Low-bias conductance of single benzene molecules contacted by direct Au–C and Pt–C bonds

Ma, Guohong; Shen, Xueju; Sun, Lili; Zhang, Ruoxing; Peng, Wei; Sanvito, Stefano; Hou, Shimin

doi:10.1088/0957-4484/21/49/495202

Cited by 28 publications

(18 citation statements)

References 45 publications

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“…The large broadening indicates strong hybridization between the valence orbitals of Pt to the conductive molecular orbitals. This observation is supported by former calculations that found a significant hybridization between the d-orbitals of Pt and the molecular π-orbitals in similar systems 27,28 . In the case of Ag, due to insignificant contribution from d-orbitals around E F , the transmission is mostly determined by the less efficient hybridization of the s valence orbital with the molecular π-orbitals and thus the junction preserves better the molecular character.…”

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confidence: 79%

Conductance saturation in a series of highly transmitting molecular junctions

et al. 2016

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Note:The published version in Nature Materials contains an extended manuscript and comprehensive supplementary information. . One of the primary experimental methods to reveal the mechanisms behind electronic transport through metal-molecule interfaces is the study of conductance as a function of molecule length in molecular junctions [4][5][6][7][8][9][10][11][12][13][14] . Previous studies focused on transport governed either by coherent tunneling or hopping, both at low conductance. However, the upper limit of conductance across molecular junctions has not been explored, despite the great potential for efficient information transfer, charge injection and recombination processes at high conductance. Here, we study the conductance properties of highly transmitting metal-molecule-metal interfaces, using a series of single-molecule junctions based on oligoacenes with increasing length. We find that the conductance saturates at an upper limit where it is independent of molecule length. Furthermore, we show that this upper limit can be controlled by the character of the orbital hybridization at the metal-molecule interface. Using two prototype systems, in which the molecules are contacted by either Ag or Pt electrodes, we reveal two different origins for the saturation of conductance. In the case of Ag-based molecular junctions, the conductance saturation is ascribed to a competition between energy level alignment and level broadening, while in the case of Pt-based junctions, the saturation is attributed to a band-like transport. The results are explained by an intuitive model, backed by ab-initio transport calculations. Our findings shed light on the mechanisms that constrain the conductance at the high transmission limit, providing guiding principles for the design of highly conductive metal-molecule interfaces.In order to study the conductance characteristics of highly transmitting molecular junctions, strong electronic coupling is required between the molecule and the electrodes, as well as within the molecule itself 10,11,15,16 . These conditions are achieved in this work by direct hybridization between the π-orbitals of the oligoacene molecules and the frontier orbitals of the metal electrodes, without employing anchoring groups such as thiols that can act as spacers between the orbitals of the molecular backbone and the frontier orbitals of the metal 13,15 . The oligoacenes (Fig. 1a) are linear π-conjugated molecules that can be viewed as short graphene nanoribbons 17 , whose electronic structure is subject to an ongoing research 18 . We study the evolution of conductance as a function of molecule length and compare the conductance characteristics of

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confidence: 79%

Conductance saturation in a series of highly transmitting molecular junctions

et al. 2016

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“…The results obtained in this work for these two chains agree with the experimental findings, the p X1 is better conductor than p P, with a decrease of its electric conductance as the number of units increases. As a remarkable finding, we must also mention that for n = 1, the occupied‐virtual electron transfer in p P is mainly due to the coupling between orbitals of sigma symmetry, in agreement with the results obtained by Green functions' techniques . However, the main EDOs correspond to π symmetry MOs for n > 1, this has not been explored yet using Green functions' techniques.…”

Section: Resultsmentioning

confidence: 99%

Analyzing the electric response of molecular conductors using “electron deformation” orbitals and occupied‐virtual electron transfer

Mandado

Ramos‐Berdullas

2014

J Comput Chem

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The concept of "electron deformation orbitals" (EDOs) is used to investigate the electric response of conducting metals and oligophenyl chains. These orbitals and their eigenvalues are obtained by diagonalization of the deformation density matrix (difference between the density matrices of the perturbed and unperturbed systems) and can be constructed as linear combinations of the unperturbed molecular orbitals within "frozen geometry" conditions. This form of the EDOs allows calculating the part of the electron deformation density associated to an effective electron transfer from occupied to virtual orbitals (valence to conduction band electron transfer in the band model of conductivity). It is found that the "electron deformation" orbitals pair off, displaying the same eigenvalue but opposite sign. Each pair represents an amount of accumulation/depletion of electron charge at different molecular regions. In the oligophenyl systems investigated only one pair contributes effectively to the charge flow between molecular ends, resulting from the promotion of electrons from occupied orbitals to close in energy virtual orbitals of appropriate symmetry and overlapping. Analysis of this pair along explains the differences in conductance of olygophenyl chains based on phenyl units.

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“…4,5 For the junction conductance, it will decrease following a cos 2 (h) law, 18,46 as the electron transfer rates scales as the square of the p-overlap, and this has been proved by experiment. 7,[47][48][49] For our BCB system, the fitting function and corresponding curve are shown in Fig. 10.…”

Section: The Cos 2 (H) Relation and Its Modulationmentioning

confidence: 99%