Dynamical analysis of low-energy-electron-diffraction intensities from InSb(110)

Dynamical calculations of the intensities of normally incident low-energy electrons diffracted from InSb(110), performed using a matrix inversion method, are reported for structures resulting from (i) a kinematical search, (ii) a dynamical search, and (iii) energy-minimization calculations. The model structures considered in all three cases embody distortions of the uppermost three atomic layers of InSb from their truncated bulk geometries. The dynamical calculations are compared with elastic-low-energy-electron-diffraction intensities measured for 14 beams with a sample temperature of T=150 K. This comparison leads to the selection of the most-probable surface structure for InSb(110) as one in which the top layer undergoes both a rigid rotation of 28.8°and a 0.05 relaxation toward the substrate. The Sb atoms in the top layer move outward and the In atoms inward, giving a relative vertical shear of 0.78. In the second layer, the In move outward 0.09 and the Sb inward 0.09. This surface atomic geometry is nearly identical to that which we reported earlier for covalently-bonded GaAs(110) but somewhat different from the reported for ZnTe(110) which exhibits a slightly more ionic bonding. We infer, therefore, that highly covalent zinc blende-structure compound semiconductors exhibit reconstructions of their (110) surfaces characterized by (i) large bond rotations in the upper-most layer, with the anion moving outward and cation inward, (ii) small bond-length alterations except for possible 4-5% contractions of the back bonds between the outermost anion and the cation in the layer beneath, and (iii) distortions from the bulk geometry which penetrate at least two atomic layers in from the surface.