Surface plasmon resonance optical gas sensing of nanostructured ZnO films

The structural and optical gas sensing properties of thin nanostructured ZnO films are investigated by total attenuation surface plasmon resonance technique. Ten nanometers thick ZnO films have been prepared by sol-gel route and thermally treated at 150 degrees C and 400 degrees C. Grazing incidence X-ray diffraction studies showed that the thermal treatment promotes the increase of grain size as the annealing temperature increases. The optical properties of both films are similar being the energy gap of the films annealed at 150 degrees C and 400 degrees C equal to 3.33 +/- 0.05 eV and 3.25 +/- 0.05 eV, respectively, both smaller than the energy gap of the bulk ZnO (3.37 eV). The surface plasmon resonance investigations show remarkable and reversible responses to different concentrations of methanol, ethanol, isopropanol and hexane vapours in dry-air. In both films the responses to ethanol and isopropanol are similar and larger than the responses to hexane and methanol. The responses to all vapours are larger in the film annealed at 400 degrees C except for the methanol for which both films exhibit similar responses.