Revealing the Role of Anchoring Groups in the Electrical Conduction Through Single‐Molecule Junctions (original) (raw)
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Nano Letters, 2008
We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes. One derivative has additional methylene groups separating the thiols from the delocalized π-electron system. The insertion of methylene groups changes the open state conductance by 3−4 orders of magnitude and changes the transport mechanism from a coherent regime with finite zero-bias conductance to sequential tunneling and Coulomb blockade behavior.
Physical Review Letters, 2002
We present an atomistic theory of electronic transport through single organic molecules that reproduces the important features of the current-voltage (I-V) characteristics observed in recent experiments. We trace these features to their origin in the electronic structure of the molecules and their local atomic environment. We demonstrate how conduction channels arise from the molecular orbitals and elucidate the contributions of individual orbitals to the current. We find that in thiol-bridged aromatic molecules many molecular orbitals contribute to a single conduction channel and discuss the implications of this result for the design of molecular devices.
The Journal of Chemical Physics, 1999
To study the electronic transport of molecular wire circuits, we present a time-independent scattering formalism which includes an ab initio description of the molecular electronic structure. This allows us to obtain the molecule-metal coupling description at the same level of theory. The conductance of junction ␣, ␣Ј xylyl dithiol and benzene-1,4-dithiol between gold electrodes is obtained and compared with available experimental data. The conductance depends dramatically on the relative position of the Fermi energy of the metal with respect to the molecular levels. We obtain an estimate for the injecting energy of the electron onto the molecule by varying the distance between the molecule and the attached gold clusters. Contrary to the standard assumption, we find that the injecting energy lies close to the molecular highest occupied molecular orbital, rather than in the middle of the gap; it is just the work function of the bulk metal. Finally, the adequacy of the widely used extended Hückel method for conductance calculations is discussed.
Physical Review B, 2012
In this first-principles study, we present density-functional calculations of the electronic structures and electron transport properties of organic molecular junctions with several anchoring groups containing atoms with different electronegativities, i.e., benzenediboronate (BDB), benzenedicarboxylate (BDC), and dinitrobenzene (DNB) molecular junctions sandwiched between two Cu(110) electrodes. The electronic-structure calculations exhibit a significant difference in the density of states not only at the anchoring groups but also at the aromatic rings of the molecular junctions, suggesting that the electron transport is specific for each system. Our transport calculations show that the BDB and DNB molecular junctions have finite electron transmissions at the zero-bias limit while the BDC molecular junction has a negligible electron transmission. Moreover, for the BDB and DNB systems, the electron transmission channels around the Fermi energy reveal fingerprint features, which provide specific functionalities for the molecular junctions. Therefore, our theoretical results demonstrate the possibility to precisely tune the electron transport properties of molecular junctions by engineering the anchoring groups at the single-atom level.
Journal of the American Chemical Society, 2012
We study the effects of molecular structure on the electronic transport and mechanical stability of single-molecule junctions formed with Au point contacts. Two types of linear conjugated molecular wires are compared: those functionalized with methylsulfide or amine aurophilic groups at (1) both or (2) only one of its phenyl termini. Using scanning tunneling and atomic force microscope break-junction techniques, the conductance of mono-and difunctionalized molecular wires and its dependence on junction elongation and rupture forces were studied. Charge transport through monofunctionalized wires is observed when the molecular bridge is coupled through a S−Au donor− acceptor bond on one end and a relatively weak Au−π interaction on the other end. For monofunctionalized molecular wires, junctions can be mechanically stabilized by installing a second aurophilic group at the meta position that, however, does not in itself contribute to a new conduction pathway. These results reveal the important interplay between electronic coupling through metal−π interactions and quantum mechanical effects introduced by chemical substitution on the conjugated system. This study affords a strategy to deterministically tune the electrical and mechanical properties through molecular wires.
Transport properties of molecular junctions from many-body perturbation theory
Physical Review B, 2011
The conductance of single molecule junctions is calculated using a Landauer approach combined to many-body perturbation theory (MBPT) to account for electron correlation. The mere correction of the density-functional theory eigenvalues, which is the standard procedure for quasiparticle calculations within MBPT, is found not to affect noticeably the zero-bias conductance. To reduce it and so improve the agreement with the experiments, the wavefunctions also need to be updated by including the non-diagonal elements of the self-energy operator. PACS numbers: 85.65.+h, Most recent theoretical studies of coherent transport in nanojuctions are based on a Landauer approach [1], in which the electron interactions are treated at a simplified mean-field level using density-functional theory (DFT). While this approach has proven quite successful for systems having a strong coupling between the molecule and the metallic leads , it overestimates the zero-bias conductance of weakly coupled systems (by up to 3 orders of magnitude) compared to experimental measurements . Many explanations have been proposed for such a discrepancy. For example, arguing an uncertainty over the experimental junction structure, the sensitiveness to the contact geometry was investigated .
Influence of functional groups on charge transport in molecular junctions
The Journal of Chemical Physics, 2008
Using density functional theory (DFT), we analyze the influence of five classes of functional groups, as exemplified by NO2, OCH3, CH3, CCl3, and I, on the transport properties of a 1,4-benzenedithiolate (BDT) and 1,4-benzenediamine (BDA) molecular junction with gold electrodes. Our analysis demonstrates how ideas from functional group chemistry may be used to engineer a molecule's transport properties, as was shown experimentally and using a semiempirical model for BDA [Nano Lett. 7, 502 (2007)]. In particular, we show that the qualitative change in conductance due to a given functional group can be predicted from its known electronic effect (whether it is σ/π donating/withdrawing). However, the influence of functional groups on a molecule's conductance is very weak, as was also found in the BDA experiments. The calculated DFT conductances for the BDA species are five times larger than the experimental values, but good agreement is obtained after correcting for self-interaction and image charge effects. arXiv:0802.2069v1 [cond-mat.mtrl-sci]
Potential-Induced High-Conductance Transport Pathways through Single-Molecule Junctions
Journal of the American Chemical Society, 2019
Employing single molecules as electronic circuit building blocks is one promising approach to electronic device miniaturization. We report single-molecule junction formation where the orientation of molecules can be controlled externally by the working electrode potential. The scanning tunneling microscopy break junction (STM-BJ) method is used to bridge tetrafluoroterephthalic acid (TFTPA) and terephthalic acid (TPA) molecules between the Au(111) electrode and the STM tip to measure the single-molecule conductance through the junction. When the Au(111) electrode is at negative potentials (with respect to the zero-charge potential), a highly ordered and flat-oriented superstructure forms, allowing for direct contact between the π system of the benzene ring of the molecules and the Au(111) electrode, leading to junction formation with no anchoring group involvement. Our first-principles nonequilibrium Green's function (NEGF) computation shows a flat configuration yields a conductance that is 3 orders of magnitude larger than for a molecule vertically connected to the electrodes via anchoring groups. Conductances of 0.24 ± 0.04 and 0.22 ± 0.02 G 0 are experimentally measured with the flat configurations of TFTPA and TPA, respectively. These values are at least 2 orders of magnitude higher than the experimental values previously reported for the conductance of TPA bridged through carboxylic acid anchoring groups (3.8 × 10 −4 −3.2 × 10 −3 G 0). In contrast, a positively charged surface triggers an order−disorder transition eliminating the high-conductance states, most likely because the formation of the flatoriented junction is prevented. The dependence of TFTPA conductance on the electrode potential (electrode Fermi level) suggests a LUMO mediated transport mechanism. Calculation confirms the lack of an effect of the addition of an electronwithdrawing group are investigated.