An official website of the United States government
Abstract In the present work we theoretically analyze thermoelectric transport in single-molecule junctions (SMJ) characterized by strong interactions between electrons on the molecular linkers and phonons in their nuclear environments where electron hopping between the electrodes and the molecular bridge states predominates in the steady state electron transport. The analysis is based on the modified Marcus theory accounting for the lifetime broadening of the bridge’s energy levels. We show that the reorganization processes in the environment accompanying electron transport may significantly affect SMJ thermoelectric properties both within and beyond linear transport regime. Specifically, we study the effect of environmental phonons on the electron conductance, the thermopower and charge current induced by the temperature gradient applied across the system.
more »
« less
Multidimensional Characterization of Single‐Molecule Dynamics in a Plasmonic Nanocavity
Abstract Nanoscale manipulation and characterization of individual molecules is necessary to understand the intricacies of molecular structure, which governs phenomena such as reaction mechanisms, catalysis, local effective temperatures, surface interactions, and charge transport. Here we utilize Raman enhancement between two nanostructured electrodes in combination with direct charge transport measurements to allow for simultaneous characterization of the electrical, optical, and mechanical properties of a single molecule. This multi‐dimensional information yields repeatable, self‐consistent, verification of single‐molecule resolution, and allows for detailed analysis of structural and configurational changes of the molecule in situ. These experimental results are supported by a machine‐learning based statistical analysis of the spectral information and calculations to provide insight into the correlation between structural changes in a single‐molecule and its charge‐transport properties.
more »
« less
- PAR ID:
- 10249308
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 30
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 16436-16441
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
A nanopore can be fairly—but uncharitably—described as simply a nanofluidic channel through a thin membrane. Even this simple structural description holds utility and underpins a range of applications. Yet significant excitement for nanopore science is more readily ignited by the role of nanopores as enabling tools for biomedical science. Nanopore techniques offer single-molecule sensing without the need for chemical labelling, since in most nanopore implementations, matter is its own label through its size, charge, and chemical functionality. Nanopores have achieved considerable prominence for single-molecule DNA sequencing. The predominance of this application, though, can overshadow their established use for nanoparticle characterization and burgeoning use for protein analysis, among other application areas. Analyte scope continues to be expanded and with increasing analyte complexity, success will increasingly hinge on control over nanopore surface chemistry to tune the nanopore, itself, and to moderate analyte transport. Carbohydrates are emerging as the latest high-profile target of nanopore science. Their tremendous chemical and structural complexity means that they challenge conventional chemical analysis methods and thus present a compelling target for unique nanopore characterization capabilities. Furthermore, they offer molecular diversity for probing nanopore operation and sensing mechanisms. This article thus focuses on two roles of chemistry in nanopore science: its use to provide exquisite control over nanopore performance, and how analyte properties can place stringent demands on nanopore chemistry. Expanding the horizons of nanopore science requires increasing consideration of the role of chemistry and increasing sophistication in the realm of chemical control over this nanoscale milieu.more » « less
-
A generalized quantum master equation approach is introduced to describe electron transfer in molecular junctions that spans both the off-resonant (tunneling) and resonant (hopping) transport regimes. The model builds on prior insights from scattering theory but is not limited to a certain parameter range with regard to the strength of the molecule–electrode coupling. The framework is used to study the simplest case of energy and charge transfer between the molecule and the electrodes for a single site noninteracting Anderson model in the limit of symmetric and asymmetric coupling between the molecule and the electrodes. In the limit of elastic transport, the Landauer result is recovered for the current by invoking a single active electron Ansatz and a binary collision approximation for the memory kernel. Inelastic transport is considered by allowing the excitation of electron–hole pairs in the electrodes in tandem with charge transport. In the case of low bias voltages where the Fermi levels of the electrodes remain below the molecular state, it is shown that the current arises from tunneling and the molecule remains neutral. However, once the threshold is reached for aligning the fermi level of one electrode with the molecular orbital, a small amount of charge transfer occurs with a negligible amount of hopping current. While inelasticity in the current has a minimal impact on the shape of the current–voltage curve in the case of symmetric electrode coupling, the results for a slight asymmetry in coupling demonstrate complete charge transfer and a significant drop in current. These results provide encouraging confirmation that the framework can describe charge transport across a wide range of electrode–molecule coupling and provide a unique perspective for developing new master equation treatments for energy and charge transport in molecular junctions. An extension of this work to account for inelastic scattering from electron–vibrational coupling at the molecule is straightforward and will be the subject of subsequent work.more » « less
-
Abstract We report the synthesis of a soluble precursor that transforms into crystalline SnSe at 200 °C. This transformation temperature is significantly lower than the 270–350 °C range of previously reported tin selenide precursors. This precursor is synthesized by reacting tin with dimethyl diselenide and we identify the precursor as tin(IV) methylselenolate using a combination of mass spectrometry, Raman spectroscopy, and nuclear magnetic resonance spectroscopy. We then chemically treat PbSe colloidal nanocrystals with this precursor and subject them to mild annealing. We characterize the chemical and structural changes during this processing using infrared spectroscopy, aberration‐corrected scanning transmission electron microscopy, and X‐ray photoelectron spectroscopy. These characterization studies indicate the successful formation of a SnSe‐like material that fills the interstitial space between the PbSe nanocrystal cores. We find that the electrical conductivity of these nanocrystal films is comparable to other excellent treatments used to improve charge transport. This excellent charge transport demonstrates the utility of tin(IV) methylselenolate as a conductive “glue” between nanocrystals.more » « less
-
Phenalenyl-based radicals are stable radicals whose electronic properties can be tuned readily by heteroatom substitution. We employ density functional theory-based non-equilibrium Green's function (NEGF-DFT) calculations to show that this class of molecules exhibits tunable spin- and charge-transport properties in single molecule junctions. Our simulations identify the design principles and interplay between unusually high conductivity and strong spin-filtering.more » « less
