2D heterostructure 2D/2D heterojunction History of engineering & technology Langmuir-Blodgett technique MoS2 MoS2 nanosheet Nb2O5 interlayer NbSe2 P-doped MoS2 P2O5 Q-switched laser Raman spectroscopy SiO2 V2Se9 WS2 WSe2 atomic crystal band-to-band tunneling (BTBT) bias stress stability bilayer-stacked structure black phosphorus carbon nitride chemical vapor deposition contact resistance disorder ferroelectrics few-layer MoS2 film-substrate interaction flexible substrate g-C3N4