Engineering the Structural and Electronic Phases of MoTe2 through W Substitution

MoTe2 is an exfoliable transition metal dichalcogenide (TMD) that crystallizes in three symmetries: the semi-conducting trigonal-prismatic 2H- or alpha-phase, the semimetallic and monoclinic 1T'- or beta-phase, and the semimetallic orthorhombic gamma-structure. The 2H-phase displays a band gap of similar to 1 eV making it appealing for flexible and transparent optoelectronics. The gamma-phase is predicted to possess unique topological properties that might lead to topologically protected nondissipative transport channels. Recently, it was argued that it is possible to locally induce phase-transformations in TMDs, through chemical doping, local heating or electric-field to achieve ohmic contacts or to induce useful functionalities such as electronic phase-change memory elements. 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 a small critical W concentration x(c) similar to 8% stabilizes the gamma-phase at room temperature. This suggests that crystals with x close to x(c) might be particularly susceptible to phase transformations induced by an external perturbation, for example, an electric field. Photoemission spectroscopy, indicates that the gamma-phase possesses a Fermi surface akin to that of WTe2.