STEM/EELS Imaging of Magnetic Hybridization in Symmetric and Symmetry-Broken Plasmon Oligomer Dimers and All-Magnetic Fano Interference.

Negative-index metamaterials composed of magnetic plasmon oligomers are actively being investigated for their potential role in optical cloaking, superlensing, and nanolithography applications. A significant improvement to their practicality lies in the ability to function at multiple distinct wavelengths in the visible part of spectrum. Here we utilize the nanometer spatial-resolving power of electron energy-loss spectroscopy to conclusively demonstrate hybridization of magnetic plasmons in oligomer dimers that can achieve this goal. We also show that breaking the dimer's symmetry can induce all-magnetic Fano interferences based solely on the interplay of bright and dark magnetic modes, allowing us to further tailor the system's optical responses. These features are engineered through the design of the oligomer's underlying nanoparticle elements as elongated Ag nanodisks with spectrally isolated long-axis plasmon resonances. The resulting magnetic plasmon oligomers and their hybridized assemblies establish a new design paradigm for optical metamaterials with rich functionality.

Imaging Energy Transfer in Pt-Decorated Au Nanoprisms via Electron Energy-Loss Spectroscopy.

Driven by the desire to understand energy transfer between plasmonic and catalytic metals for applications such as plasmon-mediated catalysis, we examine the spatially resolved electron energy-loss spectra (EELS) of both pure Au nanoprisms and Pt-decorated Au nanoprisms. The EEL spectra and the resulting surface-plasmon mode maps reveal detailed near-field information on the coupling and energy transfer in these systems, thereby elucidating the underlying mechanism of plasmon-driven chemical catalysis in mixed-metal nanostructures. Through a combination of experiment and theory we demonstrate that although the location of the Pt decoration greatly influences the plasmons of the nanoprism, simple spatial proximity is not enough to induce significant energy transfer from the Au to the Pt. What matters more is the spectral overlap between the intrinsic plasmon resonances of the Au nanoprism and Pt decoration, which can be tuned by changing the composition or morphology of either component.