Mesoporous thin films for chemical sensors

Silica mesoporous thin-films were prepared using cetyltrimethylammonium bromide surfactant as a template. The films were deposited by dip-coating on Si and alumina substrates and calcined at 250 and 450/spl deg/C. The films were characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy and Rutherford backscattering spectrometry (RBS). The films maintained the mesophase after calcination. The electrical response of the silica mesoporous thin-films was studied at various concentrations of alcohols (methanol, ethanol, 2-propanol, butanol, and hexane). A large sensitivity to the alcohols at room temperature was observed, with the possibility to discriminate between the different alcoholic species. The films were also tested as humidity sensors and showed an increase in current intensity as a function of relative humidity, with a large response at low humidity values. No memory effects were observed after cyclic testing in dry-wet conditions. Electrical characterisation indicates that the mesophase is easily accessible by the external environment.