60 research outputs found
O adsorption and incipient oxidation of the Mg(0001) surface
First principles density functional calculations are used to study the early
oxidation stages of the Mg(0001) surface for oxygen coverages 1/16 <= Theta <=
3 monolayers. It is found that at very low coverages O is incorporated below
the topmost Mg layer in tetrahedral sites. At higher oxygen-load the binding in
on-surface sites is increased but at one monolayer coverage the on-surface
binding is still about 60 meV weaker than for subsurface sites. The subsurface
octahedral sites are found to be unfavorable compared to subsurface tetrahedral
sites and to on-surface sites. At higher coverages oxygen adsorbs both under
the surface and up. Our calculations predict island formation and clustering of
incorporated and adsorbed oxygen in agreement with previous calculations. The
calculated configurations are compared with the angle-scanned x-ray
photoelectron diffraction experiment to determine the geometrical structure of
the oxidized Mg(0001) surface.Comment: 10 pages, 5 figure
Ab initio structure modeling of complex thin-film oxides: thermodynamical stability of TiC/thin-film alumina
We present an efficient and general method to identify promising candidate
configurations for thin-film oxides and to determine structural characteristics
of (metastable) thin-film structures using ab initio calculations. At the heart
of this method is the complexity of the oxide bulk structure, from which a
large number of thin films with structural building blocks, that is motifs,
from metastable bulk oxide systems can be extracted. These span a coarse but
well-defined network of initial configurations for which density functional
theory (DFT) calculations predict and implement dramatic atomic relaxations in
the corresponding, resulting thin-film candidates. The network of thin-film
candidates (for various film thicknesses and stoichiometries) can be ordered
according to their variation in ab initio total energy or in ab initio
equilibrium Gibbs free energy. Analysis of the relaxed atomic structures for
the most favored structures gives insight into the nature of stable and
metastable thin-film oxides. We investigate ultrathin alumina nucleated on TiC
as a model system to illustrate this method.Comment: Submitted to PRB; 16 pages, 11 figure
- âŠ