LEEDS studies of adsorbate-induced reconstruction of metal surfaces

Đoan-Trang V. Grimsby
Using the technique of low-energy electron diffraction (LEED), the structures of three systems have been investigated, where small, electronegative atoms chemisorb and induce reconstruction at a metal surface; these surfaces are designated Ni(111)-(2x2)-0,Cu(110)-(2x3)-N, and Pd(100)-(V5x45)R27°-0. In each case, experimental data consist of a set of intensity-versus-energy (I(E)) curves measured at normal incidence with a video LEED analyser. Multiple-scattering calculations were done for a
more » ... were done for a number of proposed models of the surface structure, and comparisons were made between calculated and experimental 1(E) curves. The objective in a LEED analysis is to find the geometry in the calculations which leads to the best match between the two sets of intensity curves. Reliability indices are used to quantify the level of correspondence between experiment and theory; a lower R-value indicates better agreement, and consequently the model is more likely to be correct. Two basic reliability indices were used in this work, and they are the modified Zanazzi-Jona R-factor and the Pendry R-factor. In addition to the more conventional LEED analysis, the recently-developed tensor LEED/directed search (TLEED) method was also used in the analyses of the N/Cu and 0/Pd surfaces. As well as determining surface structure, this work has the further objective of using the details identified to develop some principles of surface structural chemistry and to relate these principles to the broader framework of structural chemistry. For the Ni(111)-(2x2)-0 structure, oxygen atoms chemisorb on 3-fold hollow sites which continue the fcc stacking of the nickel substrate. Top-layer Ni atoms which are bonding to 0 atoms are displaced both vertically toward (by 0.12 A) and laterally away from (by 0.07 A in a rotated manner) the 0 atoms, while those Ni atoms not bonding to 0are displaced vertically toward the bulk. The determined surface O-Ni bond length of 1.83A agrees closely with the predicted value of 1.82 A for 3-coordinate 0 on Ni, and the sur [...]
doi:10.14288/1.0061777 fatcat:h53ff7n6lvawlhiyj5yfxxiktu