Overcurrent Electrodeposition of Fractal Plasmonic Black Gold with Broad-Band Absorption Properties for Excitation-Immune SERS

The dependence of plasmon resonance on the size, shape, and interparticle spacing of single, isolated nanostructures inherently limits their light-harvesting capability to a narrow spectral band. Here, we report a facile overcurrent electrodeposition strategy to prepare fractal plasmonic black gold (B-Au) with broad-band absorption properties (over 80% throughout the range of 300-1800 nm). The broad-band absorption properties are attributed to the excitation of multiple plasmons in the B-Au, which results in strong light-matter interaction over a broad-band spectral window. Consequently, the B-Au can produce strong broad-band surface-enhanced Raman scattering (SERS) regardless of the excitation light used. These findings demonstrate that the fractal B-Au allows efficient utilization of broad spectral photons and opens up exciting opportunities for highly sensitive SERS detection, photocatalysis, and photovoltaic devices.