Highly Conductive Molecular Junctions Based on Direct Binding of Benzene to Platinum Electrodes

Highly conductive molecular junctions were formed by direct binding of benzene molecules between two Pt electrodes. Measurements of conductance, isotopic shift in inelastic spectroscopy, and shot noise compared with calculations provide indications for a stable molecular junction where the benzene molecule is preserved intact and bonded to the Pt leads via carbon atoms. The junction has a conductance comparable to that for metallic atomic junctions (around $0.1–1G_0$), where the conductance and the number of transmission channels are controlled by the molecule’s orientation at different interelectrode distances.

Figure 1

Conductance histograms (normalized to the area under the curves) for a Pt junction (black), and for Pt after introducing benzene (filled). Each conductance histogram is constructed from more than 3000 conductance traces recorded with a bias of 0.1 V during repeated breaking of the contact.

Figure 2

(a) Differential conductance (top) and its derivative (bottom) for Pt contact after introduction of benzene taken at a zero bias conductance of $0.3G_0$. (b) Distribution of vibration energy at low conductance regime.

Figure 3

Shot noise as a function of the bias current across the $\mathrm{Pt}/\mathrm{\text{benzene}}$ junction. The zero bias conductance [$G(0)$] for this junction is $1.08G_0$ (filled squares), $0.71G_0$ (hollow triangles), and $0.2G_0$ (filled circles). Fitting the data with theory (curves) gives the decomposition of the total transmission in terms of transmission probabilities, ${\tau }_i$, of the conduction channels (where $G=\sum _i{\tau }_i{G}_0$) as shown in the inset.

Figure 4

Simulation of the stretching process of a $\mathrm{Pt}/\mathrm{\text{benzene}}$ junction. (a) Total conductance, $G$, the contribution of the individual conduction channels, $G_i=G_0{\tau }_i$, and the change of the total energy, $E$, as a function of the distance between the Pt tip atoms. (b) Stretching dependence of the energy of the benzene vibration modes in the range between 0 and 105 meV. The translation modes are plotted as solid lines, the rotation modes as dashed lines and the stretch modes as dotted lines. The character of the modes is indicated by symbols, where benzene is represented by a large circle, the Pt atoms by two small circles and arrows depicted the motion of the molecule.