Simulation, Preparation And Characterization Of Graded Refractive Index Antireflective Coatings With Porous Nanostructure

In order to explore the broadband and omnidirectional antireflectiveperformances optical simulations of pyramid model coatings had been accomplishedby means of running programs and software under the guidance of theoretical analysison gradient refractive index antireflective coatings. In the experiment borosilicateglass3.3(consists of wt.81%SiO2,13%B2O3,4%Na2O,2%Al2O3) that had beenannealed3hours at the temperature of550℃were leached by HNO3under differentconditions of temperature and length of time for the sake of achievinggraded-refractive-index porous nanostructured antireflective coatings. Field emissionscanning electron microscopy （SEM） was used to observe the surface andcross-section morphologies of the coatings. Spectrophotometer was used to observeparallel and variable angle of incident light transmittances. The results show:(1) Simulation results show that the reflectivity of graded-refractive-indexpyramid model coatings will decrease as the thickness increases once the light isvertical incident. The reflectivity decreases to0.0367-0.1458%when the thickness ofcoating increases to1μm. The coating owns perfect omnidirectional antireflectiveperformance. Even when the Angle of incident light increases to75°, the reflectivitystill holds at the range of13.1582-16.3702%.(2) The surface of antireflective coating turns to be steady porous SiO2nanostructure. The holes distribute evenly specifically the pore diameter of which is20-40nm and the depth is120-200nm. Once the length of leaching time of glass is tooshort the holes are sporadic and too long over-connected but the thickness of coatingnearly has no change.(3) The transmittance of antireflective glass which were leached33minutes by0.2mol/L HNO3at the temperature of50℃reaches to98.5%which is4%-7%higherthan the common ones but1%lower than the simulation one at some shortwavelength. The coating achieved by experiment really owns perfect omnidirectional antireflective performance. when the Angle of incident light increases to75°, thereflectivity is lower than20%.(4) The peak transmittance of antireflective glass decreases after increase firstlyduring a rather long length of leaching time and its corresponding wavelength has ared shift phenomenon. Within a certain temperature experiment under highertemperature can speed up the reaction resulting in shorting the cycle of preparation.(5) Meanwhile the antireflective glass owns excellent antifogging property.