B. Ashall

Magnetic Manipulation and Optical Imaging of an Active Plasmonic Single-Particle Fe-Au Nanorod

Superparamagnetic microbeads play an important role in a number of scientific and biotechnology applications including single-molecule force measurements, affinity separation, and in vivo and in vitro diagnostics. Magneto-optically active nanorods composed of single-crystalline Au and polycrystalline Fe segments were synthesized with diameters of 60 or 295 nm using templated electrodeposition. The Fe section was magnetically soft and had a saturation magnetization of approximately 200 emu/g, resulting in a 10-fold increase in magnetization relative to that iron oxide nanoparticles. The strong plasmonic response of the Au segment of the rod in both the longitudinal and transverse directions made it possible to detect the orientation of a single rod in a polarized light microscope with nanometer resolution. These nanorods provide significantly improved physical properties over iron oxide superparamagnetic beads, making it possible to simultaneously manipulate and monitor the orientation of biomolecules with well-defined forces at the nanometer scale.

Tailoring surface plasmon polariton propagation via specific symmetry properties of nanostructures

We report on an experimental investigation on surface plasmon polariton (SPP) propagation and interaction on two-dimensional arrays of differing symmetry properties. Providing the required symmetry variations and forming the basis of the arrays are tailor designed nanostructures. We demonstrate that as a result of a 120° symmetry presence, our triquetra-rotor nanostructures can be used for SPP guiding and propagation direction control. As a result, the polarization angle at which the far field SPP related minimum reflectivity occurs can be predetermined by design characteristics and orientation of the nanostructures.

Highly ordered Fe-Au heterostructured nanorod arrays and their exceptional near-infrared plasmonic signature.

The potential of highly ordered array nanostructures in sensing applications is well recognized, particularly with the ability to define the structural composition and arrangement of the individual nanorods accurately. The use of heterogeneous nanostructures generates an additional degree of freedom, which can be used to tailor the optical response of such arrays. In this article, we report on the fabrication and characterization of well-defined Fe-Au bisegmented nanorod arrays in a repeating hexagonal arrangement. Through an asymmetric etching method, free-standing Fe-Au nanorod arrays on a gold-coated substrate were produced with an inter-rod spacing of 26 nm. This separation distance renders the array capable of sustaining resonant electromagnetic wave coupling between individual rods. Owing to this coupling, the subwavelength arrangement, and the structural heterogeneity, the nanorod arrays exhibit unique plasmonic responses in the near-infrared (NIR) range. Enhanced sensitivity in this spectral region has not been identified for gold-only nanorods of equivalent dimensions. The NIR response offers confirmation of the potential of these highly ordered, high-density arrays for biomedical relevant applications, such as subcutaneous spectroscopy and biosensing.

Highly efficient broadband ultrafast plasmonics

To date, considerable experimental and theoretical focus has been placed on the spatial control of Surface Plasmon Polaritons (SPPs) using nanostructured surfaces; however, research aimed toward accessing the ultrafast dynamics of SPPs remains vastly unexplored. Despite this, SPPs have the potential to exhibit some of the fastest possible optical processes, while maintaining the advantage of nanoscale spatial manipulation. Here, we present an experimental and computational investigation of a system that provides access to the efficient excitation of broadband, propagating SPP modes. To achieve this, a surface array of tailor designed, reduced symmetry nanostructures has been fabricated to enable the required control of the plasmon dispersion map to match sub 20 fs pulses in the near infra-red. Using a combination of optical spectroscopy and frequency resolved optical gating techniques, complimented by finite element computational analysis, the efficient excitation of propagating broadband plasmonic modes is demonstrated.

Surface Plasmons on Complex Symmetry Nanostructured Arrays

In recent years it has become accepted that the direction of the plasmonics community is becoming increasingly applied. This is a natural progression, whereby scientific advances are inevitably applied to appropriate technologies. Indeed, in order for the community of plasmonics to continue growing, or at least to maintain the current status, real world technological applications are required. However, this is not to say that the level of fundamental SP research will decrease, as there are still many questions to be answered or clarified on a fundamental level. The dramatic growth of plasmonics in the modern era can be predominantly contributed to four components: nanoscale fabrication techniques, computation power, SPP applications, and the promise of plasmonics′′ [1].

Surface plasmon polaritons on arrays of nanostructures with three‐fold symmetry

The influence of nano‐holes with three‐fold symmetry on the excitation of surface plasmon polaritons (SPPs) at metallic nano‐hole arrays is studied numerically for a quadratic array of rotor‐shaped nano‐holes cut into a silver film. It is found that the SPP‐related minimum of the far‐field reflectivity shifts as a function of the polarization angle of the incident light compared to rotational invariant hole‐shapes. This was also reported in recent experiments. On contrast, the polarization angle for most efficient SPP‐excitation is found to be independent of the nano‐hole shape. We discuss optical near‐ and far‐field properties of the considered structures.