Suspended Carbon Nanowire-Based Structures for Sensor Platforms

2D nanostructures including nanowires, nanotubes, and nanobelts have shown exceptional physiochemical properties suitable for highly sensitive sensors. Typically these nanomaterials are patterned in contact with the substrate and this limits the functionality of the nanostructures due to the effect of substrate. However, deficiency of nanofabrication technologies limited the fabrication of nanomaterials in a suspended form. In this research, suspended single carbon nanowires and carbon meshes composed of nanowires were simply fabricated using carbon-MEMS (microelectromechanical system) process including successive polymer patterning and pyrolysis. The nanowire diameter could be reduced down to ~190 nm using conventional UV-lithography because of a volume reduction accompanied in the pyrolysis process. Owing to the longitudinal tensile stress developed during pyrolysis, the nanowire can be less influenced by stiction so that the nanowire surface can be selectively functionalized with gas sensing materials such as palladium and metal oxide nanowires using lift-off process and hydrothermal process. Owing to the suspended geometry and high surface-to-volume ratio of the carbon nanowires, they showed good gas sensing capability. The suspended carbon mesh was applied for an electrochemical sensor by integrating a substrate-bound carbon electrode below the carbon mesh. This novel configuration enabled the current signal from ferro-/ferricyanide to be amplified up to 37 times using redox cycling.