Technical Research On Galvanometer Scanning Laser Welding Of Silver Nanowire Networks Based On Near-field Optics

Silver nanowires are ideal materials to replace Indium Tin Oxide(ITO)to make transparent conductive electrodes in the future.The contact resistance between silver nanowires reduces the conductivity of silver nanowires and restricts the large-scale application of silver nanowires conductive electrodes.Seeking effective methods to reduce contact resistance and improve the conductivity of silver nanowire networks has become the current technology frontier and research focus.Aiming at the bottleneck problem of improving the conductivity of silver nanowire network,a laser galvanometer scanning welding method based on near-field optics is proposed.The experimental study and process parameters optimization of laser welding of silver nanowire network are carried out.The main research contents are as follows:(1)The theoretical analysis of laser welding of silver nanowire contact points was carried out.Based on the interaction between laser and metal materials,the mechanism of laser and silver nanowires in the optical near-field is analyzed.The principle and its generation conditions of near field enhancement effect of silver nanowires under laser irradiation are discussed.The process law of near-field optical enhancement effect in laser nano-welding is revealed: In the first stage,a laser with a certain power is irradiated on the surface of the silver nanowire network.In the optical near-field space,the gap between the contact points of silver nanowires produces local field enhancement and amplification,which produces heat;In the second stage,the laser irradiation continues and local field enhancement promotes heat accumulation;In the third stage,the local heat accumulation makes the temperature of the nano-gap rise,melt and weld.The technical principle of laser nano-welding is further analyzed,which lays a theoretical foundation for numerical simulation and experimental research.(2)Based on the finite-difference time-domain(FDTD)method,the welding model of silver nanowires was simulated at the wavelength of Gauss incident light,which provided a theoretical basis for carrying out specific experimental research.The simulation model of silver nanowire welding was established.The electric field distribution of the interaction between 1064 nm,532nm and 355 nm Gauss incident light and silver nanowire was simulated by finite-difference time-domain method.The effects of different incident light wavelengths on near-field enhancement effect were studied.The variation process and mechanism of field enhancement amplification,melting and welding during nanowire welding were verified.The results show that the near-field enhancement effect occurs,and the near-field enhancement effect becomes more intense with the shortening of wavelength.For the research object of this paper--silver nanowires(melting point 873K)with a diameter of 100 nm,the enhancement effect of 355 nm light irradiation is too intense to cause damage to the structure of silver nanowires;the weaker enhancement effect of 1064 nm light irradiation is difficult to ensure good welding,compared with 532 nm light irradiation,the enhancement effect is obvious,and the welding effect can also be better guaranteed.After comprehensive analysis,532 nm wavelength incident light was selected as the light source for the experimental research process.(3)Laser galvanometer scanning silver nanowire network welding experiments and process parameters optimization were carried out.In order to reduce the contact resistance of silver nanowires and improve the conductivity of electrodes,the galvanometer scanning welding experiments were carried out with 532 nm nanosecond laser and femtosecond laser.The effects of laser power and illumination time on the welding quality were studied.On the premise of ensuring effective welding,aiming at improving welding quality and efficiency,the welding parameters(laser power,illumination time)of silver nanowire network were optimized,and the post-welding performance was characterized.The results show that the contact resistance of silver nanowires is reduced by 50% after laser welding,and the conductivity of silver nanowires is greatly improved.Based on the single-point welding of silver nanowires,the laser nano-welding process in the laboratory was improved,and the silver nanowire network was welded by galvanometer scanning.The simplified process suitable for industrial laser welding of silver nanowires was designed and optimized.