Gas Phase Growth Research Articles

Computational and experimental study of soot formation in a coflow, laminar ethylene diffusion flame

A sooting, ethylene coflow diffusion flame has been studied both experimentally and computationally. The fuel is diluted with nitrogen and the flame is slightly fifted to minimize the effects of the burner. Both probe (thermocouple and gas-sampling techniques) and optical diagnostic methods (Rayleigh scattering and laser-induced incandescence) are used to measure the temperature, gas species, and soot volume fractions. A detailed soot growth model in which the equations for particle production are coupled to the flow and gaseous species conservation equations has been used to investigate soot formation in the flame. The two-dimensional system couples detailed transport and finite-rate chemistry in the gas phase with the aerosol equations in the sectional representation. The formulation includes detailed treatment of the transport, inception, surface growth, oxidation, and coalescence of soot particulates. Effects of thermal radiation and particle scrubbing of gas-phase growth and oxidation species are also included. Predictions and measurements of temperature, soot volume fractions, and selected species are compared over a range of heights and as a function of radius. The formation of benzene is primarily controlled by the recombination of propargyl radicals, and benzene production rates are found to limit the rate of inception, as well as the net rate of soot growth. The model predicted soot volume fractions well along the wings of the flame but underpredicted soot volume fractions by a factor of four along the centerline. Oxidation of particulates is dominated by reactions with hydroxyl radicals that attain levels approximately ten times higher than calculated equilibrium levels. Gas cooling effects due to radiative loss are shown to have a very significant effect on predicted temperatures.

Dust phenomena in processing plasmas

Dust phenomena in processing plasmas are reviewed from the new viewpoint of birth of material in the plasma. The gas-phase growth of particles has been extensively studied for Si4 RF plasmas. The Si particles usually grow through three distinctive stages: an initial growth phase up to about 10 nm, whose size is between size ranges dominated by plasma properties and their electron affinity; a rapid growth phase and a growth saturation phase. In the first phase, particles are localized around the plasma/sheath boundary in spite of a large fraction of neutral particles. In the second phase, extremely fast coagulations between particles appear, which can be explained by the generation of positively charged particles due to high-energy electrons. In the third phase, most of the particles are charged negatively and hence repel each other. Experiments on the formation of Coulomb solids in carbon RF plasmas and production of K-C60 plasmas are attractive since they indicate great potential for dusty plasmas. In the former experiments, almost perfectly spherical and monodisperse particles are successfully formed and transitions from liquid to solid phases and between body-centred cubic and hexagonal structures are clearly observed. In the latter experiments, plasmas composed of K+ and C60- ions are almost realized. Film properties change by controlling the energies of charged particles impinging on substrates and, under the specified plasma conditions, C60 with the K atom in its cage is successfully formed.

Assembling Small Fullerenes: A Molecular Dynamics Study

ABSTRACTUsing tight-binding molecular dynamics, we have performed two series of computer experiments assembling small fullerenes: first, we have simulated the deposition of C28 clusters on a semiconducting surface, and then we have performed calculations mimicking the gas phase growth of a small fullerene solid. The results of the two computations are discussed and compared to those obtained for ordered forms of C28 solids.

CBE growth of InP using BPE and TBP: a comparative study

Results of a comparative study on the growth of indium phosphide (InP) by chemical beam epitaxy (CBE) using two alternative phosphorous (P)-precursors, bisphosphinoethane (BPE) and tertiarybutylphosphine (TBP), are presented. For both P-precursors, ethyldimethylindium (EDMIn) was used as the indium (In) precursor. TBP has gained wide acceptance in gas phase growth techniques such as organometallic vapor phase epitaxy (OMVPE) and CBE and its variants. However, BPE has not been extensively applied to CBE growth with only preliminary results of CBE-grown InP using BPE having been published to date. This paper presents the first systematic study on the growth rate and efficiency, morphology, electrical and optical properties of CBE-grown InP using BPE. We compare these results to data obtained for CBE-grown InP using TBP. To make this comparison more meaningful, all TBP and BPE growth runs were performed in sequence using the same CBE hardware under identical experimental conditions. Duplicate sets of sample runs were grown to verify reproducibility. Details of the effects of substrate temperature, cracker cell temperature and V III ratio on the electrical transport properties determined from 77 K and room-temperature Hall measurements and the optical properties characterized by 14 K photoluminescence (PL) measurements are presented. The Hall carrier concentrations and PL data strongly correlate with the sulfur impurity levels measured by secondary ion mass spectroscopy (SIMS). All of the undoped InP epitaxial layers show n-type conductivity. Striking similarities in the electrical and optical properties of InP grown using either BPE or TBP were observed indicating that BPE and TBP, in many respects, can be viewed as interchangeable P-sources.

High-resolution time-of-flight mass-spectroscopy study of synchrotron-radiation-induced chemical reactions on Si(100).

The intermediate species involved in synchrotron-radiation-excited Si epitaxy using ${\mathrm{Si}}_{2}$${\mathrm{H}}_{6}$ was identified. High-resolution time-of-flight mass spectroscopy from ${\mathrm{Si}}_{2}$${\mathrm{H}}_{6}$-chemisorbed Si(100) clearly resolved the stimulated desorption of bulk and surface ${\mathrm{H}}^{+}$ associated with ${\mathrm{H}}_{2}^{+}$. The ${\mathrm{H}}_{2}^{+}$ arises from the dihydride and the surface ${\mathrm{H}}^{+}$ from both monohydrides and dihydrides, contributing to the surface growth channel by regeneration of dangling bonds. The gas-phase growth channel is characterized by the species of ${\mathrm{H}}^{+}$, ${\mathrm{H}}_{2}^{+}$, ${\mathrm{SiH}}_{\mathit{x}}^{+}$, and ${\mathrm{Si}}_{2}$${\mathrm{H}}_{\mathit{y}}^{+}$ resulting from ${\mathrm{Si}}_{2}$${\mathrm{H}}_{6}$ photolysis.

ＡｒプラズマによるダイヤモンドのプラズマＣＶＤ

Up to now, an extremely high density of atomic hydrogen was supposed to be necessary for the gas phase growth of diamond, so that hydrogen was usually used as the plasma base gas. Therefore, we have investigated the chemical vapor deposition of diamond in Ar/H2-CH4-O2 plasma, especially the effect of the plasma gases (Ar or H2). Only diamond phase could be successfully grown even in the Ar-based plasma, revealing that the sufficient amount of hydrogen atoms was supplied by the cracking of methane molecules in the plasma. The comparison of the deposits in Ar-based and H2-based plasmas showed that both the morphology and the growth rate were similarly dependent on substrate temperature. Although the gas-phase composition in Ar-based plasma might be different from that in H2-based plasma, the composition in the vicinity of growth interface would be virtually identical in both cases.

Redistribution of Hydrogen in Gan, Ain, and Inn

ABSTRACTHydrogen incorporation during gas-phase growth of III-V nitrides is thought to play an important role in determining the apparent doping efficiency, due to unintentional passivation of dopants. Hydrogen implantation can also be used for electrical and optical isolation of neighboring devices, as in other lll-V materials such as GaAs. We have implanted2H at 40 keV to doses of 5 × 1015cm-2at room temperature into epitaxial layers of GaN, AIN and InN grown by MOMBE on GaAs substrates, and measured the ion ranges and hydrogen redistribution upon subsequent furnace annealing. The hydrogen profiles remain unchanged for annealing temperatures up to 800–900°C for GaN and AIN, and 600° for InN. Samples were also deuterated from an ECR plasma at 250 or 400°C for 30 min, producing2H incorporation depths of ≤ 1 μ in GaN. With annealing, there is no significant hydrogen redistribution observed at temperatures up 800°C. Hydrogen concentrations remain in the range ∼ 1019cm-3under these conditions. At 900°C considerable hydrogen outdiffusion to the surface occurs. The thermal stability of hydrogen in these III-V nitride films indicates the need for post-growth annealing at high temperatures to achieve appreciable doping efficiencies.

Methyl halides as carbon sources in a hot-filament diamond CVD reactor: A new gas phase growth species

Equal amounts of carbon-12 methyl halides and carbon-13 methane, along with hydrogen, have been introduced into a hot-filament diamond CVD chamber. The isotopic ratios of the as-deposited diamond films on tantalum have been measured by Raman spectroscopy. It was found that methyl chloride yielded carbon-12 enriched diamond films, while the other methyl halides resulted in equal amounts of carbon-13 and carbon-12 in the films. Furthermore, the carbon-12 enrichment was more enhanced as the substrate temperature was lowered. Matrix-isolation FTIR analyses of the gas samples collected during the deposition indicated that there was no straightforward agreement between the 12C/13C ratios of the gas phase species, methane and acetylene, and that of the diamond films. The results imply the presence of a new chlorocarbon radical such as CH2Cl, which is postulated as a more effective growth species than the methyl radical.

Intrinsic carbon incorporation in very high purity MOVPE GaAs

The limits of intrinsic carbon incorporation in very high purity GaAs grown by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE) were investigated by using a MOVPE system designed specifically for high purity growth along with many sources of highly purified trimethylgallium (TMG) and arsine. We have systematically grown series of layers while varying the growth temperature, gas phase stoichiometry (V/III ratio) and growth rate. In addition we studied the effects of in situ arsine purification on impurity incorporation. Donor and acceptor densities were reliably determined from fitting the temperature dependence of the electron density and mobility. Lineshape analysis of donor to acceptor photoluminescence transitions provided the relative amounts of carbon and zinc acceptors. This work determined a baseline for the minimum carbon incorporation of N C ≥ 5 × 10 13 cm −3, and in addition, achieved a new standard for the electron mobility in n-type GaAs grown with TMG and AsH 3 with a peak mobility of μ(48 K) = 213,000 cm 2/ V⋯ s. Carbon incorporation showed a —1.3 power law dependence on the V/III ratio and was found to be controlled by processes with opposite temperature dependencies at high and low temperatures, thereby reaching a minimum around T g = 640 ± 20° C.

Process for preparing carbon fibres in gas phase growth : Arakawa, K. and Ohsaki, T. (Nikkiso Co, Ltd, Tokyo, Japan) US Pat 4 876 078 (24 October 1989)

Process for preparing carbon fibres in gas phase growth : Arakawa, K. and Ohsaki, T. (Nikkiso Co, Ltd, Tokyo, Japan) US Pat 4 876 078 (24 October 1989)

Process for preparing carbon fibres in gas phase growth: Arakawa, K. and Ohsaki, T. (Nikkiso Co., Ltd., Tokyo, Japan) US Pat 4 876 078 (24 October 1989)

Process for preparing carbon fibres in gas phase growth: Arakawa, K. and Ohsaki, T. (Nikkiso Co., Ltd., Tokyo, Japan) US Pat 4 876 078 (24 October 1989)

Kinetics of Gas-Phase Chemical Reactions and Growth of a-SiC:H Films from Silane and Acetylene in a Remote Hydrogen Plasma Reactor

ABSTRACTGas-phase chemical reactions of interest for the deposition of amorphous silicon carbide in a remote hydrogen plasma reactor have been quantitatively characterized with electron spin resonance, and the deposition of a-SiC:H from silane and acetylene is demonstrated.

Surface Growth and Soot Particle Reactivity

Abstract In this paper we propose modificalions to our original model of surface growth which reconciles the empirical result that surface growth is proportional to the soot surface area in normal (unseeded) flames but not in flames that have been seeded. The new model proposes: (i) The controlling experimenlally measured variable determining the rate of surface growth is the amount of soot generated in the inception stage and delivered to the growth stage, (ii) Growth stops at long times because of changes in the reactivity of the soot particles, not because of depletion of gas phase growth species. (iii) Acetylene and - to a lesser extent - diacetylene are the principal growth species in all premixed flames, although PAH may dominate during particle inception, and other species may dominate in diffusion flames, (iv) Surface growth occurs on reactive sites such as defects or edges which are lost by a temperature-dependent annealing process. The number of active sites is not directly affected by coagula...

Formation of high mass carbon cluster ions from laser ablation of polymers and thin carbon films

Three materials were studied by laser ablation/Fourier transform mass spectrometry, using 266 nm laser radiation: a copolymer of ethylene and tetrafluoroethylene (ETFE), polyphenylene sulfide (PPS), and a diamond-like carbon film (DLC). In each case, positive ion mass spectra exhibit primarily even-numbered, high mass carbon clusters (‘‘fullerenes’’) of the type previously reported for graphite ablation. In the case of ETFE, a large C+60 peak (‘‘buckminsterfullerene’’) was observed. The polymer spectra showed a strong dependence on the number of laser pulses on one spot and the laser power density. For ETFE, the fullerene ion relative intensity first increases and then decreases as a function of the number of laser pulses. For the DLC film, fullerenes are observed with a single laser pulse on a fresh spot of the sample. The results are interpreted in terms of a gas phase growth model for the fullerene ion formation.

Formation of polycyclic aromatic hydrocarbons in circumstellar envelopes

Production of polycyclic aromatic hydrocarbons in carbon-rich circumstellar envelopes was investigated using a kinetic approach. A detailed chemical reaction mechanism of gas-phase PAH formation and growth, containing approximately 100 reactions of 40 species, was numerically solved under the physical conditions expected in cool stellar winds. The chemistry is based on studies of soot production in hydrocarbon pyrolysis and combustion. Several first-ring and second-ring cyclization processes were considered. A linear lumping algorithm was used to describe PAH growth beyond the second aromatic ring. PAH production using this mechanism was examined with respect to a grid of idealized constant velocity stellar winds as well as several published astrophysical models. The basic result is that the onset of PAH production in the interstellar envelopes is predicted to occur within the temperature interval of 1100 to 900 K. The absolute amounts of the PAHs formed, however, are very sensitive to a number of parameters, both chemical and astrophysical, whose values are not accurately known. Astrophysically meaningful quantities of PAHs require particularly dense and slow stellar winds and high initial acetylene abundance. It is suggested that most of the PAHs may be produced in a relatively small fraction of carbon-rich red giants.

Selective Epitaxy of AlxGa1−x as and AlxGal−x as Based Structures

ABSTRACTSelective epitaxy of AlxGa1−x As by MOVPE was accomplished using diethyl gallium chloride and diethyl aluminum chloride as the metalorganic precursors. Selective epitaxy was achieved for Al containing compounds under certain growth conditions, but AlAs growth was not selective. Quantum wells were selectively grown on masked substrates and unpatterned GaAs wafers; QW luminescence was observed from all samples. Additionally, near gap luminescence was observed from AlxGa1−x, As heterostructures over the entire 550 °C - 850 °C growth temperature range. The ternary alloy composition was found to be a strong function of the gas phase composition and growth temperature. A simple thermodynamic model explained the dependence of growth rate and composition on these parameters.

An AES/XPS study of oxygen involved reactions on InSb

AbstractThe oxidation of ion‐etched InSb(110)‐cleavage planes was investigated by means of AES and XPS, respectively. Whereas the sticking coefficient of oxygen at indium sites was found to reach a saturation value after slight ion bombardment, the oxygen uptake rate of antimony remains low (sticking probability in the 10−7 range) with raising ion dose to a point where a drastical change in oxidation behaviour occurs at ion doses in the 10−2 As · cm−2 range. Then indium and antimony are nearly simultaneously oxidized with sticking coefficients of roughly 10−3. Cluster formation is discussed as one possible mechanism to explain the experimental findings. Adsorption experiments on disordered surfaces can contribute to a better understanding of surface reactions during gas phase growth of single crystals, since the in‐growth situation of the top layer of the latter is far away from the ideal situation that is prepared by in situ cleaving only.

13C isotopic labeling studies of growth mechanisms in the metalorganic vapor phase epitaxy of GaAs

Isotope tracer techniques using 13C are employed to obtain information on how the alkyl reactants used in MOVPE affect heterogeneous growth process and impurity incorporation reactions. GaAs growth was performed using trimethylgallium, 13C-enriched (50%) trimethylarsine and 13C-enriched (99%) methane. Data were obtained on isotope-labeled effects resulting from substrate crystallographic orientation, gas phase composition and growth temperature. Secondary ion mass spectrometry (SIMS) was used to detect the level of 13C in the deposited films. SIMS sensitivity for carbon species was improved by as much as a factor of 50 by use of the 75As13C− ion at me=88, rather than standard detection at me=13 which is subject to interference from 12CH− ions. Similarly, a factor of 10 increase in 12C sensitivity was achieved by detection at me=87 rather than me=12. The 13C experiments provide the first direct evidence that methyl groups from metalorganic reactants are a major source of carbon in MOVPE grown GaAs films. The measured 13C concentration was as high as 1017cm−3. Carbon incorporation increased with growth temperature, but was independent of the V/III molar ratio. Films deposited on misoriented substrates exhibited a monotomic increase in carbon content as the misoreintation angle from the {001} crystal plane was decreased from 6° to 0°. For substrates with different crystallographic orientations the carbon level was highest for {001} and {011} surfaces, and least for the {111} As face. Addition of 13C-methane to the reactants had no effect on either the growth process or carbon incorporation level. The implications of these results for MOVPE growth models are discussed in detail.

The effect of gas phase growth parameters on the composition of InGaAs in the hydride VPE process

A 1.4-μm thick InGaAs layer exhibiting an x-ray diffraction linewidth of 18 arcs has been grown on an InP substrate. This is the best crystalline perfection ever reported for InGaAs, as far as the author is aware. The effect of gas composition on lattice mismatch has been investigated for InGaAs layers grown under a variety of conditions. An empirical equation has been developed which relates lattice mismatch(Δa/a) to metals ratio, mole fraction of AsH3 and mole fraction of HC1. Values of(Δa/a) calculated using this equation are in good agreement with experiment. The metals ratio for lattice match is shown to vary linearly with the growth rate. This observation is shown to be consistent with mass transfer limitation in the gas phase. As a further consequence, relationships between layer thickness uniformity and lattice mismatch uniformity and between growth rate and gas composition are derived.

Analysis of cloud chamber measurements of gas phase polymerization

This paper provides a summary of some of the principal mathematical and theoretical tools for the analysis of experimental data accumulated in the course of the study of true gas phase chain polymerization, using nucleation and growth (in cloud chambers) of liquid monomer drops for detection. Included in the discussion are (1) a theory for the nucleation of supersaturated monomer vapors by single polymer molecules formed from the same monomer, (2) the development of the appropriate stochastics for the growth and transport of the polymers in a variety of experiments involving different configurations of space and time, (3) the development of mathematical methods for determining, from the data, rate constants and critical (for nucleation) polymer sizes, and (4) the development of methods for the extraction of mechanistic information from the noise (fluctuating rate) in the reaction involving only a small number of product molecules. All of these ideas are used in the treatment of experiments reported in the following and subsequent papers.