FOCUSING OF 2-KEV ELECTRONS SCATTERED FROM ATOMS ALONG THE PRINCIPAL DIRECTIONS IN A CRYSTAL

The intensity of electrons scattered from atoms in the keV range is peaked in the forward direction. This effect is the basis of the projection-imaging technique of near-surface atomic geometry in solids, using secondary electrons. By changing the angle of incidence of primary electrons that are used for the excitation, the probing depth can continuously be varied. Thus, one can investigate the degree of electron focusing as a function of the number of atoms in a chain along which the scattering occurs. It is found that, for a Pt (110) surface, the angular size of the observed spots decreases as the number of atoms along the path of emission increases. In contrast to previous conclusions, this observation shows an enhancement of electron focusing in a chain of atoms.