3,137 research outputs found
Paramagnetic adsorbates on graphene: a charge transfer analysis
We introduce a modified version of the Hirshfeld charge analysis method and
demonstrate its accurateness by calculating the charge transfer between the
paramagnetic molecule NO2 and graphene. The charge transfer between
paramagnetic molecules and a graphene layer as calculated with ab initio
methods can crucially depend on the size of the supercell used in the
calculation. This has important consequences for adsorption studies involving
paramagnetic molecules such as NO2 physisorbed on graphene or on carbon
nanotubes.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Graphene: a perfect nanoballoon
We have performed a first-principles density functional theory investigation
of the penetration of helium atoms through a graphene monolayer with defects.
The relaxation of the graphene layer caused by the incoming helium atoms does
not have a strong influence on the height of the energy barriers for
penetration. For defective graphene layers, the penetration barriers decrease
exponentially with the size of the defects but they are still sufficiently high
that very large defects are needed to make the graphene sheet permeable for
small atoms and molecules. This makes graphene a very promising material for
the construction of nanocages and nanomembranes.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Polaron effects in electron channels on a helium film
Using the Feynman path-integral formalism we study the polaron effects in
quantum wires above a liquid helium film. The electron interacts with
two-dimensional (2D) surface phonons, i.e. ripplons, and is confined in one
dimension (1D) by an harmonic potential. The obtained results are valid for
arbitrary temperature (), electron-phonon coupling strength (), and
lateral confinement (). Analytical and numerical results are
obtained for limiting cases of , , and . We found the
surprising result that reducing the electron motion from 2D to quasi-1D makes
the self-trapping transition more continuous.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Adsorption of H2O, NH3, CO, NO2, and NO on graphene: A first-principles study
Motivated by the recent realization of graphene sensors to detect individual
gas molecules, we investigate the adsorption of H2O, NH3, CO, NO2, and NO on a
graphene substrate using first-principles calculations. The optimal adsorption
position and orientation of these molecules on the graphene surface is
determined and the adsorption energies are calculated. Molecular doping, i.e.
charge transfer between the molecules and the graphene surface, is discussed in
light of the density of states and the molecular orbitals of the adsorbates.
The efficiency of doping of the different molecules is determined and the
influence of their magnetic moment is discussed.Comment: 6 pages, 6 figure
First-principles investigation of graphene fluoride and graphane
Different stoichiometric configurations of graphane and graphene fluoride are
investigated within density functional theory. Their structural and electronic
properties are compared, and we indicate the similarities and differences among
the various configurations. Large differences between graphane and graphene
fluoride are found that are caused by the presence of charges on the fluorine
atoms. A new configuration that is more stable than the boat configuration is
predicted for graphene fluoride. We also perform GW calculations for the
electronic band gap of both graphene derivatives. These band gaps and also the
calculated Young's moduli are at variance with available experimental data.
This might indicate that the experimental samples contain a large number of
defects or are only partially covered with H or F.Comment: 6 pages, 3 figures, submitted to PR
Reply to the comment by D. Kreimer and E. Mielke
We respond to the comment by Kreimer et. al. about the torsional contribution
to the chiral anomaly in curved spacetimes. We discuss their claims and refute
its main conclusion.Comment: 9 pages, revte
Dynamics of Vortex Shells in Mesoscopic Superconducting Corbino Disks
In mesoscopic superconducting disks vortices form shell structures as
recently observed in Nb disks. We study the dynamics of such vortices, driven
by an external current I_0, in a Corbino setup. At very low I_0, the system
exhibits rigid body rotation while at some critical current I_c,i vortex shells
rotate separately with angular velocities omega_i. This critical current I_c,i
has a remarkable non-monotonous dependence on the applied magnetic field which
is due to a dynamically-induced structural transition with a rearrangement of
vortices over the shells similar to the Coster-Kronig transition in hollow
atoms. Thermally-activated externally-driven flux motion in a disk with pinning
centers explains experimentally observed omega_i as a function of I_0 and T and
the dynamically-induced melting transition.Comment: 5 pages, 5 figure
- …