Mapping the intramolecular contributions to the inelastic electron tunneling signal of a molecular junction (original) (raw)
Related papers
Inelastic electron tunneling spectroscopy in molecular junctions: Peaks and dips
The Journal of Chemical Physics, 2004
We study inelastic electron tunneling through a molecular junction using the nonequilibrium Green's function formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage ⌽ when plotted against ⌽. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative dI/d⌽ and may show phonon sidebands. The dependence of the observed vibrationally induced lineshapes on the junction characteristics, and the linewidth associated with these features are also discussed.
On the Line Widths of Vibrational Features in Inelastic Electron Tunneling Spectroscopy
Nano Letters, 2004
Green function (NEGF) formalism is used to analyze the effect of the electron−phonon interaction on the tunneling spectra. We find that IETS line shapes are sensitive to junction parameters, in particular the position of the bridge electronic resonance and the molecule−lead coupling that may be controlled experimentally. Intrinsic IETS line widths are found to be dominated by the coupling of molecular vibrations to electron− hole pairs excitations in the lead(s) to which the molecule is bonded chemically. While estimated widths are of similar order of magnitude as observed in the recent experiment of Wang et al. , one cannot rule out inhomogeneous contribution to the line width in this monolayer experiment.
Electronic Resonance and Symmetry in Single-Molecule Inelastic Electron Tunneling
Physical Review Letters, 2000
Inelastic electron tunneling spectroscopy and microscopy with a scanning tunneling microscope revealed two vibrational modes showing a decrease in conductance at 682.0 and 638.3 mV sample bias for single oxygen molecules chemisorbed on the fourfold hollow sites of Ag(110) surface at 13 K. The spatial distribution of the vibrational intensities exhibited p g-orbital (perpendicular to surface) symmetry of O 2 with the molecular axis along the [001] direction. These results are attributed to resonant inelastic electron tunneling.
Physical review letters, 2017
Here we show scanning tunneling microscopy (STM), noncontact atomic force microscopy (AFM), and inelastic electron tunneling spectroscopy (IETS) measurements on an organic molecule with a CO-terminated tip at 5 K. The high-resolution contrast observed simultaneously in all channels unambiguously demonstrates the common imaging mechanism in STM/AFM/IETS, related to the lateral bending of the CO-functionalized tip. The IETS spectroscopy reveals that the submolecular contrast at 5 K consists of both renormalization of vibrational frequency and variation of the amplitude of the IETS signal. This finding is also corroborated by first principles simulations. We extend accordingly the probe-particle AFM/STM/IETS model to include these two main ingredients necessary to reproduce the high-resolution IETS contrast. We also employ the first principles simulations to get more insight into a different response of frustrated translation and rotational modes of the CO tip during imaging.
Resonant inelastic tunneling in molecular junctions
Physical Review B, 2006
Within a phonon-assisted resonance level model we develop a self-consistent procedure for calculating electron transport currents in molecular junctions with intermediate to strong electron-phonon interaction. The scheme takes into account the mutual influence of the electron and phonon subsystems. It is based on the second order cumulant expansion, used to express the correlation function of the phonon shift generator in terms of the phonon momentum Green function. Equation of motion ͑EOM͒ method is used to obtain an approximate analog of the Dyson equation for the electron and phonon Green functions in the case of manyparticle operators present in the Hamiltonian. To zero order it is similar in particular cases ͑empty or filled bridge level͒ to approaches proposed earlier. The importance of self-consistency in resonance tunneling situations ͑partially filled bridge level͒ is stressed. We confirm, even for strong vibronic coupling, a previous suggestion concerning the absence of phonon sidebands in the current versus gate voltage plot when the source-drain voltage is small ͓Mitra et al., Phys. Rev. B 69, 245302 ͑2004͔͒.
Physical Review Letters, 2010
We investigate inelastic electron tunneling spectroscopy (IETS) for alkanethiol self-assembled monolayers (SAM) with a scanning tunneling microscope and compare it to first-principles calculations. Using a combination of partial deuteration of the molecule and high-resolution measurements, we identify and differentiate between methyl (CH 3 ) and methylene (CH 2 ) groups and their symmetric and asymmetric C-H stretch modes. The calculations agree quantitatively with the measured IETS in producing the weight of the symmetric and asymmetric C-H stretch modes while the methylene stretch mode is largely underestimated. We further show that inelastic intermolecular scattering is important in the SAM by plotting the theoretical current densities.
A theoretical model for single-molecule incoherent scanning tunneling spectroscopy
Journal of Physics: Condensed Matter, 2008
Single molecule scanning tunneling spectroscopy (STS), with dephasing due to elastic and inelastic scattering, is of some current interest. Motivated by this, we report an extended Hückel theory (EHT) based mean-field Non-equilibrium Green's function (NEGF) transport model with electron-phonon scattering treated within the self-consistent Born approximation (SCBA). Furthermore, a procedure based on EHT basis set modification is described. We use this model to study the effect of the temperature dependent dephasing, due to low lying modes in far-infrared range for whichhω ≪ k B T , on the resonant conduction through highest occupied molecular orbital (HOMO) level of a phenyl dithiol molecule sandwiched between two fcc-Au(111) contacts. Furthermore, we propose to include dephasing in room temperature molecular resonant conduction calculations.