(Invited) A Single-Molecule Spin-Based Transistor

Abstract

Single molecule devices are of great interest for what they reveal about fundamental aspects of electron transport and metal-molecule interactions. They represent the ultimate level of miniaturization in molecular electronics and are also of potential interest in sensor applications. We have used an electrochemical approach to realize a single molecule transistor based on 4,4′-bipyridine contacted by Ni. The top and bottom Ni contacts are an insulated Ni STM tip and an electrodeposited Ni film respectively, which are maintained free of oxide by being held in an aqueous electrolyte under potential control. The 4,4′-bipyridine molecules are initially present in the electrolyte and contacted using the STM break junction method. From numerous repeated experiments we build up a histogram of the measured conductance. This conductance depends strongly on the potential of tip and substrate relative to the reference electrode. This is a manifestation of electrostatic gating and shows that the device functions as a transistor. Remarkably, it shows a significantly higher gain than a similar transistor with Au electrodes. Calculations show that the current in the Ni-4,4′-bipyridine-Ni transistor is highly spin-polarized and therefore the device represents a true spin-based single molecule transistor.