Comparison study of conductometric, optical and SAW gas sensors based on porous sol–gel silica films doped with NiO and Au nanocrystals

Conductometric, optical and surface acoustic wave gas sensors based on sol–gel silica porous films doped with NiO and Au nanoparticles are studied. The nanocomposite films are characterized by optical absorption in the visible and near-infrared region, spectroscopic ellipsometry, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) analysis and X-ray photoemission spectroscopy (XPS). They show poor conductometric gas sensing response toward CO and H2. However, both optical and surface acoustic wave (SAW) responses are reversible and stable to H2. Moreover, exploiting the wavelength dependence of the optical sensor response it is possible to selective recognition of H2. Choosing the appropriate wavelength, almost no variation in absorption is observed when introducing different gases into the testing chamber.