AN IR AND NMR-STUDY OF THE CHEMISORPTION OF TICL4 ON SILICA

The atomic layer epitaxy (ALE) reactions, i.e., the saturating gas-sol id reactions of TiCl4 at 175 and 450-degrees-C with silica preheated a t 200-820-degrees-C, were studied by nuclear magnetic resonance and Fo urier transform infrared spectroscopy, while etching experiments with sulfuric acid were carried out to determine the amount of amorphous ti tanium species. At 175-degrees-C TiCl4 reacted directly with the OH gr oups of silica either monofunctionally or bifunctionally depending on the preheat temperature of silica. A bifunctional reaction took place with strongly H-bonded OH groups as verified by using hexamethyldisila zane (HMDS) to prevent TiCl4 from reacting with isolated OH groups. Th e titanium species bound at 175-degrees-C was amorphous in nature, and anatase-like Ti-OH groups formed upon water treatment. At 450-degrees -C, agglomeration into TiO2 having both anatase and rutile crystal str uctures occurred, together with the formation of amorphous titanium sp ecies. A constant Cl/Ti ratio of 2 was obtained independent of the pre heat temperature of silica, which in this case, because of the agglome ration, did not indicate a bifunctional reaction. After water treatmen t only Ti-OH due to amorphous titanium species was observed. The agglo meration into TiO2 is proposed to be due either to the interaction of HCI with the OH groups of silica or direct chlorination of the OH grou ps with TiCl4.