In Situ Probing of Laser Annealing of Plasmonic Substrates with Surface-Enhanced Raman Spectroscopy

In this work, we in situ monitor the laser annealing of template-fabricated silver substrates using surface-enhanced Raman scattering (SERS) and 4-mercaptobenzoic acid (4-MBA) as a molecular probe. The annealing process, which exhibits a strong dependence on the laser power, yields a large (>50X) increase in the SERS of the immobilized 4-MBA. This increased SERS response is correlated with the changing substrate morphology using optical and scanning electron microscope images. We attribute the large enhancement to the formation of nanogaps facilitated by binding of the 4-MBA through both thiol and COO- groups in a sandwich structure, resulting in both electromagnetic and chemical enhancement. This annealing effect, associated with the continuous increase of SERS intensity, was not limited to the AgNP arrays but included Ag films deposited on a variety of nanoporous templates. This study provides a simple strategy for in situ optimization of j plasmonic SERS substrates.