Si + SiH4 Reactions and Implications for Hot-Wire CVD of a-Si:H: Computational Studies

2000 ◽  
Vol 609 ◽  
Author(s):  
Richard P. Muller ◽  
Jason K. Holt ◽  
David G. Goodwin ◽  
William A. Goddard
Keyword(s):  
Quantum Chemistry ◽  
Amorphous Silicon ◽  
Gas Phase ◽  
Computational Studies ◽  
Hot Wire ◽  
Gas Phase Reactions ◽  
High Quality ◽  
Gas Phase Chemistry ◽  
Si Films ◽  
Phase Chemistry

ABSTRACTGas phase chemistry is believed to play an important role in hot-wire CVD of amorphous silicon, serving to convert the highly-reactive atomic Si produced at the wire into a less-reactive species by reaction with ambient SiH4. In this paper, we use quantum chemistry computations (B3LYP/cc-pvTZ) to examine the energetics and rates of possible gas-phase reactions between Si and SiH4. The results indicate that formation of disilyne (Si2H2) is energetically favorable. Unlike other products of this reaction, Si2H2 does not require collisional stabilization, and thus this species is the most likely candidate for a benevolent precursor that participates in the growth of high-quality Si films.

Oxidative dealkylation of aromatic amines by "bare" FeO+ in the gas phase

1999 ◽  
Vol 77 (5-6) ◽  
pp. 774-780 ◽  
Author(s):  
Mark Brönstrup ◽  
Detlef Schröder ◽  
Helmut Schwarz
Keyword(s):  
Gas Phase ◽  
Bond Activation ◽  
Isotope Effects ◽  
Gas Phase Reactions ◽  
Electron Transfer Mechanism ◽  
Gas Phase Chemistry ◽  
Kinetic Isotope ◽  
Phase Chemistry ◽  
Cytochrome P 450 ◽  
Mass Spectrometric Techniques

The gas-phase oxidations of aniline, N-methylaniline, and N,N-dimethylaniline by FeO+ cation are examined by using mass spectrometric techniques. Although bare FeO+ is capable of hydroxylating aromatic C—H bonds, the fate of the oxidation of arylamines is determined by docking of the FeO+ unit at nitrogen. The major reactions of the metastable aniline/FeO+ complex are losses of molecular hydrogen, ammonia, and water, all involving at least one N-H proton. N-alkylation results in a complete shift of the course of the reaction. The unimolecular processes observed can be regarded as initial steps of an oxidative dealkylation of the amines mediated by FeO+. More detailed mechanistic insight is obtained by examining the C—H(D) bond activation of N-methyl-N-([D3]-methyl)aniline by bare and ligated FeO+ species. The gas-phase reactions of FeO+ with methylanilines show some similarities to the enzymatic dealkylation of amines by cytochrome P-450. The kinetic isotope effects observed experimentally suggest an electron transfer mechanism for the gas-phase reaction.Key words: mass spectrometry, gas-phase chemistry, iron, dealkylation, N,N-dimethylaniline.

Effect of pressure on the gas-phase chemistry when using monomethylsilane and dimethylsilane in hot-wire chemical vapor deposition

2015 ◽  
Vol 93 (1) ◽  
pp. 82-90 ◽  
Author(s):  
Rim Toukabri ◽  
Yujun Shi
Keyword(s):  
Free Radical ◽  
Gas Phase ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Phase Reaction ◽  
Hot Wire ◽  
Gas Phase Reaction ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

The effect of source gas pressure on the gas-phase reaction chemistry of dimethylsilane (DMS) and monomethylsilane (MMS) in the hot-wire chemical vapor deposition process has been studied by examining the secondary gas-phase reaction products in a reactor using a soft laser ionization source coupled with mass spectrometry. For DMS, the increase in sample pressure has resulted in the formation of small hydrocarbons, including ethene, acetylene, propene, and propyne. This leads to a switch from silylene dominant chemistry to a free radical dominant one with the pressure increase at low filament temperatures of 1200 and 1300 °C. At the lower pressure of 0.12 Torr, the formation of 1,1,2,2-tetramethyldisilane by dimethylsilylene insertion reaction into the Si–H bond in DMS is favored over trimethylsilane produced from a free radical recombination reaction for a short reaction time. However, when the pressure is increased by 10 times, the gas-phase chemistry becomes dominated by the formation of trimethylsilane. We have demonstrated that trapping of the corresponding active intermediates by the small hydrocarbons produced in situ is responsible for the observed switch. In the study with MMS, the gas-phase chemistry is dominated by the formation of 1,2-dimethyldisilane and 1,3-disilacyclobutane at both pressures of 0.48 and 1.2 Torr. Unlike DMS, the gas-phase reaction chemistry with MMS does not involve free radicals, which are the precursors to produce small hydrocarbons. The absence of small hydrocarbons formed in situ with MMS explains the preservation in chemistry upon the increase in pressure when MMS is used as a source gas.

MOVPE GaN Gas-Phase Chemistry for Reactor Design and Optimization

1996 ◽  
Vol 449 ◽  
Author(s):  
S. A. Safvi ◽  
J. M. Redwing ◽  
A. Thon ◽  
J. S. Flynn ◽  
M. A. Tischler ◽  
...  
Keyword(s):  
Growth Rate ◽  
Gas Phase ◽  
Growth Rates ◽  
Operating Conditions ◽  
Gas Phase Reactions ◽  
Group V ◽  
Group Iii ◽  
Design And Optimization ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

ABSTRACTThe results of gas phase decomposition studies are used to construct a chemistry model which is compared to data obtained from an experimental MOVPE reactor. A flow tube reactor is used to study gas phase reactions between trimethylgallium (TMG) and ammonia at high temperatures, characteristic to the metalorganic vapor phase epitaxy (MOVPE) of GaN. Experiments were performed to determine the effect of the mixing of the Group III precursors and Group V precursors on the growth rate, growth uniformity and film properties. Growth rates are predicted for simple reaction mechanisms and compared to those obtained experimentally. Quantification of the loss of reacting species due to oligmerization is made based on experimentally observed growth rates. The model is used to obtain trends in growth rate and uniformity with the purpose of moving towards better operating conditions.

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