Theoretical Aspects of Atom-Surface Scattering: Fid-Bau Portal

Theoretical Aspects of Atom-Surface Scattering

Manson, J. R.

Abstract Atom scattering at thermal energies has proven to be one of the most sensitive experimental methods for obtaining detailed microscopic information on surfaces [8.1]. In some cases the necessary theory is very simple, as for example in identifying surface structures from the positions of diffraction peaks, or obtaining surface phonon dispersion relations from the positions of the phonon peaks in an inelastic experiment. In most other cases, however, sophisticated theory which often involves intensive numerical calculations is necessary in order to fully exploit the extreme sensitivity of the method to surface structure, disorder and surface vibrations. As with thermal neutrons, the wavelengths of small mass and low energy atoms such as He are comparable to interparticle spacings in solids, and the energies are comparable to maximum crystal phonon energies. Thus such particles are ideally suited for studies of both surface structure and surface vibrations. The theory of scattering of atoms from an extended target such as a surface has similarities with many of the highly developed techniques used to interpret scattering from bulk solids or liquids, as for example neutron, X-ray or electron scattering. The major difference from bulk scattering is that the presence of the surface breaks the translational symmetry normal to the surface, hence momentum is no longer conserved in that direction. One immediate consequence of this is that diffraction peaks from ordered surfaces are two-dimensional in character and can be observed for all incident beam conditions.