Phase transition in nanomaterials is distinct from that in 3D bulk materials owing to the dominant contribution of surface energy. Among nanomaterials, 2D materials have shown unique phase transition behaviors due to their larger surface-to-volume ratio, high crystallinity, and lack of dangling bonds in atomically thin layers. Here, the anomalous dimensionality-driven phase transition of molybdenum ditelluride (MoTe 2 ) encapsulated by hexagonal boron nitride (hBN) is reported. After encapsulation annealing, single-crystal 2H-MoTe 2 transformed into polycrystalline T d -MoTe 2 with tilt-angle grain boundaries of 60°-glide-reflection and 120°-twofold rotation. In contrast to conventional nanomaterials, the hBN-encapsulated MoTe 2 exhibit a deterministic dependence of the phase transition on the number of layers, in which the thinner MoTe 2 has a higher 2H-to-T d phase transition temperature. In addition, the vertical and lateral phase transitions of the stacked MoTe 2 with different crystalline orientations can be controlled by inserted graphene layers and the thickness of the heterostructure. Finally, it is shown that seamless T d contacts for 2H-MoTe 2 transistors can be fabricated by using the dimensionality-driven phase transition. The work provides insight into the phase transition of 2D materials and van der Waals heterostructures and illustrates a novel method for the fabrication of multiphase 2D electronics.
Sb) have been intensively investigated for several decades because of their enormous applications for many optoelectronic devices. Here, by employing first-principles calculations, the electronic structures of bulk XY haeckelite compounds are examined. It is identified that InSb (TlN and TlP) is Dirac semimetal (are strong topological insulators). The other fifteen XY compounds are semiconducting. The effect of biaxial and uniaxial tensile and compressive strains on the electronic structures are studied. These materials offer diverse topological orders. The semiconducting band gaps are mainly found between the bonding and antibonding states of the mixed X(p)-Y(p) orbitals at the top of the valence band and the bottom of the conduction bands, respectively. The topological insulating nature of the XY compounds is explained based on the degenerate p x + p y orbitals and their orbital energies relative to the p z orbitals near the Fermi energy. The nontrivial band topologies of TlN and TlP are confirmed by calculating the Z 2 (1;000) index, surface states, and Wilson loop calculations. The bands split into two branches by including spin-orbit interaction. The results demonstrate that haeckelite compounds are fascinating materials with broad potential applications in optoelectronics and possessing the possibility of hosting emergent physical phenomena.
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