Reactant Partial Pressures Research Articles

Direct formation of cyclohexene via the gas phase catalytic dehydrohalogenation of cyclohexyl halides

The gas phase dehalogenation of cyclohexyl chloride and cyclohexyl bromide (where 423 K≤ T≤523 K) promoted using silica and zeolite supported nickel catalysts in the presence of hydrogen is presented as a viable one step route for the production of cyclohexene. Cyclohexene is generated via the internal elimination of the corresponding hydrogen halide where the process is 100% selective at T≤473 K. At higher temperatures, cyclohexane and benzene were isolated in the product mixture as a result of the combination of catalytic hydrogenolysis, hydrogenation and dehydrogenation steps. Cyclohexene yield was subject to a short term reversible decline with time-on-stream due to a surface poisoning by the hydrogen halide that was produced but the presence of hydrogen served to displace the inorganic halide and extend the productive lifetime of the catalyst. Bromine removal from cyclohexyl bromide was found to be more facile while the use of a higher loaded (15.2% (w/w) as opposed to 1.5% (w/w)) nickel silica is shown to result in appreciably higher dehydrohalogenation rates. Both Na/Y and Ni–Na/Y zeolites promoted cyclohexene formation but exhibited an irreversible deactivation which is attributed to pore blockage by occluded coke. With a view to optimising catalyst efficiency, the effect on cyclohexene yield of varying such process parameters as reaction time and temperature and reactant(s) partial pressures were studied and the catalytic data are compared with thermodynamic predictions.

A Kinetic and Spectroscopic Study of the in Situ Electrochemical Promotion by Sodium of the Platinum-Catalyzed Combustion of Propene

The electrochemical promotion (EP) of propene combustion has been studied over a platinum film catalyst supported on sodium β‘ ‘-alumina. Fully reversible promotion and poisoning are observed as a function of catalyst potential (i.e., sodium coverage), the precise behavior being dependent on reactant partial pressures. A model based on a Langmuir−Hinshelwood mechanism and Na-modified chemisorption of the reactants accounts for all the results: Na enhances the chemisorption of oxygen and inhibits the chemisorption of propene. The formation, chemical identity, stability, and electrochemical decomposition of the Na surface compounds produced in the promoted and poisoned regimes were explored using postreaction XPS, AES, and, for the first time, postreaction Na K edge XAFS. These results indicate that thick layers consisting of sodium carbonate are responsible for catalyst poisoning. The promoter phase consists of smaller amounts of sodium carbonate, and much of this material is present as three-dimensional ...

Chemical vapor etching of copper using oxygen and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione

The use of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hfacH) and oxygen to thermally dry etch copper was studied using a vertical flow reactor. The two primary reaction steps in this process are the oxidation of copper by oxygen to form copper(I) and copper(II) oxides and the subsequent removal of the oxide by reactions with hfacH to form copper(II) bis-hexafluoroacetylacetonate and water. Etch rates as high as 1.5μm at 350°C were achieved by the simultaneous flow of hfacH and oxygen. Etch rates and surface composition were found to be a function of temperature, reactant partial pressures, and surface morphology. At high hfacH to oxygen ratios the surface remained copper colored and the etch rate was nearly independent of the hfacH partial pressure but was more strongly dependent on the oxygen partial pressure and surface morphology. At low hfacH to oxygen ratio the surface became deep rose colored and the etch rate became nearly independent of the oxygen partial pressure and the surface morphology but had a strong dependence on the hfacH partial pressure. These results show that copper can be etched successfully by chemical vapor etching. However, more work needs to be done before this becomes a useful commercial process.

Solution Delivery of Cu ( hfac ) 2 for Alcohol‐Assisted Chemical Vapor Deposition of Copper

We have applied the liquid delivery technique for the thermally activated chemical vapor deposition of copper using a solution of in isopropanol [H(hfac) = 1,1,1,5,5,5‐hexafluoro‐2,4‐pentanedione]. Using a substrate temperature of 300°C and reactant partial pressures of 1.8 Torr , 12 Torr isopropanol, and 40 Torr , we obtained a maximum growth rate of . There is an induction time of about 5 min, which correlates with the time required for the initial copper clusters to grow into contact with each other (i.e., as judged from scanning electron microscope images). Film resistivities lie in the range 2.5–5.0 μΩ cm (vs. 1.68 μΩ cm for bulk Cu). The scanning electron microscope images suggest these high values are caused by residual void volume between the clusters. Growth rates and resistivities can be improved by eliminating from the starting solution, by wet‐etching the substrate or by increasing the substrate pretreatment time. © 1999 The Electrochemical Society. All rights reserved.

Synthesis of ultrafine nickel aluminide particles by the hydrogen reduction of vapor-phase mixtures of NiCl2 and AlCl3

Fine particles of nickel aluminides were synthesized for the first time by reducing mixtures of AlCl3 + NiCl2 vapors by hydrogen. A thermodynamic equilibrium calculation was carried out in the Ni–Al–H–Cl–Ar system to evaluate the effect of the reactant partial pressures and temperature on the formation of intermetallic phases. A single intermetallic phase was found to be feasible only in a very narrow range of the reactant partial pressures. For all other conditions the predicted solid product was a mixture of two phases. Experimentally, Ni3Al was formed along with metallic Ni. Though the coreduction of NiCl2 and AlCl3 by H2 to form Ni3Al is thermodynamically favorable at 1100 °C, it did not happen experimentally under the conditions of this work. However, with a small addition of aluminum vapor, the coreduction reaction proceeded as expected by thermodynamics. The effects of reactant partial pressures and temperature were studied. The content of Ni3Al was maximized to 52 mol% at 1050 °C under the partial pressures of H2, AlCl3, and NiCl2 at 57, 1.5, and 0.5 kPa, respectively. The product particles, as observed by TEM, were very fine, but usually agglomerated. The electron diffraction analysis identified the particles of NiAl and NiAl3 along with Ni3Al and metallic Ni.

Monitoring of CdTe atomic layer epitaxy using in-situ spectroscopic ellipsometry

Atomic layer epitaxy or ALE has proven to be useful for the growth of epitaxial layers of high uniformity, good quality, and well-controlled thickness. In this study, we have carried out in-situ monitoring during the atmospheric pressure ALE of CdTe on GaAs (100) substrates using spectroscopic ellipsometry (SE). The susceptor temperature, reactant partial pressures, as well as the flow and flush duration for each precursor are crucial process variables for ALE growth. Growth was carried out for 20–25 cycles under different sets of these process conditions during the experiment and in-situ SE was used to verify the presence of layer-by-layer growth, which enabled the quick determination of the process window. We observed ALE growth of CdTe at 300°C, supporting the explanation that the growth of CdTe occurs via a surface catalyzed decomposition of the Te precursor di-isopropyltelluride (DIPTe). Investigation of ALE mode growth behavior for different susceptor temperatures and DIPTe flush times indicated that the growth was limited by competition between desorption and reaction of the adsorbed DIPTe species on the Cd terminated surface.

Reaction of NO and N2O gases with graphite in TGA

Thermal analyses were conducted in a thermogravimetric analyzer by isothermal techniques in order to characterize the carbon-nitrogen oxide reaction. The carbon samples employed in the present study were SP-1 graphite and Micro 450 graphite. Carbon-NO and carbon-N2O reactions were carried out in a temperature range of 550–900 °C and 5–20 kPa of the partial pressure of reactant. In the NO reaction, reaction orders with respect to NO concentration and activation energy were 0.46-0.92 and 85–102 kJ/mol, respectively. The rate on the monolayer edge was higher than the rate on the multilayer edges. In the N2O reaction, reaction orders with respect to N2O concentration and activation energy were 0.55–1.35 and 167–190 kJ/mol, respectively.

Low temperature reaction of chlorine nitrate with water ice Formation of molecular nitric acid

We have examined the reaction of ClONO2 with water ice at 140 K and found evidence for the formation of molecular nitric acid under conditions of reduced surface water. This is very different from the behaviour of ClONO2 on ice at 180 K, where substrate-induced pre-reaction ionisation of ClONO2 leads to a reaction mechanism involving the intermediacy of [H2OCl]+ and nitrate ions. These two results are not inconsistent with a single mechanism if a subtle change in the interplay between the availability of water molecules at the surface and the variation of the substrate/adsorbate interactions of ice/ClONO2 with temperature are taken into account. This implies that reaction mechanisms and product branching ratios in the atmosphere may vary widely over a range of temperatures and reactant partial pressures.

Kinetics of the NO and CO Reaction over Platinum Catalysts: I. Influence of the Support

The kinetics of the CO+NO reaction over Pt-based catalysts was investigated using a fixed bed flow reactor at 300°C, with CO and NO partial pressure ranges of 1.5×10−3to 9×10−3atm. Pt was deposited on various supports: γ-Al2O3, Si3N4, and Cr3C2. XRD, XPS, and hydrogen chemisorption measurements seem to indicate that Pt dispersion decreases as follows: Pt/Al2O3>Pt/Si3N4>Pt/Cr3C2. Kinetic data obtained on these Pt catalysts were interpreted on the basis of four mechanisms as proposed in the literature; only one mechanism can correctly model the reactant partial pressure dependencies of the rate. This mechanism involves nondissociative CO and NO competitive adsorptions followed by a dissociation of adsorbed NO which requires a vacant nearest-neighbor adsorption site. Clearly, the adsorption equilibrium constants, λCOand λNOof CO and NO, together with the rate constant of the NO dissociation step are strongly influenced by the support, particularly λNO, which is consistently lower than λCOon Pt/Al2O3, increases notably for Pt/Si3N4, and increases even more for Pt/Cr3C2. It has been shown that Pt/Si3N4may be the most suitable catalyst if the Pt dispersion on this support can be improved. The nature of the support also has a significant effect on the selectivity of the NO transformation into N2and N2O. Pt/Cr3C2is the most selective catalyst for N2formation (much more than Pt/Si3N4and particularly Pt/Al2O3). This seems to be related to the fact that the rate constant of the step 2Nads→N2is much higher than that of the other step Nads+NOads→N2O.

Protolytic cracking of low-molecular-weight alkanes in the presence of iron- and manganese-promoted sulfated zirconia: evidence of a compensation effect

Low conversions of propane, n-butane, and 2,2-dimethylpropane were measured with each reactant in the presence of iron- and manganese-promoted sulfated zirconia in a once-through plug-flow reactor at 101 kPa, 473–723 K, and reactant partial pressures of 25, 250, and 1000 Pa. Rates of the reactions (overall conversion of propane, of n-butane, and of 2,2-dimethylpropane; formation of methane from each of the three reactants; formation of ethene from propane and from n-butane; and formation of ethane from n-butane) were determined by extrapolating the declining conversions to zero time on stream. The apparent activation energies and apparent pre-exponential factors characterizing these reactions, which are inferred to proceed via carbonium-ion transition states, fall near a straight line on a compensation effect plot. The plot is suggested to represent the family of reactions proceeding via protolytic cracking and dehydrogenation and carbonium-ion transition states.

The reaction of ClONO2 with HCl on aluminum oxide

The chlorine activation reaction ClONO2 + HCl → HNO3 + Cl2 was investigated in the laboratory on hydroxylated α‐alumina surfaces under reactant partial pressure, humidity, and temperature conditions covering those which are encountered at mid‐latitudes in the lower stratosphere. The measured reaction probability is γ∼ 0.02. This result has implications with regard to the stratospheric impact of launch vehicles utilizing solid‐fuel rocket motors (SRMs), such as the Space Shuttle. The exhaust from SRMs consists of alumina particles and of HCl and other vapors. The reaction probability measured in this work suggests that the ozone depletion potential of SRMs may be higher than that predicted on the basis of the chlorine emissions alone, especially at mid‐latitudes in the lower stratosphere, where catalytic chlorine activation by background sulfuric acid aerosols is very inefficient. The reaction probability on Pyrex glass was found to be similar to that on α‐alumina. The reaction mechanism appears to be determined by the water layers adsorbed on the surface, rather than by the detailed nature of the refractory surface itself.

Kinetics of the Hydrodenitrogenation ofortho-Propylaniline over NiMo(P)/Al2O3Catalysts

The kinetics of the hydrodenitrogenation (HDN) ofortho-propylaniline (OPA) was studied over sulfided NiMo(P)/Al2O3catalysts. A small amount of propylcyclohexylamine was observed in the reaction product, demonstrating that hydrogenation of the phenyl group of OPA was one of the first and rate-limiting steps in the HDN reaction. A Langmuir–Hinshelwood kinetic model with different sites for the HDN and hydrogenation could successfully fit the reaction network. Some kinetic parameters were obtained by varying the initial reactant partial pressure at constant space time and by simultaneous reaction, while others were determined by varying the space time at constant reactant partial pressure. The HDN rate constants and the adsorption constants of OPA and NH3were higher over the phosphate-containing catalyst than over the phosphate-free catalyst, while the activation energies as well as the heats of adsorption of OPA did not show any difference between the two catalysts. This demonstrates that the nature of the catalyst sites did not change by the introduction of phosphate. The promotive effect of phosphorus in the HDN of OPA arises from an increased number of active sites for the hydrogenation of the phenyl ring of OPA as well as from a stronger adsorption of OPA due to increased MoS2stacking and therefore less hindered adsorption. Phosphorus shows a promotive effect on the hydrogenation of pure olefins, but a negative effect when nitrogen-containing compounds are present. This is due to a stronger adsorption of the nitrogen-containing compounds on the P-containing catalyst, and hence to a stronger inhibition.

Effect of Activation Procedure and Support on the Reductive Amination of Ethanol Using Supported Cobalt Catalysts

The reductive amination of alcohols using ammonia catalyzed by supported cobalt catalysts has been studied. The catalytic activity for ethanol conversion is shown to be directly proportional to the exposed metal surface area, indicating that the activation of ethanol is metal-catalyzed and no metal-support effects were detected. The selectivity to the mono-, di-, and triethylamine varies with temperature, reactant partial pressures, and extent of reactant conversion generally as expected for a series-type reaction scheme. Both the activation procedure and the type of support also influence selectivity. Increasing the acidity of the support favors the formation of monoethylamine, probably due to disproportionation of diethylamine on the acid sites of the support indicating the bifunctionality of the catalyst.

Chemical vapour deposition of silicon carbide by pyrolysis of methylchlorosilanes

Silicon carbide (SiC) prepared by chemical vapour deposition (CVD) remains of importance for both structural [1, 2] and electronic [3, 4] applications. A variety of gaseous precursors has been used for SiC deposition under widely varying conditions of input gas composition, temperature and pressure [5]. For CVD of SiC, in general, a carrier gas is bubbled through a silicon containing liquid mixed with another stream of carrier gas. The necessary carbon is either contained in the chlorosilane or supplied by introducing a hydrocarbon. Methylchlorosilane (MTS: CH3SiCl3), as a precursor, is one of the most useful of the available chlorosilanes because it contains silicon and carbon in stoichiometric proportions [6]. Accordingly, it has been expected to give stoichiometric SiC deposition. Recently, from thermodynamic studies on the CVD of SiC in the MTS ‡ H2 gas system [7, 8], it has been shown that SiC is the only stable solid phase present in a wide range of temperature, pressure and concentration of the reactant. In experimental works, however, there have been many reports in the literature [9, 10] showing that excess Si is codeposited with SiC at lower temperature. Furthermore, in our previous work [11] conducted with the MTS ‡ H2 gas system in the temperature range 1000–1500 8C, we always found excess Si deposition at temperatures below 1400 8C. In order to obtain stoichiometric SiC deposition, we recently reported [12] the addition of propane (C3H8) as an excess carbon source to the MTS ‡ H2 gas system, which resulted in the deposition of stoichiometric SiC. Therefore, it is conceivable that silanes are more reactive with the substrate than hydrocarbon and supplying excess carbon is needed for stoichiometric SiC deposition. There are some precursors that supply excess carbon, such as dimethyldichlorosilane (DDS: (CH3)2SiCl2), trimethylchlorosilane (TCS: (CH3)3SiCl) and tetramethylsilane (TS: (CH3)4Si). These chlrorosilanes contain both silicon and carbon, and the ratios of C/Si in the molecules are 2, 3 and 4, respectively. In addition DDS, TCS and TS molecules decompose more easily than MTS and supply sufficient hydrocarbon above the substrate. The purpose of the work reported here was thus to prepare stoichiometric SiC deposit by supplying DDS, TCS or TS as a reactant and to investigate the change of the microstructure. The SiC coatings were deposited in a horizontal quartz reactor at 1000–1500 8C and under atmospheric pressure. The temperatures were measured with an optical pyrometer and corrected to approximate the temperature of substrate in accordance with a previous calibration with a thermocouple. Graphite plates and SiC-coated graphite were used as substrate and susceptor, respectively. The three types of methylchlorosilane (DDS, TCS and TS) were used and they were carried by hydrogen from the evaporator maintained at 0 8C. The concentration of methylchlorosilane was controlled with hydrogen. The total flow rate of X (X ˆ DDS, TCS or TS) ‡ H2 gas mixture was kept constant at 1600 standard cubic centimetres per minute (sccm). The growth rate was estimated by measuring the weight increase during deposition periods. The crystal structure was analysed by X-ray diffractometry (XRD) and the silicon content of the coating layer was determined by energy dispersive spectrometry (EDS) and Auger electron spectroscopy (AES). The surface morphology of the coating layer was investigated by scanning electron microscopy (SEM). Details of the experimental procedure were similar to those reported previously [11, 12]. The molar fraction dependence of the deposition rate is shown in Fig. 1. The results of previous work [11], carried out in the MTS ‡ H2 system, are also shown for comparison. The total flow rate of methylsilane was 1600 sccm and the temperature of the graphite substrate was 1300 8C. As shown in Fig. 1, the deposition rate increased linearly with increasing reactant concentration. Hunt and Stirl [13] have shown that the growth rate r is determined by the relationship expressed as r ˆ cE . P0 . TF, where cE, P0 and TF are deposition yields in experimental work, partial pressure of reactants and total system pressure, respectively. Thus, increase of the molar fraction (X/(X ‡ H2), X ˆMTS, DDS, TCS or TS) leads to linear increase in the growth rate. By using DDS (C/Si ˆ 2), a higher growth rate was achieved, while it decreased with TCS or TS. The temperature dependence of the deposition rate is shown in Fig. 2. In the MTS ‡ H2 system, as is

Infrared Free-Electron-Laser Photolysis of CFCl3 and CF2Cl2

A tunable infrared free-electron laser comprised of a train of picosecond pulses was utilized to destroy the Freons CFCl3 and CF2Cl2 by multiple-photon dissociation. The experiments explored the effects of laser frequency, laser fluence, spectral bandwidth, frequency chirping, reactant partial pressure, and oxygen (or air) partial pressure. We determined the optimum laser frequencies for dissociation of both of the Freons and also showed that a broader spectral bandwidth laser enhances reaction. A strong reduction of dissociation fraction with increasing pressure made infrared photodissociation of Freons at near atmospheric pressure difficult. Improvement of the high-pressure photolysis would require a laser macropulse much shorter than the 2 μs used in these experiments.

Control of particle size distribution of ultrafine iron particles in the gas phase reaction

Experiments on the synthesis of ultrafine iron particles have been made for the control of particle size distribution using the gas phase reduction of ferrous chloride with hydrogen. The previous studies were focused on the control of particle size of ultrafine particles with the variation of the partial pressure of reactants, residence time of feed, and reaction temperature. However, it is also very important to control the size distribution of ultrafine particles. In this study, the control of particle size distribution was investigated from the standpoint of nucleation. The variation of evaporating condition at the same evaporation rate of ferrous chloride, and of the temperature gradient of reactants between preheating zone and reaction zone were adopted as experimental variables. Ultrafine iron particles having uniform size distribution could be produced under the control of evaporating condition such as the change of the surface area at constant evaporating temperature. As the temperature gradient decreased, particle size distribution became uniform and average particle sizes were also decreased.

Kinetic oscillations and hysteresis phenomena in the NO+H2 reaction on Rh(111) and Rh(533): Experiments and mathematical modeling

Interesting kinetic phenomena, such as multiple steady states and kinetic oscillations recently found in the NO+H2 reaction over Rh(533) and Rh(111) single crystal surfaces in the 10−6 mbar pressure range have been studied by means of experiments and computer modeling. A mathematical model, consisting of five ordinary differential equations and taking into account the lateral interactions in the adlayer, has been developed for simulating the NO+H2/Rh(533) and NO+H2/Rh(111) reactions. The simulation results make it possible to explain in detail the underlying reasons for the experimentally observed complex dynamic behavior. In particular, the kinetic oscillations and their properties have been reproduced. It was found that accumulation of NHads species, which serves as an intermediate in the pathway of NH3 production, is an important step in the oscillatory mechanism. In addition, the same mathematical model is able to successfully reproduce the experimental data concerning temperature programmed desorption (TPD) spectra, hysteresis phenomena, and the dependence of selectivity upon temperature and reactant partial pressures. Lateral interactions in the adlayer are shown to play a crucial role in the adequate simulation of the experimental observations.

FTIR Spectroscopic Studies of the Mechanisms of the Halogen Atom Initiated Oxidation of Haloacetaldehydes

Product studies of Cl atom initiated oxidation of ClCH2CHO and Br atom initiated oxidation of BrCH2CHO were conducted by FTIR spectroscopy at 297 ± 2 K in 700 Torr of O2/N2 diluent, using reactant partial pressures in both the torr and millitorr ranges. The halogen atoms initiate reaction via hydrogen abstraction from the aldehydic group (CHO), producing haloacetyl radicals, XCH2CO, where X = Cl or Br. In 700 Torr of air, the XCH2CO radicals may react via three channels: (i) O2-addition, XCH2CO + O2 → XCH2C(O)O2; (ii) unimolecular dissociation by CC bond cleavage, XCH2CO (+M) → XCH2 + CO (+M); and (iii) unimolecular dissociation by CX bond cleavage, XCH2CO (+M) → X + CH2CO (+M). All three channels were observed for BrCH2CO radicals, enabling estimation of the branching ratios, but ClCH2CO reacts only by O2-addition. Subsequent reactions of XCH2C(O)O2 radicals lead to XCH2O radical and CO2 formation. The ClCH2O radical reacts with O2 to produce CHClO and HO2, while the BrCH2O radical mainly eliminates the...

Modeling and Characterization of Gas‐Phase Etching of Thermal Oxide and TEOS Oxide Using Anhydrous HF and CH 3 OH

We propose a model for a gas‐phase etching of silicon dioxide using anhydrous HF gas and methanol vapor on the basis of its mechanism and characteristics which were reported by previous researchers. Here, the etch reaction rate was assumed to be determined by the formation step of resulting from the ionization reaction between HF and adsorbed physcially on the oxide surface. The validity of this etch model was confirmed by the experimental data obtained from etching thermal oxide and tetraethylorthosilicate (TEOS) oxide at various etching conditions: HF partial pressure of 2 to 35 Torr, partial pressures of 0.3 to 4.5 Torr, and wafer temperatures of 25 to 75°C. It was shown that the gas‐phase etching of the oxides could be well characterized by the behaviors of physical adsorptions for HF and molecules on the oxides, which were expected from the Brunauer‐Emmett‐Teller (BET) equation with the values of parameters in the etch model. Also, it was shown that the etch selectivities between the thermal oxide and the TEOS were mainly dependent on the wafer temperature and the reactant partial pressures, and could be in the range of 2 to 30 according to the etching conditions in the gas‐phase regime.

Cold-wall ultrahigh vacuum chemical vapor deposition of doped and undoped Si and Si1−xGex epitaxial films using SiH4 and Si2H6

Doped and undoped silicon homoepitaxy and Si1−xGex-on-Si heteroepitaxy have been achieved by cold-wall ultrahigh vacuum chemical vapor deposition using disilane (Si2H6), silane (SiH4), digermane (Ge2H6), and germane (GeH4) as the reactant gases. Boron and phosphorus doping were achieved by flowing B2H6 and PH3 dopant gases, respectively, into the reactor. The growth mechanism and film quality of intrinsic Si, B/P-doped films, and Si1−xGex alloys using SiH4 and Si2H6 are comparatively studied in this article. The crystallinity of the films was examined by Nomarski microscopy after Schimmel etching, transmission electron microscopy (TEM), and in situ reflection high energy electron diffraction (RHEED). The defect density of the intrinsic Si films grown by Si2H6 and SiH4 was found to be below the TEM detection limit (105/cm2). B-doped and P-doped single-crystal Si were deposited using Si2H6 or SiH4 with a partial pressure of 10 mTorr at substrate temperatures from 550 to 600 °C. The B- and P-doping concentrations were determined by secondary ion mass spectroscopy (SIMS). From plan-view TEM analysis, it was found that the defect density of the B- and P-doped Si films grown using Si2H6 is lower than that grown using SiH4 at even lower substrate temperatures. It was also found that the phosphine (PH3) ‘‘poisoning effect’’ for growth rate reduction and crystallinity degradation in Si2H6 chemical vapor deposition (CVD) is not as serious as in SiH4 CVD. A model for the PH3 poisoning effect was developed to explain the growth rate reduction in SiH4 CVD with high PH3 flux. The morphology of both P-doped and B-doped Si films using Si2H6 was found to be smoother than for those using SiH4, as indicated by plan-view TEM and by RHEED analysis. Si1−xGex alloys were deposited by using various reactant gases. The thickness of the Si1−xGex alloy films and the Ge mole fraction were measured by SIMS. A 50-period Si1−xGex–Si superlattice was grown using Si2H6 and GeH4. The transition layers were found to be extremely sharp and layer thickness control using Si2H6 was found to be excellent by cross-sectional TEM analysis. In this study, Si2H6 was found to be a better Si precursor compared to SiH4 under our growth conditions. From the growth rate study, the activation energies for the Si growth rate were found to be 1.47 and 1.60 eV for Si2H6 and SiH4, respectively. The activation energies for the Ge growth rate are 0.93 and 1.0 eV using Ge2H6 and GeH4, respectively. A growth kinetic model was developed to predict the growth rate of undoped Si for various reactant gas partial pressures and substrate temperatures. The adsorption rate preexponential constant for SiH4 was found to be about twice that of Si2H6. The model can also predict the Ge mole fraction in Si1−xGex alloys and B/P doping concentrations in the Si films.