Simultaneous Measurements of Electronic Conduction and Raman Response in Molecular Junctions

Ward, Daniel R.; Halas, Naomi J.; Ciszek, Jacob W.; Tour, James M.; Wu, Yanpeng; Nordlander, Peter; Natelson, Douglas

doi:10.1021/nl073346h

Cited by 274 publications

(340 citation statements)

References 41 publications

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“…As in previous studies (20,21,23,25,33), correlations as a function of time are observed between spectral intensity fluctuations ("blinking") and the measured conductance in the tunneling regime. Because the tunneling conductance is dominated by a molecular-scale volume at the point of closest interelectrode separation, these correlations imply few-or single-molecule Raman sensitivity.…”

supporting

confidence: 79%

“…Plasmonic junctions between extended electrodes (19-25) show correlations of Raman response and conductance implying single-or few-molecule sensitivity, and enable studies of vibrational physics as a function of electrical bias. Spectral diffusion often is observed in singlemolecule SERS experiments (18,25,26), and there is some preliminary evidence of bias-driven mode shifts in such junctions (23), with the mechanisms of these phenomena remaining unclear.We report vibrational mode softening in C 60 molecules on the order of tens of wavenumbers, approximately quadratic in the external dc bias, V, applied across such a junction. We compare these observations with density functional theory (DFT) calculations to determine the underlying mechanism.…”

mentioning

confidence: 99%

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Voltage tuning of vibrational mode energies in single-molecule junctions

Doak

Kronik

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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106

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Vibrational modes of molecules are fundamental properties determined by intramolecular bonding, atomic masses, and molecular geometry, and often serve as important channels for dissipation in nanoscale processes. Although single-molecule junctions have been used 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. Our theoretical model instead suggests that the mode shifts are a signature of bias-driven addition of electronic charge to the molecule. These results imply that voltage-controlled tuning of vibrational modes is a general phenomenon at metal-molecule interfaces and is a means of achieving significant shifts in vibrational energies relative to a pure Stark effect.plasmonics | nanoscale junctions | molecular electronics M echanical couplings between atoms within molecules, manifested through vibrational spectra, are critically important in many processes at the nanoscale, from energy dissipation to chemical reactions. These couplings originate from the self-consistent electronic structure and ionic positions within the molecule (1). Vibrational spectroscopy examines this bonding, and advanced time-resolved techniques (2-5) can manipulate vibrational populations. Single-molecule junctions (6, 7) also have proven to be valuable tools for examining vibrational physics. Previous work showed that vibrational frequencies may be altered in mechanical break junctions if the chemical linkage to the moving contacts is sufficient to strain bonds in the molecule (8, 9), but also showed vibrations to be unaffected when the linkage to the contacts is less robust (10). Controllably altering vibrational energies in the steady state is difficult, however. Electric fields can redistribute the molecular electron density and shift vibrational modes in the vibrational Stark effect (11), enabling spectroscopic probes of local static electric fields in charge double layers (12, 13) and biosystems (14-16). However, other physics also may be relevant, and studies of electrical tuning of molecular vibrational energies in single-or few-molecule-based solid-state junctions, which often provide clarity that is difficult to obtain from measurements of molecular ensembles, have been lacking.Surface-enhanced Raman spectroscopy (SERS) (17, 18), in which surface plasmons enhance the Raman scattering rate for molecules, opens up the possibility of performing detailed vibrational studies at the single-molecule level. Plasmonic junctions between extended electrodes (19-25) show correlations of Raman response and conductance implying single-or few-molecule sensitivity, and enable studies of vib...

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supporting

confidence: 79%

mentioning

confidence: 99%

Voltage tuning of vibrational mode energies in single-molecule junctions

Doak

Kronik

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

106

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“…In this paper, we start by devising graphene-coated on Ag bowtie nanoantenna arrays (ABNA), as shown in Figure 1, where the paraaminothiophenol (PATP) on the substrate is an increasingly important probe molecule in SERS because of the intense SERS signal [23][24][25][26] . PATP-to-p, p9-dimercaptoazobenzene (DMAB) conversion is used to study charge transfer between the metal and molecules [27][28][29][30][31] , during which the catalytic reaction is monitored by SERS.…”

Section: Introductionmentioning

confidence: 99%

Plasmon-driven reaction controlled by the number of graphene layers and localized surface plasmon distribution during optical excitation

et al. 2015

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Graphene-plasmonic hybrid platforms have attracted an enormous amount of interest in surface-enhanced Raman scattering (SERS); however, the mechanism of employing graphene is still ambiguous, so clarification about the complex interaction among molecules, graphene, and plasmon processes is urgently needed. We report that the number of graphene layers controlled the plasmon-driven, surface-catalyzed reaction that converts para-aminothiophenol (PATP)-to-p,p9-dimercaptoazobenzene (DMAB) on chemically inert, graphene-coated, silver bowtie nanoantenna arrays. The catalytic reaction was monitored by SERS, which revealed that the catalytic reaction occurred on the chemical inertness monolayer graphene (1G)-coated silver nanostructures. The introduction of 1G enhances the plasmon-driven surface-catalyzed reaction of the conversion of PATP-to-p,p9-DMAB. The chemical reaction is suppressed by bilayer graphene. In the process of the catalytic reaction, the electron transfer from the PATP molecule to 1G-coated silver nanostructures. Subsequently, the transferred electrons on the graphene recombine with the hot-hole produced by the localized surface plasmon resonance of silver nanostructures. Then, a couple of PATP molecules lost electrons are catalyzed into the p,p9-DMAB molecule on the graphene surface. The experimental results were further supported by the finite-difference time-domain method and quantum chemical calculations.

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“…Vibrational signatures of molecular bridges have also been observed in inelastic electron tunneling spectroscopy. [35][36][37] New experimental techniques, [47][48][49] e.g., based on Raman spectroscopy, allow the characterization of the nonequilibrium state of the vibrational degrees of freedom in a molecular junction. The experimental progress has stimulated much interest in the theoretical modeling and simulation of vibrationally coupled electron transport in molecular junctions.…”

Section: Introductionmentioning

confidence: 99%

Numerically exact, time-dependent treatment of vibrationally coupled electron transport in single-molecule junctions

Wang

Pshenichnyuk

Härtle

et al. 2011

The Journal of Chemical Physics

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The multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory within second quantization representation of the Fock space, a novel numerically exact methodology to treat manybody quantum dynamics for systems containing identical particles, is applied to study the effect of vibrational motion on electron transport in a generic model for single-molecule junctions. The results demonstrate the importance of electronic-vibrational coupling for the transport characteristics. For situations where the energy of the bridge state is located close to the Fermi energy, the simulations show the time-dependent formation of a polaron state that results in a pronounced suppression of the current corresponding to the phenomenon of phonon blockade. We show that this phenomenon cannot be explained solely by the polaron shift of the energy but requires methods that incorporate the dynamical effect of the vibrations on the transport. The accurate results obtained with the ML-MCTDH in this parameter regime are compared to results of nonequilibrium Green's function theory.

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Simultaneous Measurements of Electronic Conduction and Raman Response in Molecular Junctions

Cited by 274 publications

References 41 publications

Voltage tuning of vibrational mode energies in single-molecule junctions

Voltage tuning of vibrational mode energies in single-molecule junctions

Plasmon-driven reaction controlled by the number of graphene layers and localized surface plasmon distribution during optical excitation

Numerically exact, time-dependent treatment of vibrationally coupled electron transport in single-molecule junctions

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