Strong electronic coupling between single C60 molecules and gold electrodes prepared by quench condensation at 4 K. A single molecule three terminal device study

Abstract

We report the first measurements of single C₆₀ molecules trapped in three terminal devices prepared by quench condensation of a gold source and drain electrode on top of an aluminium gate electrode covered with a thin oxide. Our experimental platform allows the source and drain electrodes to be fabricated on the gate oxide at low temperatures and in high vacuum. In a subsequent step, single molecules are evaporated in situ onto the surface and caught in the gap between a source and a drain electrode. This fabrication method ensures a clean contact between the molecule and the gold electrode due to the unbroken vacuum. Our measurements reveal a strong interaction between the C₆₀ molecule and the gold electrodes resulting in the absence of the Coulomb blockade effects observed by others. In addition, we observe an insignificant gate dependence but a pronounced negative differential resistance (NDR) at bias voltages from 20–50 meV. The position of the peak in the NDR shows a pronounced and universal temperature dependence for all six devices included in the study. The results are related to previous measurements in such devices which focus on the detailed nature of the contact region between the molecule and the gold electrode.