Formation, Stabilization and Crystallization of Mesoporous TiO2 Thin Films Studied by SAXS

M. M. ZALDUENDO; M.C. FUERTES; P. F. BOROVIK; P. C. ANGELOMÉ; P. Y. STEINBERG; H. AMENITSCH

Conferencia; XVIII International Small-Angle Scattering Conference (SAS 2022); 2022

Mesoporous TiO2 thin films (MTTFs) have attracted a great deal of attention in the last years, due to the combination of interesting properties from the material and from its structure. TiO2 is a wide band gap semiconductor and as such presents optical and electronic properties that allow its use as a photocatalyst and as a part of photovoltaic devices. Adding porosity to TiO2 increases its surface area, allowing the use of smaller amounts of material, and enhances its reactivity by boosting surface interactions. Interestingly, the high monodispersity and order of the mesopores (in the 2−10 nm range) allows controlling the species that can difuse through its structure. Also, obtaining the material as a thin film permits easy integration with well stablished techniques to prepare more complex multiscale devices. Hence, the potential applications of such engineered MTTFs include optical, electronic, and electrochemical devices, batteries, sensors, and catalyst supports. MTTFs are obtained by the combination of sol-gel reactions, which give rise to the oxide, and self-assembly of amphiphilic molecules that act as templates of the pores, in a process known as Evaporation Induced Self Assembly. The pore array structure depends on the template identity and concentration, and the processing conditions. Due to the high dree of order in the tens of nanometer range, the mesostructure can be determined and studied by SAXS, either in transmission or Grazing Incidence modes. In particular, SAXS experiments performed in synchrotron facilities allow studying all the steps involved in the MTTF preparation: synthesis, thermal stabilization and crystallization. In this presentation, we will show diéerent approaches to study by SAXS the evolution of the MTTFs mesostructure (i.e pore array and interplanar distances) as a function of synthetic and post- processing conditions. Firstly, we will show how the êrststages of the MTTFs formation can be in situ followed by GISAXS or SAXS to understand the way the solvent influences the final pore array, in the case of TiO2 templated with the diblock copolymer Brij 58 and triblock copolymer F127. Afterwards, we will present results of SAXS measurements performed along these MTTFs aging, that allowed determining which aging conditions (humidity, temperature, time) has stronger inëuence over the final pore ordering. Finally, we will present combined in situ GISAXS-WAXS studies performed during MTTFs thermal treatment (from room temperature until 500 ºC) that give interesting information about the crystallization temperature in diéerent substrates. As a whole, this work demonstrates the potentiality of in situ SAXS measurements to design synthesis and post synthesis procedures for the reproducible obtention of MTTFs.