Understanding the thermal evolution of TiO2 mesoporous thin films using XANES at Ti L-edge and O K-edge

PAULA C. ANGELOMÉ; GALO J. A. A. SOLER-ILLIA; BONGJIN S. MUN; LEANDRO ANDRINI; FÉLIX G. REQUEJO

Foz de Iguazú

Conferencia; 10th International Conference on Electronic Spectroscopy and Structure; 2006

Transition-metal Oxide based Mesoporous Thin films (MTF) are being extensively studied for their possible applications in optoelectronics or selective nanomembranes [1]. The crystalline features of the oxide walls determine the electronic properties of the inorganic framework, which are particularly important in sensors, photovoltaics and (photo)catalysis. Although MTF with crystallinewalls can be reproducibly obtained, the substrate seems to have an important role in the crystallization of the pore walls, so far not understood. We have investigated the effect of the substrate in the electronic structure of TiO2 MTF. Films were deposited by dip-coating on different substrates (Si, FTO and ITO), stabilized at 130 ◦C, treated at 200 ◦C–500 ◦C in air, and characterized through X-ray absorption spectroscopy at O K-edges and Ti L-edges (TEY mode) at beamline 9.3.2 at the ALS. The local order of the Ti atoms was determined by Ti L-XANES. A clear distinction can be made between Ti in amorphous-like TiO2 with an average coordination number lower than six, and six-fold Ti centers in anatase-TiO2. Oxygen K-edge follows this crystallization by sharpening of the peak feature. We conclude that this crystallization process which occurs between 300–500 ◦C strongly depends on the type of substrate. A clear sequence of crystallization temperatures T is found, in the following trend: TSi