Phase-Engineered Growth of Ultrathin InSe Flakes by Chemical Vapor Deposition for High-Efficiency Second Harmonic Generation.

As a novel layered indium selenide (InSe) semiconductor has been attracting considerable interest in the field of modern (opto)-electronics. Despite current progress, the synthesis of ultrathin InSe nanoflakes still poses quite a challenge, due to its universal co-existing varied stoichiometric compounds. In this work, a novel phase-engineered route is proposed for synthesizing ultrathin single-crystalline InSe nanoflakes with the assistance of a stable mass-transfer process in a space-confined chemical vapor deposition (CVD) system. By finely tuning the growth parameters, InSe can be obtained through engineering a phase-transition thereby eliminating the undesirable In2 Se3 phase, revealed by the synergistic effect of high-content H2 and deficient Se. Furthermore, owing to the non-centrosymmetric structure, the CVD-grown InSe nanoflakes exhibit a high-performance second harmonic generation (SHG), making it very promising for future SHG applications in 2D configurations. This approach paves the way for the synthesis of other similar ultrathin materials with multiphase homologous compounds.