Surface Modification of ZnO Nanowires with CuO: A Tool to Realize Highly-Sensitive H 2 S Sensor

Hydrothermally grown ZnO nanowires (NWs) have been successfully synthesized and surface modified by an ultrathin layer of CuO using dip coating technique to achieve a highly sensitive H 2 S sensor. XRD analysis confirmed the hexagonal structure of ZnO without any Cu sub-oxide peaks. After CuO modification, the peak shift was observed in the electronic states of O and assigned to the defects and increase in adsorbed oxygen species. Similarly, a red shift was also observed in the band edge absorption after CuO modification arising due to defects. The sensor film showed an overall n -type character as confirmed using I ( V ) characteristics. Interestingly, sensor response kinetics towards H 2 S were enhanced after CuO modification. The highest sensor response value of 298 was measured towards 10 ppm H 2 S at 150°C for CuO:ZnO NWs sample having 1.26 at % of Cu. This improved sensor response has been attributed mainly to the formation of randomly distributed p – n nano-hetero-junctions between p -type CuO and n -type ZnO over the sensor surface. In particular, the p – n nano-hetero-junctions collapsed due to conversion of semiconducting CuO into metallic CuS after the unique interaction with H 2 S.