Spectroscopic characterization of the as-grown 2D In2Se3 in the confined micro-reactor. (a) Raman spectra of In2Se3. The three typical Raman peaks at ~108, ~180, and ~203 cm−1 are attributed to the A1(LO+TO), A1(TO), and A1(LO) phonon modes of In2Se3. (b) Raman intensity map of a 2D In2Se3 flake with a thickness of ~10 nm, showing good uniformity. (c, d) XPS spectra of the In 3d and Se 3d in In2Se3. (e) UV-Vis-NIR absorption spectrum of the In2Se3 grown on mica. (f) hν versus (αhν)2 plot of the sample.