One-step growth of needle and dendritic gold nanostructures on silicon for surface enhanced Raman scattering

Light-induced deposition of gold nanostructures onto both n-type and p-type silicon was performed by galvanic displacement. On illuminating the n-type silicon with a 530 nm laser during the deposition process, a clustered deposit was observed whereas on using a 635 nm laser, gold nano-needles were formed. In comparison, on depositing gold on p-type silicon, flat dendritic structures were obtained and no significant changes in morphology were observed in the presence or absence of light. In the dark, only irregular gold clusters formed. The influence of light in changing the morphology was related to the surface plasmon resonance of the gold nuclei as well as the excess charge present in the conduction band of the silicon. To evaluate the sensoric property of the substrates, Raman spectroscopy was conducted on the metal–semiconductor couple for the detection of ruthenium red molecule. Among the substrates, the gold needle–silicon couple gave the highest surface enhanced Raman scattering (SERS) enhancement. We could also conclude from the SERS measurements that the metal–semiconductor interface plays an important role in increasing the SERS signal.