8 research outputs found
Ab initio calculations for bromine adlayers on the Ag(100) and Au(100) surfaces: the c(2x2) structure
Ab initio total-energy density-functional methods with supercell models have
been employed to calculate the c(2x2) structure of the Br-adsorbed Ag(100) and
Au(100) surfaces. The atomic geometries of the surfaces and the preferred
bonding sites of the bromine have been determined. The bonding character of
bromine with the substrates has also been studied by analyzing the electronic
density of states and the charge transfer. The calculations show that while the
four-fold hollow-site configuration is more stable than the two-fold
bridge-site topology on the Ag(100) surface, bromine prefers the bridge site on
the Au(100) surface. The one-fold on-top configuration is the least stable
configuration on both surfaces. It is also observed that the second layer of
the Ag substrate undergoes a small buckling as a consequence of the adsorption
of Br. Our results provide a theoretical explanation for the experimental
observations that the adsorption of bromine on the Ag(100) and Au(100) surfaces
results in different bonding configurations.Comment: 10 pages, 4 figure, 5 tables, Phys. Rev. B, in pres
Growth and properties of strained VOx thin films with controlled stoichiometry
We have succeeded in growing epitaxial films of rocksalt VOx on MgO(001)
substrates. The oxygen content as a function of oxygen flux was determined
using 18O2-RBS and the vanadium valence using XAS. The upper and lower
stoichiometry limits found are similar to the ones known for bulk material
(0.8<x<1.3). From the RHEED oscillation period a large number of vacancies for
both vanadium and oxygen were deduced, i.e. ~16% for stoichiometric VO. These
numbers are, surprisingly, very similar to those for bulk material and
consequently quite strain-insensitive. XAS measurements reveal that the
vacancies give rise to strong low symmetry ligand fields to be present. The
electrical conductivity of the films is much lower than the conductivity of
bulk samples which we attribute to a decrease in the direct overlap between t2g
orbitals in the coherently strained layers. The temperature dependence of the
conductivity is consistent with a variable range hopping mechanism.Comment: 12 pages, 16 figures included, revised versio