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

Abstract

Electroless deposition of gold has been carried out on Si(100) surfaces precoated with laserablated carbon layers of different thicknesses, and the resulting substrates have beencharacterized by a host of techniques. We first established the porous nature of the amorphouscarbon layer by Raman and profilometric measurements. The Au uptake from the platingsolution 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 ofAu3+ electroless reduction on the Si surface through porous channels present in theamorphous carbon matrix. Importantly, this nanostructured substrate exhibited highreflectivity in the near IR region besides being effective as a substrate for surfaceenhanced Raman scattering (SERS) measurements with enhancement factors up to107.