Kavli Affiliate: Michael F. Crommie
| First 5 Authors: Franklin Liou, Hsin-Zon Tsai, Andrew S. Aikawa, Kyler C. Natividad, Eric Tang
| Summary:
The spatial arrangement of adsorbates deposited onto a clean surface in
vacuum typically cannot be reversibly tuned. Here we use scanning tunneling
microscopy to demonstrate that molecules deposited onto graphene field-effect
transistors exhibit reversible, electrically-tunable surface concentration.
Continuous gate-tunable control over the surface concentration of charged
F4TCNQ molecules was achieved on a graphene FET at T = 4.5K. This capability
enables precisely controlled impurity doping of graphene devices and also
provides a new method for determining molecular energy level alignment based on
the gate-dependence of molecular concentration. The gate-tunable molecular
concentration can be explained by a dynamical molecular rearrangement process
that reduces total electronic energy by maintaining Fermi level pinning in the
device substrate. Molecular surface concentration in this case is fully
determined by the device back-gate voltage, its geometric capacitance, and the
energy difference between the graphene Dirac point and the molecular LUMO
level.
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