Laser‐Induced Phase Transition and Patterning of hBN‐Encapsulated MoTe₂

Abstract

Transition metal dichalcogenides exhibit phase transitions through atomic migration when triggered by various stimuli, such as strain, doping, and annealing. However, since atomically thin 2D materials are easily damaged and evaporated from these strategies, studies on the crystal structure and composition of transformed 2D phases are limited. Here, the phase and composition change behavior of laser‐irradiated molybdenum ditelluride (MoTe2) in various stacked geometry are investigated, and the stable laser‐induced phase patterning in hexagonal boron nitride (hBN)‐encapsulated MoTe2 is demonstrated. When air‐exposed or single‐side passivated 2H‐MoTe2 are irradiated by a laser, MoTe2 is transformed into Te or Mo3Te4 due to the highly accumulated heat and atomic evaporation. Conversely, hBN‐encapsulated 2H‐MoTe2 transformed into a 1T′ phase without evaporation or structural degradation, enabling stable phase transitions in desired regions. The laser‐induced phase transition shows layer number dependence; thinner MoTe2 has a higher phase transition temperature. From the stable phase patterning method, the low contact resistivity of 1.13 kΩ µm in 2H‐MoTe2 field‐effect transistors with 1T′ contacts from the seamless heterophase junction geometry is achieved. This study paves an effective way to fabricate monolithic 2D electronic devices with laterally stitched phases and provides insights into phase and compositional changes in 2D materials.

Optical grade transformation of monolayer transition metal dichalcogenides via encapsulation annealing

“…For the STEM characterization, 1L-graphene was used as an encapsulation layer as the graphene has a small background signal (see Methods for details of the TEM sample preparation). [28][29][30] The high-angle annular dark field (HAADF) STEM images of Fig. 5a and b show the atomic structures of as-stacked and annealed 1L-WSe 2 .…”

Photoinduced Structural Dynamics of 2H-MoTe2Under Extremely High-Density Excitation Conditions

“…Saturable absorption at an incident pump fluence of ∼4 mJ/cm 2 (∼0.4% electronic excitation) and sample damage in the high fluence regime indicate that it is challenging to realize the electronic excitation of more than several percent of valence electrons only via photoexcitation with ultrashort pulsed laser, which is necessary for the 2H-to-1T′ phase transition, as predicted by theoretical calculations. − To further investigate the structural phase transition, other steps are needed, e.g., the preparation of a sample encapsulated by h-BN, the use of THz pulses, and the use of single-shot measurements…”

Phase Engineering of 2D Materials

“…(c) Phase diagram of the Mo–Te system as a function of temperature and composition. Reproduced with permission from ref . Copyright 2023 Wiley-VCH GmbH.…”