Research On Multi-spectral Zinic Sulfide Surface With Subwavelength Antireflective Micro-nano Structure

Multispectral zinc sulfide?ZnS?has a high spectral transmittance,wide transmission band,which can meet the current development trend of composite imaging.In order to further improve the infrared detection quality of ZnS windows,it is necessary to improve the transmittance of materials.The surface anti-reflection subwavelength structure?AR SWS?of ZnS is a kind of microstructure which is much smaller than the wavelength of incident wave on ZnS surface,and it can effectively reduce the reflection of material.In this thesis,the structure parameters of ZnS AR SWS were calculated by the thin film permeation theory and the equivalent medium theory,and then the subwavelength structure of ZnS surface was simulated by RsoftCVD7.0 software.Silica microspheres were prepared by St?ber method,and monolayer silica microspheres were prepared by vertical deposition on the surface of ZnS as etching mask.Silica microspheres were prepared by St?ber method,and monolayer silica microspheres were prepared by vertical deposition on the surface of ZnS as etching mask.The subwavelength structure of ZnS surface was prepared by inductively coupled plasma etching?ICP?with Cl2 and Ar gas.Finally,the Al₂O₃ film was prepared on the prepared ZnS surface antireflection microstructure by atomic layer deposition?ALD?technique to improve the mechanical properties of ZnS and enhance the reliability of the ZnS infrared window under harsh conditions.The structural parameters of the anti-reflective microstructure of ZnS surface were calculated based on the theory of thin film transmission and the equivalent dielectric theory.Then,the period,fill factor and height were simulated and optimized by RsoftCVD7.0 software.The optimum parameters of the subwavelength structure are determined?T=1 ?m,H=1.68 ?m,f=0.55?.The influence of the Al₂O₃ film thickness on the transmittance was also simulated,the simulation results show that: the proper thickness of the Al₂O₃ film has little effect on the transmittance of the ZnS subwavelength structure.Therefore,we have chosen the Al₂O₃ film with thickness of 100 nm to meet the requirement of increasing the mechanical properties.Single-layer silica microspheres were prepared by vertical deposition on the surface of ZnS substrate as etching mask.The effects of evaporation temperature and solution concentration on the distribution of silica microspheres were systematically studied.When the evaporation temperature is 50 °C and the mass fraction of the solution is 0.15%,the monolayer silica microsphere mask with homogeneous distribution can be prepared.After etching with ICP,it was found that the addition of BCl3 in the etching gas reduced the etching rate,and the etching rate increased with the increase of ICP power,and then decreased with the increase of RF power.Finally,the optimum structure of ZnS subwavelength structure was fabricated by using the best parameters.Finally,a 100 nm thick Al₂O₃ protective film was deposited on the surface of ZnS microstructures using the self-limiting properties of atomic layer deposition?ALD?,the nano-hardness,composition of the Al₂O₃ film and the infrared transmittance and the surface wetting angle of the ZnS subwavelength structure with Al₂O₃ protective film were measured.The results show that: when the deposition temperature is 240 ?,the nano–hardness of Al₂O₃ is 6.51 GPa,which is higher than the hardness of ZnS?2.5 GPa?.The transmittance of sub-wavelength structure of ZnS prepared by the optimal etching parameters in 400¹500 nm band is increased by nearly 12.5% compared with that of bare ZnS?70.92%?;and in 3¹2 ?m band,the transmittance relative to the bare ZnS is improved by nearly 6.7%,and the antireflection in the wide band is realized;the surface hydrophobicity of modified ZnS was enhanced,its wetting angle increased from 101.33 ° to 105.48 °,which improved the hydrophobicity of the surface.