Gradient nanoporous gold: a novel surface-enhanced Raman scattering substrate

The design and fabrication of surface-enhanced Raman scattering (SERS) substrates with high Raman enhancement, stability, homogeneity and processing compatibility is still one of the most challenging issues in SERS research. In this work, a novel nanoporous gold (NPG) structure that contains a gradient of ligament and pore structures along the thickness direction is designed and simply fabricated by combination of the traditional magnetron sputtering and dealloying technique. This novel nanoporous gold structure (we called it gradient nanoporous gold, GNPG) brings abundant inner structures into conventional nanoporous gold, which can produce remarkable properties for GNPG, such as the surface enhanced Raman scattering. GNPG was demonstrated to have ultrahigh and homogeneous surface enhanced Raman scattering. A simple method was proposed to estimate the relative enhancement factor (EF). The EF of GNPG was estimated to be similar to 8-fold higher than conventional NPG, which means that its EF should over 10(7). It is believed that the gradient ligament structure of GNPG plays a key role for its Raman scattering enhancement.