在本文中，我们通过化学气相沉积法 ( CVD) 和湿法转移技术可控地制备TBG样品，利用STM 和STM针尖的操控技术，实现对TBG 层间耦合强度的调控与表征，进一步地结合扫描隧道谱学探测手段 ( STS ) 对TBG表面的电学性质进行探测。基于此，本文主要研究内容和结果如下：

1． 利用STM针尖调控TBG体系的层间耦合强度

利用STM针尖的操纵技术，探究两种调控TBG体系的电学性质的方法。一种是通过改变扫图角度或针尖-样品距离，进而改变二者之间的范德华相互作用；另一种是施加针尖脉冲 ( tip-pulse )以提供局域的强应力场，有效地调节体系的层间耦合强度。

2.     STM针尖脉冲诱导TBG层间距离的周期性振荡行为

我们通过对解耦的TBG施加针尖脉冲的作用，诱导上层石墨烯产生极低频的振荡行为，致使两层石墨烯之间的层间距离发生周期性变化。在双层转角石墨烯中，范霍夫峰能量间距与层间耦合强度线性相关，层间耦合强度在平衡距离附近与层间间距有着近似指数的依赖关系。因此，通过扫描隧道谱测量范霍夫峰能量间距可以得到亚埃级精度的层间间距信息。在此基础之上，我们创新地提出一种可以实现动态探测石墨烯晶格面外振动的方法。进一步地结合理论计算，我们发现STM针尖脉冲引起的层间距离的大小变化，等效于在体系施加10 GPa大小的压强，这为实现二维平面材料电学性质的调控提供一种全新的实验探测手段。

The rise of two-dimensional layered materials is due to the discovery of graphene. Previously, scientific researchers generally believed that two-dimensional materials cannot be stable. Monolayer graphene has the characteristic of atomic layer thickness, which makes the behavior of massless Dirac fermions easily regulated. The commonly used control methods include: back-gated control, external electric or magnetic field, heterostructures and so on. When two graphene layers are combined together by a certain van der Waals interaction force to form graphene-graphene homojunction (twisted bilayer graphene), they exhibit completely different properties from monolayer graphene. The electrical properties of twisted bilayer graphene (TBG) are extremely dependent on the twisted angle and interlayer interaction. Theoretical calculation results show that graphene with different twisted angles has completely different band structures, taking rich physical phenomenas to TBG system, which has been further proved in subsequent experimental studies. In addition, the experimental scientists found that the properties of the system differed even at a certain twist Angle. For example, in the "magic angle" system, different groups of researchers reported different results. Another example is the van Hove singularities energy spacing obtained by different groups in scanning tunneling microscopy (STM) experiment varies with the twisted angle. It was found that the van Hove singularities energy spacing was slightly different even the same twisted angle, which is due to the introduction of strain or impurity defects, resulting in the different coupling strength between layers of the system. The interlayer coupling strength provides a new degree of freedom for regulating the electrical properties of the system. Compared with the controllable precision of twisted angle ~0.02°, we still lack an experimental method to accurately characterize the change of interlayer coupling between layers of the TBG system.

In this paper, TBG samples were prepared by chemical vapor deposition (CVD) and wet transfer. Then, STM and STM tip manipulation techniques were used to control and characterize the interlayer interaction of TBG, and scanning tunneling spectroscopy (STS) was used to detect the electrical properties of the sample surface. Based on this, the main results are as follows:

1. The interlayer interaction of TBG system was controlled by STM tip

Using the manipulation techniques of STM tip, we explore two methods to regulate the electrical properties of TBG system. One is to change the sweep angle and the tip-sample distance, leading to the changes of the van der Waals interaction. The other is to apply a tip-pulse, which can effectively adjust the interlayer coupling strength of the TBG system by quoting a high local force between tip and sample.

2. Periodic oscillation behavior of TBG interlayer distance induced by STM tip pulse

By applying a tip pulse to the decoupled TBG, we induced the upper layer of graphene to oscillate at extremely low frequencies, resulting in periodic changes in the interlayer distance between the two layers. In TBG, the van Hove singularities energy spacing is linearly correlated with the interlayer coupling strength, while the interlayer coupling strength is approximately exponentially dependent on the interlayer spacing near the equilibrium distance. Therefore, the interlayer spacing with sub-angstrom accuracy can be obtained by measuring the energy spacing of Van Hove singularities obtained by scanning tunneling spectrum. We propose an innovative method to dynamically detect the out-of-plane vibration of graphene lattice. Combined with the further theoretical calculation, we find that the change of the distance between layers caused by the STM tip pulse is equivalent to the pressure of 10 GPa applied to the system, which provides a new method to achieve the control of electrical properties of two-dimensional planar materials.