Polarization dependence of plasmon enhanced fluorescence on Au nanorod array

Characterisation and Manipulation of Polarisation Response in Plasmonic and Magneto-Plasmonic Nanostructures and Metamaterials

Optical properties of metal nanostructures, governed by the so-called localised surface plasmon resonance (LSPR) effects, have invoked intensive investigations in recent times owing to their fundamental nature and potential applications. LSPR scattering from metal nanostructures is expected to show the symmetry of the oscillation mode and the particle shape. Therefore, information on the polarisation properties of the LSPR scattering is crucial for identifying different oscillation modes within one particle and to distinguish differently shaped particles within one sample. On the contrary, the polarisation state of light itself can be arbitrarily manipulated by the inverse designed sample, known as metamaterials. Apart from polarisation state, external stimulus, e.g., magnetic field also controls the LSPR scattering from plasmonic nanostructures, giving rise to a new field of magneto-plasmonics. In this review, we pay special attention to polarisation and its effect in three contrasting aspects. First, tailoring between LSPR scattering and symmetry of plasmonic nanostructures, secondly, manipulating polarisation state through metamaterials and lastly, polarisation modulation in magneto-plasmonics. Finally, we will review recent progress in applications of plasmonic and magneto-plasmonic nanostructures and metamaterials in various fields.

Reconfigurable Positioning of Vertically-Oriented Nanowires Around Topographical Features in an AC Electric Field

We report the effect of topographical features on gold nanowire assemblies in a vertically applied AC electric field. Nanowires 300 nm in diameter ×2.5 μm long, and coated with ∼30 nm silica shell, were assembled in aqueous solution between top and bottom electrodes, where the bottom electrode was patterned with cylindrical dielectric posts. Assemblies were monitored in real time using optical microscopy. Dielectrophoretic and electrohydrodynamic forces were manipulated through frequency and voltage variation, organizing nanowires parallel to the field lines, i.e., standing perpendicular to the substrate surface. Field gradients around the posts were simulated and assembly behavior was experimentally evaluated as a function of patterned feature diameter and spacing. The electric field gradient was highest around these topographic features, which resulted in accumulation of vertically oriented nanowires around the post perimeters when dielectrophoresis dominated (high AC frequency) or between the posts when electrohydrodynamics dominated (low AC frequency). This general type of reconfigurable assembly, coupled with judicious choice of nanowire and post materials/dimensions, could ultimately enable new types of optical materials capable of switching between two functional states by changing the applied field conditions.