Controlled assembly of highly Raman-enhancing silver nanocap arrays templated by porous anodic alumina membranes.

A convenient nanoscale technique is reported for the fabrication of highly ordered hemispherical silver nanocap arrays templated by porous anodic alumina (PAA) membranes as robust and cost-efficient surface-enhanced Raman scattering (SERS) substrates. This geometry produces a high Raman signal due to its periodic hexagonal arrangements and control of the gap between the nanostructures in the sub-10-nm regime. The surface structure can be tuned further to optimize the enhancement factor according to optional PAA fabrication and silver deposition parameters. Finite-difference time-domain calculations indicate that the structure may possess excellent SERS characteristics due to the high density and abundance of hot spots.