Silver nanostructures are containers for surface plasmons - the collective oscillation of conduction electrons in phase with incident light. By controlling the shape of the container, one can control the ways in which electrons oscillate, and in turn how the nanostructure scatters light, absorbs light, and enhances local electric fields. With a series of discrete dipole approximation (DDA) calculations, each of a distinctive morphology, we illustrate how shape control can tune the optical properties of silver nanostructures. Calculated predictions are validated by experimental measurements performed on nanocubes with controllable corner truncation, right bipyramids, and pentagonal nanowires. Control of nanostructure shape allows optimization of plasmon resonance for molecular detection and spectroscopy.

Silver nanocubes with sharp or truncated corners were synthesized, deposited on silicon substrates, and functionalized with Raman-active thiols for surface-enhanced Raman scattering (SERS) studies. The use of substrates with registration marks allowed us to correlate the SERS spectra from individual nanocubes to their physical parameters revealed by high-resolution SEM imaging. We observed dramatic variations in SERS intensity when the nanocubes were oriented at different angles relative to the polarization of excitation laser. This angular dependence was less significant when the nanocubes were truncated and became nearly spherical in profile. Numerical calculations were employed to confirm our observations, and to attribute the source of variation to the difference in near-field distribution between different laser polarizations.