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

The measured intensities of 14 diffracted beams of low-energy ($30\le E\le 240$ eV) electrons normally incident on InAs(110) are reported. The temperature of the InAs surface during the measurements was $T=110\mathrm{}$ K. The surfaces were prepared by ion-bombardment and annealing cycles followed by a verification of surface stochiometry (to within 10%) via Auger electron spectroscopy. Two separate crystals were examined in two separate vacuum instruments in order to verify the reproducibility of the intensity data. The data were analyzed using a relativistic, Hara-exchange electron—ion-core potential and an x-ray $R$-factor structure-analysis methodology. This analysis leads to the best-fit structure of InAs(110) being a rotation of the uppermost layer with the As rotated outward and the In inward. The second layer also is reconstructed with the In being displaced upward by 0.07±0.1 Å relative to its position in the bulk and the As being displaced downward by an equal amount. The x-ray $R$ factor for the best-fit structure is $R_{\mathrm{x}}=0.23\mathrm{}$. This structure gives a satisfactory visual description of the measured intensities. For bond-length-conserving top-layer rotations the angle between the plane of the surface In-As chains and the plane of truncated bulk surface is ${\omega }_1=31\mathrm{}°\pm 3°$, in accordance with expectations based on correlations of covalent radii with prior zinc-blende-structure compound-semiconductor surfaces. The structure of InAs(110) provides the first test of these correlations. The best-fit $R$-factor structure corresponds to reduced relaxation parallel to the surface of the top-layer As relative to that for the bond-length-conserving structure. This best-fit structure is, however, equivalent to its bond-length-conserving counterpart (${\omega }_1=31\mathrm{}°$) to within the accuracy of the $R$-factor methodology.