Geometrically Controlled Au-Decorated ZnO Heterojunction Nanostructures for NO₂ Detection

A comparative analysis of NO2 gas-sensing performances of geometry-controlled Au-decorated ZnO heterojunction nanostructures (nanospheres, nanorods, ultralong nanorods, and nanofibers) has been demonstrated with an emphasis toward exploration of their mechanistic pathways using in situ electrical and Raman spectroscopic studies. Room-temperature photo luminescence (RT-PL) studies indicate that the electron transfer from ZnO nanorods to Au nanocluster develops high resonant electron density with higher energy states. Among the investigated ZnO-Au heterojunction nanostructures, ultralong ZnO-Au nanorods possess superior sensing properties because of their directed electron transport, active heterojunctions, favorable band-bending, and spillover sensitization, which have been justified by performing in situ measurements. The investigation implies that enhanced gas sensing properties of ultralong ZnO-Au heterojunction nanorods mainly originate from a combined effect of spillover and back spillover based electron transfer mechanism along with higher activation energy. Understanding the complex mechanistic aspects of the gas-sensing process prevailing on metal-oxide-based heterojunction nanostructures can open a new paradigm toward the design of novel sensing materials, facilitating commercialization of nanomaterial-based gas sensors.