EFFECTS OF PARTICLE-SIZE OF AU ADDED TO CUO-ZNO COMPOSITE ON GAS-SENSING PROPERTIES

CuO-ZnO composites with or without ultrafine Au particles were fabrica ted by infiltrating cupric solution with or without gold cyanide into a porous ZnO matrix and firing. The particle size of Au was controlled within 5-100 nm by changing heating process of the cupric solution an d gold cyanide concentration, The rectifying current(I)-voltage(V) cha racteristics and gas sensitivity largely depended on the Au particle s ize. Evident nonlinear I-V characteristics, due to p-n junction of CuO and ZnO semiconductors, were not observed in composites with Au parti cles, When the Au particle size was about 10 nm, the gas sensitivity o f the composite was substantially improved; the current was increased about 20 times by an introduction of CO and H-2 gas (4000 ppm) at 150 degrees C in the bias region within +/-6 V, However, in composites wit h Bu particles smaller than 10 nm and larger than 20 nm, current chang es by introduction of the gases were only below 10% of the current in air, The interface capacitance of the composites also showed changes b y the gases depending on the Au particle size, which is similar to tho se in gas sensitivity. It was found that the addition of Au particles with controlled size is effective to improve gas sensitivity in CuO-Zn O composites.