We have demonstrated that by coating with a thin dielectric layer of tetrahedral amorphous carbon (ta-C), a biocompatible and optical transparent material in the visible range, the Ag nanoparticle-based substrate becomes extremely suitable for surface-enhanced Raman spectroscopy (SERS). Our measurements show that a 10 Å or thicker ta-C layer becomes efficient to protect the oxygen-free Ag in air and prevent Ag ionizing in aqueous solutions. Furthermore, the Ag nanoparticles substrate coated with a 10 Å ta-C film shows a higher enhancement of Raman signals than the uncoated substrate. These observations are further supported by our numerical simulations. We suggest that biomolecule detections in analytic assays could be easily realized using ta-C-coated Ag-based substrate for SERS especially in the visible range. The coated substrate also has higher mechanical stability, chemical inertness, and technological compliance, and may be useful, for example, to enhance TiO2 photocatalysis and solar-cell efficiency by the surface plasmons.

Self-assembly of colloidal spheres confined within cells of different shapes formed with two slides under capillary forces are studied. It is found that by controlling the shape of the cell the curvature of the drying front can result in a significant effect on the self-organization process. A curved drying front formed within parallel slides is always associated with growth of colloidal crystal structures with a high density of disorder. We demonstrate that single-domain two-dimensional colloidal crystals with centimeter size can be grown under capillary forces under a straight drying front formed in a wedge-shaped cell. These findings are demonstrated by laser diffraction, microscopy imaging methods and off-normal optical transmission measurements. The present growth method should be of importance in expanding colloidal crystal applications in angle-resolved nanosphere lithography, as well as in preparation of high-quality quasi-three-dimensional plasmonic crystals.

We studied theoretically the diffraction coupling of magnetic resonances in metamaterials consisting of a planar rectangular array of metal rod pairs with a dielectric spacer. A narrow-band mixed mode was observed due to a strong interaction between magnetic resonances in individual pairs of metal rods and an in-plane propagating collective surface mode arising from the array periodicity. Upon the excitation of this mixed mode, a five-fold enhancement of magnetic field in the dielectric spacer was achieved as compared with the purely magnetic resonance. It was also found that only a collective surface mode with its magnetic field parallel to the array plane could mediate the excitation of such a mixed mode.Metallic nanoparticles exhibit rich optical properties and have many applications because they support surface plasmon (SP) resonances associated with a huge enhancement of electric fields in their vicinity. 1 Due to radiative or nonradiative (absorptive) damping, however, the particle SP resonances usually have a broad bandwidth or short lifetime, which will limit their applications in some cases. Now recent studies have shown that the SP bandwidth could be tuned through interparticle near-field interaction 2,3 or far-field diffraction coupling 4-8 in periodic arrays of metallic nanoparticles. In the later case, a narrow-band plasmon mode near particle SPs was predicted 4,5 and observed experimentally, 6-8 when the array period is close to the particle resonance wavelength. It is well known that the arrangement of metallic nanoparticles into a periodic lattice can give rise to an in-plane propagating collective surface mode (also referred to as lattice resonance), which appears near the Wood anomaly. 9 The narrow-band mode steps from the interaction between a particle SP mode and this type of collective surface mode. 4-9 Because of a narrow bandwidth, such a hybridized plasmon mode is anticipated to find potential applications. For example, it has been used to enhance and direct fluorescent emission in periodic plasmonic nanoantenna arrays. 8 In metamaterials, specially shaped metallic nanoparticles, like split-ring resonators (SRRs) 10 and paired rods 11,12 or nanodisks, 13 can induce a magnetic moment counteracting the external magnetic field and thus produce diamagnetic responses, termed magnetic SP resonances to differentiate them from electric SP resonances observed in usual metallic nanoparticles. These metallic nanostructures have been widely employed as artificial magnetic atoms to fabricate negative-permeability or negative-refractive-index metamaterials 14 with peculiar electromagnetic properties. 15 Although the interactions of electric SP resonances in metallic nanostructures have been extensively studied and well understood, less is known about the interactions of magnetic SP resonances which could result in interesting physical phenomena. 16 Very recently, a classical analog for electromagnetic induced transparency (EIT) observed in a three-level atomic system 17 has been demonstrated in metamate...

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