22-32-201
Vittorio Bellani, Department of Physics, University of Pavia
Abstract
Controlling surface diffusion on two-dimensional devices offers new pathways for manipulating nanoscale processes such as nano-assembly, thin-film growth, and catalysis. Here, we demonstrate electrostatic control of the surface diffusion of F4TCNQ molecules on clean graphene field-effect transistors (FETs) [1]. By tuning the back-gate voltage (Vg), molecular adsorbates are reversibly switched between neutral and negatively charged states, resulting in pronounced changes in their diffusion behavior. Scanning tunneling microscopy measurements show that the diffusivity of neutral molecules decreases rapidly with decreasing Vg and involves significant rotational diffusion. In contrast, negatively charged molecules exhibit nearly gate-independent diffusivity over a broad Vg range and diffuse predominantly through translational motion. First-principles density functional theory calculations reveal that these distinct diffusion mechanisms originate from fundamentally different energy landscapes for neutral and charged molecules, in agreement with experiment. The ability to electrostatically tune diffusion barriers establishes graphene FETs as active platforms for switching molecular diffusion.
