Post-Synthesis Design of 2D Materials—Surface Functionalization and Intercalation

The large surface areas and interlayer gaps of 2D materials enable surface functionalization and intercalation as effective post-synthesis design knobs to tune the properties of 2D materials using ions, atoms, and organic molecules. For complete engineering control, detailed understanding of the interactions between the 2D materials and the molecules adsorbed on 2D materials surface or between the 2D materials and the intercalants is necessary.<br/>I will first discuss surface functionalization to tune the electrical properties of 2D materials. We developed an experimental approach to quantitatively measure the doping powers of organic electron donors (OEDs) to monolayer MoS₂. Using novel and previously studied OEDs, we demonstrate experimentally that the measured doping power is a sensitive function of molecule’s reduction potential, size, surface coverage, and orientation to 2D materials [1, 2]. Because we can experimentally measure the doping powers of the molecules, our results can be compared with DFT calculations to validate and predict new OEDs.<br/>I will then discuss electrochemical intercalation into 2D materials to induce novel phases that were previously undetected and to study heterointerface effects on the intercalation induced phase transition [3, 4]. We discover a new structural phase in T_d-WTe₂ with lithium intercalation and this new phase is semiconducting even though the initial WTe₂ is semimetallic and lithium ions donate electrons to WTe₂. In the lithium intercalation-induced phase transition from the 2H to 1T’ phase of MoS₂, we show that the nucleation of the 1T’ phase proceeds via heterogeneous nucleation where the nature of heterointerface dictates the thermodynamics of the phase transition.<br/>[1] Advanced Electronic Materials 7, 2000873 (2021).<br/>[2] arXiv: 2107.12470 (2021).<br/>[3] ACS Applied Materials & Interfaces 13, p.10603-10611 (2021).<br/>[4] arXiv:2107.02255 (2021).