Department of Physics, University of California, Berkeley, California 94720, United States.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Nano Lett. 2021 Oct 27;21(20):8770-8776. doi: 10.1021/acs.nanolett.1c03039. Epub 2021 Oct 15.
The spatial arrangement of adsorbates deposited onto a clean surface under vacuum typically cannot be reversibly tuned. Here we use scanning tunneling microscopy to demonstrate that molecules deposited onto graphene field-effect transistors (FETs) exhibit reversible, electrically tunable surface concentration. Continuous gate-tunable control over the surface concentration of charged FTCNQ molecules was achieved on a graphene FET at = 4.5K. This capability enables the 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. Gate-tunable molecular concentration is explained by a dynamical molecular rearrangement process that reduces total electronic energy by maintaining Fermi level pinning in the device substrate. The molecular surface concentration 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.
在真空中沉积到清洁表面上的吸附物的空间排列通常是不可逆转调节的。在这里，我们使用扫描隧道显微镜证明，沉积在石墨烯场效应晶体管 (FET) 上的分子表现出可逆的、电可调的表面浓度。在 = 4.5K 下，我们在石墨烯 FET 上实现了连续的栅极可调谐对带电荷 FTCNQ 分子的表面浓度的控制。这种能力使石墨烯器件的精确杂质掺杂成为可能，并且还为基于分子浓度对栅极的依赖性来确定分子能级对准提供了一种新方法。通过动态分子重排过程来解释栅极可调谐分子浓度，该过程通过保持器件衬底中的费米能级钉扎来降低总电子能量。分子表面浓度完全由器件背栅电压、其几何电容以及石墨烯狄拉克点和分子 LUMO 能级之间的能量差决定。
