Optical properties of sol-gel deposited Al2O3 films

Highly transparent, uniform and corrosion resistant Al2O3 films were prepared on stainless-steel and quartz substrates by the sol-gel process from stable coating solutions using aluminum-sec-butoxide, Al(OBu5)(3) as precursor, acetylacetone, AcAcH as chelating agent and nitric acid, HNO3, as catalyzer. Films up to 1000 nm thick were prepared by multiple spin coating deposition, and were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), optical spectroscopy and micro Vickers hardness test. XRD of the film heat treated at 400 degrees C showed that they had an amorphous structure. XPS confirmed that they were stoichiometric Al2O3. The refractive index (n) and extinction coefficient (k) were found to be n = 1.56 +/- 0.01 and k = 0.003 +/- 0.0002 at 600 nm, respectively. The surface microhardness and corrosion resistance investigations showed that Al2O3 films improved the surface properties of stainless-steel substrates. (C) 1999 Elsevier Science B.V. All rights reserved.