Fabrication And Regulation Of Optically Active Defects In Two-dimensional Hexagonal Boron Nitride Atomic Layers

Single photon emitter(SPE)with high brightness,high purity,long lifetime and narrow linewidth has attracted much attention of fundamental frontiers and significantly technical research of multiple fields such as quantum compute,quantum communication and quantum sensing.Defects in hexagonal boron nitride(h BN)have been attracted much attention and investigated in related fields,since these defects have realized the bright and stable SPE under room-temperature.Particularly,h BN offer a great platform for defects modulate photon emission owing to the inherent twodimensional(2D)nature and ultra-wide bandgap(~6 e V).Therefore,the study for optically active defects is important for the scientific significance and practical applications.Recent studies have proved that defects can be created by surface treatments such as chemical etching,ion implantation,plasma etching,electron beam irradiation and other methods in h BN.However,many studies indicate that the defects created by these methods were mainly located at the edge or wrinkle of h BN,which greatly limited the applications of defects,meanwhile the 2D surface of h BN have not been adequately applied.Therefore,generate and regulate defects on a large scale remains the significant challenge.In addition,the nature of the defects induced the photon emission are ambiguous in many studies related the create defects,such as the photon emissions have same energy have classified as different defect states.However,understanding the nature of defect-induced luminescence is crucial for the application of h BN materials in photonics and optoelectronics.Herein,combine the foundation of previous work,the 2D h BN atomic layers prepared by chemical exfoliation were used as the luminescent host,through the hydrogen plasma irradiation under high vacuum environment and annealing at high temperature in air to artificially promote the creation of defect structure in h BN.The following are the main content:(1)The defect engineering of h BN atomic layers were conducted via hydrogen plasma irradiation under high vacuum environment,and have realized the evolution from blue region to yellow region in room-temperature photoluminescence(PL)spectra through change the parameters of hydrogen plasma irradiation.The X-ray photoelectron spectroscopy(XPS)measurement and density functional theory(DFT)have combined to confirm that hydrogen plasma irradiation unintentionally introduced oxygen impurity atoms into h BN,and the luminescence evolution is related to the energy state induced by oxygen-related defects.Through the excitation powerdependent PL spectra measurement,X-ray diffraction(XRD)spectrum and valence band spectra(VBS)for h BN before and after hydrogen plasma irradiation,we found that hydrogen plasma irradiation could effectivelyreduce the effect of trap state,compensate vacancy defects and modulate electronic structure.(2)The defect engineering of h BN atomic layers were conducted through annealing at high temperature in air environment,the modulation of annealing temperature on defects and the influence of the energy states induced by defects on the luminescence properties of h BN were investigated,and we had successfully realized the sharp zero-phonon-line(ZPL).Combine the Fourier transform infrared(FTIR)spectrum,XPS and DFT calculation,we confirmed that annealing introduced the oxygen impurity atoms into the crystal in the form of boroxyl rings,and the evolution of PL spectra is strongly related to the energy states induced by boroxy rings.The XRD patterns of h BN before and after annealing show that annealing at high temperature can significantly reduce the lattice distortion caused by the defects in sample,but the introduction of boroxyl rings makes the lattice distortion of the sample slightly increased.In this work,there are two different methods were used to create the luminescent defects in h BN atom layers exfoliated by chemical methods.Through defect engineering to modulate luminescent,and combine the measurement and theory to confirm the defect-induced luminescence mechanism.Our results provide a reference for modulating the photoelectric properties of h BN and other 2D van der Waals materials.