SURFACE-DIFFUSION - AN STM VIEW

We employ a high-speed high-temperature scanning tunneling microscope to investigate two manifestations of surface diffusion. The step fluct uations observed on metal surfaces are shown to be the result of the f ast diffusive motion of pre-existing kinks in the steps. We find that a high density of kinks can be induced by a minute concentration of im purities. At sufficiently high temperatures, surfaces can ''jump'' to physical contact with the tip of the microscope. Such jumps are follow ed by a ''sintering'' process in which a massive connecting neck rapid ly builds up between the surface and the tip.