Two-dimensional (2D) PtSe2 has attracted intensive attention in energy-related fields, due to its high catalytic activity, electrical conductivity, and chemical stability, etc. However, the active sites of 2D PtSe2 nanosheets synthesized on conventional planar substrates are limited to the edge sites. Herein, the direct synthesis of three-dimensional (3D) vertically oriented 1T-PtSe2 nanosheets featured with abundant edge sites is reported on the nanoporous gold template via a chemical vapor deposition route. Moreover, Ar+ sputtering treatment of as-grown sample is introduced to generate more abundant surface defects, thus boosting the electrocatalytic activity of the inert basal planes. In this regard, the vertical growth configuration and abundant defects of PtSe2 nanosheets are revealed to afford remarkable electrocatalytic activity for hydrogen evolution reaction. This work hereby provides a new route for the morphology engineering of noble metal related transition-metal dichalcogenides toward 3D vertical configurations, which should promote their practical applications in high-current-density water splitting.

As an important member of the IVA–VIA group compounds, 2D SnSe2 has emerged as a perfect platform for developing diverse applications, especially in high‐performance optoelectronic devices and data storage, etc. However, the bottom‐up synthesis of large‐area uniform, atomically thin SnSe2 crystals with controlled thicknesses has not yet been realized. Herein, we report the large‐area uniform growth of monolayer (1L), bilayer (2L), and few‐layer (FL) 1T‐SnSe2 single‐crystal flakes on mica substrates via a facile chemical vapor deposition (CVD) route. The feeding amount of Sn precursor and flow rate of hydrogen carrier are found to be the key parameters for the thickness‐controlled growth of uniform SnSe2 flakes. More intriguingly, obvious second harmonic generation (SHG) is revealed in the retained inversion symmetry structure of 1T‐SnSe2, with its intensity showing linear dependence with the thickness from monolayer to multilayers. The new findings reported herein should pave the ways for the thickness‐tunable growth of atomically thin SnSe2 crystals, and their unique optical property explorations and applications in nonlinear optics.

Enhanced second‐harmonic generation (SHG) responses are reported in monolayer transition metal dichalcogenides (e.g., MX2, M: Mo, W; X: S, Se) due to the broken symmetries. The 3R‐like stacked MX2 spiral structures possessing the similar broken inversion symmetry should present dramatically enhanced SHG responses, thus providing great flexibility in designing miniaturized on‐chip nonlinear optical devices. To achieve this, the first direct synthesis of twisted 3R‐stacked chiral molybdenum diselenide (MoSe2) spiral structures with specific screw dislocations (SD) arms is reported, via designing a water‐assisted chemical vapor transport (CVT) approach. The study also clarifies the formation mechanism of the MoSe2 spiral structures, by precisely regulating the precursor supply accompanying with multiscale characterizations. Significantly, an up to three orders of magnitude enhancement of the SHG responses in twisted 3R stacked MoSe2 spirals is demonstrated, which is proposed to arise from the synergistic effects of broken inversion symmetry, strong light–matter interaction, and band nesting effects. Briefly, the work provides an efficient synthetic route for achieving the 3R‐stacked TMDCs spirals, which can serve as perfect platforms for promoting their applications in on‐chip nonlinear optical devices.