Nanocoax arrays via NIL for high resolution sensing applications*

We have used nanoimprint lithography to fabricate nanocoax array-based chemical sensors, starting from SU-8 polymer replicas of silicon nanopillars. Nanocoaxes are formed by metalizing the polymer pillars, followed by oxide dielectric coating and outer metal deposition, and a polymer filling for stabilization. Chemical mechanical polishing and reactive ion etching were then used to open the ends of the coaxes and form coaxial cavity (with a nanoporous component) structures, respectively. Adsorption of water and organic solvent molecules into the coax annuli caused significant changes to the complex impedance of the coaxial capacitor array ($\Delta $C/C $>$ 100{\%} for 50{\%} relative humidity air). Impedance measurements with such coaxial nanocavity arrays thus provide highly sensitive and selective information for molecular detection, with ultimate sensitivity below 1 ppb, or $\sim $1 $\mu $g/m$^{3}$.