Design And Sol-gel Preparation Of Optical TiO₂/SiO₂ Multilayer Films

The optical thin films can be classified as high-reflective thin film,band pass filter and antireflective thin films.They have wide application in the fields of liquid crystal displays,laser system,sensors,solar cells,and so on.Presently,optical thin filmsare mainly fabricated using PVD techniques such as electron beam deposition,which enables the deposite of thin films with fine-controlled thickness,uniform film surface and good adhesion.However,films by PVD are prepared in vacuum conditions resulting in high production cost.As a wet chemical method,sol-gel preparation of thin films has advantages of vacuum-free,excellent compositional control and lower crystallization temperature,making it a potential method to fabricate low-cost optical thin films.In this paper,the Essential Macleod software was combinedwith the sol-gel method to design and fabricate the TiO₂/SiO₂ based high-reflective thin film,TiO₂/SiO₂ based long wave band pass filter,TiO₂/SiO₂ and SnO2/SiO₂ antireflective thin films?AR?.Additionlly,in order to obtain optical thin films with tunable refractive-index,sol-gel preparation of porous TiO₂ thin film was also attempted.The optical constants of raw material used in the Essential Macleod design were directly extracted from the TiO₂ and SiO₂ thin filmsfabricated by the sol-gel methold.With the optical constants of raw materials,periodic multilayers with structure of Glass|?HL?^s|Air were employed to design the TiO₂/SiO₂ based high-reflective thin films with center wavelength of 600 nm.Following the simulated results,the multilayers fabricated by the sol-gel methold.The experimental results reveal that the average transmittance of the TiO₂/SiO₂ multilayersare 0,2.60% and 59.32% in the range of 550⁶50 nm,500⁷00 nm and 700¹100 nm,respectively,which is consisitent with the design value.Furthermore,periodic multilayers with structure of Glass|?0.5HL0.5H?s|Air were employed to design the TiO₂/SiO₂ based long-pass filter,which is fruther fabricated by the sol-gel methold.The average transmittance of the experimental TiO₂/SiO₂ filteris 1.23% and 77.48% in the range of 550⁷00 nm and 700¹100 nm,repectively.Especially,0% transmittance in 550⁶50 nm implys the complete filtering of light in this range.The Essential Macleod software was used to design and optimize the two broadband TiO₂/SiO₂ and SnO2/SiO₂ multilayer antireflective coatings.The design results show that the average transmittance of the 6-layer TiO₂/SiO₂ and the 5-layer SnO2/SiO₂ are 95.44% and 97.89% in the range of 400⁸00 nm,respectively.The experiment results reveal that the average transmission of TiO₂/SiO₂ and SnO2/SiO₂ multilayers are 95.07% and 95.07%.The TiO₂-ZnO composite films with different compositional ratios were firstly produced by the sol-gel methold,and porous TiO₂ thin films with low refractive-index was obtained after the the composite films were subjected to acidic etching.The experiments show that the refractive-index of the porous TiO₂ thin film at 520 nm can be tuned from 2.33 to 1.85.The porosity of the TiO₂ film increases with the etching time increasing,resulting in a lower refractive-index and extinction coefficient;however,the transmittanceof the films also becomes poor.