A novel route to control refractive index of sol-gel derived nano-porous silica films used as broadband antireflective coatings

A relatively new method to adjust refractive index of nano-porous silica fi lms rapidly and continuously is reported. The thin films were prepared with the base/acid two-step catalytic sol-gel process and the dip-coating metho d. The structure, reflective spectra and refractive index of the films were analyzed with TEM, AFM, SEM, spectrophotometer, and ellipsometery, respect ively. The experimental results have shown that the base/acid two-step cata lysis can adjust the refractive index of the nano-porous silica films from 1.18 to 1.42 rapidly and continuously. And a broadband antireflective coati ng made with the method has very low reflectance. The average reflectance o f the coated glass in the solar energy spectrum decreases to 1.5% from simi lar to7% of the glass. (C) 2000 Elsevier Science S.A. All rights reserved.