321 research outputs found
Effect of bonding of a CO molecule on the conductance of atomic metal wires
We have measured the effect of bonding of a CO molecule on the conductance of
Au, Cu, Pt, and Ni atomic contacts at 4.2 K. When CO gas is admitted to the
metal nano contacts, a conductance feature appears in the conductance histogram
near 0.5 of the quantum unit of conductance, for all metals. For Au, the
intensity of this fractional conductance feature can be tuned with the bias
voltage, and it disappears at high bias voltage (above 200 mV). The
bonding of CO to Au appears to be weakest, and associated with monotomic Au
wire formation.Comment: 6 figure
Absence of magnetically-induced fractional quantization in atomic contacts
Using the mechanically controlled break junction technique at low
temperatures and under cryogenic vacuum conditions we have studied atomic
contacts of several magnetic (Fe, Co and Ni) and non-magnetic (Pt) metals,
which recently were claimed to show fractional conductance quantization. In the
case of pure metals we see no quantization of the conductance nor
half-quantization, even when high magnetic fields are applied. On the other
hand, features in the conductance similar to (fractional) quantization are
observed when the contact is exposed to gas molecules. Furthermore, the absence
of fractional quantization when the contact is bridged by H_2 indicates the
current is never fully polarized for the metals studied here. Our results are
in agreement with recent model calculations.Comment: 4 pages, 3 figure
Vibrationally Induced Two-Level Systems in Single-Molecule Junctions
Single-molecule junctions are found to show anomalous spikes in dI/dV
spectra. The position in energy of the spikes are related to local vibration
mode energies. A model of vibrationally induced two-level systems reproduces
the data very well. This mechanism is expected to be quite general for
single-molecule junctions. It acts as an intrinsic amplification mechanism for
local vibration mode features and may be exploited as a new spectroscopic tool.Comment: 4 pages, 4 figure
Evidence for a single hydrogen molecule connected by an atomic chain
Stable, single-molecule conducting-bridge configurations are typically
identified from peak structures in a conductance histogram. In previous work on
Pt with H at cryogenic temperatures it has been shown that a peak near 1
identifies a single molecule Pt-H-Pt bridge. The histogram shows
an additional structure with lower conductance that has not been identified.
Here, we show that it is likely due to a hydrogen decorated Pt chain in contact
with the H molecular bridge.Comment: 4 pages, 4 figure
Highly conductive molecular junctions based on direct binding of benzene to platinum electrodes
Highly conductive molecular junctions were formed by direct binding of
benzene molecules between two Pt electrodes. Measurements of conductance,
isotopic shift in inelastic spectroscopy and shot noise compared with
calculations provide indications for a stable molecular junction where the
benzene molecule is preserved intact and bonded to the Pt leads via carbon
atoms. The junction has a conductance comparable to that for metallic atomic
junctions (around 0.1-1 Go), where the conductance and the number of
transmission channels are controlled by the molecule's orientation at different
inter-electrode distances.Comment: 4 pages, 4 figure
Stretching dependence of the vibration modes of a single-molecule Pt-H2-Pt bridge
A conducting bridge of a single hydrogen molecule between Pt electrodes is
formed in a break junction experiment. It has a conductance near the quantum
unit, G_0 = 2e^2/h, carried by a single channel. Using point contact
spectroscopy three vibration modes are observed and their variation upon
stretching and isotope substitution is obtained. The interpretation of the
experiment in terms of a Pt-H_2-Pt bridge is verified by Density Functional
Theory calculations for the stability, vibrational modes, and conductance of
the structure.Comment: 5 pages, 4 figure
A Software-Agnostic Agent-based Platform for Modelling Emerging Mobility Systems
Due to the rapidly accelerated innovation cycle in
transport and the emergence of new mobility concepts and
technologies, public authorities, policy makers, and transport
planners are currently in need of the tools for sustainable
spatial and transport planning in the new mobility era. In
this paper, a new modular, software-agnostic and activity-based
spatial and transport planning platform is designed, i.e, the
HARMONY Model Suite, that facilitates a novel integration of
new and existing spatial and transport modelling tools. The paper
focuses on describing the architecture of the platform and its
passenger mobility simulation framework, which integrates -in
an interoperable manner- activity-based models, mobility service
management, and traffic simulation tools for evaluating new
mobility system dynamics. The service management controllers
for new mobility concepts are discussed in more detail with
regards to their functionality and applicability
The number of transmission channels through a single-molecule junction
We calculate transmission eigenvalue distributions for Pt-benzene-Pt and
Pt-butadiene-Pt junctions using realistic state-of-the-art many-body
techniques. An effective field theory of interacting -electrons is used to
include screening and van der Waals interactions with the metal electrodes. We
find that the number of dominant transmission channels in a molecular junction
is equal to the degeneracy of the molecular orbital closest to the metal Fermi
level.Comment: 9 pages, 8 figure
The molecular signature of highly conductive metal-molecule-metal junctions
The simplicity of single-molecule junctions based on direct bonding of a
small molecule between two metallic electrodes make them an ideal system for
the study of fundamental questions related to molecular electronics. Here we
study the conductance properties of six different molecules suspended between
Pt electrodes. All the molecular junctions show a typical conductance of about
1G0 which is ascribed to the dominant role of the Pt contacts. However, despite
the metallic-like conductivity, the individual molecular signature is
well-expressed by the effect of molecular vibrations in the inelastic
contribution to the conductance.Comment: 7 pages, 7 figures, 1 table. Related paper: J. Ferrer and V. M.
Garc\'ia-Su\'arez, Phys. Rev. B 80, 085426 (2009
Shot noise suppression at room temperature in atomic-scale Au junctions
Shot noise encodes additional information not directly inferable from simple
electronic transport measurements. Previous measurements in atomic-scale metal
junctions at cryogenic temperatures have shown suppression of the shot noise at
particular conductance values. This suppression demonstrates that transport in
these structures proceeds via discrete quantum channels. Using a high frequency
technique, we simultaneously acquire noise data and conductance histograms in
Au junctions at room temperature and ambient conditions. We observe noise
suppression at up to three conductance quanta, with possible indications of
current-induced local heating and noise in the contact region at high
biases. These measurements demonstrate the quantum character of transport at
room temperature at the atomic scale. This technique provides an additional
tool for studying dissipation and correlations in nanodevices.Comment: 15 pages, 4 figures + supporting information (6 pages, 6 figures
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