A study of the photodissociation physics of methyl bromide on gallium arsenide(110)
A study of the effects of laser light at various wavelengths, from UV (193 nm) to IR (860 nm), on the reaction of a well characterized ordered GaAs (110) surface with physisorbed CH[sub 3]Br is described. The adsorption of CH[sub 3]Br on the surface is found to be molecular. The amount of coverage is determined by a calibration of exposure versus number of monolayers. Information about the dynamics is obtained by the use of pulsed laser light of 20 ns pulse width combined with time-of-flight (TOF) measurements. The TOF spectra show five distinct features: (1) A direct dissociation peak is observed with UV light of 193 and 248 nm wavelength on samples with coverages >1 ML. For coverages <1 ML this channel is quenched due to resonant electron tunneling. (2) The peak initiated by DEA of hot electrons is fixed in energy at 1.1 eV, independent of the wavelength of the incident light, and has a threshold slightly below 351 nm. This peak is only detectable for coverages >1 ML. (3) The DEA feature due to thermalized electrons appears at different energies for 1 and 2 ML coverage. These energies are not sensitive to the wavelength of the incident laser light, and are located at 0.6 eV for 1 ML and at 0.25 eV for 2 ML. The threshold for this process coincides with the fundamental band gap of GaAs. Both peaks decays as a function of irradiation exposure. The DEA reaction product Br[sup [minus]] reacts with the surface to form GaBr, introducing surface states into the band gap that add an additional decay channel and reduce the lifetime of the very electrons that are responsible for the DEA. (4) The peak, stemming from the molecular desorption of CH[sub 3]Br due to a displacement reaction involving a vibrationally excited CH[sub 3], is only observed with 193 nm laser light and occurs at an energy of 0.45 eV. (5) The ejection of CH[sub 3]Br by collision with higher energetic fragments is more pronounced for higher energetic photons and has an energy of [approximately]0.15 eV.
- Research Organization:
- Columbia Univ., New York, NY (United States)
- OSTI ID:
- 7044145
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
74 ATOMIC AND MOLECULAR PHYSICS
GALLIUM ARSENIDES
PHOTOCHEMICAL REACTIONS
SURFACE PROPERTIES
METHYL BROMIDE
DISSOCIATION
SORPTION
CHEMICAL PHYSICS
LASER RADIATION
TIME-OF-FLIGHT METHOD
ARSENIC COMPOUNDS
ARSENIDES
BROMINATED ALIPHATIC HYDROCARBONS
CHEMICAL REACTIONS
ELECTROMAGNETIC RADIATION
GALLIUM COMPOUNDS
HALOGENATED ALIPHATIC HYDROCARBONS
ORGANIC BROMINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
PHYSICS
PNICTIDES
RADIATIONS
400500* - Photochemistry
664200 - Spectra of Atoms & Molecules & their Interactions with Photons- (1992-)