Engineering the Structural and Electronic Phases of MoTe₂ through W Substitution

Abstract

MoTe2 is an exfoliable transition metal dichalcogenide (TMD) which crystallizes in three symmetries; the semiconducting trigonal-prismatic 2H−phase, the semimetallic 1T ′ monoclinic phase, and the semimetallic orthorhombic T d structure 1-4 . The 2H−phase displays a band gap of ∼ 1 eV 5 making it appealing for flexible and transparent optoelectronics. The T d−phase is predicted to possess unique topological properties 6-9 which might lead to topologically protected non-dissipative transport channels 9 . Recently, it was argued that it is possible to locally induce phasetransformations in TMDs 3,10,11,14 , through chemical doping 12 , local heating 13 , or electric-field 14,15 to achieve ohmic contacts or to induce useful functionalities such as electronic phase-change memory elements 11 . The combination of semiconducting and topological elements based upon the same compound, might produce a new generation of high performance, low dissipation optoelectronic elements. Here, we show that it is possible to engineer the phases of MoTe2 through W substitution by unveiling the phase-diagram of the Mo1−xWxTe2 solid solution which displays a semiconducting to semimetallic transition as a function of x. We find that only ∼ 8 % of W stabilizes the T d−phase at room temperature. Photoemission spectroscopy, indicates that this phase possesses a Fermi surface akin to that of WTe2 16 .The properties of semiconducting and of semimetallic MoTe 2 are of fundamental interest in their own right, but are also for their potential technological relevance. In the mono-or few-layer limit it is a direct-gap semiconductor, while the bulk has an indirect bandgap 5,17,18 of ∼ 1 eV. The size of the gap is similar to that of Si, making 2H−MoTe 2 particularly appealing for both purely electronic devices 19,20 and optoelectronic applications 21 . Moreover, the existence of different phases opens up the possibility for many novel devices and architectures. For example, controlled conversion of the 1T ′ −MoTe 2 phase to the 2H−phase, as recently reported 22 , could

Dimensionality-driven orthorhombic MoTe2 at room temperature

“…MoTe2 is one of the few TMDCs in that it stabilizes both semiconducting and metallic polytypes, transitions between which can be further controlled by temperature, alloying, strain, and electrostatic gating [4][5][6][7][8][9][10]. 1T-MoTe2 is unstable, however-distortion of in-plane bonds gives rise to an enlarged monoclinic unit cell ( or 1T' phase) at room temperature [11].…”

Atomic Insights into Phase Evolution in Ternary Transition‐Metal Dichalcogenides Nanostructures

“…The properties of TMDs are closely associated with the polymorphism in crystal symmetry . In MoTe 2 , the room‐temperature stable phase is hexagonal 2H ( Figure a), which displays a bandgap of ≈1 eV, appealing for flexible and transparent optoelectronics devices . Through controllable conversion from 2H to the other semimetallic phases Tʹ (monoclinic, Figure b) and T d (orthorhombic, Figure c), the semiconducting to metallic transition can be realized, which helps achieve ohmic contact in heterojunctions and make broad applications including memory and phase‐change devices .…”

Band Gap Engineering of Hybrid 2-D Nanomaterials Some Recent Developments

“…Phase engineering of MoTe 2 by W-substitution was revealed in the phase-diagram of the Mo 1-x W x Te 2 solid solution, which displays a semiconducting to semi metallic transition as a function of x. A small critical W concentration x c ∼ 8% was observed to stabilize the γ-phase at room temperature suggesting that crystals with x close to x c might be particularly susceptible to phase transformations induced by an externally applied electric field [73].…”