Intercalation and Functionalization in 2D Materials

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. 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 MoS 2 . 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]. 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 new structural phases in T d -WTe 2 and T’-MoTe 2 with lithium intercalation and these new phases are semiconducting even though the initial WTe 2 and MoTe 2 are semimetallic and lithium ions donate electrons to the host materials. In the lithium intercalation-induced phase transition from the 2H to 1T’ phase of MoS 2 , 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. For these studies, multi-modal, in-situ probes were necessary to track the changes in the structure-property relation of the layered materials as a function of intercalation. [1] Advanced Electronic Materials 7, 2000873 (2021). [2] Nano Letters 22, p.4501 (2022). [3] ACS Applied Materials & Interfaces 13, p.10603-10611 (2021). [4] Advanced Materials 34, 2200861 (2022).