Vertical Heterophase for Electrical, Electrochemical, and Mechanical Manipulations of Layered MoTe₂

Phase engineering is a breakthrough for various electronic and energy device applications with transition metal dichalcogenides (TMDs). Chemical methods, such as lithium intercalation, are mostly used for phase engineering, which achieves atomically thin flakes and high catalytic performances in several group 6 TMDs including MoS₂. However, chemical methods cannot be applied to MoTe₂, a widely investigated group 6 TMD with intriguing semiconducting, topological, and catalytic properties. The lack of modifying MoTe₂ by chemical methods remains a puzzling issue considering the small energy difference between the polymorphs of MoTe₂. Here, a convection-assisted lithium ion intercalation and phase transition is reported to achieve a vertical heterophase in a MoTe₂ crystal. The vertical heterophase in MoTe₂ reduces the Schottky barrier with metal electrodes down to 66 meV, enhancing the overall ion conductance for electrochemical hydrogen production. Moreover, the weakened adhesion of the 1T' phase layers on the top and bottom surfaces in the vertical heterophase, formed by the intercalation, enables a unique surface tension-driven exfoliation of MoTe₂ flakes. The heterophase chemical engineering suggests a new platform for hybrid catalysts and next-generation electronic devices based on 2D materials.