Vertically Aligned WO3-CuO Core-Shell Nanorod Arrays Detect Toxic NH3 Gas

A research team from the School of Microelectronics in Tianjin University has identified a two-step sputtering and subsequent annealing treatment technique that can be used to prepare vertically aligned WO₃-CuO core-shell nanorod arrays. These nanorods are capable of detecting poisonous NH₃ gas. The study has been reported in NANO.

Among the various transition metal oxides, WO₃ has historically generated a great deal of attention as a wide band-gap n-type semiconductor in the detection of a wide range of gases, for example, NH₃, NOx, H₂, and H₂S.

CuO has a special property of being intrinsically p-type. In the last 10 years, due to the interface between CuO and n-metal oxide, p-n heterojunction sensors composed of CuO and an n-type metal oxide were reported to have an excellent sensitivity to reducing gases.

A substantial effort has been made on the WO₃-based nanocomposites because the synergetic improvement and heterojunction effects attribute to the improved gas sensing properties. Conversely, gas sensors that are based on 1D WO₃-CuO composite structures are rather limited. Moreover, the catalyst or template was often required to synthesize WO₃-based nanorod arrays, including the use of electrochemical anodization, chemical vapor deposition, and hydrothermal techniques.

Among the harmful gases that have an adverse effect on living organisms, NH₃ is one of the most hazardous substances known. Ultrasensitive NH₃ gas sensors with short response and recovery time have to be constructed. In gas sensor applications, metal oxides have been extensively applied. In order to achieve excellent sensing performances of metal oxide sensors, 1D heterojunction composite nanostructures and 1D metal oxide nanostructures have been extensively studied because of their size-dependent properties, large surface area, and the nano-heterojunction effects. The dense stacking of rod monomers is effectively prevented by vertically aligned, ordered 1D arrays, particularly leading to new physicochemical characteristics, for example, shorter gas recovery and higher gas response.

Here, a non-catalytic two-step annealing process of sputtered metal film was used on a silicon wafer to synthesize vertically aligned WO₃-CuO core-shell nanorod arrays. Also discussed is the growth mechanism of the vertically aligned nanorod arrays. The NH₃ sensing behaviors of the WO₃-CuO core-shell arrays at varying temperatures are reported. A potential NH₃ sensing mechanism for the hybrid has been suggested.

The National Natural Science Foundation of China (Grant No. 61271070, 61274047) and Tianjin Key Research Program of Application Foundation and Advanced Technology, China (Grant No. 11JCZDJC15300) financially supported the work. Wenjun Yan is the corresponding author of this study.