Inelastic current-voltage characteristics of atomic and molecular junctions

Nano Letters

Volumn 4, Issue 9, 2004, Pages 1709-1712

  Chen, Yu Chang ^a   Zwolak, Michael ^b   Di Ventra, Massimiliano ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

GOLD;

ARTICLE; ATOM; CALCULATION; ELASTICITY; ELECTRIC CURRENT; ELECTRIC POTENTIAL; ELECTRODE; EXPERIMENT; GEOMETRY; MOLECULE; STRUCTURE ANALYSIS;

EID: 4644363101     PISSN: 15306984     EISSN: None     Source Type: Journal    
DOI: 10.1021/nl0490927     Document Type: Article

References (24)

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16. Since we are in the regime of weak electron-phonon coupling we neglect the elastic phonon renormalization of the electronic spectrum [see, e.g., Mahan, G. D. Many Particle Physics, 2nd ed.; Plenum Publishers: New York, 1990; p 285].
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19. A quantitative way of distinguishing between longitudinal versus transverse character of each mode is to sum up the absolute values of all the z-component (i.e., along the current flow) matrix elements of A.
20. We have employed Hartree-Fock total energy calculations [see, e.g., Boatz, J. A.; Gordon, M. S. J. Phys. Chem, 1989, 93, 1819] to evaluate the vibrational modes of the single-molecule junctions and the gold point contact. For these calculations, the assumed surface orientation is [111], represented by a triangular pad of gold atoms with infinite mass (see insets of Figures 1 and 2). The structures were relaxed starting from an initial geometry where the single gold atom of the point contact faces the center of the triangular pad at a distance of 2.3 Å; and for the single-molecule junction with symmetric contacts the initial S-surface distance is 2.4 Å. In the case of asymmetric contacts, the S atom on one side of the junction is bonded to a H atom (see insets of Figure 3). This thiol termination is assumed to be far from the nearby surface so that the modes of this structure are not influenced by the gold atoms of the surface.
21. Note that the inelastic correction to the current is actually negative. For convenience we plot in this paper the absolute value of this correction.
22. In the molecular junction cases, the dominant net contribution to the electron-phonon coupling is from the S atoms and the adjacent C atoms (i.e., the two C atoms that form a straight line with the S atoms). This implies that those modes that do not have large displacements of these atoms along the z direction will contribute negligibly to the inelastic current, even if the global character of the mode is longitudinal, as inferred from the procedure outlined in ref 15. This is, e.g., the case for the mode at about 90 meV shown schematically in Figure 2.
23. A broadening of 1 meV is introduced in all calculations to make the second derivative of the inelastic current as a function of bias finite at the conduction jumps.
24. 10 The corresponding resistance for the asymmmetric case is about an order of magnitude larger. However, to facilitate the comparison with the previous case, we have assumed in this calculation the same coupling constants, partial density of states, and unperturbed current as for the symmetric junction case.