Gate-Tunable Conductivity and Impurity Scattering in Molecule-Decorated Graphene Devices

We investigate how molecular adsorbates influence charge transport in gate-tunable graphene field-effect transistors. Using scanning tunneling microscopy and transport measurements performed on F4TCNQ-decorated graphene, we directly correlate nanoscale molecular configurations with macroscopic conductivity. The experiments reveal strong asymmetry between electron and hole conduction and a pronounced deviation from the carrier-density dependence expected for pristine graphene. Theoretical analysis shows that these effects arise from charge-transfer-induced scattering and hybridization between molecular orbitals and graphene's Dirac bands. By systematically varying the gate voltage and molecular coverage, we demonstrate tunable transitions between Fermi level pinning and resonant impurity scattering regimes, linking molecular adsorption, charge state, and device performance. Together, these findings provide a microscopic picture of how individual molecular impurities reshape electronic transport in two-dimensional materials, offering key insights into the coupling between molecular orbitals and graphene's electronic structure.