Patterning Charge States on 2D Materials by van der Waals Assembly Stacking

在过去的几十年里，低维纳米结构的科学和技术兴趣显著增长，碳纳米管和石墨烯在这一进展中发挥了核心作用。尽管将这种纳米结构集成到有用的器件中取得了重大进展，但在大规模使用之前，对其电子特性的控制仍然是一个主要限制。人们对一类更大的二维材料也越来越感兴趣，其中电子性质从导体（石墨烯）到绝缘体（六方氮化硼，h-BN）和半导体（黑磷，bP和过渡金属二硫族化合物，TMD）。然而，即使考虑到用于调制带隙值和输运载流子数量的不同方法，这些二维材料仍然缺乏对电子特性的控制。这种限制对技术的发展产生了巨大的影响，但是计算建模的支持对指导实验工作非常有益。*** ***我们建议研究一种有前途的途径来改变二维材料的电子特性，即自组装网络的物理吸附。我们将考虑范德华（vdW）异质结构，这种异质结构是由分子纳米多孔组件吸附在有前途的二维材料（如石墨烯、氢氮化硼和其他材料）上形成的。分子组装在这种vdW异质结构中的目标作用是调节和控制二维材料的电子特性，目的是发现和实现新的功能。一种功能是利用分子组装体的形状，借助接枝在分子构建单元上的供体/受体（D/ a）基团，在表面上印上电荷掺杂图案。按照这种方法，具有特定电子特性的原始材料的域将被掺杂区域很好地划分在衬底上。D/A基团的选择将取决于它们在二维材料中调制电荷掺杂的能力。我们的主要目标是控制整体纳米孔网络的形状，包括孔的大小，以及分子组装和二维材料之间电荷转移的性质和大小。为了解决与带结构工程相关的基本问题，我们将使用第一性原理密度泛函理论（DFT）计算和扫描隧道显微镜（STM）模拟。我们的计算方法将使我们能够揭示vdW异质结构中分子-表面和分子-分子相互作用的基本方面。虽然这种类型的接口的描述在材料科学中是至关重要的，但电荷调制的基本方面对开发小型但高度可扩展的构建模块具有重大影响，可以用于更高效的高性能设备。

The scientific and technological interests for low-dimensional nanostructure have remarkably grown during the last decades, carbon nanotubes and graphene have played a central role to this progress. Despite the major advancement observed to integrate such nanostructure into useful devices, the control of their electronic properties remains a major limitation before their use at a larger scale. There is also an increasing interest for a larger class of 2D materials in which the electronic properties go from conductor (graphene) to insulators (hexagonal-boron nitride, h-BN), and semiconductor (black phosphorus, bP and transition-metal dichalcogenides, TMD). Nevertheless, the lack of the control of electronic properties remains for those 2D materials, even when considering the different approaches used to modulate the band gap value and the number of transport carriers. This limitation has a dramatic impact on the development of technologies, but where a support from computational modeling can be highly beneficial to guide the experimental efforts.*** ***We are proposing to investigate one promising route to modify the electronic properties of 2D materials, the physisorption of self-assembled networks. We will consider van der Waals (vdW) heterostructures built from a molecular nanoporous assembly adsorbed on promising 2D materials such as graphene, h-BN, and other materials. The targeted role of the molecular assembly in such vdW heterostructures is to modulate and control the electronic properties of the 2D materials with the aim to uncover and implement new functionalities. One functionality would be to capitalize the shape of the molecular assembly to imprint a charge doping pattern on a surface with the help of donors/acceptors (D/A) groups grafted on the molecular building units. Following this approach, domains of pristine materials with specific electronic properties that are well delimited by doped regions will be carved on the substrate. The choice of the D/A group will be guided by their ability to modulate charge doping in the 2D materials. Our main objectives aimed at controlling the overall nanoporous network shape including the size of the pores, but also on the nature and magnitude of the charge transfer between the molecular assembly and the 2D materials. To address the fundamental issue related to band structure engineering, we will use first principles density functional theory (DFT) calculations and scanning tunneling microscopy (STM) simulations. Our computational approach will allow us to reveal the fundamental aspects of molecule-surface and molecule-molecule interactions within the vdW heterostructures. Although the description of this type of interface is of primary importance in material science, the fundamental aspects of the charge modulation have a major impact to develop small but highly scalable building blocks for more efficient high performance devices.