Dynamical calculation of low-energy electron diffraction intensities from GaAs(110): Influence of boundary conditions, exchange potential, lattice vibrations, and multilayer reconstructions

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Abstract
Dynamical calculations of the intensities of normally incident low-energy electrons diffracted from GaAs(110), performed using a matrix-inversion method, are compared both with earlier kinematical calculations and with measured intensities. The insensitivity of the calculated intensities to the choice of exchange potential and vacuum-solid boundary conditions is displayed. Surface lattice vibrations are found to be adequately described by the bulk Debye temperature. We consider second- and third-layer structural distortions as well as top-layer reconstructions. This analysis leads to the selection of the most probable surface structure for GaAs(110) as one in which the top layer undergoes both a rigid rotation of 27.4° and a 0.05-Å contraction with the As atoms moving outward and the Ga atoms inward, giving a relative vertical shear of 0.65 Å. In the second layer the Ga moves outward 0.06 Å and the second-layer As moves inward 0.06 Å. The dynamical analysis reported herein shows no evidence for third-layer distortions.