Laser Thinning,Modification And Patterning Of Two-dimensional TMDC

Two-dimensional(2D)materials can be applied to new electronic and photonic devices due to their unique physicochemical properties,such as quantum confinement effect,easy regulation of charge carriers,strong nonlinear optics,and easy stacking integration.Obtaining 2D materials with controllable size,shape,and thickness on substrates is an important step to realize functional devices.Due to the advantages of good controllability and high efficiency of laser processing of 2D materials,it has received great attention in recent years,and there have been many reports on this research direction.In this thesis,we mainly focus on the laser thinning and modification of 2D transition metal dichalcogenides(TMDC),and realize the thinning of four kinds of mechanically exfoliated thick-layer TMDC crystal materials.modulating the electrical properties of WS₂and WSe₂devices by laser modulation of water and oxygen adsorption;using laser oxidation and doping effects to alter the photoluminescence(PL)intensity of GaSe and WS₂single crystals.The specific research contents and conclusions are as follows:(1)The energy absorption and transfer in the process of continuous laser acting on two-dimensional materials were analyzed,and the feasibility of laser thermal effect thinning was verified by COMSOL software simulation.This study designed a laserdirect writing experimental platform integrating multiple functions of microscopic observation,laser writing,and test characterization,and two scanning modes,rectangular and graphic,were realized,and the feature size test was completed.The diameter of the focused laser spot was about 1.3?m.(2)In the thinning work,the four kinds of thick-layer crystals(WS₂,MoS₂,WSe₂,and MoSe₂)mechanically exfoliated on the Si/SiO₂substrate can be thinned into monolayer by using the thermal effect of the CW laser.The effects of laser intensity and exposure time on the thinned minimum feature size were explored,and micro-patterned etching of thin layers of materials was achieved.(3)In the study of laser affecting the optoelectronic properties of materials,this thesis found that the responsivity and response time of the WS₂photoconductive detector were affected by water and oxygen molecules,and were regulated by laser treatment.For bipolar WSe₂FET devices,the introduction of water and oxygen at the contact position between the electrode and the material by laser action can effectively reduce the interface contact resistance and improve the hole carrier mobility.(4)In the study of laser affecting the fluorescence properties of materials,this study found the effect of oxygen atoms repairing defects under the action of laser,which enhanced the photoluminescence(PL)intensity of WS₂monolayer materials.For the fluorescence quenching effect of GaSe multilayer materials,the mechanism of accelerated material oxidation by laser local high energy was explained.Laser action(processing)technology provides a new method for the controllable processing and property tuning of 2D TMDC materials.The experimental research in the paper proves that the laser action can be used to obtain single-layer materials,improve the contact characteristics between the material and the electrode,and adjust the carrier transport characteristics of the device and the luminescence characteristics of the material.It is foreseeable that the site-specificity and high-efficiency patterning capability of laser processing will provide new ideas for the application of new device structure design,fabrication,and device arraying of two-dimensional materials.