Functionalized ZnO/ZnO2 n-N straddling heterostructure achieved by oxygen plasma bombardment for highly selective methane sensing

• Published in: Physical chemistry chemical physics : PCCP 2015-01, Vol.17 (41), p.27777-27788
• Main Authors: Ghosh, Sugato, Bhattacharyya, Raghunath, Saha, Hiranmay, Chaudhuri, Chirasree Roy, Mukherjee, Nillohit
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp04947d

Metal oxide semiconductors have been extensively used as reducing gas sensors with major limitations regarding selectivity and operating temperature which is relatively high for most of the cases making the device unusable in some critical situations. Higher operating temperature is also associated with the higher power consumption, which goes against the miniaturization of the device. In order to resolve these problems, here we introduced a ZnO/ZnO 2 straddling 'n-N' isotype heterostructure as a highly selective and sensitive methane sensor at moderately low operating temperature. ZnO-Zn(OH) 2 precursor films were treated in oxygen plasma in a pulsed DC magnetron sputtering system. Morphological analyses by field emission scanning electron microscopy showed flake like growth of the grains with high surface roughness, whereas X-ray diffraction (XRD) showed polycrystalline nature of the films. Polycrystalline ZnO 2 peaks were observed in the XRD pattern in addition to the existing ZnO, which indicates modification of the precursor to oxygen rich heterostructure of ZnO/ZnO 2 . This was further supported by the shifting of the O 1s peak in the X-ray photoelectron spectroscopic analysis. Plasma treated ZnO/ZnO 2 heterostructured films were found to show high selectivity towards methane (with respect to H 2 S and CO) and sensitivity (∼96%) at a comparatively low operating temperature. Fabrication of a highly selective and stable methane sensor prototype based on ZnO/ZnO 2 n-N heterostructure obtained by oxygen plasma bombardment of the ZnO-Zn(OH) 2 precursor film is reported.