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

二维(2D)材料的特征是一个平面内原子之间的强化学键和层之间的弱物理键。它们在平面上表现出很高的机械强度，同时非常灵活。电子结构的二维简化导致了许多有趣的性质，如石墨烯中的高载流子迁移率或MoS2中电子自旋的强耦合。施沃朋克计划将探索2D材料堆叠中的新物理，其中层的接近感应集体电子态。在这个项目中，我们将探索一种新的力学性能和电导在堆积层中被外部载荷压缩的机制。由于高压缩短了距离，即使是暂时的化学键也可能在层之间形成。这种杂交对传导和机械反应有很大影响。我们将施加压力，并通过原子力显微镜的纳米级导电尖端来探测材料的性质。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。在滑动速度和温度不同的原子摩擦测量中，将探索层-层相互作用的动力学。这些实验跟踪临时化学键的形成所引起的耗散，并探索它们的寿命。同时，还将测量不同杂化材料的电导变化。在SPP中，该项目将是为制备具有最高结构质量的2D材料的堆叠异质结构而合作的一部分。将与在原子尺度上模拟化学键的理论小组合作，研究压力引起的机械性能和电输运的变化。了解压缩应变对堆叠2D材料的影响将有助于制造新型柔性电子设备和开发压敏器件。

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.