IETS and quantum interference: Propensity rules in the presence of an interference feature

Lykkebo, Jacob; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C.

doi:10.1063/1.4896234

Cited by 24 publications

(22 citation statements)

References 38 publications

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“…37). This curvature only appears if the energy of the interference in the assembled junction is close enough to E f that the feature lies almost entirely within the bias window15. The dip in transmission for PCP and AH-crystal in Fig.…”

Section: Discussionmentioning

confidence: 92%

“…And although SAMs are crystalline and can be highly ordered over small areas, defects and grain boundaries can influence the current-density versus voltage ( J / V ) properties in large-area (μm 2 ) measurements14. In addition to these experimental challenges, distinguishing between destructive QI and differences in conductance arising from conjugation length require fortuitous level-alignment in the assembled junction15. Through-space QI is potentially useful beyond validating theoretical predictions as it could couple small structural or conformational changes (for example, from external mechanical forces) into exponential changes in conductance.…”

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confidence: 99%

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Conformation-driven quantum interference effects mediated by through-space conjugation in self-assembled monolayers

et al. 2016

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Tunnelling currents through tunnelling junctions comprising molecules with cross-conjugation are markedly lower than for their linearly conjugated analogues. This effect has been shown experimentally and theoretically to arise from destructive quantum interference, which is understood to be an intrinsic, electronic property of molecules. Here we show experimental evidence of conformation-driven interference effects by examining through-space conjugation in which π-conjugated fragments are arranged face-on or edge-on in sufficiently close proximity to interact through space. Observing these effects in the latter requires trapping molecules in a non-equilibrium conformation closely resembling the X-ray crystal structure, which we accomplish using self-assembled monolayers to construct bottom-up, large-area tunnelling junctions. In contrast, interference effects are completely absent in zero-bias simulations on the equilibrium, gas-phase conformation, establishing through-space conjugation as both of fundamental interest and as a potential tool for tuning tunnelling charge-transport in large-area, solid-state molecular-electronic devices.

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Section: Discussionmentioning

confidence: 92%

mentioning

confidence: 99%

Conformation-driven quantum interference effects mediated by through-space conjugation in self-assembled monolayers

et al. 2016

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“…However, for the case of molecules strongly coupled to the leads, such as in the quantum interference regime, IETS remains a better spectroscopic tool [20][21][22][23][24][25][26][27]. Recent theoretical works have calculated the inelastic contributions to the current in the presence of QI [28] and have explored propensity rules that can play a role in this case [29,30]. QI is not completely quenched by the decoherence due to the inelastic interaction of electrons with molecular vibrational modes; furthermore, the inelastic contributions to the current in the presence of QI is predicted to be larger than in molecules without interference meaning that QI can be exploited to investigate vibrational mode signatures on electronic transport.…”

Section: Introductionmentioning

confidence: 99%

Inelastic electron tunneling spectroscopy in molecular junctions showing quantum interference

et al. 2017

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Destructive quantum interference effect is implemented in large area molecular junctions to improve signatures of electron-phonon interaction. Vertical molecular junctions based on a cross-conjugated anthraquinone layer were fabricated and low-noise transport measurements were performed by acquiring simultaneously the current-voltage characteristics, its second derivative, and the differential conductance. Signatures of vibrational modes excited by inelastic events are present in the whole measured voltage range and superpose to the conductance suppression induced by destructive quantum interference. As a consequence vibrational modes have improved visibility in the low energy window (<80 meV). Inelastic electron transport spectroscopy data are compared to infrared attenuated total reflection spectroscopy on Au/anthraquinone thin films. Common vibrational modes can be clearly identified, but inelastic electron tunneling spectroscopy reveals the existence of vibrational modes in a wider energy range (0-400 meV) where infrared spectroscopy is lacking.

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“…Although the IETS signal for molecular vibrations that are not directly involved in the electron-transport pathways can undergo mode suppression, such phenomena are also likely to occur as a result of quantum interference effects. According to a recent study made by Lykkebo et al [58], the non-overlapping of transmission channels stemming from quantum interference within the molecular motif may cause suppression of the corresponding vibrational modes. Metal centers in single-molecule junctions may thus have diverse yet discernible impact on the inelastic transmission whose resonant peaks or dips are often determined by the relative values of elastic and inelastic contributions to the net current near the phonon excitation threshold.…”

Section: Fano Resonancementioning

confidence: 99%

“…On the other hand, the localized state, as assisted by phonons through either emission or absorption, gives rise to an indirect pathway. Once these two transport pathways interfere at the band continuum provided by the semi-infinite quasi-1D electrodes, it results in the resonant suppression of the electronic transmission leading to the destructive QI, while the peaks may occur due to the constructive QI at their respective phonon excitation thresholds [58,68,69,70,71,72]. In the HOMO dominated transport junctions such as a-CrCrCr and s-CoCoRu (see Figures 6a and 6c), an incoming electron from the left electrode tunnels inelastically through a delocalized state near the renormalized HOMO by absorbing a phonon of certain energy (Ω 1 or Ω 3 ) to reach the right electrode.…”

Section: Fano Resonancementioning

confidence: 99%

Conformation controllable inelastic charge transport and shot noise behavior in metal-string single molecular devices

Roy

Sen

2020

Applied Surface Science

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It is often intriguing experimentally to take stock of how conformational changes in the device configuration may impact the overall charge transport behavior of single-molecule junctions. Based on the allied approach of density functional theory and non-equilibrium Green's function formalism, we explore here the effect of junction heterogeneity on inelastic charge transport in various metal-string based single-molecule devices. The constituent active elements being sensitive to the resonant levels, transition metal centers are found to influence stretching, bending, and torsional excitation modes, while rocking and scissoring modes are controlled largely by the axial ligands. For certain molecular conformations and electrode orientations, phonon-assisted quantum interference effect may crop up, leading to the suppression of higher wavenumber vibrational modes. The resulting inelastic spectra are likely to take the shape of dominant Fano resonance or anti-resonance, depending on whether phonons are emitted or absorbed. Such nanoscale quantum interference effect is manifested especially in those metal-string molecular junctions for which the energy gap (between localized and delocalized virtual states) lies well within the optical phonon energies (∆E |HOM O−LU M O| < 40 meV). It also turns out that single molecular shot noise can exhibit nearly Poissonian behavior if the inter-channel tunneling through frontier orbitals is accompanied by phonon absorption or emission following a slow relaxation process. Our results thus suggest that charge transport properties across metal-string complexes can be potentially tuned by selective architecture of the metal centers and also, by preferred orientation of nanoscale electrodes in a bid to build up molecular devices with desirable controllability.

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IETS and quantum interference: Propensity rules in the presence of an interference feature

Cited by 24 publications

References 38 publications

Conformation-driven quantum interference effects mediated by through-space conjugation in self-assembled monolayers

Conformation-driven quantum interference effects mediated by through-space conjugation in self-assembled monolayers

Inelastic electron tunneling spectroscopy in molecular junctions showing quantum interference

Conformation controllable inelastic charge transport and shot noise behavior in metal-string single molecular devices

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