STEP CONTRAST IN LOW-ENERGY-ELECTRON MICROSCOPY

A wave-optical. model for surface step-phase contrast in low energy el ectron microscopy (LEEM) is presented. Step contrast is calculated as the interference of the Fresnel diffracted waves from terrace edges wh ich meet at a step. Instrumental resolution and beam coherence, i.e., as defined by source extension and energy spread, are also considered. Model predictions are compared to experimental observations of steps on the W(1 1 0), Mo(1 0 0) and Si(1 1 1) surfaces. This work allows fo r the routine identification of the step sense with LEEM. (C) 1998 Pub lished by Elsevier Science B.V. All rights reserved.