Living on the edge: STM studies of the creation, diffusion and annihilation of surface vacancies

Abstract

This thesis describes an STM study of the creation, diffusion and

annihilation of missing atoms, so-called surface vacancies, in the

Cu(100) surface. Because of the extremely high mobility of surface

vacancies in combination with their extremely low density, we have been forced to use tracer particles, in form of indium atoms incorporated in the topmost copper layer, in order to investigate the behavior of the surface vacancies. In this study we have employed tailor-made geometries in the copper surface, in which indium atoms were surrounded exclusively by upward or by downward terrace ledges. Our STM movies show a striking difference between these two cases, with differences in jump frequencies and average jump lengths of more than one order of magnitude. This allowed us to determine that surface vacancies are primarily created and annihilated at the upper side of terrace ledges, which can be formulated, in analogy with the energetics of ad-atoms, in terms of an Ehrlich-Schwoebel barrier for surface vacancies. Dedicated low-temperature measurements, where surface vacancies have been artificially created, have directly revealed the diffusion characteristics of individual surface vacancies. These measurements allow us to construct the complete energy landscape for the birth, life and death of surface vacancies in Cu(100).