ZnO nano-tree active layer as heavy hydrocarbon sensor: From material synthesis to electrical and gas sensing properties

ZnO with dense, porous, nano-wire and nano-tree morphologies was successfully synthesized via reactive magnetron sputtering at high pressure (10 Pa) and with different deposition temperatures (RT -> 1273 K). The morphological properties of prepared ZnO coatings were revealed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis was performed to determine crystalline structure of the films in relation with their deposition temperature. Hall effect measurements were used to investigate the electrical resistivity, free carrier concentration and mobility in the coatings as a function of their morphology in a temperature range from 293 K to 473 K. Finally, C12H26 dodecane gas sensing properties of ZnO nano- trees were investigated at different temperatures (from 323 K to 566 K) and the results were discussed depending on dodecane concentration. A remarkable response of 39% was observed at 415 K for a low concentration of dodecane in air [1 ppm(v)]. High response to low concentrations of C12H26 as well as good chemical stability of ZnO nano-trees make this kind of structure a potential candidate as sensing layer for practical sensor applications. (C) 2015 Elsevier B.V. All rights reserved.