Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-nano Devices, Department of Physics, Renmin University of China, Beijing 100872, China.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, China.
Nanoscale. 2023 Mar 23;15(12):5825-5833. doi: 10.1039/d2nr07242d.
Tailoring the interlayer twist angle of bilayer graphene (BLG) significantly affects its electronic properties, including its superconductivity, topological transitions, ferromagnetic states, and correlated insulating states. These exotic electronic properties are sensitive to the work functions of BLG samples. In this study, the twist angle-dependent work functions of chemical vapour deposition-grown twisted bilayer graphene (tBLG) were investigated in detail using Kelvin probe force microscopy (KPFM) in combination with Raman spectroscopy. The thickness-dependent surface potentials of Bernal-stacked multilayer graphene were measured. It is found that with the increase in the number of layers, the work function decreases and tends to saturate. Bernal-stacked BLG and tBLG were determined KPFM due to their twist angle-specific surface potentials. The detailed relationship between the twist angle and surface potential was determined KPFM and Raman spectral measurements. With the increase in the twist angle, the work function of tBLG will increase rapidly and then increase slowly when it is greater than 5°. The thermal stability of tBLG was investigated through a controlled annealing process. tBLG will become Bernal-stacked BLG after annealing at 350 °C. Our work provides the twist angle-dependent surface potentials of tBLG and provides the relevant conditions for the stability of the twist angle, which lays the foundation for further exploration of its twist angle-dependent electronic properties.
对双层石墨烯 (BLG) 的层间扭转角进行调整会显著影响其电子特性，包括超导性、拓扑转变、铁磁态和关联绝缘态。这些奇异的电子特性对 BLG 样品的功函数很敏感。在这项研究中，我们使用 Kelvin 探针力显微镜 (KPFM) 结合拉曼光谱，详细研究了化学气相沉积生长的扭曲双层石墨烯 (tBLG) 的扭转角相关功函数。我们还测量了伯纳尔堆叠多层石墨烯的厚度相关表面势。结果发现，随着层数的增加，功函数减小并趋于饱和。由于 BLG 和 tBLG 的扭转角具有特异性，因此可以使用 KPFM 确定其伯纳尔堆叠结构。通过 KPFM 和拉曼光谱测量，我们确定了扭转角和表面势之间的详细关系。随着扭转角的增加，tBLG 的功函数会先快速增加，然后在大于 5°时缓慢增加。通过控制退火过程，我们研究了 tBLG 的热稳定性。在 350°C 退火后，tBLG 将转变为伯纳尔堆叠的 BLG。我们的工作提供了 tBLG 的扭转角相关表面势，并为扭转角的稳定性提供了相关条件，这为进一步探索其扭转角相关电子特性奠定了基础。
