Visualizing Dynamic Molecular Manipulation on a Graphene Field Effect Transistor

Harnessing electric fields at the nanoscale to manipulate molecular motion unlocks new prospects for nanotechnology. By coordinating molecular movements, we can build novel nanostructures, promote mass transport, and alter device characteristics. To fully understand these dynamics, it is essential to directly track individual molecular motion while simultaneously probing the local electronic structure. In this presentation, I will introduce an approach for manipulating the charge state and spatial distribution of individual molecular adsorbates on a graphene field-effect transistor (FET) using scanning tunneling microscopy. Once charged, the molecules behave as surface ions whose behavior can be tuned through the electrochemical potential of the device. Applying a gate electric field drives F4TCNQ molecules on graphene to switch between a charge-neutral self-organized solid phase and a negatively charged correlated liquid phase. This change in molecular organization also modifies the device conductivity, revealing Fermi-level pinning by molecular orbitals. Furthermore, we created stop-motion movies of molecular redistribution by applying brief current pulses through the graphene FET. These measurements allow us to visualize single-molecule diffusion and non-equilibrium phase-transition dynamics in real space. Our observations provide new insights into controlling molecular assemblies with external electric fields and into the relationship between molecular charge states, intermolecular interactions, and surface diffusion at the nanoscale.

Nano Lett. 2021, 21, 20, 8770–8776

Adv. Mater. 2023, 35, 2300542.

ACS Nano 2024, 18, 35, 24262–24268