Insufficient active sites and weak vertical conduction are the intrinsic factors that restrict the electrocatalytic HER for transition-metal dichalcogenides. As a prototype, we proposed a model of spiral MoTe 2 to optimize collectively the above issues. The conductive atomic force microscopy of an individual spiral reveals that the retentive vertical conduction irrespective of layer thickness benefits from the connected screw dislocation lines between interlayers. Theoretical calculations uncover that the regions near the edge step of the spiral structures more easily form Te vacancies and have lower ΔG H * as extra active sites. A single spiral MoTe 2 -based on-chip microcell was fabricated to extract HER activity and achieved an ultrahigh current density of 3000 mA cm À 2 at an overpotential of 0.4 V, which is about two orders of magnitude higher than the exfoliated counterpart. Profoundly, this unusual spiral model will initiate a new pathway for triggering other inert catalytic reactions.

Transition metal dichalcogenides (TMDs) are of great promise for various nonlinear optical (NLO) applications due to their unique electronic and optoelectronic properties, such as tunable optical bandgap, strong spin-orbit coupling, and exciton effects. However, the desired NLO performances of regular 2H-TMDs are usually restricted by their limited absorption at atomic thickness. With this regard, a structurally novel spiral MoTe 2 (s-MoTe 2 ) nanopyramids is reported with unique and superior NLO response, enabled by their broken inversion symmetry, weak interlayer coupling, exciton resonance, and strong light-matter interaction from the edge-rich 3R-like quasi-multilayer structure. The excellent NLO response over a wide spectral range from the near-infrared to visible region is demonstrated, where second-and third-order NLO responses have been simultaneously observed. Moreover, the secondorder nonlinear susceptibility of s-MoTe 2 is estimated to be around 1-2 order(s) of magnitude larger than those of most reported TMDs. The demonstration of a superior NLO response in such s-MoTe 2 not only paves a new way for designing the best NLO TMD structures, but also greatly prompts their practical applications in micro-nano NLO devices on chips in future.

Insufficient active sites and weak vertical conduction are the intrinsic factors that restrict the electrocatalytic HER for transition-metal dichalcogenides. As a prototype, we proposed a model of spiral MoTe 2 to optimize collectively the above issues. The conductive atomic force microscopy of an individual spiral reveals that the retentive vertical conduction irrespective of layer thickness benefits from the connected screw dislocation lines between interlayers. Theoretical calculations uncover that the regions near the edge step of the spiral structures more easily form Te vacancies and have lower ΔG H * as extra active sites. A single spiral MoTe 2 -based on-chip microcell was fabricated to extract HER activity and achieved an ultrahigh current density of 3000 mA cm À 2 at an overpotential of 0.4 V, which is about two orders of magnitude higher than the exfoliated counterpart. Profoundly, this unusual spiral model will initiate a new pathway for triggering other inert catalytic reactions.