Large-scale 2D PbI2 monolayers: experimental realization and their indirect band-gap related properties.

Large-scale PbI2 monolayers and few layers with high crystallinity and a uniform hexagonal shape were synthesized via a facile physical vapour deposition (PVD) method. The transition from a direct band-gap in the bulk to an indirect band-gap in the monolayer is verified by photoluminescence (PL) spectra, optoelectronic properties, and first principle calculations.