High-resolution electron microscopy of interfaces and surfaces

Abstract The enhanced resolution available in the latest generation of medium-voltage high-resolution electron microscopes can be utilized to study semiconductor interfaces in zone axes such as 〈100〉, 〈111〉 and 〈112〉, as well as the more familiar 〈100〉. This permits both “structural imaging” and three-dimensional reconstruction from two different projections. Preliminary results on semiconductor interfaces obtained with the JEOL 4000EX 400 kV instrument with point resolution better than 1.7 A are presented. In the discussion of interpretation of interface images the serious limitation of signal-to-noise ratio is raised. This is particularly poor in the case of ion-thinned samples. If signal-to-noise ratio could be improved to the theoretical shot-noise limit, it would permit much more extensive image interpretation and perhaps new classes of experiment such as point-defect imaging. We show that the high signal-to-noise ratio is attainable with in-situ specimen cleaning in a UHV electron microscope and report some results on Si surface science performed with our home-modified UHV high-resolution instrument.