SiF sub 4 -sensitized decomposition of GeH sub 4 by a pulsed CO sub 2 TEA laser
- Pennsylvania State Univ., University Park (USA)
The decomposition of GeH{sub 4}, sensitized by multiphoton absorption of unfocused infrared laser radiation by SiF{sub 4}, has been studied in the fluence range 0.2-0.9 J/cm{sup 2} and over a total pressure range of 1-70 Torr. Strong absorption of energy from a pulsed CO{sub 2} laser photon field (P40 line; 1027.4 cm{sup {minus}1}) and subsequent energy-transfer processes cause an increase in the temperature of the system. As a result of these processes, decomposition of GeH{sub 4} occurs leading to the formation of stoichiometric amounts of metallic germanium and molecular hydrogen. The effects of initial composition, pressure, fluence, and presence of foreign gases (He, H{sub 2}) on the yield of GeH{sub 4} decomposition were examined. A reaction model is proposed which assumes that molecules initially present in the absorption volume are heated by the laser pulse and subsequently decompose unimolecularly. Since the decomposition process is exothermic, it prompts a further increase in temperature and thus enhances the decomposition process. Both absorption and decomposition create a shock wave causing expansion of hot gas into cool surrounding volume. The latter process brings about cooling of the hot gas and quenches the decomposition process. Taking into account the above-mentioned effects the temperature profiles (T versus time and geometry of the reaction zone) were evaluated on the basis of statistical thermodynamics, assuming that, at any stage, the system attains thermal equilibrium. Yields of decomposition were then derived with k{sub uni} values calculated by the RRKM method. The proposed approach accounts satisfactorily for the experimentally observed dependencies, and we believe it can be generally applied to the description of photosensitized processes in the infrared region.
- OSTI ID:
- 6972049
- Journal Information:
- Journal of Physical Chemistry; (USA), Vol. 93:24; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
36 MATERIALS SCIENCE
GERMANIUM HYDRIDES
PHYSICAL RADIATION EFFECTS
DATA ANALYSIS
DECOMPOSITION
EXPERIMENTAL DATA
LASER RADIATION
MEASURING INSTRUMENTS
MEASURING METHODS
SEMICONDUCTOR MATERIALS
THERMAL ANALYSIS
CHEMICAL REACTIONS
DATA
ELECTROMAGNETIC RADIATION
GERMANIUM COMPOUNDS
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
MATERIALS
NUMERICAL DATA
RADIATION EFFECTS
RADIATIONS
400000* - Chemistry
400600 - Radiation Chemistry
360603 - Materials- Properties