LAUSR

Abstract Nanostructured materials play a significant role in numerous advanced and diversified applications many of which exploit their optical properties. Among these are nanostructured substrates for surface-enhanced Raman scattering (SERS). The objective of our study was to contribute to understanding of topological aspects influencing and underlying SERS on nanostructured substrates. To that purpose we fabricated Ag-decorated Si-nanowires (SiNWs) substrates with different fractal and lacunar characteristics. We demonstrated that fractal dimension and lacunarity have a profound influence on SERS enhancement. We discussed the involved interplay between long-range properties of nanostructured substrate, namely its fractal topology, and short-range local features on a nanometer scale related to the distribution of inter-wire gaps (i.e. lacunarity) which strongly affect the local field enhancement, altogether precipitating in significant increase of SERS. Explanation of a strong correlation found to exist between fractal dimension D, lacunarity and SERS enhancement and the observed abrupt increase of SERS at D ≈ 2.54 are provided within the framework of the percolation theory. For a percolated fractal structure a strong enhancement depends on the excitation wavelength resonantly matching the heterogeneity sizes of inter nanowire gaps as characterized with a high lacunarity determining the distribution of localized optical excitations i.e. hot spots.