Tailoring The Luminescence Properties Of Two-dimensional Hexagonal Boron Nitride Atomic Layers Via Defect Engineering

Defects play an important role in determining material properties.In particular,in low-dimensional systems,defects have a very significant effect on the movement and regulation of photons and electrons in materials.In order to the ultimate functionalization of two-dimensional materials,it is necessary to deeply understand and accurately control the defects.Hexagonal boron nitride(h-BN)is a typical layered two-dimensional material,which has broad application prospects in the fields of catalysts,optoelectronics and semiconductor devices.h-BN is an ultra-wide band gap semiconductor material(>6 e V)with abundant defect centers,which provides an ideal platform for in-depth study of defect types,precise control of defects and modulation of photoelectric properties.In this work,two-dimensional atomic thin layer of h-BN was prepared by chemical exfoliation,with a thickness of about 1-3 atomic layers.Hydrogen plasma irradiation is used to create control the defects on the surface of the two-dimensional h-BN atomic thin layers in a high vacuum environment.The evolution of room-temperature photoluminescence spectrum of h-BN is observed from purple to green according to the hydrogen plasma irradiation.By using high-resolution electron transmission microscope,the defect concentrations of boron vacancy(V_B)and nitrogen vacancy(V_N)are statistically obtained,in which V_B and V_N monotonously increases with the increase of the hydrogen flow.Combined exploitation of multiple analysis tools,the-OH functional groups are observed throughout the surfaces of h-BN,which are introduced via hydrogen plasma irradiation.Theoretical calculation results show that with the gradual increase of hydrogen plasma irradiation,a large number of shallow electronic states with low activation energy are generated near the edge of the conduction band,resulting in a strong delocalization of bound exciton states.Based on the experimental observations of hydrogen plasma irradiation to regulate defects and their substantive effects on photoluminescence and the joint characterization of first-principles theoretical predictions,the defect center and the luminescence mechanism have been confirmed.These findings provide a feasible and effective way to tailor the optically active defect centers of h-BN as well as other 2D materials for the future applications in atomic-level optoelectronic devices.