Metallic films of palladium (Pd) and palladium-tin (Pd-Sn) have been deposited by evaporation technique. They were used as sensitive material for optical sensor by measuring the variation of absorbance. All samples were then oxidized by annealing at 500°C in low vacuum atmosphere. All the films were investigated by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) to observe the influence of the structure and morphology on the optical properties of the films, carrying useful information for the sensing properties of the different sensing materials. Furthermore, the sensing performances were tested by monitoring the variation on the optical absorbance induced during the absorption / desorption of hydrogen gas. While the use of Pd for gas sensing has been widely covered for electrical and SPR sensors, this work aims to extend our comprehension of the optical sensing behavior, especially in absorbance-mode, of the thin films of PdO, Pd-Sn and PdO-SnO<sub>2</sub>.
Large attention has been directed toward carbon nanotubes as material for chemical sensors. However, little attention was paid toward the different behavior of the metallic and semiconductive carbon nanotubes as optical sensing materials.
Semiconductive or metallic Single Wall Carbon Nanotubes (SWCNTs) have been deposited on gold nanoparticles (NPs) monolayer and used as plasmonic based gas sensor.
The coupling between SWCNTs and Au NPs has the aim of combining the reactivity of the nanotubes towards hazardous gases, such as H2, CO, NO2, with the Localized Surface Plasmon Resonance (LSPR) of gold NPs. The LSPR is known to be extremely sensitive to the changes in the dielectric properties of the surrounding medium, a characteristic that has been widely exploited for the preparation of sensing devices. While the use of SWCNTs for gas sensing has been covered in multiple reports, to the best of our knowledge this is the first time that SWCNTs are used as sensing material in an optical sensor for the detection of reducing and oxidizing gases.
Two different techniques, ink-jet printer and dropcasting, were used for depositing the transparent CNTs film on the plasmonic layer. Both the deposition techniques proved to be effective for the development of transparent optical sensing films.
Metallic SWCNTs showed high sensitivity toward H2 at low temperature and an enhancement of performance at 300°C with the detection of low concentration of H2 and NO2. On the contrary, the semiconductive SWCNTs displayed very poor gas sensing properties, especially for the thinner film.