Understanding the inelastic electron-tunneling spectra of alkanedithiols on gold

Solomon, Gemma C.; Gagliardi, Alessio; Pecchia, Alessandro; Frauenheim, Thomas; Carlo, Aldo Di; Reimers, Jeffrey R.; Hush, Noel S.

doi:10.1063/1.2166362

Cited by 107 publications

(128 citation statements)

References 57 publications

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“…17 More recently, most formalisms have been developed under the Born approximation (BA), either in its self-consistent version [20][21][22] (SCBA) or perturbatively, typically exploiting the small e-VM coupling and/or the small applied bias. 20,23,26 Whereas the SCBA requires large computational resources and therefore its use is generally limited within simple one-dimensional (1D) effective models, perturbative approaches permit lighter implementations and the use of ab initio schemes for the evaluation of the Hamiltonian terms. Apart from TH-based approaches, [17][18][19]29 which are specifically suited for the STM setup albeit they neglect any tip features, it is surprising that hardly any of the above-mentioned schemes, when applied to the simulation of IETS spectra, take additional advantage of the small tunneling terms typically involved in STM-IETS experiments.…”

Section: Introductionmentioning

confidence: 99%

“…[9][10][11][12][13][14][15] From the theoretical side, a wealth of formalisms dealing with the inelastic transport have been developed in parallel to these delicate experiments. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] The earliest models for IETS employed a multiple scattering formalism (multichannels) with simplified semiempirical Hamiltonians 16 or a Tersoff-Hamman-(TH-) type approach. 17 More recently, most formalisms have been developed under the Born approximation (BA), either in its self-consistent version [20][21][22] (SCBA) or perturbatively, typically exploiting the small e-VM coupling and/or the small applied bias.…”

Section: Introductionmentioning

confidence: 99%

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Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data

2013

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We have developed an efficient and accurate formalism which allows the simulation at the ab initio level of inelastic electron tunneling spectroscopy data under a scanning tunneling microscope setup. It exploits fully the tunneling regime by carrying out the structural optimization and vibrational mode calculations for surface and tip independently. The most relevant interactions in the inelastic current are identified as the inelastic tunneling terms, which are taken into account up to lowest order, while all other inelastic contributions are neglected. As long as the system is under tunneling regime conditions and there is no physisorbed molecule on the surface or tip apex, this lowest order in inelastic tunneling (LOIT) approach reduces drastically the computational cost compared to related approaches while maintaining a good accuracy. Adopting the wide-band limit for both tip and surface further reduces calculation times significantly, and is shown to give similar results to when the full energy dependence of the Green's functions is taken into account. The LOIT is applied to the Cu(111) + CO system probed by a clean and a CO contaminated tip to find good agreement with previous works. Different parameters involved in the calculations such as basis sets, k sampling, tip-sample distance, or temperature, among others, are discussed in detail.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data

2013

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“…Based on a self-consistent tight-binding procedure with parameters obtained from DFT, 30 Pecchia et al considered vibrational effects in octanethiols bonded to gold electrodes using NEGF and the Born approximation ͑BA͒ for the e-ph interaction. 69 Solomon et al further used this method to simulate the experimental IETS spectra of Wang et al 22,70 Sergueev et al studied a 1,4-benzenedithiolate molecule contacted by two aluminum leads. 71 This study addressed the bias dependence of the vibrational modes and e-ph couplings, but not the inelastic current itself.…”

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confidence: 99%

Inelastic transport theory from first principles: Methodology and application to nanoscale devices

et al. 2007

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We describe a first-principles method for calculating electronic structure, vibrational modes and frequencies, electron-phonon couplings, and inelastic electron transport properties of an atomic-scale device bridging two metallic contacts under nonequilibrium conditions. The method extends the density-functional codes SIESTA and TRANSIESTA that use atomic basis sets. The inelastic conductance characteristics are calculated using the nonequilibrium Green's function formalism, and the electron-phonon interaction is addressed with perturbation theory up to the level of the self-consistent Born approximation. While these calculations often are computationally demanding, we show how they can be approximated by a simple and efficient lowest order expansion. Our method also addresses effects of energy dissipation and local heating of the junction via detailed calculations of the power flow. We demonstrate the developed procedures by considering inelastic transport through atomic gold wires of various lengths, thereby extending the results presented in Frederiksen et al. ͓Phys. Rev. Lett. 93, 256601 ͑2004͔͒. To illustrate that the method applies more generally to molecular devices, we also calculate the inelastic current through different hydrocarbon molecules between gold electrodes. Both for the wires and the molecules our theory is in quantitative agreement with experiments, and characterizes the system-specific mode selectivity and local heating.

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“…1), the only added experimental requirement is the ability to cool the junction. From comparison between experiments and computations (10)(11)(12)(13)(14)(15)(16)(17), IETS is useful for characterizing numerous aspects of molecular junctions such as the actual presence of the molecule, information on the nature of the interfaces (18), the orientation of the molecule (19), and some symmetry aspects of the junction (20, 21).…”

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confidence: 99%

Tracing electronic pathways in molecules by using inelastic tunneling spectroscopy

Troisi

Beebe

Picraux

et al. 2007

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

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Using inelastic electron tunneling spectroscopy (IETS) to measure the vibronic structure of nonequilibrium molecular transport, aided by a quantitative interpretation scheme based on Green's functiondensity functional theory methods, we are able to characterize the actual pathways that the electrons traverse when moving through a molecule in a molecular transport junction. We show that the IETS observations directly index electron tunneling pathways along the given normal coordinates of the molecule. One can then interpret the maxima in the IETS spectrum in terms of the specific paths that the electrons follow as they traverse the molecular junction. Therefore, IETS measurements not only prove (by the appearance of molecular vibrational frequencies in the spectrum) that the tunneling charges, in fact, pass through the molecule, but also can be used to determine the transport pathways and how they change with the geometry and placement of molecules in junctions. molecular electronics ͉ molecular junctions ͉ molecular transport T he electron-transfer process is crucial in chemistry, materials science, condensed matter physics, and electrical engineering. Although it is always modeled either explicitly or implicitly by pathways (how electrons actually move within the molecule), there is as yet no direct measurement or observation of such pathways. The pathways idea has been present in physical organic chemistry for years in connection with reaction mechanisms and has been widely used in the interpretation of electron tunneling pathways in proteins (1), but no distinct observations have been made. The absence of direct measurement of pathways is because the measurements are usually made starting with an equilibrium structure, exciting quickly (optical spectroscopy), and then observing the new perturbed structure. Although it is instructive to observe these initial and final states, they are static snapshots and cannot capture the dynamics of the electrontransport process. In molecular transport junctions, where current is moving continuously through the molecule, the nonequilibrium inelastic electron tunneling spectroscopy (IETS) probe permits direct observation of how different modes modulate the transport and, therefore, can be used to deduce actual pathways.It is well established that tunneling electrons can lose energy through excitation of a molecular vibrational level contained within the tunnel junction (2-5). The threshold for such excitation is eV ϭ -h where V is the bias voltage and -h is the energy of the molecular vibration. Peaks in d 2 I/dV 2 versus V, or more commonly the normalized quantity (d 2 I/dV 2 )/(dI/dV) versus V, correspond to molecular vibrations. IETS has become quite popular in the field of molecular electronics over the last 3 years (6-9) and has distinguished itself as a unique spectroscopic probe of molecular junctions. Because an IET spectrum is acquired directly from the measured transport characteristics (Fig. 1), the only added experimental requirement is the ability to cool the ju...

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Understanding the inelastic electron-tunneling spectra of alkanedithiols on gold

Cited by 107 publications

References 57 publications

Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data

Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data

Inelastic transport theory from first principles: Methodology and application to nanoscale devices

Tracing electronic pathways in molecules by using inelastic tunneling spectroscopy

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