Manipulation On The Photoluminescence Properties Of Monolayer MoS₂ By Laser Field And Its Applications

Since the successful of monolayer graphene was acquired by mechanical exfoliation in 2004,the research on the basic physical properties and application of two-dimensional materials has become one of the most active and concerned fields in physics,and even chemistry,biology and materials science.In particular,the discovery of two-dimensional transition metal dichalcogenides?TMDs,such as MoS₂,WS₂,etc.?with band gaps not only fills the limitations of graphene which is without band gaps,but also displays its own unique physical and chemical properties,such as the conversion from indirect band gap to direct band gap with decreasing number of layers,which lead to a significant increase in exciton radiation caused by quantum confinement effects and dielectric shielding effects,and stable multibody interactions can be exist at room temperature?charged Excitons and double excitons,etc.?.In recent years,it has also been discovered that the"valley"physics?including valley spin,valley Hall effect,etc.?and Mohr superlattice at room temperature,too.These characteristics on the one hand provide an effective experimental platform for the study of basic physical properties,on the other hand provide unlimited opportunities for the development of optoelectronic devices based on two-dimensional materials.At present,Field Effect Transistor?FETs?,flexible electronic wearable devices,sensors,micro/nano lasers,photodetectors and other devices based on two-dimensional materials of TMDs have shown excellent performance and have become important candidate to replace traditional silicon-based electronic devicesIn the application of TMDs-based devices,the manipulation of their exciton radiation characteristics is one of the most attractive directions,which will make an important foundation for optimizing the performance of optoelectronic emitters,lasers and photodetectors.Among the so many control methods reported,defect doping and electric field control have the best effect.However,defect doping?including chemical molecular doping,gas molecular doping and lattice defect doping,etc.?is often accompanied by permanent damage to the monolayer TMDs material structure,and the control effect cannot be reversible.Although the electric field control has the characteristics of flexibility and convenience,reversible control,etc.However,the biggest problem is that the micro-nano electrode will destroy the crystal structure to some extent during the preparation process,and the complexity of the preparation process brings certain limitations to practical applications.In particular,these two control methods are all global control,the spatial resolution is low,which means it is lack of micro-nano devices that should be displayed as an advantage in spatial resolution,and it is difficult to achieve the control of the photoelectric characteristics of specific regions according to needs.In order to simplify the regulation process and improve the spatial resolution of regulation,this paper is mainly to study the exciton radiation on lattice defects and gaseous environment which is combines the laser mode,laser power,and laser power with parameters such as excitation power and irradiation time based on the monolayer MoS₂.Sensitivity,it is proposed to realize continuous reversible regulation of monolayer MoS₂fluorescence spectrum,fluorescence intensity,and spin-orbit coupling?referred to as SOC?by using lasers with different parameters.By using continuous laser irradiation with low power density,the precise control of the fluorescence spectrum of monolayer MoS₂ has been achieved,and high-density optical storage applications based on wavelength division multiplexing of fluorescence spectrum have been explored.By using short-pulse,high-power-density femtosecond laser irradiation,the MoS₂ fluorescence intensity was increased to two orders of magnitude,and the modulation time was reduced to two orders.The preparation of micro/nano structures illuminated by femtosecond irradiation was explored.Combining the laser irradiation with the gas environment,spin-orbit coupling of monolayer MoS₂ was achieved.The main innovations of this thesis:1.A new principle is proposed to precisely regulate the radiation characteristics of monolayer MoS₂ photoluminescence.According to the sensitivity of monolayer MoS₂exciton radiation to lattice defects and the dependence of laser-induced defects on laser mode and excitation power,it is proposed to adjust the number of defects by optimizing laser parameters:continuous laser irradiation with low power density,used to gradually increasing the number of defects in monolayer MoS₂.It is can be used to precisely adjust the ratio of neutral excitons and charged excitons which can achieve the precise control of the fluorescence spectrum of monolayer MoS₂.The use of high power density femtosecond laser irradiation can quickly increase the number of defects in monolayer MoS₂.The fluorescence intensity is greatly improved in this way.With gas-assisted,reciprocal regulation of the A and B exciton ratio by laser irradiation is achieved to achieve reversible regulation of the monolayer MoS₂ spin-orbit coupling.2.Realize the precise fluorescence spectrum control of monolayer MoS₂.The monolayer MoS₂ was irradiated with a 405 nm continuous laser,and the lattice defect of monolayer MoS₂ was controlled.The conversion of neutral excitons and charged excitons was controlled by optimizing the laser power.The center position of the spectrum was regulated from 700 nm to 674 nm continuously,and the maximum regulation rate reaches0.1 nm/s.Based on continuous and precise control of the fluorescence spectrum,wavelength division multiplexed optical storage is realized on monolayer MoS₂,which can significantly increase the optical storage capacity.3.Greatly enhanced the fluorescence intensity of monolayer MoS₂.Irradiate by 780nm femtosecond laser,fluorescence intensity of monolayer MoS₂ increases by more than two orders,and the maximum enhancement range is more than 500 times;on the other hand,compared with the traditional method,the enhancement time is shortened by two orders of magnitude.4.Spin-orbit coupling is realized in our lab based on monolayer MoS₂.By 532 nm continuous laser irradiation,we successfully realized the reversible regulation of spin-orbit coupling of the monolayer MoS₂ combined with its sensitive to the gas environment.The results show that the corresponding A exciton and B exciton peaks can be achieved;and its fluorescence spectrum can be continuously adjusted from 684 nm to 641 nm.At the same time,the fluorescence intensity was increased more than 30 times.Erasable information can be stored and displayed based on reversible fluorescence regulation.And the stability of this operation was also verified very well.