GROWTH AND ATOMIC GEOMETRY OF BISMUTH AND ANTIMONY ON INP(110) STUDIED USING LOW-ENERGY ELECTRON-DIFFRACTION

Low-energy electron-diffraction (LEED) intensities are reported for 17 or 18 symmetry-inequivalent beams of normally incident electrons diffracted from InP(110), InP(110)-p (1 X 1)-Sb (1 monolayer), and InP(110)-p(1 X 1)-Bi (1 monolayer). These intensities were obtained over an energy range 40 eV less-than-or-equal-to E less-than-or-equal-to 300 eV for samples at T = 120 K. Structural determinations are given for all three systems, based on comparing the calculated and measured diffracted intensities using x-ray R factors as measures of the quality of the description of the measured intensities. The InP(110) surface exhibits a nearly bonding-length-conserving top-layer rotational relaxation characterized by a tilt angle of omega = 31-degrees with the P species displaced outward from the surface and the In inwards, in accord with prior structure analyses of this surface. Adsorption of either Sb or Bi removes this relaxation, with the adsorbed species forming chains with atoms near the positions which were occupied by In and P in the clean surface (i.e., the "expitaxical continued layer structure"). The adsorbed atom bonded to the In top-layer substrate species is slightly displaced outwards from the surface, giving a top-layer tilt angle of omega = 4-degrees for Sb and omega = 5-degrees for Bi. Bond lengths are approximtely those expected for covalent bonds between adsorbates and between the adsorbates and substrate species. The adsorbate-adsorbate bond is lengthened by 1-2%, the adsorbate-phosphorus bond by about 2%, and the adsorbate-indium bond is shortened by 1 % or less.