Compressive strain in stacked 2D materials: from proximity to metastable hybridization

二维（2D）材料的特征在于一个平面中的原子之间的强化学键和层之间的弱物理键。它们在平面上具有很高的机械强度，同时也非常柔韧。将电子结构减少到两个维度导致许多有趣的性质，例如石墨烯中的高载流子迁移率或MoS 2中电子自旋的强耦合。Schwerpunktprogramm将探索2D材料堆栈中的新物理学，其中层的接近诱导集体电子状态。在这个项目中，我们将探索一个新的制度的机械性能和导电性的堆叠层被压缩的外部负载。随着高压减小的距离，甚至可以在层之间形成临时的化学键。这种杂化对传导和机械响应具有显著影响。我们将通过原子力显微镜的纳米导电尖端施加压力并探测材料特性。原子灵敏度和分辨率将通过在超高真空中对非常干净的样品进行实验来获得。层-层相互作用的动力学将在原子摩擦测量中进行探索，其中滑动速度和温度是变化的。这些实验跟踪由临时化学键的形成引起的耗散，并探测它们的寿命。与此同时，还将测量不同杂化材料的电导率变化。在SPP内，该项目将是一项合作的一部分，旨在制备最高结构质量的2D材料堆叠异质结构。压力引起的机械性能和电输运的变化将与模拟原子尺度上的化学键合的理论组合作进行研究。了解压缩应变对堆叠的2D材料的影响将有助于构建新型柔性电子器件和开发压敏器件。

Two-dimensional (2D) materials are characterized by strong chemical bonds between the atoms in one plane and weak physical bonds between layers. They exhibit high mechanical strength in the plane and are very flexible at the same time. The reduction of the electronic structure to two dimensions leads to many interesting properties such as high carrier mobility in graphene or strong coupling of the electron spin in MoS2. The Schwerpunktprogramm will explore the new physics in stacks of 2D materials, where the proximity of the layers induces collective electronic states. In this project we will explore a new regime of mechanical properties and electrical conductance in stacked layers which are compressed by an external load. With the distance reduced by high pressure, even temporary chemical bonds can form between the layers. This hybridization has an dramatic influence on conduction and mechanical response. We will apply the pressure and probe the material properties by the nanoscale conductive tip of an atomic force microscope. Atomic sensitivity and resolution will be obtained by performing the experiments on very clean samples in ultra-high vacuum. The dynamics of layer-layer interaction will be explored in atomic friction measurements, where sliding velocity and temperature are varied. These experiments track the dissipation arising from the formation of temporary chemical bonds and probe their lifetime. Simultaneously, the changes in the electrical conductance, which are expected for different hybridization, will be measured.Within the SPP, the project will be part of a collaboration towards the preparation of stacked heterostructures of 2D materials in the highest structural quality. The pressure-induced changes in mechanical properties and electrical transport will be investigated in collaboration with theory groups simulating the chemical bonding at the atomic scale. Understanding the impact of compressive strain on stacked 2D materials will help to build novel flexible electronics and to develop pressure-sensitive devices.