SULFUR ADATOM DIFFUSION ON THE CU(111) SURFACE

This paper presents the first low-energy, quasi-elastic He-atom scattering study of adsorbate atom diffusion. At 820 K sulfur adatoms segregated onto the close-packed (111) surface of a copper crystal at a rate approximately 0.01 ML/h. These adatoms produce significant diffuse intensity of scattered He and, as evident from the quasielastic energy broadening, are highly mobile. The diffusion coefficient (D = 2.9 x 10(-5) cm2 s-1) exhibits no surface coverage dependence, indicating relatively weak sulfur-sulfur interactions on the Cu(111) substrate.