Chen Wenjing, Wang Xinxin, Li Shujing, Yan Chao, He Lin, Zhang Ping, Yang Yu, Ma Donglin, Nie Jiacai, Dou Ruifen
Department of Physics, Beijing Normal University, Beijing, 100875, People's Republic of China.
Phys Chem Chem Phys. 2020 Oct 15;22(39):22711-22718. doi: 10.1039/d0cp03322g.
Wafer-scale growth of the unidirectional graphene monolayer on Ge surfaces has rejuvenated the intense study of the surfaces and interfaces of semiconductors underneath graphene. Recently, it was reported that the Ge atoms in the Ge(110) surface beneath a graphene monolayer underwent a rearrangement and formed an ordered (6 × 2) reconstruction. However, a plausible atomic model related to this (6 × 2) reconstruction is still lacking. Here, by using scanning tunnelling microscopy/spectroscopy (STM/S) and density functional theory (DFT) calculations, we deeply investigated the structural and electronic properties of the Ge(110) (6 × 2) surface encapsulated by a graphene monolayer. The (6 × 2) surface reconstruction was confirmed for the post-annealing-graphene-covered Ge(110) surface via STM, and was found to be quite air-stable, owing to the protection of the graphene monolayer against surface oxidation. Our study disclosed that the topographic features of the topmost graphene monolayer and the Ge(110) surface could be selectively imaged by utilizing suitable scanning biases. According to the STM results and DFT calculations, a rational ball-and-stick model of the (6 × 2) reconstruction was successfully provided, in which an elemental building block comprising two Ge triangles and two isolated Ge atoms adsorbed on the unreconstructed ideal Ge(110) surface. Local density of states of the graphene/Ge surface was explored via scanning tunneling spectroscopy (STS), presenting four well-defined differential conductance (dI/dV) peaks, protruding at energies of 0.2, 0.4, 0.6 and 0.8 eV, respectively. The four peaks predominantly originated from the surface states of the reconstructing adatoms and were well reproduced by our theoretical simulation. This result means that the Ge surface is very robust after being encapsulated by the epitaxial graphene, which could be advantageous for directly fabricating graphene/Ge-hybrid high-speed electronics and optoelectronics based on conventional microelectronics technology.
在锗表面上进行单向石墨烯单层的晶圆级生长，重新激发了人们对石墨烯下方半导体表面和界面的深入研究。最近，有报道称，石墨烯单层下方的Ge(110)表面中的锗原子发生了重排，并形成了有序的(6×2)重构。然而，仍然缺乏与这种(6×2)重构相关的合理原子模型。在此，通过使用扫描隧道显微镜/光谱(STM/S)和密度泛函理论(DFT)计算，我们深入研究了被石墨烯单层包裹的Ge(110)(6×2)表面的结构和电子性质。通过STM确认了退火后石墨烯覆盖的Ge(110)表面的(6×2)表面重构，并且发现由于石墨烯单层对表面氧化的保护作用，该重构相当稳定。我们的研究表明，利用合适的扫描偏压可以选择性地成像最顶层石墨烯单层和Ge(110)表面的形貌特征。根据STM结果和DFT计算，成功提供了(6×2)重构的合理球棍模型，其中一个基本结构单元由两个锗三角形和两个吸附在未重构的理想Ge(110)表面上的孤立锗原子组成。通过扫描隧道光谱(STS)探索了石墨烯/锗表面的局域态密度，呈现出四个清晰定义的微分电导(dI/dV)峰，分别在0.2、0.4、0.6和0.8 eV的能量处突出。这四个峰主要源于重构吸附原子的表面态，并被我们的理论模拟很好地再现。该结果意味着锗表面在被外延石墨烯包裹后非常稳定，这对于基于传统微电子技术直接制造石墨烯/锗混合高速电子器件和光电器件可能是有利的。
