  Surface-enhanced Raman spectroscopy (SERS) allows single-molecule detection
due to the strong field localization occurring at sharp bends or kinks of the
metal-vacuum interface. An important question concerns the limits of the signal
enhancement that can be achieved via a judicious design of the surface. By
using a specific example of a technologically realizable nanopatterned surface,
we demonstrate that while very high enhancement factors (~10^12) can be found
for an ideal surface, these are unlikely to be achieved in laboratory samples,
because even a minute, inevitable rounding-off strongly suppresses the
enhancement, as well as shifts the optimal frequency. Our simulations indicate
that the geometric enhancement factors are unlikely to exceed ~10^8 for real
samples, and that it is necessary to consider the geometric uncertainty to
reliably predict the frequency for maximum enhancement.

Optics;Other Condensed Matter;Chemical Physics;Computational Physics