Controllable Synthesis of Atomically Thin 1T‐SnSe 2 Flakes and Its Linear Second Harmonic Generation with Layer Thickness

As an important member of the IVA–VIA group compounds, 2D SnSe 2 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 SnSe 2 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‐SnSe 2 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 SnSe 2 flakes. More intriguingly, obvious second harmonic generation (SHG) is revealed in the retained inversion symmetry structure of 1T‐SnSe 2 , 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 SnSe 2 crystals, and their unique optical property explorations and applications in nonlinear optics.