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A sol–gel process was exploited to produce porous inorganic thin films from phenyl-bridged silsesquioxanes. The evolution of both structural and optical properties of the starting hybrid sol–gel films were monitored, during synthesis and successive thermal curing steps, by Fourier transform infrared (FT-IR) spectroscopy, differential thermal analysis (DTA), thermogravimetric analysis (TGA) and spectroscopic ellipsometry (SE). Involved chemical species, structural and chemical modifications were identified when thermal treatments at increasing temperatures in the range of 60–800 °C were applied to the hybrid films. The progressive formation of a crosslinked silica network, template elimination and film densification were observed, resulting in completely inorganic porous thin films of low refractive index. The distinctiveness of this system directly comes from the extremely controlled and uniform dispersion of the porogen at a molecular level, which is intrinsic to the bridged silsesquioxane precursor choice. A quantitative porosity analysis was performed by environmental ellipsometric porosimetry (EEP), studying inorganic film optical and mechanical properties under different relative humidity conditions. A transmission electron microscopy (TEM) in-situ characterization of porosity size and distribution confirms the presence of a spatially structured organization of pores of a few nanometers in diameter. [ABSTRACT FROM AUTHOR]

Anomalous responses of acoustic humidity sensors coated with mesoporous titania sensitive films have been observed at high humidity levels, due to capillary contraction that alters the film mechanical behavior. As the methods commonly used to assess the elasticity of thin films are difficult to apply during sorption, a dedicated method for the characterization of the variations of the elastic shear modulus of thin films under humidity exposure has been developed. The method combines a Love wave platform with environmental ellipsometric porosimetry (EEP). In the presented approach, EEP measures the thickness of the film and the adsorbed humidity volume fraction under vapor exposure, while the Love wave platform provides the phase velocity shifts induced by water sorption. These parameters then feed an accurate model of Love wave propagation in the multilayered platform for the derivation of the shear modulus of the sensitive film. The method was applied to 100 ± 10 nm thick mesoporous titania films, with 25 ± 1% porosity, under relative humidity exposure in the 3%-95% range. It successfully determined decreases of 39% and 67% of the shear modulus during adsorption and desorption, respectively, from a 3.1 GPa initial value. [ABSTRACT FROM PUBLISHER]