Photodesorption of gases from metal and semiconductor surfaces
Moore, Robert David
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https://hdl.handle.net/2142/25559
Description
Title
Photodesorption of gases from metal and semiconductor surfaces
Author(s)
Moore, Robert David
Issue Date
1979
Doctoral Committee Chair(s)
Flynn, C.P.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
photodesorption
gases
metal surfaces
semiconductor surfaces
Language
en
Abstract
This thesis describes an investigation of molecular photodesorption from metal and semiconductor surfaces. In the process of photodesorptiona a photon causes a molecule to desorb from the surface. The techniques employed to obtain adequate sensitivity made use of a chopped light beam and synchronous particle counting by means of a mass spectrometer. This work provides definitive measurements of the photodesorption efficiencies of several molecular species (C02, CO, H2, and CH4) from a number of metals and semiconductors. Photodesorption is a weak, temperature independent process, and it is rather difficult to measure. The photodesorbed fluxes of residual gases appear to follow Langmuir isotherms in their dependence on ambient vacuum conditions. In the one case of rare gases on aluminum, for which measurements were made on a freshly doped clean surface, no photodesorption could be observed. The variations of the observed efficiencies for photon energies between 4 and 11.5 ev point to a dominant role of intramolecular excitations in the main channel for photodesorption of more complex molecules. Previously proposed models involving band gap excitations in semiconductors and adsorbate-substrate bond excitations appear to bear no relationship to the observed effects.
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