Reflection electron microscope study of the initial stages of oxidation of Si(111)-7 × 7 surfaces

Abstract

A gas inlet device was constructed for an ulra-high-vacuum electron microscope and initial stages of oxidation of Si(111)-7 × 7 surfaces at various temperatures were observed in-situ by reflection electron microscopy (REM). Below 500°C the REM images did not show appreciable changes after an introduction of molecular oxygen. Above 500°C hollows with unit depth 0.31 nm were formed and grew in the central part of the terraces between the successive atomic surface steps. At the same time the steps moved so as to shrink the terraces. As oxygen pressure increased, oxide covered the surface and the surface structure transformed to the 1 × 1 structure. The oxide sublimed on heating above 750°C. During the oxygen exposure above 750°C rapid motions of steps and large hollow formations were observed throughout the oxygen exposure process. The growth kinetics of the hollows was analyzed. High-resolution REM observations showing the 7 × 7 lattices during oxidation were also carried out.