The structure of overlayers. II. Si on Mo[001

Abstract

The Mo{001}1 \ifmmode\times\else\texttimes\fi{} 1-Si structure formed upon adsorption of a monolayer of Si on a clean Mo{001} surface is investgated by means of low-energy electron diffraction (LEED). Diffracted beam intensities are calculated with the layer-Korringa-Kohn-Rostoker method for different models and compared with extensive experimental data. Good agreement between calculated and observed LEED spectra for six nondegenerate beams at an angle of incidence of 8\ifmmode^\circ\else\textdegree\fi{} and for four nondegenerate beams at an angle of incidence of 21\ifmmode^\circ\else\textdegree\fi{} is found for a model in which the Si atoms are adsorbed in the fourfold pyramidal hollows formed by four adjacent Mo atoms on the Mo {001} surface. The distance between the plane of adsorbed Si atoms and that of the top layer of Mo atoms is 1.16\ifmmode\pm\else\textpm\fi{}0.1 \AA{} and the Si-Mo bond length is 2.51\ifmmode\pm\else\textpm\fi{}0.05 \AA{}. The effects caused by different choices of a number of structural and nonstructural parameters in the calculated LEED spectra are discussed, and the results of calculations based on wrong models are presented for comparison. The importance of studying many beams and several angles of incidence is emphasized.