Optical properties of sol-gel deposited Al sub 2 O sub 3 films

Highly transparent, uniform and corrosion resistant Al sub 2 O sub 3 films were prepared on stainless-steel and quartz substrates by the sol-gel process from stable coating solutions using aluminum-sec-butoxide, Al(OBu exp s ) sub 3 as precursor, acetylacetone, AcAcH as chelating agent and nitric acid, HNO sub 3 , 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 deg C showed that they had an amorphous structure. XPS confirmed that they were stoichiometric Al sub 2 O sub 3 . The refractive index (n) and extinction coefficient (k) were found to be n = 1.56 plus /minus 0.01 and k = 0.003 plus/minus 0.0002 at 600 nm, respectively. The surface microhardness and corrosion resistance investigations showed that Al sub 2 O sub 3 films improved the surface properties of stainless-steel substrates.