Initial Stage of Oxygen Adsorption onto a Si(111)–7×7 Surface Studied by Scanning Tunneling Microscopy

Abstract

The initial stage of oxygen adsorption onto a Si(111)-7×7 surface has been studied at room temperature by scanning tunneling microscopy. The surface was exposed to oxygen under a partial pressure of 1×10-9 Torr. Initial exposure led to bright and dark features at adatom sites. This dark feature, which was previously reported as a main channel for oxidation, only appeared in the faulted half of the dimer adatom stacking-fault (DAS) structure. The images suggest that the adsorption onto the un-faulted half starts after the faulted half are occupied with oxygen atoms. This clearly indicates that oxygen adsorption occurs at adatom sites with higher energy states.