13 research outputs found
IETS and quantum interference: propensity rules in the presence of an interference feature
Destructive quantum interference in single molecule electronics is an
intriguing phe- nomenon; however, distinguishing quantum interference effects
from generically low transmission is not trivial. In this paper, we discuss how
quantum interference ef- fects in the transmission lead to either low current
or a particular line shape in current-voltage curves, depending on the position
of the interference feature. Sec- ondly, we consider how inelastic electron
tunneling spectroscopy can be used to probe the presence of an interference
feature by identifying vibrational modes that are se- lectively suppressed when
quantum interference effects dominate. That is, we expand the understanding of
propensity rules in inelastic electron tunneling spectroscopy to molecules with
destructive quantum interference.Comment: 19 pages, 6 figure
Single-molecule Electronics: Cooling Individual Vibrational Modes by the Tunneling Current
Electronic devices composed of single molecules constitute the ultimate limit
in the continued downscaling of electronic components. A key challenge for
single-molecule electronics is to control the temperature of these junctions.
Controlling heating and cooling effects in individual vibrational modes, can in
principle, be utilized to increase stability of single-molecule junctions under
bias, to pump energy into particular vibrational modes to perform
current-induced reactions or to increase the resolution in inelastic electron
tunneling spectroscopy by controlling the life-times of phonons in a molecule
by suppressing absorption and external dissipation processes. Under bias the
current and the molecule exchange energy, which typically results in heating of
the molecule. However, the opposite process is also possible, where energy is
extracted from the molecule by the tunneling current. Designing a molecular
'heat sink' where a particular vibrational mode funnels heat out of the
molecule and into the leads would be very desirable. It is even possible to
imagine how the vibrational energy of the other vibrational modes could be
funneled into the 'cooling mode', given the right molecular design. Previous
efforts to understand heating and cooling mechanisms in single molecule
junctions, have primarily been concerned with small models, where it is unclear
which molecular systems they correspond to. In this paper, our focus is on
suppressing heating and obtaining current-induced cooling in certain
vibrational modes. Strategies for cooling vibrational modes in single-molecule
junctions are presented, together with atomistic calculations based on those
strategies. Cooling and reduced heating are observed for two different cooling
schemes in calculations of atomistic single-molecule junctions.Comment: 18 pages, 6 figure
Single-Molecule Electronics with Cross- Conjugated Molecules: Quantum Interference, IETS and Non-Equilibrium "Temperatures"
Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules:a prediction from theory
[Image: see text] Cross-conjugated molecules are known to exhibit destructive quantum interference, a property that has recently received considerable attention in single-molecule electronics. Destructive quantum interference can be understood as an antiresonance in the elastic transmission near the Fermi energy and leading to suppressed levels of elastic current. In most theoretical studies, only the elastic contributions to the current are taken into account. In this paper, we study the inelastic contributions to the current in cross-conjugated molecules and find that while the inelastic contribution to the current is larger than for molecules without interference, the overall behavior of the molecule is still dominated by the quantum interference feature. Second, an ongoing challenge for single molecule electronics is understanding and controlling the local geometry at the molecule-surface interface. With this in mind, we investigate a spectroscopic method capable of providing insight into these junctions for cross-conjugated molecules: inelastic electron tunneling spectroscopy (IETS). IETS has the advantage that the molecule interface is probed directly by the tunneling current. Previously, it has been thought that overtones are not observable in IETS. Here, overtones are predicted to be strong and, in some cases, the dominant spectroscopic features. We study the origin of the overtones and find that the interference features in these molecules are the key ingredient. The interference feature is a property of the transmission channels of the π system only, and consequently, in the vicinity of the interference feature, the transmission channels of the σ system and the π system become equally transmissive. This allows for scattering between the different transmission channels, which serves as a pathway to bypass the interference feature. A simple model calculation is able to reproduce the results obtained from atomistic calculations, and we use this to interpret these findings
IETS and quantum interference: Propensity rules in the presence of an interference feature
Racemization Mechanisms and Electronic Circular Dichroism of [4]Heterohelicenium Dyes: A Theoretical Study
Strong Overtones Modes in Inelastic Electron Tunneling Spectroscopy with Cross-Conjugated Molecules: A Prediction from Theory
Cross-conjugated molecules are known to exhibit destructive quantum interference, a property that has recently received considerable attention in single-molecule electronics. Destructive quantum interference can be understood as an antiresonance in the elastic transmission near the Fermi energy and leading to suppressed levels of elastic current. In most theoretical studies, only the elastic contributions to the current are taken into account. In this paper, we study the inelastic contributions to the current in cross-conjugated molecules and find that while the inelastic contribution to the current is larger than for molecules without interference, the overall behavior of the molecule is still dominated by the quantum interference feature. Second, an ongoing challenge for single molecule electronics is understanding and controlling the local geometry at the molecule-surface interface. With this in mind, we investigate a spectroscopic method capable of providing insight into these junctions for cross-conjugated molecules: inelastic electron tunneling spectroscopy (IETS). IETS has the advantage that the molecule interface is probed directly by the tunneling current. Previously, it has been thought that overtones are not observable in IETS. Here, overtones are predicted to be strong and, in some cases, the dominant spectroscopic features. We study the origin of the overtones and find that the interference features in these molecules are the key ingredient. The interference feature is a property of the transmission channels of the π system only, and consequently, in the vicinity of the interference feature, the transmission channels of the σ system and the π system become equally transmissive. This allows for scattering between the different transmission channels, which serves as a pathway to bypass the interference feature. A simple model calculation is able to reproduce the results obtained from atomistic calculations, and we use this to interpret these findings