APPLICATION OF X-RAY DIRECT-METHODS TO SURFACE RECONSTRUCTIONS - THE SOLUTION OF PROJECTED SUPERSTRUCTURES

The projections of surface reconstructions are normally solved fi om t he interatomic vectors found in two-dimensional Patterson maps compute d with the intensities of the in-plane superstructure reflections. Sin ce for difficult reconstructions this procedure is not trivial, an alt ernative automated one based on the ''direct methods'' sum function [R ius, Miravitlles, and Allmann, Acta Crystallogr. A52, 634 (1996)] is s hown. It has been applied successfully to the known c(4 X 2) reconstru ction of Ge(001) and to the so-far unresolved In0.04Ga0.96As (001) p(4 X 2) surface reconstruction. For this last system we propose a modifi cation of one of the models previously proposed for GaAs(001) whose ch aracteristic feature is the presence of dimers along the fourfold dire ction. [S0163-1829(98)50908-3].