Combining black silicon
(BS), a nanostructured silicon containing
highly roughened surface morphology with plasmonic materials, is becoming
an attractive approach for greatly enhancing light–matter interactions
with promising applications of sensing and light harvesting. However,
precisely describing the optical response of a heavily decorated BS
structure is still challenging due to the increasing complexity in
surface morphology and plasmon hybridization. Here, we propose and
fully characterize BS-based multistacked nanostructures with randomly
distributed nanoparticles on the highly roughened nonflat surface.
We demonstrate a realistic 3D modeling methodology based on parametrized
scanning electron microscopy images that provides high-precision morphology
details, successfully linking the theoretical analysis with experimental
optical response of the complex nanostructures. Far-field calculations
very nicely reproduce experimental reflectance spectra, revealing
the dependency of light trapping on the thickness of the conformal
reflector and the atop nanoparticle size. Near-field analysis clearly
identifies three types of stochastic “hotspots”. Their
contribution to the overall field enhancement is shown to be very
much sensitive to the nanoscale surface morphology. The simulated
near-field property is then used to examine the measured surface-enhanced
Raman scattering (SERS) response on the multistacked structures. The
present modeling approach combined with spectroscopic characterizations
is expected to offer a powerful tool for the precise description of
the optical response of other large-scale highly disordered realistic
3D systems.
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