Structure determination of adsorbate-covered vanadium single crystal surfaces

Many processes take place over the surface or properties of mechanical components or electronic devices are determined by the properties of the surface (thin films, microelectronics, plating, catalysis, corrosion etc.). For the understanding of the involved processes or reactions the knowledge of the surface structure is essential. The aim of this work was the structure determination of adsorbate-induced reconstructions on the low index vanadium single crystal surfaces V(100) and V(110). The interest in vanadium has its roots in technological applications, e.g. heterogeneous catalysis and hydrogen storage technology. The techniques used to determine the geometry, the coverage and the adsorption sites were Auger electron spectroscopy, scanning tunneling microscopy and diffraction of low energy electrons. Adsorption of oxygen on V(100) induces a p(1x5) reconstruction with a total oxygen coverage of approx. 0.75 ML (monolayers). In this reconstruction the oxygen atoms preferably reside in fourfold hollow sites. However, every fifth vanadium lattice constant the oxygen atoms occupy the unusual bridge site. On V(110) a c(6x2) reconstruction is induced by oxygen with a coverage of 0.5 ML. On V(110) the vanadium atoms in the first layer offer threefold and fourfold hollow sites which are partially occupied by oxygen. The driving force behind these reconstructions is the optimization of the vanadium-oxygen bond lengths, which amount to roughly 0.2 nm. Carbon on V(100) is preferably arranged in chains, locally forming a p(1x2) superstructure. Small amounts of oxygen additionally present lead to a c(2x2) reconstruction. In both reconstructions the adsorbates occupy fourfold hollow sites to form as many bonds as possible. (author)