In a paper published in NANO, researchers from the School of Microelectronics in Tianjin University have discovered a two-step sputtering and subsequent annealing treatment method to prepare vertically aligned WO3-CuO core-shell nanorod arrays which can detect toxic NH3 gas.
Over the years, WO3 has received considerable attention among the numerous transition metal oxides as a wide band-gap n-type semiconductor in various gas detection, such as NOx, H2S, H2, and NH3. CuO has the unique property of being intrinsically p-type. In the last decade, p-n heterojunction sensors composed of an n-type metal oxide and CuO were reported to have a good sensitivity to reducing gases owing to the interface between n-metal oxide and CuO. Much effort has been focused on the WO3-based nanocomposites, since the synergetic enhancement and heterojunction effects attributes to the enhanced gas sensing properties. However, gas sensors based on 1D WO3-CuO composite structures are limited. Additionally, the template or catalyst was usually necessary to synthesize WO3-based nanorod arrays, including using chemical vapor deposition, electrochemical anodization and hydrothermal approaches.
Among toxic gases causing adverse impact on living organisms, NH3 is one of the most hazardous substances. It is necessary to build up ultrasensitive NH3 gas sensors with short response and recovery time. Metal oxides have been widely used in gas sensor applications. In order to obtain great sensing performances of metal oxide sensors, 1D metal oxide nanostructures and 1D heterojunction composite nanostructures have been investigated due to their large surface area, size-dependent properties, and the nano-heterojunction effects. Vertically aligned ordered 1D arrays effectively avoid the dense stacking of rod monomers, especially, resulting in novel physicochemical characteristics, such as higher gas response and shorter gas recovery.
Here, vertically aligned WO3-CuO core-shell nanorod arrays are synthesized using a non-catalytic two-step annealing process of sputtered metal film on silicon wafer. The growth mechanism of the vertically aligned nanorod arrays are discussed. The NH3 sensing behaviors of the WO3-CuO core-shell arrays at different temperatures are reported. A possible NH3sensing mechanism for the hybrid is proposed.