In Situ Imaging of an Anisotropic Layer-by-Layer Phase Transition in Few-Layer MoTe2

Understanding the phase transition mechanisms in two-dimensional (2D) materials is a key to precisely tailor their properties at the nanoscale. Molybdenum ditelluride (MoTe2) exhibits multiple phases at room temperature, making it a promising candidate for phase-change applications. Here, we fabricate lateral 2H-Td interfaces with laser irradiation and probe their phase transitions from micro-to atomic scales with in situ heating in the transmission electron microscope (TEM). By encapsulating the MoTe2 with graphene protection layers, we create an in situ reaction cell compatible with atomic resolution imaging. We find that the Td-to-2H phase transition initiates at phase boundaries at low temperatures (200-225 degrees C) and propagates anisotropically along the b -axis in a layer-by-layer fashion. We also demonstrate a fully reversible 2H- Td-2H phase transition cycle, which generates a coherent 2H lattice containing inversion domain boundaries. Our results provide insights on fabricating 2D heterophase devices with atomically sharp and coherent interfaces.

Automated summary

This study investigates the phase transition mechanisms of 2D molybdenum ditelluride (MoTe2) materials and demonstrates the creation of lateral 2H-Td interfaces using laser irradiation. By using in situ heating in a transmission electron microscope (TEM), the researchers observe the phase transitions from micro-to atomic scales and find that the Td-to-2H phase transition initiates at phase boundaries at low temperatures and propagates anisotropically. The study also presents a fully reversible 2H- Td-2H phase transition cycle and provides insights for fabricating 2D heterophase devices with atomically sharp and coherent interfaces.