Charge Mediated Reversible Metal–Insulator Transition in Monolayer MoTe₂ and W_xMo_1–xTe₂ Alloy

Abstract

Metal-insulator transitions in low-dimensional materials under ambient conditions are rare and worth pursuing due to their intriguing physics and rich device applications. Monolayer MoTe2 and WTe2 are distinguished from other TMDs by the existence of an exceptional semimetallic distorted octahedral structure (T') with a quite small energy difference from the semiconducting H phase. In the process of transition metal alloying, an equal stability point of the H and the T' phase is observed in the formation energy diagram of monolayer WxMo1-xTe2. This thermodynamically driven phase transition enables a controlled synthesis of the desired phase (H or T') of monolayer WxMo1-xTe2 using a growth method such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). Furthermore, charge mediation, as a more feasible method, is found to make the T' phase more stable than the H phase and induce a phase transition from the H phase (semiconducting) to the T' phase (semimetallic) in monolayer WxMo1-xTe2 alloy. This suggests that a dynamic metal-insulator phase transition can be induced, which can be exploited for rich phase transition applications in two-dimensional nanoelectronics.

The structural phases and vibrational properties of Mo 1−x W x Te 2 alloys

“…A more practical application driving investigations of MoTe 2 is the development of atomically thin phase change memory. MoTe 2 has a small energy difference between the 2H and 1T′ phases, making the prospect of engineering ondemand transitions with low power consumption realistic [24][25][26][27][28]. Unfortunately, reversible and rapid phase changes in MoTe 2 have yet to be demonstrated.…”

“…Importantly, the separation of the Weyl nodes in the alloys can be tuned with composition [20], which facilitates the observation of topological electronic states. Additionally, the ground state energy difference between the semiconducting 2H and semimetallic 1T′ or T d phases in − Mo 1 x W x Te 2 alloys can also be tuned with composition [25,27], thereby reducing the energy required to trigger a semiconductor-semimetal phase transformation. The desirable combination of tunable phase transitions with the low-dimensionality of TMDs makes [33,34].…”

Composition and temperature-dependent phase transition in miscible Mo1−xWxTe2 single crystals

“…However, the existence of orthorhombic Td phase MoTe 2 is still under hot debate because it is quite challenging to directly distinguish the subtle differences between the Td and β phase. As for the Mo 1− x W x Te 2 system, there are some experimental studies on ceramic samples3536 and theoretical predictions on monolayers3738, but no any phase-transitions works for single crystal samples at present, to the best of our knowledge.…”

2D Layered Materials for Memristive and Neuromorphic Applications

“…Electron. [85,170,171] With continued effort along this direction, practical applications in memory or neuromorphic computing may be achievable in the near future. 2020, 6,1901107 phase transition mechanisms of 2D layered materials for proof-of-concept applications.…”