  We demonstrated fabrication of black silicon with slanted nanocone array on
both planar and 3D micro and meso scale structures produced by a
high-throughput lithography-free oblique-angle plasma etching process.
Nanocones with gradual change in height were created on the same piece of
silicon. The relation between the slanted angle of nanocones and incident angle
of directional plasma is experimentally investigated. In order to demonstrate
the monolithic integration of nanostructures on micro and meso scale non-planar
surfaces, nanocone forest is fabricated on non-planar silicon surfaces in
various morphologies such as silicon atomic force microscopy (AFM) tips and
pyramidal pits. By integrating nanocones on inverse silicon micro-pyramid array
devices, we further improved the surface enhanced Raman scattering (SERS)
enhancement property of this optimized commercial SERS substrate by several
folds even when using 66% less noble metal coating. We investigated the length
gradient dependence and asymmetric properties of SERS effects for slanted
nanocone with polarized excitation. This versatile and angle-controllable
nanocone fabrication and monolithic 3D nano-micro-meso integration method
provides new dimensions for production and optimization of SERS and other
nanophotonic sensors.
