Sonochemical Synthesis, Optical Properties, and Electrical Properties of Core/Shell-Type ZnO Nanorod/CdS Nanoparticle Composites

A simple sonochemical route for the surface synthesis of CdS nanoparticles on ZnO nanorods is reported. Ultrasonic irradiation of a mixture of ZnO nanorods, cadmium chloride, and thiourea in an aqueous medium for 2 h yields ZnO nanorod/CdS nanoparticle (ZnO/CdS) composites with core/shell-type geometry. The powder X-ray diffraction of the ZnO/CdS composites shows additional diffraction peaks corresponding to the hexagonally structured CdS, apart from the signals from the ZnO nanorod cores. Transmission electron microscopy images of the ZnO/CdS composites reveal that the ZnO nanorods are coated with CdS nanoparticles with typical diameters of about 5−10 nm. The room temperature photoluminescence spectrum of the ZnO/CdS composites has two emission bands: an ultraviolet emission peak at 376 nm and a green emission around 523 nm. The conductance of the ZnO/CdS composites shows an enhancement compared with that of the uncoated ZnO nanorods. The appealing application of the ZnO/CdS composites as ethanol sensors is presented and a possible sensing mechanism is discussed.