Laurianne Blanc

Love Wave Characterization of the Shear Modulus Variations of Mesoporous Sensitive Films During Vapor Sorption

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.

Mesoporous thin films as versatile sensitive matrices on Love wave sensors for fast sub-ppm vapor detection

Love wave gas sensors with mesoporous thin film as sensitive layers are presented. They are dedicated to volatile organic compound vapor detection. Mesoporous films of SiO2 were prepared using the Sol-Gel process and deposited on the devices acoustic path. The obtained films have been characterized by ellipsometry resulting in the determination of porosity and pore size distribution in the film and of water adsorption isotherms. Ethanol (130–2000ppm) and toluene (70–1000ppm) exposures resulted in frequency shifts up to 20 kHz, showing the high sensitivity of the mesoporous-based Love wave devices.

Chimie douce route to novel acoustic waveguides based on biphenylene-bridged silsesquioxanes

Novel silsesquioxane thin films were conveniently synthesized by the sol–gel route under mild conditions. Thus, a sol was prepared from 4,4′-bis(triethoxysilyl)-1,1′-biphenyl (4,4′-BTEBp) under a hydroalcoholic medium without a surfactant, deposited by spin-coating on silica supports, and dried at 280 °C. The resulting biphenylene-bridged films exhibited very smooth surfaces, excellent mechanical behavior and no cracks. Moreover, SEM and TEM studies showed flawless, homogeneous interfaces with silica substrates. The acoustic waveguide properties of these films on piezoelectric quartz microsensors were investigated at high frequency through a network analyzer. For an optimal thickness close to 1 μm, a marked frequency shift of the main broad lobe and a decrease of the insertion loss were observed. These results show a strong effect of the waveguide for trapping the acoustic energy, promising an unprecedented ability to provide a new generation of sensors. The capability of this device in the detection of mass is also demonstrated through the immobilization of Bovine Serum Albumin (BSA). This novel approach appears very promising in view of the development of surface acoustic wave sensors and biosensors.

Guided SH-SAW characterization of elasticity variations of mesoporous TiO 2 sensitive films during humidity sorption

Anomalous responses of acoustic humidity sensors coated with mesoporous titania 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 guided shear-horizontal surface acoustic wave (guided SH-SAW or Love wave) platform with environmental ellipsometric porosimetry (EEP). In the presented approach, EEP measures the thickness of the film and its adsorbed humidity volume fraction under vapor exposure, while the guided SH-SAW 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.

Guided SH-SAW toluene sensors with mesoporous silica sensitive coatings: Increased sensitivity through mesostructuration control

Thanks to high specific surface areas, mesoporous silica films have been considered as sensitive coatings for guided shear-horizontal surface acoustic wave toluene sensors. In order to increase their sensitivity, the influence on toluene detection of the structuring agent used in the evaporation-induced-self-assembly fabrication process of these inorganic films has been studied. In this paper, F127 block copolymer is compared to cethyltrimethylammonium bromide (CTAB). Sensors coated with 100 nm thick films structured with CTAB show an average sensitivity of 14 Hz.ppm−1 for toluene concentrations in the 130–1040 ppm range at room temperature, which is 4.5 times higher than the sensitivity obtained with films of similar thicknesses and porosities that were structured with F127.

Mesoporous TiO2 Sensitive Films for Love Wave Humidity Detection: Origins of Stress Release Induced by Sorption

Mesoporous titania-coated acoustic humidity sensors show strongly non-linear responses at high exposure, not fully explained by water condensation. Three possible sources of stresses that alter the film mechanical behavior have been considered in this work: increased swelling, unreleased sol-gel stress, and capillary contraction. If the latter is linked to the film porous nature and cannot be avoided, the two other are mainly side effects of the specific fabrication process developed for the deposition of mesoporous oxides on quartz piezoelectric substrates: partial crystallization and a large pore size distribution.