The Self-Assembly, Optical Response and Stretch Tunability of Plasmonic Nanoparticle Monolayers
The optical properties of self-assembled plasmonic nanoparticle monolayers of varying den sities are explored. These particles are sensitive to changes in their local environment and proximity to other particles. By altering these factors, the appearance of nanoparticle assemblies is changed, enabling their measurement optically. Additionally, the manipulation of near-field enhancement between particles via the application of strain increases the degree of enhancement observed in surface enhanced Raman spectroscopy. By manipulating forces such as interfacial tension and by tuning the electrostatic repulsion exhibited by charge stabilised nanoparticles, the fabrication of long-range organised structures can be directed. Self-assembly methods are used here to fabricate different densities of nanoparticle monolayers. Spin coating methods are used to fabricate sparsely packed nanoparticle monolayers. These methods are investigated as a potential high intensity scattering film with minimal surface coverage. An alternative fabrication method using capillary aided deposition on vertically aligned substrates is also detailed. Interfacial trapping is explored as a means to fabricate large-scale close-packed nanoparticle monolayers. By fabricating close-packed nanoparticle mats onto elastomeric substrates, interparticle distances can be manipulated with strain, creating a dynamic and tunable plasmonic material. An anisotropic polarisation dependent response to uniaxial strain is observed in the optical behaviour of these mats. Perpendicular to the strain axis, particles are able to move closer together due to contraction in this plane. The dependence of the optical response on nanoparticle surfactant is explored as well as the sensitivity to local refractive index changes. In addition to the optical response, stretch tunable near-field enhancement is explored via its effects on surface enhanced Raman spectroscopy. A relative enhancement of the SERS signal is observed with applied strain. By changing the refractive index medium between particles, the resonance position can be changed and therefore the behaviour under strain altered.
Plasmonics, SERS, Surface Enhanced Raman Scattering, Stretch Tunability, Optics, Nanophotonics, Nanoparticle, Localised Surface Plasmon
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