Correlation of interfacial bonding mechanism and equilibrium conductance of molecular junctions

We report theoretical investigations on the role of interfacial bonding mechanism and its resulting structures to quantum transport in molecular wires. Two bonding mechanisms for the Au-S bond in an Au(111)/1,4-benzenedithiol(BDT)/Au(111) junction were identified by ab initio calculation, confirmed by a recent experiment, which, we showed, critically control charge conduction. It was found, for Au/ BDT/Au junctions, the hydrogen atom, bound by a dative bond to the Sulfur, is energetically non-dissociative after the interface formation. The calculated conductance and junction breakdown forces of H-non-dissociative Au/BDT/Au devices are consistent with the experimental values, while the H-dissociated devices, with the interface governed by typical covalent bonding, give conductance more than an order of magnitude larger. By examining the scattering states that traverse the junctions, we have revealed that mechanical and electric properties of a junction have strong correlation with the bonding configuration. This work clearly demonstrates that the interfacial details, rather than previously believed many-body effects, is of vital importance for correctly predicting equilibrium conductance of molecular junctions; and manifests that the interfacial contact must be carefully understood for investigating quantum transport properties of molecular nanoelectronics.Comment: 18 pages, 6 figures, 2 tables, to be appeared in Frontiers of Physics 9(6), 780 (2014

Two-directional N2 desorption in thermal dissociation of N2O on Rh(110), Ir(110), and Pd(110) at low temperatures

Two-directional N2 desorption was found in N2O dissociation on Rh(110), Ir(110), and Pd(110) below 160 K by angle-resolved thermal desorption. N2O(a) is mostly dissociated during heating procedures, emitting N2(g) and leaving O(a). N2 showed four desorption peaks in the temperature range of 110–200 K. One of them commonly showed a cosine distribution, whereas the others sharply collimated off the surface normal in the plane along the [001] direction. The collimation angle was about 70° on Rh(110), 65° on Ir(110), and 43°–50° on Pd(110). A high-energy-atom assisted desorption model was proposed for N2 inclined emission

CO2 desorption dynamics on specified sites and surface phase transitions of Pt(110) in steady-state CO oxidation

The spatial and velocity distributions of desorbing product CO2 were studied in the steady-state CO oxidation on Pt(110) by cross-correlation time-of-flight techniques. The surface structure transformation was monitored by LEED in the course of the catalyzed reaction. In the active region, where the surface was highly reconstructed into the missing-row form, CO2 desorption split into two directional lobes collimated along 25° from the surface normal in the plane including the [001] direction, indicating the CO2 formation on inclined (111) terraces. The translational temperature was maximized at the collimation angle, reaching about 1900 K. On the other hand, CO2 desorption sharply collimated along the surface normal at CO pressures where (1×2) domains disappeared. The distribution change from an inclined desorption to a normally directed one was abrupt at the CO pressure where the half-order LEED spot already disappeared. This switching point was more sensitive than LEED towards the complete transformation from (1×2) to (1×1) and was then used to construct a surface phase diagram for working reaction sites in the pressure range from 1×10–7 Torr to 1×10–4 Torr of oxygen. The turnover frequency of CO2 formation was enhanced on (1×2) domains with increasing CO pressure