Analytical Scanning Electron Microscopy Under Ultra High Vacuum

Abstract

The usual techniques of electron beam surface investigation such as AES, LEED, RHEED, ELS have been improved in recent years by important developments; these techniques can now be performed in an actual Ultra High Vacuum Scanning Electron Microscope (UHV-SEM) with a focused beam at the submicronic scale. The flexibility of the optical column of the microscope gives suitable beams allowing us to perform these techniques in the same area with appropriate detectors. A UHV chamber makes it possible to observe clean surfaces without contamination. To enhance surface information, low beam energy must be used. But it is well known that for an optical system when the beam size or the beam energy decrease the beam intensity decreases too; compared with macroscopic investigation higher performance guns and more efficient detectors are therefore needed. Another method to improve the detector is by using low beam intensity to reduce the irradiation damage by the electron beam. These techniques must be consistent with in situ preparation facilities e.g. ionic bombardment, specimen heating, fracture attachment, gas introduction devices, evaporating systems… So a preparation chamber is often coupled to UHV-SEM. The purpose of this paper is to point out the new possibilities given by UHV-SEM at medium and low beam energy; the reflected modes of conventional STEM /I/ or TEM /2/ are not developed. However, the field of investigation of these techniques is very wide, involves the topographic, chemical, electronic, crystallographic observations; so we will limit our study to the focused aspects in surface applications. In the present paper the surface information is examined according to three principal modes: secondary, spectroscopic (Auger, EELS) and diffracting (RHEED, LEED, low losses).