Synergistic Enhancement of Ammonia Sensing Using ZnO/Au-Decorated Carboxylated SWCNT Heterostructures

Single-walled carbon nanotubes (SWCNTs) have long been used as active sensing materials in the fabrication of gas sensors for the detection of various gases and organic vapors. Often, modifications to the pristine material are needed either to generate a response to the exposure to a specific analyte or to enhance the response to higher levels beyond what is possible with the pristine baseline material alone. In this study, we systematically investigate the individual and combined effects of carboxylation of SWCNTs, addition of gold nanoparticles, and formation of a heterostructure with ZnO on ammonia sensing performance. The combination of all of these modifications provides the highest sensitivity for ammonia detection. The ZnO/Au-decorated SWCNT-COOH/Si heterostructure sensor exhibits an exceptional response of 1128% to 30 ppm ammonia at 40% relative humidity and maintains this sensing performance even under high humidity conditions. The sensing mechanism is analyzed using an energy band diagram and technology computer-aided design simulation, which reveals that enhanced response arises from synergistic charge transfer and interfacial barrier modulation at the ZnO/SWCNT heterointerface.