Surface sensitivity of Kikuchi-electron diffraction patterns.

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Since the realization by several workers that the electron diffraction from localized sources can be interpreted in a holographic sense, there has been increasing interest in electron holography. Photoelectron and Auger electrons are considered good localized electron sources, but 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 KED signal-to-noise ratio and allows us to take KED patterns over a wide range of energies within a short time. Using this method we have shown that Kikuchi electrons can be treated as having come from localized emitters. The results presented here clearly show the surface sensitivity of KED images in the energy range 450--800 eV. This sensitivity is revealed by the subtraction of the bulk contribution to the KED images by acquiring two image sets under exactly the same conditions, one from Si(111)(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{}-Pb and one from Si(111)7\ifmmode\times\else\texttimes\fi{}7, and subtracting them. Furthermore, these difference images show intensities 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.