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

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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.