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

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- contraction with the As atoms moving outward and the Ga atoms inward, giving a relative vertical shear of 0.65. In the second layer the Ga moves outward 0.06 and the second-layer As moves inward 0.06. The dynamical analysis reported herein shows no evidence for third-layer distortions.