Porosity of mesoporous silica thin films: kinetics of the template removal process by ellipsometry

Mesoporous silica (MPS) films were prepared by the sol-gel route using the acid-catalysed procedure starting from tetraethoxysilane. Three different organic templates, Brij56, Pluronic F127 and CTAB have been tested. The dependence of porosity on the organic template, the surfactant/Si molar ratio and on the calcination temperature and annealing time is investigated using spectroscopic ellipsometry for real time monitoring of the pore formation kinetics. We show that the template removal is a fast process already occurring at temperatures as low as 160 degrees C, and that development of porosity is characterized by a saturating behaviour. Furthermore, the higher the organic content in the starting hybrid material, the higher the porosity in the final SiO2 film. Finally, data show that a porosity as high as 58% can be achieved, and that the most stable SiO2 mesoporous materials are obtained using the Brij56 template.