A new nanostructured substrate for surface enhanced Raman spectroscopy

Abstract

Surface Enhanced Raman Spectroscopy (SERS) is a very promising analytical technique that was first discovered 30 years ago. The substrate most commonly used, for achieving SERS spectra, are roughened silver or gold electrodes. The metals are roughened through a series of oxidation and reduction cycles using electrochemical cycling. However, these surfaces are very irregular with random peaks and troughs, which lead to very irreproducible SERS spectra. In this project a new nanostructured surface has been produced that consists of regularly aligned nanocavities. They are created by electrodepositing gold around a template of polystyrene spheres that are then removed, leaving the inverse structure. The polystyrene sphere diameter used through the project ranged from 400 nm up to 900 nm, corresponding to the visible region of light. It was found that templates based on a 600 nm sphere diameter produced the largest SERS enhancement; the reason for this is believed to be a combination of surface plasmons and confined plasmons leading to an enhanced signal. The 600 nm sample gave rise to excellent SERS spectra using both the 633 nm HeNe and 785 nm diode lasers; however the signal from the 785 nm spectra were of greater intensity. The enhancement factors observed from the nanostructures in this project are factors of 10^ larger than those observed from roughened gold. In addition the enhancement is reproducible across the sample. The results from this project imply that the surfaces could be tuned to a specific laser wavelength using different sphere sizes and film heights.

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