SURFACE SENSITIVITY OF KIKUCHI-ELECTRON DIFFRACTION PATTERNS

Since the realization by several workers that the electron diffraction from localized sources can be interpreted in a holographic sense, the re has been increasing interest in electron holography. Photoelectron and Auger electrons are considered good localized electron sources, bu t their use experimentally in holography usually requires access to a synchrotron radiation source. We report here the use of our technique to obtain Kikuchi-electron diffraction (KED) patterns using normal low -energy electron-diffraction facilities. This technique improves the R ED signal-to-noise ratio and allows us to take KED patterns over a wid e range of energies within a short time. Using this method we have sho wn that Kikuchi electrons can be treated as having come from localized emitters. The results presented here clearly show the surface sensiti vity of KED images in the energy range 450-800 eV. This sensitivity is revealed by the subtraction of the bulk contribution to the KED image s by acquiring two image sets under exactly the same conditions, one f rom Si(111)(root 3X root 3)R30 degrees-Pb and one from Si(111)7X7, and subtracting them. Furthermore, these difference images show intensiti es which are very strongly dependent on the primary energy, unlike the raw KED images. This energy dependence suggests that a backscattering geometry is dominating the contributions to the intensities in these difference images.