Fishing-Mode Tip-enhanced Raman Spectroscopy (FM-TERS) for Studying Single-Molecule Junctions (original) (raw)
Related papers
Nature Communications, 2011
The conductance of single-molecule junctions may be governed by the structure of the molecule in the gap or by the way it bonds with the leads, and the information contained in a Raman spectrum is ideal for examining both. Here we demonstrate that molecule-tosurface bonding may be characterized during electron transport by 'fishing-mode' tipenhanced Raman spectroscopy (Fm-TERs). This technique allows mutually verifiable singlemolecule conductance and Raman signals with single-molecule contributions to be acquired simultaneously at room temperature. Density functional theory calculations reveal that the most significant spectral change seen for a gold-4,4′-bipyridine-gold junction results from the deformation of the pyridine ring in contact with the drain electrode at high voltage, and these calculations suggest that a stronger bonding interaction between the molecule and the drain may account for the nonlinear dependence of conductance on bias voltage. Fm-TERs will lead to a better understanding of electron-transport processes in molecular junctions.
Simultaneous Measurements of Electronic Conduction and Raman Response In Molecular Junctions
Nano Lett, 2008
Electronic conduction through single molecules is affected by the molecular electronic structure as well as by other information that is extremely difficult to assess, such as bonding geometry and chemical environment. The lack of an independent diagnostic technique has long hampered single-molecule conductance studies. We report simultaneous measurement of the conductance and the Raman spectra of nanoscale junctions used for single-molecule electronic experiments. Blinking and spectral diffusion in the Raman response of both para-mercaptoaniline and a fluorinated oligophenylyne ethynylene correlate in time with changes in the electronic conductance. Finite difference time domain calculations confirm that these correlations do not result from the conductance modifying the Raman enhancement. Therefore, these observations strongly imply that multimodal sensing of individual molecules is possible in these mass-producible nanostructures.
Research on Chemical Intermediates, 2014
The SERS spectra of 4,4 0-bipyridine/gold single molecule junction in different conductance states at room temperature are calculated by performing ab initio molecular dynamics simulations, in connection with a Fourier transform of the polarizability autocorrelation function, to illustrate that the Raman peaks of the ON state are enhanced by an additional one or two orders of magnitude in comparison with the OFF state. Considering the relative intensities of SERS spectra, the largest enhanced peak for the OFF state is the ring breathing mode due to the simultaneous contribution from structural change, vibrational coupling, and charge transfer. For the ON state, the C-H bending mode has the largest enhancement due to structural change and charge transfer effects. Finally, the SERS spectra of 4,4 0bipyridine junction in the the ON state with perpendicular and tilted orientations are examined to understand the reason why the tilted junction has lower SERS spectrum intensity with doublet feature of the CC stretching mode.
Small, 2010
A combined experimental and theoretical study is presented revealing the influence of metal-molecule coupling on electronic transport through single-molecule junctions. Transport experiments through tolane molecules attached to gold electrodes via thiol, nitro, and cyano anchoring groups are performed. By fitting the experimental current-voltage characteristics to a single-level tunneling model, we extract both the position of the molecular orbital closest to the Fermi energy and the strength of the metal-molecule coupling. The values found for these parameters are rationalized with the help of density-functional-theory-based transport calculations. In particular, these calculations show that the anchoring groups determine the junction conductance by controlling not only the strength of the coupling to the metal but also the position of the relevant molecular energy levels.
Nano Letters, 2008
We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes. One derivative has additional methylene groups separating the thiols from the delocalized π-electron system. The insertion of methylene groups changes the open state conductance by 3−4 orders of magnitude and changes the transport mechanism from a coherent regime with finite zero-bias conductance to sequential tunneling and Coulomb blockade behavior.
Voltage tuning of vibrational mode energies in single-molecule junctions
Proceedings of the National Academy of Sciences, 2014
bonding, atomic masses, and molecular geometry, and often serve as important channels for dissipation in nanoscale processes. Although single-molecule junctions have been employed to manipulate electronic structure and related functional properties of molecules, electrical control of vibrational mode energies has remained elusive. Here we use simultaneous transport and surface-enhanced Raman spectroscopy measurements to demonstrate large, reversible, voltage-driven shifts of vibrational mode energies of C 60 molecules in gold junctions. C 60 mode energies are found to vary approximately quadratically with bias, but in a manner inconsistent with a simple vibrational Stark effect.
Probing metal-molecule contact at the atomic scale via conductance jumps
Physical Review B, 2021
Understanding the formation of metal-molecule contact at the microscopic level is the key towards controlling and manipulating atomic scale devices. Employing two isomers of bipyridine, 4, 4 bipyridine and 2, 2 bipyridine between gold electrodes, here, we investigate the formation of metal-molecule bond by studying charge transport through single molecular junctions using a mechanically controlled break junction technique at room temperature. While both molecules form molecular junctions during the breaking process, closing traces show the formation of molecular junctions unambiguously for 4, 4 bipyridine via a conductance jump from the tunneling regime, referred as ‘jump to molecular contact’, being absent for 2, 2 bipyridine. Through statistical analysis of the data, along with, molecular dynamics and first-principles calculations, we establish that contact formation is strongly connected with the molecular structure of the electrodes as well as how the junction is broken during b...
Charge Transport in Single Molecular Junctions at the Solid/Liquid Interface
Topics in Current Chemistry, 2011
Charge transport characteristics in metal-metal nanocontacts and single molecular junctions were studied at electrified solid-liquid interfaces employing a scanning tunneling microscope-based break junction technique, in combination with macroscopic electrochemical methods, in non-conducting solvents and in an electrochemical environment. We aim to demonstrate recent attempts in developing fundamental relationships between molecular structure, charge transport characteristics, and nanoscale electrochemical concepts. After an introduction and brief description of the experimental methodology, a case study on the electrical and mechanical properties of gold atomic contacts in aqueous electrolytes is presented. In experiments with alkanedithiol and a,o-biphenyldithiol molecular junctions the role of sulfur-gold couplings and molecular conformation, such as gauche defects in alkyl chains and the torsion angle between two phenyl rings, are addressed. The combination with quantum chemistry calculations enabled a detailed molecular-level understanding of the electronic structure and transport characteristics of both systems. Employing the concept of "electrolyte gating" to 4,4 0 -bipyridine and redox-active molecules, such as perylene bisimide derivatives, the construction of "active" symmetric and asymmetric molecular junctions with transistor-and diode-like behavior upon polarization in an electrochemical environment will be demonstrated. The latter experimental data could be represented quantitatively by the Kutznetsov/Ulstrup model, assuming a two-step electron transfer with partial vibration relaxation. Finally, we show that (individual) surfaceimmobilized gold clusters within the quantum-confined size range exhibit features of locally addressable multistate electronic switching upon electrolyte gating, which appears to be reminiscent of a sequential charging through several redox states. The examples addressed here demonstrate the uniqueness and capabilities of an electrochemical approach for the fundamental understanding and for potential applications in nano-and molecular electronics.
Journal of the American Chemical Society, 2012
We study the effects of molecular structure on the electronic transport and mechanical stability of single-molecule junctions formed with Au point contacts. Two types of linear conjugated molecular wires are compared: those functionalized with methylsulfide or amine aurophilic groups at (1) both or (2) only one of its phenyl termini. Using scanning tunneling and atomic force microscope break-junction techniques, the conductance of mono-and difunctionalized molecular wires and its dependence on junction elongation and rupture forces were studied. Charge transport through monofunctionalized wires is observed when the molecular bridge is coupled through a S−Au donor− acceptor bond on one end and a relatively weak Au−π interaction on the other end. For monofunctionalized molecular wires, junctions can be mechanically stabilized by installing a second aurophilic group at the meta position that, however, does not in itself contribute to a new conduction pathway. These results reveal the important interplay between electronic coupling through metal−π interactions and quantum mechanical effects introduced by chemical substitution on the conjugated system. This study affords a strategy to deterministically tune the electrical and mechanical properties through molecular wires.