Preparation And Study Of Hydrophobic SiO₂ Antireflective Film

The ordered mesoporous SiO2 antireflective films(AR)prepared by sol-gel method have the advantages of high transmittance,regular and orderly pore structure,large specific surface area and porosity,as well as low cost and have been widely used in optical components.In actual use,the film’s optical properties will obviously decrease due to the moisture and organic matter in the environment.After reasonable modification,the environmental stability of the film can be improved.In this thesis,the stability of mesoporous silica optical AR coatings in environments is improved by surface modification with fluorosilane chains or methyl groups.A stable silica colloid is prepared using the sol-gel method by hydrolysis and condensation of tetraethyl orthosilicate(TEOS)as a precursor in an acid-catalyzed ethanol solvent using triblock copolymer F127 as a template.The coating is prepared by dip-coating after the colloid has aged.After ammonia exposure and heat-treament,the ordered mesoporous silica film shows high transmittance of 99.83%at central wavelength and omnidirectional AR property under both p-polarization and spolarization.To effectively prevent water adsorption due to hydroxyl groups and microporous openings,surface modifications are performed by grafting fluorosilane chains or methyl groups.The modified coatings are stored in a controlled environment at 80%RH and 40℃,and the transmittance peak at the central wavelength is almost not degraded in the first month.With increasing the test time to 2 months,the minimum loss of transmittance peak is found to be only 0.22%for the film modified with longchain fluoroalkylsilane.The mechanism of the surface treatment is discussed based on the combined analysis of the porous structure and film optical performance by UV-Vis spectrophotometer,TEM,N2 adsorption-desorption,and ARM.According to the λ/4-λ/2-λ/4 type of film system design,three layers of antireflective film were constructed.Assisted by Filmstar thin film design software,film thickness for each layer is optimized based on actual optical constants of the three mesoporous silica films.By adjusting the molar ratio of the template ethylene oxide-propylene oxide-ethylene oxide triblock copolymer to silicon source.A three-layer tri-wavelength broadband antireflection coating with a refractive index gradient was prepared on quartz substrate.The top layer achieved an ultra-low refractive index.The three layers generate a reasonable refractive index gradient from the air and thus the obtained AR coating possesses high transmittance of 99.24%,99.66%,and 99.64%at 351 nm,527 nm,and 1053 nm,respectively.The microstructure of the single layer was observed,and the surface morphology of the multilayers was characterized.The mesoporous SiO2 films with tough skeletons despite different porosity endow the coating with good abrasion-resistance,and 1H,1H,2H,2H-Perfluorodecyltriethoxysilane is further used to modify the surface of the AR coating,which can improve the stability of the coating.This work provides beneficial references for AR coating production of the sol-gel technique.