Preparation of hard optical coatings based on an organic/inorganic composite by sol–gel method

Hard optical coating films based on SiO 2/TiO 2/organically modified silane (ORMOSIL) were obtained by the sol–gel technique. Tetraethoxysilane [TEOS, Si(OC 2H 5) 4], γ-Glycidoxypropyltrimethoxysilane [GLYMO, (CH 2OCH)CH 2O(CH 2) 3Si(OCH 3) 3], and tetrapropylorthotitanate [TIP, Ti(O-i-C 3H 7) 4] were used as precursors for the SiO 2/TiO 2/ORMOSIL coatings. The hardness and Young's modulus of the coatings were characterized and found to depend on the heat-treatment temperature. Hardness as high as 10 GPa was achieved at a heat-treatment temperature of 1000°C for 20 min. Thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and Raman spectroscopy were also used to investigate the structural properties of the coating. It is proposed that the high hardness of the coating film is related to the carbon and titanium content in the film.