Department of Physics, Indian Institute of Technology Indore, Indore453552, India.
Indian Statistical Institute (Laboratory for Cognitive Systems and Cybernetics Research, Center for Soft Computing Research)Kolkata700108, India.
Langmuir. 2022 Dec 27;38(51):16067-16072. doi: 10.1021/acs.langmuir.2c02676. Epub 2022 Dec 13.
Bi-layer epitaxial graphene (BLG) on 6H-SiC(0001) (EG/SiC) was grown and modified by thermal deposition of the molecular electron acceptor tetrafluoro-tetra cyano quinodimethane (F4-TCNQ). The surface-modified system, F4-TCNQ/EG/SiC, was studied by X-ray photoelectron spectroscopy (XPS) and angle-resolved polarized Raman spectroscopy (ARPRS). XPS results indicate that bonding of deposited F4-TCNQ molecules depends on their concentration. Although bonding through the cyano groups is present at all concentrations, charge transfer from graphene to fluorine is evident only at sub-monolayer concentrations. The corresponding change in bond character is coupled with a change in molecular orientation. Raman spectroscopy not only provides results consistent with the findings from the XPS study but also reveals a significant degree of molecular stacking above the monolayer concentration. Thus, both the variation of the acceptor concentration and the number of graphene layers provide further handles to manipulate charge and doping that may be useful in device applications.
双层外延石墨烯（BLG）在 6H-SiC（0001）（EG/SiC）上生长，并通过热沉积分子电子受体四氟四氰对醌二甲烷（F4-TCNQ）进行修饰。通过 X 射线光电子能谱（XPS）和角分辨偏振拉曼光谱（ARPRS）研究了表面修饰系统 F4-TCNQ/EG/SiC。XPS 结果表明，沉积的 F4-TCNQ 分子的键合取决于其浓度。尽管在所有浓度下都存在通过氰基的键合，但只有在亚单层浓度下才明显存在从石墨烯到氟的电荷转移。相应的键合特性变化与分子取向的变化相关联。拉曼光谱不仅提供了与 XPS 研究结果一致的结果，而且还揭示了在单层浓度以上存在显著程度的分子堆积。因此，受体浓度和石墨烯层数的变化都为操纵电荷和掺杂提供了进一步的手段，这在器件应用中可能是有用的。
