Mechanical properties of ordered mesoporous oxides thin films

Ordered mesoporous oxides obtained by combining sol-gel and self-assembly exhibit high surface area, controlled porosity, monodisperse pores in the mesoscale and amorphous or crystalline inorganic framework. In the particular form of thin films, they have been widely studied for a diversity of applications. In this context, the mechanical stability of devices based on mesoporous thin films (MTF) is one of the critical factors to consider for assuring robustness and reliability. Measuring and understanding the mechanical and tribological behavior of these designed materials are therefore issues of crucial importance when large-scale applications are pursued, such as photovoltaic devices, catalysis, sensors, microfluidic systems, biocompatible films and microelectronics. In this review, two aspects are discussed and critically evaluated: the mechanical properties of ordered MTF and the experimental techniques used to measure them. The relationship between hardness and elastic modulus with structural features (porosity, pore ordering, crystalline phase, among others) are analyzed for several mesoporous systems. Tribological and fractomechanical features are also assessed. Besides, the experimental techniques dedicated to measure the mechanical properties of porous thin film, including surface acoustic waves, Brillouin light scattering, ellipsometric porosimetry, X-Rays and neutron-based techniques and nanoindentation are described in detail, discussing the possibilities and limitations of these techniques applied to a diversity of systems. In this review, the mechanical properties of ordered mesoporous thin films and the experimental techniques used to measure them are presented and discussed. The relationship between hardness (H) and elastic modulus (E) with structural features as the porosity (P), among others, are analyzed for several mesoporous systems.