Adhesion (Binding) of Adsorbed Atoms in the Ion Bombardment of Clean Surfaces

Abstract

The sorption of positive gas ions by a solid differs from ordinary physical adsorption and chemisorption mainly by virtue of the fact that the ions are electrically charged and possess an energy far higher than the thermal energy. The first of these factors is not particularly important for studying sorption processes, since the ion is neutralized before falling on the solid surface [1]. Far more important is the second property, in view of the fact that ions penetrate well into the solid by virtue of their high energy and suffer absorption in the material. In this process, atoms may be freed from the solid target, i.e., the target material is sputtered, and lattice defects are formed in the sites so freed. Some of the gas atoms captured in the solid may become firmly attached to the lattice, while others may migrate from place to place. Subsequently the migrating gas atoms may return to the vacuum after a relatively long period. It is extremely likely that the activation energy will differ from that of normal diffusion, as it may depend on the point of entry of the gas atom.