UHV Transmission and Reflection Electron Microscopies for Surface Studies

Abstract

This paper reviews recent results of surface structure studies of mono-layer levels done in our group with use of an UHV electron microscope (EM) of 10-8∿10-10Torr, which was originally designed for in-situ thin film growth studies [1]. Our techniques of UHV EM and of in-situ deposition and clean surface preparation were applied to studies of microtopographies of surfaces, in which previous surface researches mainly done by LEED, AES and RHEED are lacking. Some efforts to get topographic informations were done with use of AES and RHEED in scanning mode [2] but their resolutions were much poorer than that of conventional EM. We observed surfaces in two modes, transmission (TEM) and reflection (REM). TEM had been considered to be insensitive to details in depth direction in contrast to its high resolving power in lateral directions. Recent reports, however, showed that atomic steps stand out both in bright and dark field images with appreciable contrast due to diffraction extinction effects [3]. The REM method is based on the fact that RHEED is sensitive to surface structures [4]. The previous REM works, however, did not succeeded in observing clean surfaces on account of poor vacuum of the microscope and lack of preparation techniques of specimens with clean surfaces [5].