Large Area Metal Nanowire Arrays with Tunable Sub-20 nm Nanogaps

We report a new top-down nanofabrication technology to realize large area metal nanowire (m-NW) arrays with tunable sub-20 nm separation nanogaps without the use of chemical etching or milling of the metal layer. The m-NW array nanofabrication technology is based on a self-regulating metal deposition process that is facilitated by closely spaced and isolated heterogeneous template surfaces that confine the metal deposition into two dimensions, and therefore, electrically isolated parallel arrays of m-NW can be realized with uniform and controllable nanogaps. Au-NW and Ag-NW arrays are presented with high-density similar to 10(5) NWs cm(-1), variable NW diameters down to similar to 50 nm, variable nanogaps down to similar to 5 nm, and very large nanogap length density similar to 1 km cm(-2). The m-NW arrays are designed and implemented as interdigitated nanoelectrodes for electrochemical applications and as plasmonic substrates where the coupled-mode localized surface plasmon resonance (LSPR) wavelength in the nanogaps between adjacent m-NW dimers can be precisely tuned to match any excitation source in the range from 500 to 1000 nm, thus providing optimal local electromagnetic field enhancement. A spatially averaged (n = 2500) surface-enhanced Raman scattering (SERS) analytical enhancement factor of (1.2 +/- 0.1) x 10(7) is demonstrated from a benzenethiol monolayer chemisorbed on a Au-NW army substrate with LSPR wavelength matched to a He Ne laser source.