Molecular Vibration Spectra by Inelastic Electron Tunneling

Lambe, John; Jaklevic, R. C.

doi:10.1103/physrev.165.821

Cited by 538 publications

(248 citation statements)

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“…Recent work, focussing on constructing and exploring model systems that capture the important physical processes, 24,27 has shown that this is indeed a viable proposition. The suggested mechanism, which harnesses vibrationally-assisted ET in a similar manner to inelastic electron tunneling spectroscopy, 41,42 can be viewed as an example of a molecular switch, wherein specific vibrations of an external molecule actuate the receptor and lead to a pronounced electron flow. Detection via the frequency of vibrations could help to discern two molecules that are otherwise very similar.…”

Section: Introductionmentioning

confidence: 99%

Dissipation enhanced vibrational sensing in an olfactory molecular switch

Chęcińska

Pollock

Heaney

et al. 2015

The Journal of Chemical Physics

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Motivated by a proposed olfactory mechanism based on a vibrationally-activated molecular switch, we study electron transport within a donor-acceptor pair that is coupled to a vibrational mode and embedded in a surrounding environment. We derive a polaron master equation with which we study the dynamics of both the electronic and vibrational degrees of freedom beyond previously employed semiclassical (MarcusJortner) rate analyses. We show: (i) that in the absence of explicit dissipation of the vibrational mode, the semiclassical approach is generally unable to capture the dynamics predicted by our master equation due to both its assumption of one-way (exponential) electron transfer from donor to acceptor and its neglect of the spectral details of the environment; (ii) that by additionally allowing strong dissipation to act on the odorant vibrational mode we can recover exponential electron transfer, though typically at a rate that differs from that given by the Marcus-Jortner expression; (iii) that the ability of the molecular switch to discriminate between the presence and absence of the odorant, and its sensitivity to the odorant vibrational frequency, are enhanced significantly in this strong dissipation regime, when compared to the case without mode dissipation; and (iv) that details of the environment absent from previous Marcus-Jortner analyses can also dramatically alter the sensitivity of the molecular switch, in particular allowing its frequency resolution to be improved. Our results thus demonstrate the constructive role dissipation can play in facilitating sensitive and selective operation in molecular switch devices, as well as the inadequacy of semiclassical rate equations in analysing such behaviour over a wide range of parameters.

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Section: Introductionmentioning

confidence: 99%

Dissipation enhanced vibrational sensing in an olfactory molecular switch

Chęcińska

Pollock

Heaney

et al. 2015

The Journal of Chemical Physics

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“…STM tunnel current is generally enhanced if the bias voltage is high enough to provide tunnelling electrons with enough energy to induce excitations that have some threshold energyhω 0 (Fig. 4c) 13 . This opens up a new inelastic tunnelling channel at bias voltages of ±hω 0 /e, causing steps in dI /dV spectra that are symmetric around E F and that lead to a gap-like feature with width 2hω 0 .…”

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confidence: 99%

Giant phonon-induced conductance in scanning tunnelling spectroscopy of gate-tunable graphene

et al. 2008

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The honeycomb lattice of graphene is a unique two-dimensional system where the quantum mechanics of electrons is equivalent to that of relativistic Dirac fermions 1,2 . Novel nanometre-scale behaviour in this material, including electronic scattering 3,4 , spin-based phenomena 5 and collective excitations 6 , is predicted to be sensitive to charge-carrier density. To probe local, carrier-density-dependent properties in graphene, we have carried out atomically resolved scanning tunnelling spectroscopy measurements on mechanically cleaved graphene flake devices equipped with tunable back-gate electrodes. We observe an unexpected gap-like feature in the graphene tunnelling spectrum that remains pinned to the Fermi level (E F ) regardless of graphene electron density. This gap is found to arise from a suppression of electronic tunnelling to graphene states near E F and a simultaneous giant enhancement of electronic tunnelling at higher energies due to a phonon-mediated inelastic channel. Phonons thus act as a 'floodgate' that controls the flow of tunnelling electrons in graphene. This work reveals important new tunnelling processes in gate-tunable graphitic layers.Graphene provides an ideal platform for the local study of high-mobility two-dimensional (2D) electrons because it can be fabricated on top of an insulating substrate. The availability of a back-gate electrode makes graphene the first gate-tunable 2D system directly accessible to scanning probe measurement (Fig. 1a). Previous experiments have demonstrated the power of scanning tunnelling microscopy (STM) to probe the local electronic structure of graphene grown epitaxially on SiC (refs 7-9). That system, however, cannot be easily gated, and questions remain as to the influence of the SiC substrate on the graphene layer 6,10 . Mechanically cleaved graphene is a desirable alternative to graphene grown on SiC because it can be readily gated and placed on wellcontrolled substrates (Fig. 1a), thus making it useful for extracting intrinsic graphene properties.The STM topography of a gated graphene flake device is shown in Fig. 2a. Corrugations with a lateral dimension of a few nanometres and a vertical dimension of ∼1.5Å (r.m.s. value over a 60 × 60 nm 2 area) are observed, probably due to roughness in the underlying SiO 2 (refs 11,12). The graphene honeycomb lattice can be clearly resolved on top of the surface corrugation, as seen more clearly in Fig. 2b. We explored the local electronic structure of these graphene flake devices using dI /dV measurements at zero gate voltage, as shown in Fig. 2c. Strikingly, the spectrum shows a ∼130 mV gap-like feature centred at the Fermi energy, E F , as opposed to the linear density of states that might be expected from elastic tunnelling to a Dirac cone. A local minimum in the tunnelling conductance spectrum can also be seen at V D = −138 mV, making the spectrum asymmetric about E F . Close examination of the low-bias spectrum (Fig. 2c, inset) reveals that the tunnelling conductance does not go to absolute zero in the gap...

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“…2(a), where it is seen that the PT resonance appears as a peak in d 2 I=dV 2 , rather than in dI=dV as for SET. The reason is that, analogous to inelastic cotunneling, the number of electron states in the reservoirs available for a PT process is proportional to the bias voltage [2]. Another clear way to separate PT and SET resonances is that the PT resonance exhibits no Zeeman splitting; see Fig.…”

Section: Fig 1 (Color Online) Energy Differences Between Many-bodymentioning

confidence: 99%

“…The corresponding integrals can be solved analytically [9] without the need for ad hoc regularization. Equation (2) shows that the peak in the derivative of the differential conductance directly maps out the energy dependence of the pair tunneling rate. Neglecting all terms not contributing to the PT peak in the second derivative, assuming equal capacitances to the left and right reservoirs, we are left with…”

Section: Fig 1 (Color Online) Energy Differences Between Many-bodymentioning

confidence: 99%

“…As a result, the bias positions of differential conductance (dI=dV) resonances depend linearly on the gate voltage due to capacitive effects [1]. In addition, inelastic cotunneling (COT) processes can often be distinguished as steps in dI=dV [2], allowing for spectroscopy of quantum dot excitations with increased energy resolution [3]. Here an electron is transferred from the high to the low biased electrode through the dot, using the excess biasenergy to excite the dot by an energy Á .…”

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Pair Tunneling Resonance in the Single-Electron Transport Regime

Leijnse

Wegewijs

Hettler³

2009

Phys. Rev. Lett.

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We predict a new electron pair tunneling (PT) resonance in nonlinear transport through quantum dots with positive charging energies exceeding the broadening due to thermal and quantum fluctuations. The PT resonance shows up in the single-electron transport (SET) regime as a peak in the derivative of the nonlinear conductance, d 2 I=dV 2 , when the electrochemical potential of one electrode matches the average of two subsequent charge addition energies. For a single level quantum dot (Anderson model) we find the analytic peak shape and the dependence on temperature, magnetic field, and junction asymmetry and compare with the inelastic cotunneling peak which is of the same order of magnitude. In experimental transport spectroscopy the PT resonance may be mistaken for a weak SET resonance judging only by the voltage dependence of its position. Our results provide essential clues to avoid such erroneous interpretation. Introduction.-Electron tunneling spectroscopy has nowadays become a standard tool for investigating the in situ properties of single-electron transistors based on quantum dots in semiconductor heterostructures, nanowires, carbon nanotubes, and even single molecules. The basic spectroscopy rules derive from the simple energy resonance conditions for single-electron tunneling (SET) onto the dot. As a result, the bias positions of differential conductance (dI=dV) resonances depend linearly on the gate voltage due to capacitive effects [1]. In addition, inelastic cotunneling (COT) processes can often be distinguished as steps in dI=dV [2], allowing for spectroscopy of quantum dot excitations with increased energy resolution [3]. Here an electron is transferred from the high to the low biased electrode through the dot, using the excess biasenergy to excite the dot by an energy Á . Since these electron-hole charge transfer resonances involve only a virtual charging of the dot, they appear at a bias threshold V ¼ Á , independent of the gate voltage. These processes arise only in second order perturbation theory in the tunnel rate À.In this Letter we show that, in the same order of À, electron pair tunneling (PT) gives rise to distinct, measurable transport effects which, to our knowledge, have been overlooked so far. In a single coherent process, a pair of electrons is extracted from (added to) one electrode, resulting in a real (dis)charging of the dot by two electrons, involving a positive charging energy much larger than broadening due to thermal and quantum charge fluctuations. The corresponding PT resonance appears deep inside the SET region where a finite current is flowing and its position has the same gate-dependence as SET resonances. It might thus be mistaken for a weak SET resonance belonging to some excited state and one might thereby extract an erroneous level-structure from the spectroscopic

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Molecular Vibration Spectra by Inelastic Electron Tunneling

Cited by 538 publications

References 11 publications

Dissipation enhanced vibrational sensing in an olfactory molecular switch

Dissipation enhanced vibrational sensing in an olfactory molecular switch

Giant phonon-induced conductance in scanning tunnelling spectroscopy of gate-tunable graphene

Pair Tunneling Resonance in the Single-Electron Transport Regime

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