UHV-Sem Observation of Si(111) Surface Partially Covered with Surface Structure Induced by Au or Ag

Abstract

It is well known from LEED (low energy electron diffraction) and RHEED (reflection high energy electron diffraction) studies that when Au or Ag is deposited onto a clean Si (111) surface, many surface superstructures, for example 5×2-Au, √3 × √3-Ag etc. are formed depending upon the substrate temperatures and the coverages of the metals. Applying REM (reflection electron Microscopy) method. Osakabe et al. observed domains of these surface structures in real space, but detailed domain structures are not clear because the method cannot obtain high resolution due to the foreshortening effect. We have developed a SEM (scanning electron microscope) apparatus which have very high resolution and can be operated in UHV (ultra high vacuum). Using this UHV-SEM detecting the secondary electron, the clear domain structures of the two dimensional surface superstructures have been observed for the first time.This UHV-SEM can obtain 2.2×l0-8 Pa by baking all parts related to the vacuum. The lattice image of Au(11O) has been clearly observed with STEM (scanning transmission electron microscope) mode, thus the resolution of 0.143 nm has been obtained. In the secondary electron imaging mode, the resolution of 0.5-0.7 nm has been obtained for the Au particles evaporated on a thin carbon film. This UHV-SEM apparatus has a sample preparation chamber equipped with a RHEED system and Au or Ag evaporation source, in which samples are cleaned, formed into the aimed structures and transferred into the UHV-SEM apparatus.