Fabrication and characterisation of TiO2 anti-reflection coatings with gradient index

Nano-textured anti-reflection (AR) films are designed elaborately to improve the transmittance character and to reduce the surface reflection loss. This work reports the gradient-index titanium dioxide (TiO2) AR coatings (ARCs) with the thickness of 50-400 nm, which was deposited by radio-frequency magnetron sputtering-assisted with the oblique-angle deposition technique on the low-iron glass substrates. The technological parameters related with this deposition were discussed such as the base pressure and target-substrate distance, as well as the vapour incident angle. Then, optical characteristics of the graded-index coating were discussed. An ellipsometric model was built to account for the structural and optical differences. The optimal thickness of the TiO2 ARC was about 250 nm. It exhibited a higher transmittance at the visible light regions over a large wavelength range than that of the primitive glass substrate. The value of refractive index for the TiO2 ARC was 2.245 at the wavelength of 632.8 nm.