Transport properties of a biphenyl-based molecular junction system-the electrode metal dependence.

We investigate the transport properties of a biphenyl-dithiol molecule sandwiched between electrodes made of metal Y (Y = Cu, Ag and Au) using the non-equilibrium Green's function method based on a density functional theory. The electrode metal Y has an influence on the coupling between the molecule and electrodes, and thus on the transmission peak height. For the transmission T(Y) at the Fermi energy, we obtain T(Cu)∼T(Ag)<T(Au). As a result, the current value at low bias voltage for the junction system with Ag or Cu electrodes is smaller than that for Y = Au. At high bias voltage, on the other hand, the current value of an Ag electrode system becomes larger than the others due to the higher transmission peak around -1.5 eV below the Fermi energy. Besides this, it is shown that the transmission peak value for all the electrode metals can be expressed generally as a function of a ratio of the coupling between the two phenyl rings to the peak width of the projected density of states with respect to a corresponding molecular orbital.