  We fabricate and compare nanocomposite thin-film ZnO chemoresistive acetone
sensors with gold or palladium nanoparticles on the surface, at low operating
temperatures. The sensors are fabricated by pulsed laser deposition and operate
in the temperature range 159-200oC. The ZnO films are polycrystalline,
crystallizing mainly at the (002) and (101) orientations of the hexagonal
phase. The nanocomposite ZnO:Au and ZnO:Pd sensors have a lower detection limit
and show a response enhancement factor between 2-7, compared with pure ZnO
sensors. The ZnO:Pd sensor performs better than the ZnO:Au sensor. The ZnO:Pd
sensor sensitivity increases with the amount of palladium on the surface, while
it remains roughly unchanged with the ZnO thickness. The lowest acetone
concentration we detect is 26 ppm for the operating temperature of 200oC.
