Study On Preparation And Properties Of Sapphire With Micro-nano Structure Based On Facile Masks

Sapphire as one of the most important optical materials has become widely uesd in many fields,such as optical window,optical detectors and flat plan displays.Sapphire has a lot of advantages,such as high hardness,transmittance,and strong ability to resist radiation.However,the wettability of sapphire is poor and it cannot meet the requirement of high performance.Anti-reflective coatings(ARCs)have evolved into highly effective reflectance and glare reducing components for various optical equipments,due to the thermal expansion coefficient between coatings and sapphire are different,that will lead the film be falling off easily.Inspired by the moth-eye structure,a large quantity of biomimetic antireflective surfaces have been fabricated on transparant materials using high cost etching equipment.Hence,a simple method for prepare etching masks has been proposed by the evaporative coassembly of a sacrificial polystyene(PS)colloidal spheres template with sol-gel silicate infiltration in one step.The prepared template act as etching mask for the wet etching of sapphire.This paper use scanning electron microscopy and atomic force microscopy to characterize silica mask and sapphire subwavelength surface,use ultraviolet–visible transmission spectra and angle contact tester to characterize its antireflective and wettability.Based on the theory of equivalent dielectric theroy,the structural papameters of the subwavelength microstructure of sapphire surface were calculated.The period,fill facter and depth of subwavelength structure were simulated and optimized by Comsol Multiphysics software.The optimum parmeters of the subwavelength structure are determined(T = 100 nm,H = 175 nm,f = 0.78).The reflection of sub-wavelength structure of optimum parameter in 400~800 nm band is 3.69%.Monolayer pore-like silica mask were prepared by co-assembly of polystyene and sol-gel silicate.The effects of solution concentration of polystyene and Evaporation solvent were systematically studied.When the volume of the solution is 0.5%,The momolayer pore-like silica mask with homogeneous distribution can be prepared.Results show that the surface morphology of the prepared template was the best when the temperature was 45 ? and the volume ratio of ethanol and water is 2:3.At the same time,the effect of sintering temperature on the corrosion resistance of silica mask was also explored.It is found that the best etching resistance is achieved when the sintering temperature is 800 ?,and the morphology of the mask does not change at this temperature,which can be used for wet etching.Wet etching is used to etch the sapphire with the silica mask covered on the sapphire surface,and the influence of different temperature and time on the morphology of the etching is systematically studied.The results show that the morphology is relatively regular at 300 ? and close to the simulated value.With the extension of etching time,the fill factor of subwavelength structure changed,and three kinds of etching topographies appeared.According to the characteristics of sapphire crystal structure,the formation mechanism of different morphologies was systematically analyzed.The transmittance and the contact angle of sapphire samples with different etched morphology on the surface were tested.The results show that the cone subwavelength structure with the largest occupancy ratio has the best transmittance of 91.7%.Compared with the bare sapphire transmittance increased by 6.7%,the maximum pyramid sapphire sub-wavelength structure occupies the wetting angle from 60° to 12.6°,so that the hydrophilic surface of the material is improved.The visible light transmittance of sapphire with bionic pyramidal subwavelength structure on the surface was tested.The results show that the structure improves the transmittance of sapphire from 85% to 90.2%.