. Solid particle formation at temperatures below the melting point of silver (962°C) was attributed to sufficiently long residence times (3.5–54 s) which allowed aerosol-phase densification of the porous silver particles resulting from reaction of the precursor.

KrF laser deposition of chromium films from Cr(CO) 6: in situ detection of film growth by laser transmission experiments

The results of a detailed study of laser-induced chemical vapour deposition (LICVD) of thin chromium films from Cr(CO) 6 using a KrF excimer laser are presented. The following deposition parameters were varied: the laser fluence, the pulse repetition rate, the total gas pressure in the deposition cell, the flow rate of the gas mixture supply, the type of carrier or buffer gas and the substrate temperature. The influence of these parameters on the nucleation time and rate, and the main film growth rate as well as on film properties such as the optical absorption coefficient was investigated. The film growth kinetics was monitored in situ by measuring the transmission of an HeNe laser probe beam through the deposit. The experimental results are discussed in the framework of a model of pulsed LICVD based on gas phase diffusion mass transport to the substrate surface of chromium-containing precursor species as the rate-limiting step. The model describes the experimental data reasonably well, the deviations observed being indicative of processes not included in the model such as reactions at the film surface. The results indicate that in pulsed LICVD of chromium films from Cr(CO) 6 at 248 nm the main precursors of the film growth during the nucleation period are chromium atoms and other highly reactive unsaturated chromium carbonyls formed on illumination in the gas phase, while during the main growth stage the role of more stable saturated species adsorbed on the surface between the laser pulses may be dominant.

Vapor etching of GaAs and AlGaAs by CH3I

With the objective of developing an improved process for in situ etching of GaAs-based materials in organometallic vapor phase epitaxy reactors, GaAs wafers and AlxGa1−xAs epilayers have been etched with CH3I vapor in a horizontal reactor operated at atmospheric pressure with H2 or He carrier gas. For a H2 flow rate of 2.1 s lpm, etching temperatures from 400 to 625 °C, and CH3I mol fractions (yCH3I)from 0.0012 to 0.015, the measured GaAs etch rate r (in Å min−1) is given by r = k0 y0.83CH3I exp[ − 45(kcal mol−1)/RT] with k0=3.2×1016 Å min−1. The value of k0 depends on the type of carrier gas, flow rate, total pressure, and reactor geometry. The etch rate appears to be controlled mainly by the decomposition of CH3I to CH3 and I, for which the activation energy has been reported to be 43.5 kcal mol−1. The etch rate of AlxGa1−xAs epilayers with x up to 0.7, which was measured at 480 °C with yCH3I= 0.015, does not depend on Al content. The surface morphology of etched GaAs wafers improves with decreasing temperature. Specular surfaces are maintained at temperatures below 500 °C for etch depths up to 5000 Å.

Study of matrix effects on rare earth elements in hollow cathode discharges

By applying a copper hollow cathode discharge (HCD) to the determination of rare earth elements (REE), matrix effects have been studied. The carrier gas type and the matrix effects caused by other REE (Y, La, Ce, Eu), Group IIA elements (Ca, Sr, Ba) and potassium (KCl, KI) have been examined. The ion:atom line intensity ratios reflecting electron density changes versus matrix composition have been investigated. Argon was found to be a better carrier gas than He for excitation of the analysed REE. The lowered analyte signals caused by the REE matrices (at various mass ratios of analyte to matrix) was relatively small; La was the most interacting matrix element and the Ce and Y matrices were the lowest. The matrix effects of Ca, Sr and Ba increased significantly with a decrease in the relative atomic mass of the element and were very strong for Ca. The matrix effects of KCl and KI were not very significant and both the cation and anion contributed. The HCD has been shown to be a good source for the determination of REE traces in the matrices of other lanthanides. Calcium should be removed from a sample before the determination of the REE traces.

Sample decomposition in an electrically heated cold‐trap inlet system for high speed gas chromatography

AbstractThermal decomposition of some hydrocarbon and chlorinated hydrocarbon compounds in metal capillary tubes used in an inlet system for high speed gas chromatography has been investigated. The metal tube is cooled to about −75°C by a flow of cold nitrogen gas in order to focus a vapor sample cryogenically. A capacitive discharge power supply is then used to heat the metal tube resistively in order to revaporize the sample and introduce it to the separation column as a plug 5‐10 ms wide. The effects of tube temperature, tube material, sample vapor residence time, and type of carrier gas on thermal cracking are described. Use of a copper‐nickel alloy tube resulted in less cracking than either pure platinum or pure nickel. Cracking is more significant with hydrogen as carrier gas than with helium. Cracking also increases with increasing sample residence time in the hot tube. Quantitative sample injection with minimum decomposition can be obtained for a variety of aliphatic and aromatic hydrocarbons and chlorinated hydrocarbon compounds.

How a limited mass transfer in the gas phase may affect the steady-state response of a Pd-MOS hydrogen sensor

The hydrogen sensitivity of palladium MOS sensors in an oxygen-containing atmosphere is shown to depend on the area of the Pd film, the rate of the gas flow, the total pressure and the type of carrier gas. All observations can be explained by the influence of a limited mass transfer in the gas phase. This model is confirmed by mass spectrometric studies using a local gas-sampling technique. Requirements upon the sensor size and the H 2 supply to minimize mass-transfer influence are discussed.

Water Vapor Effects on Titanium Diffusion into LiNbO3 Substrates

This paper describes experimental studies on titanium diffusion into Z-cut LiNbO3 substrates as a function of water vapor content in the diffusion atmosphere of oxygen and argon. LiNbO3 crystal characteristics were found to depend mainly on water vapor content, while Ti-diffusion characteristics were found to be affected not only by water vapor content but also by the type of carrier gas. This study has important implications for the successful fabrication of Ti-diffused LiNbO3 waveguides; for oxygen carrier gas, a small amount of water vapor should be introduced, while for argon carrier gas, a medium amount of water vapor should be introduced.

Interfacial studies of chemical-vapor-infiltrated ceramic matrix composites

The objective of this program was to investigate the fiber-matrix interfacial chemistry in chemical-vapor-infiltrated SiC matrix composites utilizing NICALON SiC and Nextel 400 mullite fibers and how this interface influences composite properties such as strength, toughness and environmental stability. The SiC matrix was deposited using three different reactants: methyldichlorosilane, methyltrichlorosilane and dimethyldichlorosilane. It was found that by varying the reactant gas flow rates, the ratio of carrier gas to reactant gas, the type of carrier gas (hydrogen or argon), the flushing gas used in the reactor prior to deposition (hydrogen or argon) or the type of silane reactant gas used, the composition of the deposited SiC could be varied from very silicon rich (75 at.%) to carbon rich (60%) to almost pure carbon. Stoichiometric SiC was found to bond very strongly to both NICALON and Nextel fibers, resulting in a weak and brittle composite. A thin carbon interfacial layer deposited either deliberately by the decomposition of methane or inadvertently by the introduction of argon into the reactor prior to silane flow resulted in a weakly bonded fiber-matrix interface and strong and tough composites. However, composites with this type of interface were not oxidatively stable. Preliminary results point to the use of a carbon-rich SiC (mixture of carbon plus SiC) interfacial zone to achieve a relatively weak, crack-deflecting fiber-matrix bond but also exhibiting oxidative stability.

Blanket and Selective Copper CVD from Cu (Fod)2 For Multilevel Metallization

ABSTRACTAs the focus of integration technology inevitably shifts from the present very large scale integration (VLSI) to ultra large scale integration (ULSI) schemes, thus leading to continuous decrease in circuit dimensions, the limitations of present multilevel metallization technologies become increasingly important. Because of the appreciably higher speeds and more complex multi-functional layering involved in the newest ULSI circuits, the electrical resistance and capacitance of presently used interconnects and their electromigration and stress resistance stand as major limiting factors to signal processing throughput. In this paper, some recent results achieved by the present investigators in their studies of blanket and selective low-temperature metal-organic chemical vapor deposition (LTMOCVD) of copper for potential use in multilevel metallizations in ULSIC’s are presented. The films were produced at 300–400°C in atmospheres of pure H2 or Ar from the β-diketonate precursor bis(6, 6, 7,7, 8, 8, 8-heptafluoro-2, 2-dimethy1-3, 5-octanediono)copper(II), Cu(fod)2. The films were analyzed by x-ray diffraction (XRD), Rutherford Backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDXS), and four-point resistivity probe. The results of these studies showed that films deposited on metallic substrates were uniform, continuous, adherent, highly pure, and exhibited very low resistivity, as low as 1.8 μΩcm for films deposited in pure H2 atmosphere. Preliminary investigations of selective LTMOCVD of copper showed that selectivity is indeed possible, but is a function of a wide range of parameters that include reactor geometry, substrate type and temperature, working pressure, type of carrier gas, and precursor chemistry.

Cluster Beam Deposition of High Temperature Material

ABSTRACTWe present our latest attempts to utilize a Smalley-type cluster beam source, to generate novel thin films. This technique employs entraining, within a high pressure molecular beam expansion, the products generated from laser ablation of a rotating target rod. We will show how such a cluster beam source can be used to generate a high temperature material within a molecular beam and deposit it intact on a relatively cool substrate. By tailoring the various expansion conditions (ie., expansion pressure, laser fluence, type of carrier gas, pulse delay, etc...) one can drastically effect the morphology and chemical nature of the surface generated. This technique has the promise that it may be able to fabricate a wide variety of thin films with obvious industrial applications (superconducting thin films, diamond-like carbon films, patterned or multi-layered thin films, etc...)

Parametric analysis of thermal swing cycles for multicomponent adsorption

AbstractA study was made of the effect of design and operating parameters on the regeneration of a fixed bed of activated carbon. Two adsorbed species were removed by a hot gas purge, making the study relevant to thermal swing cycles used commercially. The analysis utilized direct experimental results as well as simulated results using a model described earlier by the authors (Huang and Fair, 1988).Regeneration parameters studied were: type of purge gas, purge gas contact time and velocity, regeneration temperature, initial bed loading, and bed pressure. These were related to certain parameters influencing the adsorption step: type of carrier gas, feed concentration, contact time and velocity, pressure, and initial bed temperature. The results are summarized in the form of guidelines for optimal regeneration cycle specification.

Return flows in horizontal MOCVD reactors studied with the use of TiO 2 particle injection and numerical calculations

Flow visualization experiments with the use of TiO 2 particles were performed for a horizontal MOCVD reactor which was resistance-heated from below and water-cooled on top. It is shown that, due to the heating of the incoming gas, very pronounced return flows can occur at the leading edge of the heated susceptor. The formation of these return flows was systematically studied as a function of pressure, flow velocity and temperature. We show that for typical flow rates, carrier gases and reactor design used in MOCVD growth of GaAs and AlGaAs, it is possible to avoid return flows by decreasing the pressure to about 0.2×10 5 Pa. Besides these experimental studies also numerical calculations on gas flows based on the differential equations for the conservation of mass, energy and momentum were performed, using a two-dimensional finite difference procedure. Parameters in this study were again pressure, flow velocity and temperature, and in addition also the height of the reactor and the type of carrier gas were varied. In comparing the results obtained by the flow simulation experiments and the numerical calculations, it is found that the occurrence of return flows is predicted accurately by the numerical flow calculations. Small differences can be ascribed to three dimensional effects which are not included in the 2D numerical calculations. Both flow visualization experiments and numerical calculations show that the occurrence of return flows is mainly determined by only two dimensionless hydrodynamic numbers: the Grashoff number Gr and the Reynolds number Re. It is possible to define a number α crit such that no return flow occurs for Gr Re κ <α crit . Here κ equals 1 for small Reynolds numbers (Re ≤ 4) and goes to 2 for larger Reynolds numbers (Re ≥ 8), being independent of all other hydrodynamic parameters. The critical value α crit was found to depend slightly on the temperature difference and is independent of all other parameters. The criterion is confirmed by both the TiO 2 experiments and the numerical calculations for 0.1 < Re < 10 and 10 < Gr < 10 000.

The role of tellurium and antimony in [formula omitted] and [formula omitted] reforming catalysts

PtTe Al 2O 3 and PtSb Al 2O 3 bimetallic catalysts were studied using the model n-hexane isomerization, aromatization, and hydrocracking reactions at 673 K and the cyclohexane dehydrogenation reaction at 573 K, under atmospheric pressure in a recirculation batch reactor. An increase in the selectivity for isomerization (and a corresponding decrease in hydrocracking selectivity) was found for all coimpregnated PtTe Al 2O 3 and PtSb Al 2O 3 catalysts compared to Pt Al 2O 3 . The change in selectivity can be caused either by electronic effects, which increase the specific activities for isomerization, or by geometric effects, which reduce the rate of hydrocracking. The results of the kinetic experiments, along with FTIR spectroscopy of adsorbed CO using the isotopic dilution method, suggest that electronic effects can be identified with Te Pt alloying in catalysts of low ( Te Pt < 0.06 ) Te content, while geometric effects predominate in catalyst formulations more concentrated in the post-transition metal. The dehydrogenation turnover frequencies were also enhanced at low Te Pt ratio; in this respect the dehydrogenation and isomerization reactions are similar. Direct six-member ring closure, rather than ring expansion by way of an adsorbed methylcyclopentane intermediate, accounted for most of the production of benzene. PtTe Al 2O 3 catalysts were also prepared by vapor deposition of Te onto Pt Al 2O 3 . These catalysts exhibited selectivities which were influenced by the type of carrier gas used to deposit the tellurium. A carrier gas containing n-hexane improved the selectivity relative to hydrogen or helium carrier gases. The mechanism of this selectivity effect is unknown but possibly due to carbon incorporation into a PtTe alloy.