Strain-driven Semiconducting-to-metallic Phase Transition in Mo(1-x)W(x)Te2 Alloys

Nathan Finney, Columbia University

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Relatively defect-free two‐dimensional (2-D) materials (e.g. graphene, boron nitride, etc.) can be strained up until their extreme elastic limit, which is constrained by the intrinsic strength of the material. This offers an opportunity to explore properties of materials in the limit of extreme strain for flexible device applications and engineering new, super-strong "smart" elastic materials. In this study, we probe geometric-phase change in molybdenum ditelluride (MoTe2), a group-VI transition metal dichalcogenide (TMD), along with two different alloys of MoTe2 with increased tungsten:molybdenum ratio. Since the geometric phase in these materials shifts from two layers per hexagonal unit cell (2H phase: semiconducting MoTe2) to one layer per trigonal unit cell (1T’ phase: metallic MoTe2) when a critical strain energy density is reached, we can observe the shift from semiconducting to metallic state as a transformation of vibrational response in the crystal lattice. We observe any potential shifts in vibrational response by performing Raman spectroscopy. While performing Raman we simultaneously vary applied strain using a compact strain jig compatible with a Raman microscope. The preparation of the flexible substrate and sample, including the exfoliation of thin films, bonding and dicing, allows us to apply the strain theoretically required to observe phase change without slip. In addition, in order to perform experiments on MoTe2 and other air-sensitive 2-D materials, we developed a nitrogen glovebox system specifically tailored for the exfoliation, characterization and encapsulation of these materials. The combination of the tools and procedures developed here will inform future work, including increasing the limit of applied strain and development of device applications.

Abstract Author(s): N.Finney, A. Dadgar, D. Chenet, A. Pasupathy, J. Hone