Tunable Microstructured Surface-Enhanced Raman Scattering Substrates via Electrohydrodynamic Lithography

Readily fine-tuned structures are
an important requirement for
the optimization of surface-enhanced Raman scattering (SERS) to obtain
the highest enhancements. Here, a lateral modulation of an electric
field applied to a dielectric interface enables the rapid replication
of nearly any topographic morphology with micrometer resolution by
electrohydrodynamic lithography (EHL). Gold-covered periodic EHL-generated
arrays yielded the reproducible enhancement of adsorbed SERS-active
molecules. Periodic arrays of micropillars with square and circular
cross sections give rise to the effective coupling of surface plasmon
modes, which generate enhanced SERS signals. The overall enhancement
factors depend on the geometry of the gold-coated structures, and
intriguingly, a strong correlation is found with the gap-to-width
ratio of the square pillar morphology. A numerical simulation of the
EHL-based SERS substrates is consistent with this dependence. The
EHL surface architectures can be easily tailored at micrometer-to-submicrometer
dimensions, allowing the fabrication of reliably engineered and cost-effective
highly sensitive SERS substrates.