Density-functional and Monte Carlo study ofO∕Mo(110): Structures and desorption

Abstract

Structures of oxygen layers on the Mo(110) surface and desorption kinetics have been investigated by means of density-functional theory and generalized gradient approximation calculations and Monte Carlo simulations. It has been found that triply coordinated hollow sites are favorable for oxygen adatoms. All energies of lateral interactions, used in the Monte Carlo simulations of the formation of oxygen structures, are found to be positive, which means that neither trio interactions nor explicit attraction between oxygen adatoms is needed to explain the formation of the $p(2\ifmmode\times\else\texttimes\fi{}1)$ oxygen structure. Simulated scanning tunneling microscopy (STM) images reveal a strong dependence of the relative brightness of images of O adatoms on the sample bias voltage. In particular, protrusions in STM images of oxygen-covered Mo(110) surface, obtained with a negative sample bias, cannot be attributed to images of substrate Mo atoms, but correspond to increased electron density induced by the overlap of atomic densities of neighboring oxygen adatoms. The estimated binding energy between adsorbed O atoms and Mo surface substantially exceeds the binding energy between two oxygen atoms in a free molecule. This feature is suggested to be responsible for the atomic form of oxygen desorption from the Mo(110) surface.