Structural Control of 2H vs. 1T’ polytypes in Single-Crystalline MoTe₂ Layers

The ability to manipulate electronic, chemical, magnetic, and optical properties of layered van-der-Waals materials via controllable synthesis and processing enables their use for logic, memory, sensor, optoelectronic, and energy-related applications. This talk focuses on the chemical-vapor-transport (CVT) growth of MoTe2 single crystals to demonstrate the synthesis of specific crystal phases: a) semiconducting 2H-MoTe2 with tailored n- and p-type doping and b) semimetallic 1T’-MoTe2. The 2H vs. 1T’ polytype formation was controlled by manipulating processing temperature during crystal growth or a follow-up annealing, while the doping of the 2H phase was controlled by utilizing relevant CVT transport agents, I₂ and TeCL₄ for p- and n-type, respectively. In addition, alloying MoTe₂ with W produced a composition-dependent array of Mo_1-xW_xTe₂ solid solutions of both 2H and 1T’ polytypes. Reversibility of the 2H-1T’ phase transition was achieved by repeatable annealing and quenching at the temperatures derived from the Mo-Te phase diagram. Such transformations, including a “frozen” co-existence of both polytypes in the same single-crystalline flake, were verified using TEM, SEM/EBSD, micro-XRD, and Raman spectroscopy.<br/>Control of crystal phases in MoTe₂ and other van-der-Waals layered metal chalcogenides is important for device design and engineering [1-3].<br/><br/>References:<br/>1. D. Kim et al., Phase Engineering of 2D Materials, Chemical Reviews 2023, 123, 11230<br/>2. F. Zhang at al., Electric-field induced structural transition in vertical MoTe2 and MoWTe2-based resistive memories, Nature Materials 2019, 18, 55<br/>3. R. Ma et al., MoTe2 Lateral Homojunction Field-Effect Transistors Fabricated using Flux-Controlled Phase Engineering, ACS Nano 2019, 13, 8035