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Plasmon Coupling in 1-D Assemblies of NanostructuresA surface plasmon is created when the mobile electrons at a metal surface oscillate in phase with an interacting light wave. For isolated metallic nanoparticles, the plasmon oscillation is localized at the particle and causes a strong absorption and scattering of visible and infrared light. The spectral position of the plasmon resonance is determined by the particle size and shape, the refractive index of the local environment, and the metal. The plasmon absorption for spheres occurs in the visible part of the electromagnetic spectrum for the noble metals allowing for easy observation.
As two or more particles are separated by distances smaller than the wavelength of the light, the plasmon
oscillations are no longer independent and couple with each other giving rise to new plasmon modes and
enhancement of the electromagnetic field around the nanoparticle assembly. The optical near-field coupling
greatly enhances the spectroscopic signal (e.g. fluorescence, Raman, second harmonic generation) from analyte
molecules at the surface of the nanoparticles. This is important for many sensing applications like surface
enhanced Raman scattering. Plasmon coupling in pairs of nanoparticles is also exploited to build novel plasmon
rulers. In addition, the coupling of nanoparticle plasmons can also cause a plasmon wave to propagate along an
extended nanoparticle assembly. This has potential applications for plasmonic waveguides, which support light
propagation with subwavelength confinement in contrast to optical fibers that must have diameters of at least
half the light’s wavelength.
We use single particle imaging and spectroscopy techniques based on scattering and absorption together with transmission and scanning electron microscopy to correlate structural and optical properties in assembled nanoparticle arrays. The figure above shows a TEM image (left) of a ring of nanorods prepared in the Zubarev lab together with the corresponding optical scattering image (right) taken on a home-built microscope designed for single particle imaging and spectroscopy. Our present goal is to characterize the optical near-field coupling in different nanoparticle assemblies composed of various particle sizes and shapes using polarization sensitive spectroscopy and microscopy to probe the coupled plasmon modes. Group members involved: Publications:
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