Accession Number : AD0773120

Title :   4He Atomic Beam Scattering from Clean Surfaces of Silicon, Germanium, and Lithium Fluoride.

Descriptive Note : Technical rept.,

Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF PHYSICS

Personal Author(s) : Houston,Douglas E.

Report Date : DEC 1973

Pagination or Media Count : 117

Abstract : 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)

Descriptors :   *Silicon, *Germanium, *Surface properties, Experimental design, Single crystals, Atomic beams, Helium, Surfaces, Elastic scattering, Inelastic scattering, Nozzles, Diffraction, Adsorption, Modulation, Laboratory equipment, Contamination, Mass spectrometers

Subject Categories : Physical Chemistry

Distribution Statement : APPROVED FOR PUBLIC RELEASE