Crystallinity dependent gas-sensing abilities of ZnO hollow fibers

The grain size and crystallinity are important factors in considering the gas sensing properties of metal oxide based miniaturized gas sensors. This study reports the effects of the grain size and crystallinity on the CO sensing abilities of ZnO hollow fibers (HFs) synthesized by electrospinning. The grain size and crystallinity of the HFs were controlled by changing the heat treatment time during their synthesis and were characterized by SEM, TEM and XRD. Both the nanograin size and crystallinity of the HFs change significantly with increasing heat treatment time. Longer heat treatments result in improved sensing abilities irrespective of the evolution of larger-sized nanograins. Sensing measurements were carried out at various temperatures in the range 300-400 °C. The improved crystallinity likely compensates the adverse effects of grain growth in terms of the sensor response. That is, crystallinity rather than grain size, is the dominant factor determining the sensing abilities of HFs. This result provides useful guidelines for the fabrication of HF-based chemiresistive-type gas sensors.