7,493 research outputs found
Reversible enhancement of the magnetism of ultrathin Co films by H adsorption
By means of ab initio calculations, we have investigated the effect of H
adsorption in the structural, electronic and magnetic properties of ultrathin
Co films on Ru(0001). Our calculations predict that H occupies hollow sites
preserving the two-dimensional 3-fold symmetry. The formation of a complete H
overlayer leads to a very stable surface with strong H-Co bonds. H tends to
suppress surface features, in particular, the enhancement of the magnetic
moments of the bare film. The H-induced effects are mostly confined to the Co
atoms bonded to H, independent of the H coverage or of the thickness and the
structure of the Co film. However, for partial H coverages a significant
increase occurs in the magnetic moment for the surface Co atoms not bonded to
H, leading to a net enhancement of surface magnetism.Comment: 6 pages, 4 figures, 3 table
Chlorine Adsorption on Graphene: Chlorographene
We perform first-principles structure optimization, phonon frequency and
finite temperature molecular dynamics calculations based on density functional
theory to study the interaction of chlorine atoms with graphene predicting the
existence of possible chlorinated graphene derivatives. The bonding of a single
chlorine atom is ionic through the transfer of charge from graphene to chlorine
adatom and induces negligible local distortion in the underlying planar
graphene. Different from hydrogen and fluorine adatoms, the migration of a
single chlorine adatom on the surface of perfect graphene takes place almost
without barrier. However, the decoration of one surface of graphene with Cl
adatoms leading to various conformations cannot sustain due to strong Cl-Cl
interaction resulting in the desorption through the formation of Cl
molecules. On the contrary, the fully chlorinated graphene, chlorographene CCl,
where single chlorine atoms are bonded alternatingly to each carbon atom from
different sides of graphene with -type covalent bonds, is buckled. We
found that this structure is stable and is a direct band gap semiconductor,
whose band gap can be tuned by applied uniform strain. Calculated phonon
dispersion relation and four Raman-active modes of chlorographene are
discussed.Comment: http://pubs.acs.org/doi/abs/10.1021/jp307006
Absence of stable atomic structure in fluorinated graphene
Based on the results of first-principles calculations we demonstrate that
significant distortion of graphene sheets caused by adsorption of fluorine
atoms leads to the formation of metastable patterns for which the next step of
fluorination is considerably less energetically favorable. Existence of these
stable patterns oriented along the armchair direction makes possible the
synthesis of various CFx structures. The combination of strong distortion of
the nonfluorinated graphene sheet with the doping caused by the polar nature of
C-F bonds reduces the energy cost of migration and the energy of migration
barriers, making possible the migration of fluorine atoms on the graphene
surface as well as transformation of the shapes of fluorinated areas. The
decreasing energy cost of migration with increasing fluorine content also leads
to increasing numbers of single fluorine adatoms, which could be the source of
magnetic moments.Comment: 16 pages, 6 figures (one figure added), accepted in PCC
- …