Nanogranular Au films deposited on carbon covered Si substrates for enhanced optical reflectivity and Raman scattering

Abstract

Electroless deposition of gold has been carried out on Si(100) surfaces precoated with laser ablated carbon layers of different thicknesses, and the resulting substrates have been characterized by a host of techniques. We first established the porous nature of the amorphous carbon layer by Raman and profilometric measurements. The Au uptake from the plating solution was optimal at a carbon layer thickness of 90 nm, where we observed nanogranules of ∼60–70 nm, well separated from each other in the carbon matrix (mean interparticle spacing ∼7 nm). We believe that the observed nanostructure is a result of Au³⁺ electroless reduction on the Si surface through porous channels present in the amorphous carbon matrix. Importantly, this nanostructured substrate exhibited high reflectivity in the near IR region besides being effective as a substrate for surface enhanced Raman scattering (SERS) measurements with enhancement factors up to 10⁷.