Microscopic study of electrical transport through individual molecules with metallic contacts. II. Effect of the interface structure

We investigate the effect on molecular transport due to the different structural aspects of metal-molecule interfaces. The example system chosen is the prototypical molecular device formed by sandwiching the phenyl dithiolate molecule (PDT) between two gold electrodes with different metal-molecule distances, atomic structure at the metallic surface, molecular adsorption geometry, and with an additional hydrogen end atom. We find the dependence of the conductance on the metal-molecule interface structure is determined by the competition between the modified metal-molecule coupling and the corresponding modified energy level lineup at the molecular junction. Due to the close proximity of the highest occupied molecular orbital (HOMO) of the isolated PDT molecule to the gold Fermi level, this leads to the counterintuitive increase of conductance with increasing top-metal\char21{}molecule distance that decreases only after the energy level line up saturates to that of the molecule chemisorbed on the substrate. We find that the effect on molecular transport from adding an apex atom onto the surface of a semi-infinite electrode is similar to that from increasing the metal-molecule distance. The similarity is reflected in both the charge and potential response of the molecular junction and consequently also in the nonlinear transport characteristics. Changing the molecular adsorption geometry from a threefold to a top configuration leads to slightly favorable energy level lineup for the molecular junction at equilibrium and consequently larger conductance, but the overall transport characteristics remain qualitatively the same. The presence of an additional hydrogen end atom at the top-metal\char21{}molecule contact substantially affects the electronic processes in the molecular junction due to the different nature of the molecular orbitals involved and the asymmetric device structure, which leads to reduced conductance and current. The results of the detailed microscopic calculation can all be understood qualitatively from the equilibrium energy level lineup and the knowledge of the voltage drop across the molecular junction at finite bias voltages.

[1]  M. Ratner,et al.  Microscopic study of electrical transport through individual molecules with metallic contacts. I. Band lineup, voltage drop, and high-field transport , 2003, cond-mat/0303179.

[2]  J. Naciri,et al.  Metal-molecule contacts and charge transport across monomolecular layers: measurement and theory. , 2002, Physical review letters.

[3]  Hongkun Park,et al.  Kondo resonance in a single-molecule transistor , 2002, Nature.

[4]  Jonas I. Goldsmith,et al.  Coulomb blockade and the Kondo effect in single-atom transistors , 2002, Nature.

[5]  Zhenan Bao,et al.  Conductance of small molecular junctions. , 2002, Physical review letters.

[6]  S. Datta,et al.  First-principles based matrix Green's function approach to molecular electronic devices: general formalism , 2001, cond-mat/0112136.

[7]  John K. Tomfohr,et al.  Reproducible Measurement of Single-Molecule Conductivity , 2001, Science.

[8]  S. Datta,et al.  Charge transfer and “band lineup” in molecular electronic devices: A chemical and numerical interpretation , 2001 .

[9]  R Ochs,et al.  Driving current through single organic molecules. , 2001, Physical review letters.

[10]  J. Gimzewski,et al.  Electronics using hybrid-molecular and mono-molecular devices , 2000, Nature.

[11]  Supriyo Datta,et al.  Molecular conductance spectroscopy of conjugated, phenyl-based molecules on Au(111): the effect of end groups on molecular conduction , 2000 .

[12]  Lang,et al.  First-principles calculation of transport properties of a molecular device , 2000, Physical review letters.

[13]  Chen,et al.  Large On-Off Ratios and Negative Differential Resistance in a Molecular Electronic Device. , 1999, Science.

[14]  Robert M. Metzger,et al.  ELECTRICAL RECTIFICATION BY A MOLECULE : THE ADVENT OF UNIMOLECULAR ELECTRONIC DEVICES , 1999 .

[15]  M. Reed.  Molecular-scale electronics , 1999, Proc. IEEE.

[16]  B. Stipe,et al.  Localization of Inelastic Tunneling and the Determination of Atomic-Scale Structure with Chemical Specificity , 1999 .

[17]  S. Datta,et al.  Negative differential resistance in the scanning-tunneling spectroscopy of organic molecules , 1998, cond-mat/9811402.

[18]  Mark A. Ratner,et al.  Molecule-interface coupling effects on electronic transport in molecular wires , 1998 .

[19]  S. Datta,et al.  CONDUCTANCE SPECTRA OF MOLECULAR WIRES , 1998 .

[20]  Ho,et al.  Single-molecule vibrational spectroscopy and microscopy , 1998, Science.

[21]  T. D. Dunbar,et al.  Insertion, Conductivity, and Structures of Conjugated Organic Oligomers in Self-Assembled Alkanethiol Monolayers on Au{111} , 1998 .

[22]  M. Reed,et al.  Conductance of a Molecular Junction , 1997 .

[23]  Supriyo Datta,et al.  Current-Voltage Characteristics of Self-Assembled Monolayers by Scanning Tunneling Microscopy , 1997 .

[24]  N. D. Lang.  Negative differential resistance at atomic contacts , 1997 .

[25]  G. Whitesides,et al.  Reduction in the size of features of patterned SAMs generated by microcontact printing with mechanical compression of the stamp , 1995 .

[26]  P. Avouris,et al.  Negative Differential Resistance on the Atomic Scale: Implications for Atomic Scale Devices , 1989, Science.

[27]  R. O. Jones,et al.  The density functional formalism, its applications and prospects , 1989 .

[28]  Wang,et al.  Jellium work function for all electron densities. , 1988, Physical review. B, Condensed matter.

[29]  A. Becke,et al.  Density-functional exchange-energy approximation with correct asymptotic behavior. , 1988, Physical review. A, General physics.

[30]  Harold Basch,et al.  Compact effective potentials and efficient shared‐exponent basis sets for the first‐ and second‐row atoms , 1984 .

[31]  Paul Baybutt,et al.  Ab initio effective core potentials: Reduction of all-electron molecular structure calculations to calculations involving only valence electrons , 1976 .

[32]  B. Lundqvist,et al.  Exchange and correlation in atoms, molecules, and solids by the spin-density-functional formalism , 1976 .

[33]  M. Tsukada,et al.  First-principles theory of scanning tunneling microscopy , 1991 .

[34]  W. R. Wadt,et al.  Ab initio effective core potentials for molecular calculations , 1984 .