Plasmonic Properties of Supported Silver Nanocrystals: Tuning and Anisotropy

Small silver nanoparticles are known for their remarkable optical properties enabled by their ability to support localized surface plasmon resonances (LSPR). The the plasmonic properties of silver nanoparticles are highly sensitive to multiple factors including, size, shape, and the refractive index and symmetry in their local environment. This allows for easily monitoring and accurate tuning of optical properties applicable to sensing, field enhanced spectroscopy, nanopositioning and optical materials. This work focuses on the optical properties of ensembles of silver nanocubes (AgNC) supported by dielectric materials. AgNCs absorb light very strongly in the ultraviolet-visible region of the spectrum. The nanocrystals in this work were synthesized via the polyol method, dispersed as Langmuir films, and transferred qualitatively to various dielectric substrates for study. When placed on a dielectric substrate, the interaction between the AgNCs and the substrate generates two relatively narrow, strongly absorbing plasmonic modes that can be tuned independently over a large range in the visible spectrum. The range and sensitivity of plasmon modes varies considerably, and were quantified for colloidal AgNCs, and contrasted with various dielectric supported systems. This platform is an excellent substrate for surface enhanced Raman spectroscopy as it can be tuned to the desired wavelength for study. Similarly, dielectric supported AgNCs allow tuning of scattering, absorption, and transmission across the visible region in terms of intensity, polarization, and angle of incidence. Additionally, utilization of the spatially, and energetically separated plasmonic modes produces a set of nanorulers that are used to probe dynamics in the glass transition temperature of a thin polymer film, achieving a dynamic range of 60nm.