Low-Temperature Photochemical Conversion of Organometallic Precursor Layers to Titanium(IV) Oxide Thin Films

Thin layers of titanium(IV) ethoxide [Ti(OEt) 4 ] as a metal–organic precursor were spin-coated onto silicon wafers under inert conditions and subsequently photochemically converted to thin titanium(IV) oxide (TiO x ) films employing vacuum ultraviolet (VUV) radiation from a xenon excimer lamp. The photochemical conversion was performed below 35 °C and at ambient pressure in a nitrogen atmosphere with an optimized content of oxygen. Ti(OEt) 4 decomposition and its kinetics were monitored and analyzed by gas chromatography and infrared spectroscopy. Precursor layers with a thickness between 270 and 1060 nm could be converted into much thinner TiO x films (40–165 nm). The decrease in thin film thickness was found to coincide with the removal of organic side chains and densification to a compact oxide network. For precursor layers with a thickness of up to 550 nm, VUV irradiation with a moderate radiant exposure ( H e ) of 2.3 J cm –2 led to almost carbon-free amorphous layers with a composition close to stoichiometric titanium dioxide (TiO 2 ) having a density of ∼2.95 g cm –3 determined by X-ray photoelectron spectroscopy and X-ray reflectometry, respectively. In turn, crack-free thin films exhibiting high UV–visible transparency and smooth surface topography were obtained. The highlighted example of Ti(OEt) 4 shows that photochemically initiated decomposition of a metal alkoxide is a powerful approach for the generation of thin metal oxide layers at normal pressure and near ambient temperatures.