Study of tri-layer antireflection coatings prepared by sol-gel method

Antireflective coatings (ARCs) on tri-layer thin film stacks were studied in this paper. Silica sols have been prepared by acid-catalyzed or base-catalyzed hydrolysis and condensation reactions of tetraethyl orthosilicate. Antireflective nanometric SiO2/TiO2 films are formed on both sides of the glass substrates by combining the sol-gel method and the dip-coating technique. Seen from the transmittance spectra of different films, a maximum light transmittance of 99.9% was obtained at the band of 300-800 nm. Scanning electron microscope (SEM) and atomic force microscopy (AFM) confirm the well-covered surface morphology. By the SEM observations we can see that the films are full of coverage on glass surface and containing no voids or cracks. The image root mean square roughness of the two types of ARCs provided by the AFM is 1.21 and 3.04 nm, respectively. Furthermore, a surface profiler was used to determine the thickness of each layer in the obtained multi-layer coating system.