Chemical vapor deposition preparation of nanostructured ZnO particles and their gas-sensing properties

Nanostructured ZnO materials including Zn-ZnO core–shell structure (CS), ZnO hollow sphere (HS), and hierarchically structured ZnO hollow microsphere with nanorods (HSNR) grown on the outer surface were prepared by a simple and versatile chemical vapor deposition process. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and room temperature photoluminescence spectroscopy were used to characterize the morphology and crystalline structure of the samples. It was found that the gas-sensing property of the three structured ZnO had different responses in resistive mode using formaldehyde gas as the probe. In contrast with CS and HS samples, the HSNR exhibits better sensing property because it has more oxygen vacancies and more surface sites, which produce a higher resistance. However, the higher work function of Zn core than that of the ZnO sheath forms the ohmic contact, producing negative charge accumulating layers within ZnO side of Zn–ZnO junction, thus contributing a lower sensing response of CS model when exposed to the targeted formaldehyde gas.