7,453 research outputs found
Influence of structural disorder and large-scale geometric fluctuations on the Coherent Transport of Metallic Junctions and Molecular Wires
Structural disorder is present in almost all experimental measurements of
electronic transport through single molecules or molecular wires. To assess its
influence on the conductance is computationally demanding, because a large
number of conformations must be considered. Here we analyze an approximate
recursive layer Green function approach for the ballistic transport through
quasi one-dimensional nano-junctions. We find a rapid convergence of the method
with its control parameter, the layer thickness, and good agreement with
existing experimental and theoretical data. Because the computational effort
rises only linearly with system size, this method permits treatment of very
large systems. We investigate the conductance of gold- and silver wires of
different sizes and conformations. For weak electrode disorder and imperfect
coupling between electrode and wire we find conductance variations of
approximately 20%. Overall we find the conductance of silver junctions well
described by the immediate vicinity of narrowest point in the junction, a
result that may explain the observation of well-conserved conductance plateaus
in recent experiments on silver junctions. In an application to flexible
oligophene wires, we find that strongly distorted conformations that are
sterically forbidden at zero temperature, contribute significantly to the
observed average zero-bias conductance of the molecular wire
Molecular origin of the anisotropic dye orientation in emissive layers of organic light emitting diodes
Molecular orientation anisotropy of the emitter molecules used in organic light emitting diodes (OLEDs) can give rise to an enhanced light-outcoupling efficiency, when their transition dipole moments are oriented preferentially parallel to the substrate, and to a modified internal quantum efficiency, when their static dipole moments give rise to a locally modified internal electric field. Here, the orientation anisotropy of state-of-the-art phosphorescent dye molecules is investigated using a simulation approach which mimics the physical vapor deposition process of amorphous thin films. The simulations reveal for all studied systems significant orientation anisotropy. Various types are found, including a preference of the static dipole moments to a certain direction or axis. However, only few systems show an improved outcoupling efficiency. The outcoupling efficiency predicted by the simulations agrees with experimentally reported values. The simulations reveal in some cases a significant effect of the host molecules, and suggest that the driving force of molecular orientation lies in the molecule-specific van der Waals interactions of the dye molecule within the thin film surface. The electrostatic dipole-dipole interaction slightly reduces the anisotropy. These findings can be used for the future design of improved dye molecules.</p
X-ray response of silicon surface barrier diodes at 8 and 17.5 keV: evidence that the x-ray sensitive depth is not generally the depletion depth
Homologies between thyroid autoantigenes in Graves' disease (GD) and plasmid encoded proteins (PEP) of enteropathogenic Yersinia
Interactions of hydrophobic and hydrophilic self-assembled monolayers with water as probed by sum-frequency-generation spectroscopy
Pre-selectable integer quantum conductance of electrochemically fabricated silver point contacts
The controlled fabrication of well-ordered atomic-scale metallic contacts is
of great interest: it is expected that the experimentally observed high
percentage of point contacts with a conductance at non-integer multiples of the
conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects
resulting from the fabrication process. Here we demonstrate a combined
electrochemical deposition and annealing method which allows the controlled
fabrication of point contacts with pre-selectable integer quantum conductance.
The resulting conductance measurements on silver point contacts are compared
with tight-binding-like conductance calculations of modeled idealized junction
geometries between two silver crystals with a predefined number of contact
atoms
Local Electronic Charge Transfer in the Helical Induction of Cis-Transoid Poly(4-carboxyphenyl)acetylene by Chiral Amines
Breakdown of the Luttinger sum-rule at the Mott-Hubbard transition in the one-dimensional t1-t2 Hubbard model
We investigate the momentum distribution function near the Mott-Hubbard
transition in the one-dimensional t1-t2 Hubbard model (the zig-zag Hubbard
chain), with the density-matrix renormalization-group technique. We show that
for strong interactions the Mott-Hubbard transition occurs between the
metallic-phase and an insulating dimerized phase with incommensurate spin
excitations, suggesting a decoupling of magnetic and charge excitations not
present in weak coupling. We illustrate the signatures for the Mott-Hubbard
transition and the commensurate-incommensurate transition in the insulating
spin-gapped state in their respective ground-state momentum distribution
functions
- …