Low-energy recoil ion spectroscopy studies of H on Si(111)-7 × 7

Abstract

The adsorption of hydrogen on a Si(111)-7 × 7 surface has been studied by means of low-energy recoil ion spectroscopy (LERIS) and low-energy electron diffraction (LEED). From a series of experiments performed at low incident ion energies ranging from 400 to 700 eV, we find two peaks in the energy distributions of recoil hydrogen ions from hydrogen adsorbed on a Si(111) surface. One of the peaks can be satisfactorily explained by the binary elastic collision model, as being due to the direct-recoil process. The other peak, however, cannot be easily explained by the binary elastic collision model because it appears either on the high- or low-energy side of the direct-recoil ion peak, depending on the recoil angle. From the comparison of the experimental results with computer simulations, it is shown that this new peak can be interpreted by events in which the direct-recoil hydrogen atoms hit the surface silicon atoms and then exit as the ions, i.e., the surface-recoil process. Surface-recoil ion detection is very useful for obtaining information on the hydrogen locations at the Si(111) surface.