Behaviors of Auger Intensities Emitted from a Si(111)$\sqrt{\textbf 3}\times\sqrt{\textbf 3}$-Al Surface During Incident Beam Rocking of Reflection High-Energy Electron Diffraction

In recent years there has been a trend in the structure determination of reconstructed surfaces to use high energy electron diffraction techniques, and to employ a kinematic approximation in analyzing the intensities of surface superlattice reflections. Experimentally this is motivated by the great success of the determination of the dimer adatom stacking fault (DAS) structure of the Si(111) 7 × 7 reconstructed surface.While in the case of transmission electron diffraction (TED) the validity of the kinematic approximation has been examined by using multislice calculations for Si and certain incident beam directions, far less has been done in the reflection high energy electron diffraction (RHEED) case. In this paper we aim to provide a thorough Bloch wave analysis of the various diffraction processes involved, and to set criteria on the validity for the kinematic analysis of the intensities of the surface superlattice reflections.The validity of the kinematic analysis, being common to both the TED and RHEED case, relies primarily on two underlying observations, namely (l)the surface superlattice scattering in the selvedge is kinematically dominating, and (2)the superlattice diffracted beams are uncoupled from the fundamental diffracted beams within the bulk.

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A `three-beam' analysis of resonance scattering in reflection high-energy electron diffraction

Acta Crystallographica Section A Foundations of Crystallography ◽

10.1107/s0108767398009003 ◽

1999 ◽

Vol 55 (2) ◽

pp. 197-203 ◽

Cited By ~ 1

Author(s):

G. R. Anstis

Keyword(s):

Electron Diffraction ◽

Crystal Surface ◽

Incident Beam ◽

Resonance Scattering ◽

High Energy ◽

Energy Electron ◽

Quantitative Prediction ◽

Perturbation Approach ◽

High Energy Electron ◽

Depth Of Penetration

Enhanced reflection of fast electrons from a crystal surface and a decrease in the depth of penetration of the primary beam occurs when diffraction conditions are such as to set up a wave travelling just beneath the crystal surface. This is the surface resonance condition for reflection high-energy electron diffraction (RHEED). Quantitative prediction of these effects can be achieved by assuming that only the primary and two diffracted beams are significant. Expressions for the coefficient of reflection and the depth of penetration in terms of a few Fourier coefficients of an effective potential are derived. These coefficients depend sensitively on incident-beam direction and are significantly different from the values for the bulk crystal. In particular, the mean potential experienced by the electrons in the resonance state is increased. It can be estimated using Bethe's perturbation approach. Predictions of the position, height and width of the peak in reflectivity resulting from resonance scattering from the (111) surface of platinum are in reasonable agreement with the values obtained from many-beam computations. The three-beam approach gives insight into resonance scattering using the standard formalism of diffraction theory.

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