Fabrication and characterization of TiO<inf>2</inf> antireflection coatings with gradient-index

Abstract

Nano-textured anti-reflection films are designed elaborately to improve the transmittance character and to reduce the surface reflection loss. This paper reports the gradient-index TiO 2 anti-reflection coatings (ARC) of 50–400 nm were deposited at low pressure (0.6Pa) and target-substrate distance (85mm) on low-iron glass substrates using magnetron sputtering (MSP) assisted with the oblique angle deposition (OAD) technique with different vapor incident angled module. The impact of growth on the film characteristics was studied by in situ spectroscopic ellipsometry (SE), scanning electron microscopy (SEM), Raman spectroscopy and UV-VIS spectrophotometer. Suitable ellipsometric models were built to account for the structural and optical differences. The experimental results were discussed on annealing temperature or incident angle, crystallization parameters of the sub-wavelength nano-structural anti-reflection film. The optimal thickness of the TiO 2 ARC was about 250nm. 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 TiO 2 coating was 2.245 at the wavelength of 632.8 nm.