DETERMINATION OF ATOMIC BINDING-SITES ON THE FCC(111) PLANE

On the close-packed (111) plane of the fcc lattice, two different types of positions at which atoms are bound can be distinguished: bulk (fcc) and surface (hcp) sites. Although the detailed atomic arrangement of the fcc (111) plane is not resolved in the field ion microscope, the location and nature of the sites can be readily determined by observing the location of an adatom after diffusion. This mapping technique, although basic to site identification, is quite time consuming. In its stead, the appearance of the image spot produced by an individual adatom serves as a reliable indicator of the type of site occupied. Observations of the intensity distribution as well as of the site occupation for chemically different atoms suggest a strong dependence of both upon the electronic structure of the adatom.