UC Berkeley

The ability to control nanoscale molecular motion with device-scale electric fields opens many exciting possibilities for nanotechnology. Collective motion of molecules can be used to assemble new nanostructures, induce mass and charge transport, transform device properties by surface modifications, and can potentially be used as a tool for constructing nanoscale machines. As components for electromechanical devices approach the nanometer length scale, how they interact with local electric fields and currents becomes increasingly important. This dissertation focuses on exploring how macroscopic electric fields and currents can manipulate and probe the collective motion of adsorbed molecules on gate-tunable devices.

The movement of F4TCNQ molecules on a graphene field-effect transistor was controlled by the application of a gate voltage and source-drain current, and concurrently imaged using a scanning tunneling microscope. Various field-induced molecular phenomena were investigated on the device, including gate-tunable surface molecular concentrations, gate-tunable molecular phase transitions, gate-dependent molecular diffusion, molecule density-dependent current transport, and current-induced electromigration. These phenomena provide insight into how nanoscale molecular motion can be controlled by external electric fields, and how force and momentum are transmitted between electrons and adsorbates under non-equilibrium conditions.