Tuning the optical properties by engineering the topologic shape of Ag nanorods

Abstract

ABSTRACT We use the discrete dipole approximation (DDA) method to investigate the optical extinction spectra and the E -field enhancement distribution of Ag nanorods with different topologic shapes, such as cylindrical-, needle-, period-, L -, parallel-, U-shaped, and helical nanorod st ructures. Compared to Ag nanorods with a simple sh ape such as cylinder and needle, irregular nanorod structures show many distinct pl asmon resonance modes over a large spectral range. More hot spots are observed for nanorods with more kinks and bendings, such as period-shaped and L-shaped nanorods, and the E- field distribution depends on the polarization and propagation direction of the excitation light. For the parallel-nanorod structure, when the incident E -field is perpendicular to the nanorod axis, only transverse plasmon modes are excited. However, for a U-shaped nanorod, longitudinal plasmon modes can also be stimulated along the vertical nanorod direction. Helical nanorod interacts differently with left- and right-handed circular polarized lights, which provides another way to tune the plasmon peak and arrange the E -field distribution.