Size-Reduction Template Stripping of Smooth Curved Metallic Tips for Adiabatic Nanofocusing of Surface Plasmons.

We present a new technique to engineer metallic interfaces to produce sharp tips with smooth curved surfaces and variable tip angles, as well as ridges with arbitrary contour shapes, all of which can be integrated with grating couplers for applications in plasmonics and nanophotonics. We combine template stripping, a nanofabrication scheme, with atomic layer deposition (ALD) to produce the ultra-sharp nanoscale tips and wedges using only conventional photolithography. Conformal ALD coating of insulators over silicon trench molds of various shapes reduces their widths to make nanoscale features without high-resolution lithography. Along with a metal deposition and template stripping, this size-reduction scheme can mass-produce narrow and ultra-sharp (< 10 nm radius of curvature) metallic wedges and tips over an entire 4-inch wafer. This size-reduction scheme can create metallic tips out of arbitrary trench patterns that have smooth curved surfaces to facilitate efficient adiabatic nanofocusing, which will benefit applications in near-field optical spectroscopy, plasmonic waveguides, particle trapping, hot-electron plasmonics, and nonlinear optics.