Self-organization of colloidal particles on surfaces to form 2D or 3D nanofabrication templates has been explored actively in the past decade as an effective bottom-up method to produce a plethora of nanoarchitectures with diverse functionalities. Specifically, several elegant approaches to pattern surfaces with large-scale 2D arrays of nanosized structures through lateral self-assembly of colloidal spheres have been developed. These methods are commonly termed colloidal lithography (CL). A frequently used version of CL, nanosphere lithography (NSL) employs organized 2D colloidal crystals with a hexagonal close-packed motif as an evaporation mask, often in combination with reactive ion etching. Evaporation through the holes between close-packed nanospheres defines the resulting pattern, and in many applications material deposition conditions such as evaporation angle or specific deposition technique (e.g., sputtering, thermal deposition) are used to vary the achieved patterns. With this method facile production of vast planar arrays of diverse nanostructures has been accomplished. [1][2][3][4][5][6][7][8] In an alternative approach, referred to here as sparse colloidal lithography (SCL), charged colloidal beads are utilized in a similar manner as in NSL. [9,10] This method, developed in our group, enables facile production of large areas (several cm 2 ) of nanoscopic features like holes in thin films, disc-, ringand crescent-shaped structures with overall sizes currently down to 20 nm and which occupy 10 to 50 % of the total surface area. [11][12][13][14][15][16] The size distribution of SCL-fabricated nanostructures is largely determined by the size dispersions of the masking colloids and is typically less than 5 % for colloids with average diameters > 100 nm and up to 10 % for smaller colloids. In contrast to NSL, a sparse monolayer of colloidal particles defines the evaporation/etch mask in SCL. The convenience of this technique, employing charged polystyrene (PS) nanoparticles as etch and/or evaporation mask, has recently been demonstrated in a variety of applications such as investigation of fibroblast response to nanotopography, [17] model catalysts of Pt/alumina and Pt/ceria [18] and in the study of optical properties of macroscopic arrays of supported metallic nanostructures like discs, crescents, or rings or nanoholes in optically thin films. [11,13,14,16] In spite of the general advantage of facile bottom-up nanofabrication and a large variety of possible nanostructural motifs, SCL has so far been subject to limitations in producing nanostructures composed of materials with unfavourable etching selectivity, that is, where the substrate or polystyrene etch rates compete with the etch rate of the actual materials of the nanostructure. Examples of such systems are Pt on Au or Au-silica hybrid structures on glass. Another disadvantage of the method is the necessity of the reactive oxygen treatment for the PS mask removal so that nanostructures composed of the materials prone to oxidation (like Ag or Ru) rap...

The optical response of isolated holes in 20 nm thin gold is probed as a function of alkanethiol CH(3)(CH2)x SH (x epsilon in 1-15) and protein adsorption using dark-field spectroscopy. We establish that the plasmon excitations of single and short-range ordered 60 nm holes exhibit similar E-field decay lengths delta approximately 10-20 nm and that a single hole can be used to resolve the successive adsorption of a protein (biotin-BSA) and its interaction partner (neutravidin). The data confirm the localized character of the hole plasmon and demonstrate that its applicability for bio/chemosensing is similar to that of particle plasmons.

Efficient light-matter interaction lies at the heart of many emerging technologies that seek on-chip integration of solid-state photonic systems. Plasmonic waveguides, which guide the radiation in the form of strongly confined surface plasmon-polariton modes, represent a promising solution to manipulate single photons in coplanar architectures with unprecedented small footprints. Here we demonstrate coupling of the emission from a single quantum emitter to the channel plasmon polaritons supported by a V-groove plasmonic waveguide. Extensive theoretical simulations enable us to determine the position and orientation of the quantum emitter for optimum coupling. Concomitantly with these predictions, we demonstrate experimentally that 42% of a single nitrogen-vacancy centre emission efficiently couples into the supported modes of the V-groove. This work paves the way towards practical realization of efficient and long distance transfer of energy for integrated solid-state quantum systems.

It is well known that localized surface plasmon resonances (LSPRs) greatly influence the optical properties of metallic nanostructures. The spectral location of the LSPR is sensitive to the shape, size, and composition of the nanostructure, as well as on the optical properties of the surrounding dielectric. [1] The latter effect has been used to develop different types of optical biosensors for which biological reactions near the surface of the nanostructure can be monitored through the changes in the frequency of the LSPR. [2][3][4][5][6] The induced electromagnetic field associated with the LSPR is greatly enhanced at the metal/dielectric interface, a phenomenon that is the basis for various types of surface-enhanced spectroscopy, such as surface-enhanced Raman scattering. [7] Furthermore, metallic nanoparticles have been shown to have light-guiding capabilities on the nanometer scale. This makes them suitable for the development of nano-optic devices. [8] The overwhelming majority of LSPR studies have focused on Au or Ag nanoparticles because these metals have suitable optical constants for application with visible wavelengths of light. However, once the morphology and composition of a nanostructure have been fixed, it is difficult to change or control the LSPR properties by external means, which would be desirable for the development of active nanoplasmonic devices. One way to overcome this problem could be to embed the metal nanostructure in an active medium, such as a liquid crystal, [9] which can be controlled by an external electrostatic field, or a ferromagnetic garnet, [10,11] which can be moderated by a magnetic field. An alternative approach could be to let the controlling field act directly on the metallic nanostructure, for instance, using nanoparticles made of ferromagnetic metals. Such metals have strong magneto-optical (MO) activity, that is, their optical properties change markedly even if the applied magnetic field is weak. Unfortunately, this high optical absorption results in a strong damping of any intrinsic LSPR that prevents the development of active plasmonic devices made solely of ferromagnetic metals. A promising route forward could be to combine ferromagnetic materials that would promote strong MO activity with noble metals that could induce plasmonic response. The large enhancement and spatial localization of the electromagnetic field associated with the LSPR suggest that a strong enhancement of the MO properties should be possible. [12] Several attempts to develop these kinds of structures have been carried out using different chemical synthesis methods to fabricate complex onion-like nanoparticles made of noble metals and ferromagnetic materials. [13][14][15][16] These systems do exhibit LSPRs, but so far no MO activity has been reported. On the other hand, continuous thin films made of Au/Co/Au trilayers were found to lead simultaneously to well-defined propagating surface plasmon polaritons and to strong MO activity at low magnetic fields. [17] Moreover, such composite structure...

The optical properties of single nanoholes in optically thin (t=20 nm) gold films on glass have been studied experimentally and theoretically. The measured elastic scattering spectra from the nanoholes exhibit a broad resonance in the red part of the visible spectrum, which is qualitatively similar to localized surface

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We investigate the dipolar plasmon modes of nanoparticle trimers formed by three equal silver disks of diameter D = 100 nm located on the vertexes of an equilateral triangle. Samples were fabricated by electron-beam lithography and studied experimentally by dark-field spectroscopy. The results are found to be in good agreement with electrodynamical simulations based on the discrete dipole approximation (DDA). Similar to nanoparticle dimers, the trimer system exhibits two hybridized dipole resonances to the red and to the blue of the single particle resonance. However, the far-field spectra are polarization-insensitive for light incident normal to the plane of the trimer, and the peak shifts, which occur as the edge-to-edge distance d between the particles decrease, are smaller than for dimers. Moreover, we find that the dipolar displacement patterns are well described by linear combinations of bonding and antibonding symmetry adapted coordinates obtained through symmetry analysis based on the ideal D 3h point-group.

We report on the polarization-dependent optical response of elongated nanoholes in optically thin gold films. We measured elastic scattering spectra of spatially isolated ellipsoidal nanoholes with varying aspect ratio and compared the results to electrodynamic simulations. Both experiments and theory show that the plasmon mode that is polarized parallel to the short axis of the ellipsoidal hole red-shifts with increasing aspect ratio. This behavior is completely opposite to the case of elongated metal particles. We present a simple analytical model that qualitatively explains the observations in terms of the different orientations of the induced dipole moments in holes and particles.