Tuneable photonic crystal structures as highly reproducible Surface Enhanced Raman Spectroscopy (SERS) substrates

Abstract

SERS is a very useful analytical technique which was discovered over 30 years ago, however it has never fulfilled its potential due to inherently irreproducible surfaces used to enhance the Raman signals. If a robust and reliable surface was to be produced SERS could have applications in trace drug detection and catalytic reactions amongst others. Gold nanostructured void surfaces have been produced which yield full control over the enhancement, simply by tuning the surface to the correct laser wavelength. It was discovered that SER signals varied depending on the void size and film thickness, and that a 350 nm void structure gave rise to enhancements in Raman signals of the order 108. and the 600 nm structures have a reproducibility of <10% variation, in terms of signal, across a surface. The theory as to why the structures give rise to a strong enhancement comes from the fully controllable plasmon modes within the structures, which are based on molecular orbital fields. The strongest SER signal arose when the laser light and outgoing Raman band were encompassed within a P type of plasmon modex The underlying background in every SERS spectra was also attributed to photoluminescence (PL) from the gold surface, and an excellent correlation between the PL and surface plasmons was observed. The detection of pyridine and carbon monoxide using in-situ electrochemical experiments have shown that the substrate has widened the (electrochemical) potential window for monitoring reactions, and show excellent promise as future chemical sensors.

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