4He Atomic Beam Scattering from Clean Surfaces of Silicon, Germanium, and Lithium Fluoride.
PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF PHYSICS
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A modulated, nozzle-type molecular beam system was constructed and used to study the scattering of thermal-energy helium atoms from clean surfaces of silicon, germanium, and lithium fluoride. Experimental design and apparatus and beam characteristics are described. The surfaces are prepared by cleaving single crystals in situ under ultra-high vacuum. Silicon and germanium show sub-specular directed scattering, whereas lithium fluoride yields a strong specular peak and well defined diffraction peaks. Surface contamination is shown to have pronounced effects on the scattering of 4He atoms from LiF. The position of the diffraction peaks is not affected, but the specular peak intensity falls off relative to that of the first order diffraction peak as the contamination layer accumulates. The phenomenon of selective adsorption is a very sensitive indicator of surface cleanliness. Modified author abstract
- Physical Chemistry