199 research outputs found
Simulating the nanomechanical response of cyclooctatetraene molecules on a graphene device
We investigate the atomic and electronic structures of cyclooctatetraene
(COT) molecules on graphene and analyze their dependence on external gate
voltage using first-principles calculations. The external gate voltage is
simulated by adding or removing electrons using density functional theory (DFT)
calculations. This allows us to investigate how changes in carrier density
modify the molecular shape, orientation, adsorption site, diffusion barrier,
and diffusion path. For increased hole doping COT molecules gradually change
their shape to a more flattened conformation and the distance between the
molecules and graphene increases while the diffusion barrier drastically
decreases. For increased electron doping an abrupt transition to a planar
conformation at a carrier density of -810 e/cm is observed.
These calculations imply that the shape and mobility of adsorbed COT molecules
can be controlled by externally gating graphene devices
Strongly reshaped organic-metal interfaces: Tetracyanoethylene on Cu(100)
The interaction of the strong electron-acceptor tetracyanoethylene (TCNE)
with the Cu(100) surface has been studied with scanning tunneling microscopy
experiments and first-principles density functional theory calculations. We
compare two different adsorption models with the experimental results and show
that the molecular self-assembly is caused by a strong structural modification
of the Cu(100) surface rather than the formation of a coordination network by
diffusing Cu adatoms. Surface atoms become highly buckled and the chemisorption
of TCNE is accompanied by a partial charge-transfer.Comment: 4 pages, 3 figures, to appear in Physical Review Letter
Theory of a Scanning Tunneling Microscope with a Two-Protrusion Tip
We consider a scanning tunneling microscope (STM) such that tunneling occurs
through two atomically sharp protrusions on its tip. When the two protrusions
are separated by at least several atomic spacings, the differential conductance
of this STM depends on the electronic transport in the sample between the
protrusions. Furthermore two-protrusion tips commonly occur during STM tip
preparation. We explore possible applications to probing dynamical impurity
potentials on a metallic surface and local transport in an anisotropic
superconductor.Comment: revtex, 11 pages, 6 figures upon reques
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