Adsorption and diffusion of Mg, O, and O-2 on the MgO(001) flat surface

摘要

A thorough investigation of the adsorption and diffusion of Mg, O, and O-2 on MgO(001) terraces is performed by first-principles calculations. The single Mg adatom weakly binds to surface oxygens, diffuses, and evaporates easily at room temperatures. Atomic O strongly binds to surface oxygens, forming peroxide groups. The diffusion of the O adatom is strongly influenced by the spin polarization, since energy barriers are significantly different for the singlet and triplet states. The crossing of the two Born-Oppenheimer surfaces corresponding to the distinct spin states is also analyzed. Although the O-2 molecule does not stick to the perfect surface, it chemisorbs on surface nonstoichiometric point defects such as O vacancies or Mg adatoms, forming in the latter case new chemical species on the surface. We show that the oxidation rate limiting factor in an O-2 atmosphere is the concentration of point defects (O vacancies and Mg adatoms) in the growing surface. The simulated O core-level shifts for the various adsorption configurations enable a meaningful comparison with the measured values, suggesting the presence of peroxide ions on growing surfaces. Finally, the computed energy barriers are used to estimate the Mg and O surface lifetimes and diffusion lengths, and some implications for the homoepitaxial growth of MgO are discussed. (c) 2005 American Institute of Physics.