Research On Deterministically Engineering Of Defects In Hexagonal Boron Nitride And Their Optical And Spin Properties

Hexagonal boron nitride(hBN)is a chemically stable layered van der Waals crystal,and few-layer hBN can be prepared with bottom-up or top-down methods.At present,the host of solid-state spin systems exhibits a trend of expanding from three-dimensional solids to twodimensional materials.Researchers have discovered optically active defects with quantum application prospects in hBN.These defects are widely used in advanced technologies such as quantum computing,quantum communication,and quantum sensing,whether as single photon sources or due to the correlation between optical excitation-recombination cycle and spin orientation.However.the emissions of optically active defects in hBN are complex,with wavelengths involving ultraviolet.visible.and near-infrared.For many of them,researchers cannot yet correspond to an exact crystallographic source.However,there has gradually been a widespread recognition of two emission characteristics,namely visible light emission with a zero phonon line of about 2 eV and boron vacancy fluorescence with a central wavelength of about 850 nm.under excitation at 532 nm.This work notes that most studies focus on the characterization of solid-state spin systems,often neglecting the uncertainty of the preparation process,as a result,making the correlation between the preparation method and the spectrum(type)or space of defects still relatively vague.Two methods,high-energy electron irradiation and femtosecond laser direct writing,were used to prepare optically active defects in hBN flakes in this article,and we studied the optical properties of all and spin properties of part of these defects.At the same time,this article is also committed to exploring the deterministic relationship between preparation methods and the generation of optically active defects,striving to improve the controllability both spectrally and spatially.NBVN defects were introduced in hBN flakes through highenergy electron irradiation.Due to the influence of strain and dielectric environment,this defect exhibits two different optical emission characteristics:629 nm and 650 nm.Thereby,the relationship between the optical properties of defects and irradiation energy and dose was obtained.We built a femtosecond laser direct writing optical system which is distinctive and suitable for preparation of various solid-state defects.We first performed laser irradiation on the hBN flakes to produce defects,and then characterized the their fluorescence,confirming the creation of NBVN defects with a central wavelength of 629 nm.This method simultaneously generated boron vacancy defects,spin properties of which was studied.The optically detected magnetic resonance spectrum showed a fluorescence intensity dependent on microwave frequency near the resonance frequency of boron vacancy defect.In addition,we compared the differences in preparation effect between femtosecond laser and electron irradiation,and found the applicability of femtosecond laser direct writing for different host materials,providing a reference for device integration of two-dimensional materials.