COMBINED EFFECTS OF SMALL GOLD PARTICLES ON THE OPTICAL GAS-SENSING BY TRANSITION-METAL OXIDE-FILMS

The combination of small Au particles with NiO, CuO and Co3O4 films le d to improved or new optical gas sensitivity via different mechanisms. The deposition of small Au particles on NiO film enhanced the detecti on of CO in air through a decreasing change of absorbance in the whole visible-near IR region. This can be explained by the change in positi ve hole density change of NiO, which was enhanced by an increase in ca talytic formation and decomposition of surface carbonates with Au. In the case of GO-insensitive CuO film, gold deposition made it sensitive only at plasmon absorption region. This might be because the absorban ce by small Au particles in plasmon band was influenced by the change in the dielectric constant of copper oxide which surrounded small Au p articles. A Au-Co3O4 composite film showed a novel function to recogni ze CO and H-2, probably for the first time as inorganic materials for optochemical sensors. This owes to the fact that CO and H-2 bring abou t the specific absorbance change of the film at different wavelengths. Carbon monoxide decreased the absorbance of Co3O4 moiety, while H-2 n ot only decreased the absorbance of Co3O4 moiety but also increased pl asmon absorbance of Au.