Metal films deposited over two-dimensional colloidal crystals (MFoCC) constitute a low-cost periodic structure with interesting photonic and plasmonic properties. It has previously been shown that this structure exhibits a behaviour similar to the well-known Extraordinary Optical Transmission (EOT) of metallic hole arrays in planar films. Here, we explore the transmission characteristics of AgFoCC by systematic comparison with that of the bare CC. Furthermore with additional reflectivity measurements we evaluate the AgFoCC overall plasmonic response, which, notably, exhibits a strong plasmon absorption band at wavelengths larger than those of the transmitted maximum. By corroborating these results with finite-difference time-domain electromagnetic simulations, we identify a hybrid metal-dielectric propagative mode in the transmission mechanism. On the contrary a strongly localized mode is responsible for the maximum light absorption by this structure. These results shed new light on the current understanding of this highly promising plasmonic structure, being useful for the design of surface-enhanced Raman scattering and enhanced fluorescence substrates.

The ability to provide large electric field enhancements renders triangular nanoprisms and branched nanoparticles very attractive for applications in surface-enhanced Raman spectroscopy (SERS). Theoretical studies on the optical properties of triangular prisms in a water solution are presented in this paper to determine how structural modifications and incident field polarization affect the extinction spectrum and enhanced local electric fields (E-field) around particles in the wavelength range of 300–1000 nm. The near-field properties, such as the E-field close to the particle, determine the electromagnetic enhancements in SERS. The optical response of a triangular nanoprism can be fully characterized using three different orientations of the incident field polarization. The orientations where the polarization vector is parallel to the triangular cross section are the most important for the overall extinction, rather than those where the polarization vector is perpendicular to the plane. The extinction spectrum presents three distinct localized surface plasmon resonances (LSPRs) for a silver triangular nanoprism. These are assigned as in-plane dipolar and quadrupolar plasmon excitations using electrodynamic modeling based on the finite difference time domain. The dipole resonance is found to be very intense, and its peak wavelength is extremely sensitive to the thickness and edge length of the nanoprism. In contrast, the intensity of the quadrupole resonances is much weaker relative to the dipole resonance. The distribution of the local field around the particle at specified wavelengths, showing the values of the peak field, is presented. All the LSPRs are clearly resolved in the visible. The experimental data are used for comparison. These new spectral features are very promising in the field of nano-optics and for bio-sensing applications.

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The ability of metallic nanostructures to support surface plasmon excitations is widely exploited nowadays for developing new technologies and applications in many fields, like communications, medicine or environment. It is known that the plasmonic response of a nanostructure is strongly dependent on its size and shape, and thus a fine control of these features is required for developing applications. In this paper uniaxial colloidal crystal arrays are prepared by convective self-assembly on DVD surfaces. These are then used as template/mask for metal film deposition, in order to obtain two original kinds of metallic nanostructures with controllable morphology: (i) linear arrays of metal half-shells (LAMHSs) and (ii) arrays of periodically serrated plasmonic strips (PSPSs). Angle-resolved optical transmittance measurements reveal the presence of several surface plasmon resonances, while polarized light transmission demonstrates the anisotropic plasmonic response of both LAMHSs and PSPSs. FDTD simulations support the experimental observations and help in the assignments of observed plasmon modes. The proposed linear metallic nanostructures can prove useful for the design of plasmonic components.

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