Effect of dopant oxidation states on enhanced low ppm CO sensing by copper doped zinc oxide

Abstract

Chemiresistive gas sensing by functional ceramics, like semiconductor metal oxides have been so far explained in terms of parameters such as particle size, morphology, temperature, oxygen vacancies, surface charge imbalance and so on. However, the effects of oxidation states of dopants in shaping gas sensing behavior in chemiresistors have been largely ignored. In this work, the role of oxidation states of Cu dopants on improved CO sensing behaviour of ZnO has been categorically analyzed. In this process, a multi-fold enhanced and selective sensing response towards low ppm CO in comparison to pure zinc oxide has been achieved by n-type Cu doped Zinc Oxide. Extensive studies on surface electronic and bulk crystal structures have revealed that relative amount of Cu1+ and Cu2+ is the probable primary cause behind enhanced CO sensing response by Cu doped zinc oxide. Our results thus indicate that by modifying the relative amounts of different oxidation states of dopants, semiconductor metal oxide systems may be tuned to show improved sensing response towards CO and other gases.