Utilization of the effect in the high-resolution electron microscopy of surfaces

Abstract

A top-bottom contrast effect which arises in dark-field images of aperiodic surface detail may be utilized to achieve separate imaging of either surface. The upper or lower crystal surface is brought into contrast according to whether the excitation error of the diffracted beam being used is positive or negative. This has been found to apply almost independently of the N-beam diffraction condition and to be effective in imaging at the highest instrumental resolution. In this investigation, an MgO platelet with a distinctive surface structure has been used as a test sample. The preliminary results presented show how the technique may allow the dynamics of a surface structure to be studied under conditions where high contrast and high resolution are compatible entities, close to Gaussian focus.