Development of a Novel Gas-Sensing Platform Based on a Network of Metal Oxide Nanowire Junctions Formed on a Suspended Carbon Nanomesh Backbone

Junction networks made of longitudinally connected metal oxide nanowires (MOx NWs) have been widely utilized in resistive-type gas sensors because the potential barrier at the NW junctions leads to improved gas sensing performances. However, conventional MOx–NW-based gas sensors exhibit limited gas access to the sensing sites and reduced utilization of the entire NW surfaces because the NW networks are grown on the substrate. This study presents a novel gas sensor platform facilitating the formation of ZnO NW junction networks in a suspended architecture by growing ZnO NWs radially on a suspended carbon mesh backbone consisting of sub-micrometer-sized wires. NW networks were densely formed in the lateral and longitudinal directions of the ZnO NWs, forming additional longitudinally connected junctions in the voids of the carbon mesh. Therefore, target gases could efficiently access the sensing sites, including the junctions and the entire surface of the ZnO NWs. Thus, the present sensor, based on a suspended network of longitudinally connected NW junctions, exhibited enhanced gas response, sensitivity, and lower limit of detection compared to sensors consisting of only laterally connected NWs. In addition, complete sensor structures consisting of a suspended carbon mesh backbone and ZnO NWs could be prepared using only batch fabrication processes such as carbon microelectromechanical systems and hydrothermal synthesis, allowing cost-effective sensor fabrication.

C-MEMS/NEMS: A Novel Technology for Nanoscale Material Formation From Graphite Fiber to Ni and Si Nanowires

Carbon microelectromechanical systems (C-MEMS) and carbon nanoelectromechanical system (C-NEMS) have received much attention because of the many potential applications. Some important applications include: DNA arrays, glucose sensors, microbatteries and biofuel cells. Microfabrication of carbon structures using current processing technology, including focused ion beam (FIB)1 and reactive ion etching (RIE)2, is time consuming and expensive. Low feature resolution, and poor repeatability of the carbon composition as well as widely varying properties of the resulting devices limits the use of screen printing of commercial carbon inks for C-MEMS. Our newly developed C-MEMS microfabrication technique is based on the pyrolysis of photo patterned resists34. Figure 1(a) shows a typical SEM image of C-MEMS/NEMS features with carbon posts connected by carbon fibers. Figure 1(b) shows a typical carbon post with carbon nanofibers on its side surfaces.