| In recent years,the rapid development of electronic information technology and the excessive use of electronic equipment have caused serious electromagnetic radiation interference.The undesirable electromagnetic interference not only provokes the malfunction of electronic device,threatens the information security of communication equipment,but also presents a hazard to human body that has become a serious concern in modern society.Therefore,many fields have put forward the requirements for electromagnetic interference shielding.In this thesis,with the guide of the cutting-edge research and protection demands on sophisticated instruments and equipment,there provides solutions for different application scenarios based on the bottleneck problem of the index contradictoriness between traditional shielding material,in order to meet the demand for electromagnetic shielding on precision optoelectronic devices and aircraft optical windows.That comprehensively realizes the compatibility and integrated design of electromagnetic protective materials with both high shielding efficiency and high optical transmission.This thesis adopts the micro-nano processing with the combination of micro-nano patterning and selective electrodeposition method,to realize the independently regulation of optical transmittance and electrical conductivity,so as to achieve the electromagnetic shielding films of high optical transmittance and strong shielding efficiency.Based on the adjustable metallic mesh,three types of high-performance flexible and transparent electromagnetic shield films are proposed:freestanding metallic mesh electrodes,silver nanowires(AgNWs)/metallic mesh composited freestanding electrodes,and double-layer metallic mesh electrodes.These electrodes effectively break through the contradiction between the optical transmission and electromagnetic shielding properties of existing electromagnetic interference shielding materials,and simultaneously equipped with good image quality and mechanical stability.The main contents and results are as follows:(1)In order to solve the problem of poor flexibility and attachment of metallic mesh electrode,a freestanding Ni mesh electrode without substrate is proposed and prepared.The Ni mesh electrode is obtained with the combination of graphical laser direct writing technique and Ni electrodeposition process.The freestanding Ni mesh electrode is achieved by peeling off from the substrate deftly.The freestanding electrode without substrate avoids a serious of shortcomings on account of the properties of substrate(Optical transmittance～92%,working temperature<150℃,characteristic thickness of hundreds of microns,et al.).The substrate-free property enables the metallic mesh electrode with superior optical transmittance(92%～94%),ultrathin thickness(2.5 μm～6.0 μm)and lightweight(0.23 mg/cm2)characteristics that guarantees the freestanding Ni mesh with outstanding flexibility and mechanical strength.With the sample analysis and experimental test,it indicates that,the fabricated freestanding Ni mesh can sling up the weight of more than 4000 times of its own without any deformation.The Ni mesh can maintain stable conductivity(～95%)under bending radii from 1 mm to 3 mm even after cyclic bending up to 2000 times.Meanwhile,owing to the hollowed-out mesh character and dismissing the effect of the substrate,the micro-mesh structure can support a certain amount of deformation which provides the freestanding electrode a 30%tensile.The foldable,bendable and stretchable properties deliver that the freestanding Ni mesh electrode can be attached to arbitrary shaped objects.(2)In order to solve the problem of concentrated distribution of high order diffraction in metallic mesh,a randomly structured metallic mesh arrangement is designed after exploring the diffraction characteristic of the existing metallic mesh.Both the simulation and experimental test indicate that the metallic mesh with random structure possesses homogeneous high-order diffraction distribution,the uniform distribution of high-order diffraction avoids the concentrated stray light and the further influence on image quality.Additionally,for the double layer metallic mesh,the randomly structured mesh arrangement effectively eliminates the Moire fringe generated by double layer periodic meshes,ensures the high-quality optical imaging with clear macro visual effect.(3)In view of the contradictoriness between optical transmittance and shielding effectiveness(SE)of the metallic mesh,this paper proposes three solutions based on the randomly structured metallic mesh electrode,as follow:1)Adjust the vertical thickness of the fabricated metallic meshes when keeps the aspect ratio unchanged to ensure the electrodes with identical optical transmittance.The electrode thickness can be accurately controlled by adjusting the nickel deposition time.The electrodes deliver an enhancement of 4 dB in SE value with the thickness increased from 2.5 μm to 6.0μm while remains the transmittance of 92%～93%at 550 nm wavelength.2)Enhance the shielding efficiency of the freestanding metallic mesh with the combining of AgNWs.With the compound of AgNWs,the hybrid freestanding AgNWs/Ni mesh electrode reveals a significant improvement throughout the X-band(8.2～12.4 GHz),the SE value of the hybrid electrode increases to 41.5 dB which is much better than the bare Ni mesh of 30 dB.Meanwhile,compared with the Ni mesh with a micrometric width,the AgNWs of nanoscale diameter have teeny impact on the width of the hybrid electrode,giving the hybrid electrode excellent optical transmittance(93%～94%at 550 nm).3)Achieve higher electromagnetic shielding performance through the superimposing of double layer Ni mesh(～80 dB).In the case of the same transmittance,the double layer Ni mesh has an obviously increase in SE value(5～9 dB)compared to the single layer Ni mesh.And for the double layer and single layer Ni mesh of same SE value,the double layer Ni mesh reveals a better optical transmittance.In addition,by increasing the separation distance between the double layer Ni mesh,the SE value can also be improved without transmittance loss.The freestanding metallic mesh electrode,hybrid AgNWs/metallic mesh electrode and double layer metallic mesh electrode in this thesis can all realize the performance of high optical transmittance,good mechanical flexibility,well image quality and strong shielding efficiency,which can satisfy the demands for different shielding requirements and application scenarios. |
