| 1. |
- Shegai, Timur, 1982, et al.
(författare)
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A bimetallic nanoantenna for directional colour routing
- 2011
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress in nanophotonics includes demonstrations of meta-materials displaying negative refraction at optical frequencies, directional single photon sources, plasmonic analogies of electromagnetically induced transparency and spectacular Fano resonances. The physics behind these intriguing effects is to a large extent governed by the same single parameter-optical phase. Here we describe a nanophotonic structure built from pairs of closely spaced gold and silver disks that show phase accumulation through material-dependent plasmon resonances. The bimetallic dimers show exotic optical properties, in particular scattering of red and blue light in opposite directions, in spite of being as compact as similar to lambda(3)/100. These spectral and spatial photon-sorting nanodevices can be fabricated on a wafer scale and offer a versatile platform for manipulating optical response through polarization, choice of materials and geometrical parameters, thereby opening possibilities for a wide range of practical applications.
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| 2. |
- Miljkovic, Vladimir, 1982, et al.
(författare)
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Mode-specific directional emission from hybridized particle-on-a-film plasmons
- 2011
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Ingår i: Optics Express. - 1094-4087. ; 19:14, s. 12856-12864
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the electromagnetic interaction between a gold nanoparticle and a thin gold film on a glass substrate. The coupling between the particle plasmons and the surface plasmon polaritons of the film leads to the formation of two localized hybrid modes, one low-energy. film-like. plasmon and one high-energy plasmon dominated by the nanoparticle. We find that the two modes have completely different directional scattering patterns on the glass side of the film. The high-energy mode displays a characteristic dipole emission pattern while the low-energy mode sends out a substantial part of its radiation in directions parallel to the particle dipole moment. The relative strength of the two radiation patterns vary strongly with the distance between the particle and the film, as determined by the degree of particle-film hybridization. (C) 2011 Optical Society of America
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| 3. |
- Shegai, Timur, 1982, et al.
(författare)
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Angular Distribution of Surface-Enhanced Raman Scattering from Individual Au Nanoparticle Aggregates
- 2011
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 5:3, s. 2036-2041
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Tidskriftsartikel (refereegranskat)abstract
- Nano-optical antennas based on plasmonic metal particles are well-known for their ability to dramatically concentrate electromagnetic energy. However, not much attention has been devoted to the directionality properties of nanoantennas. Here, we report on the angular distribution of surface-enhanced Raman scattering (SERS) emitted by isolated aggregates of gold nanoparticles. We find that most of the radiation appears at angles exceeding the critical angle of the air-glass interface supporting the aggregates, and we demonstrate that angle-resolved imaging can be used as a fast and facile method for determination of the three-dimensional orientation and symmetry of the nanoantenna.
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| 4. |
- Shegai, Timur, 1982, et al.
(författare)
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Unidirectional Broadband Light Emission from Supported Plasmonic Nanowires
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:2, s. 706-711
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Tidskriftsartikel (refereegranskat)abstract
- Metal nanowires are thought to become key elements in future nanophotonics applications. Here we show that single crystal silver nanowires supported on a dielectric interface behave similar to broadband unidirectional antennas for visible, light. The degree of directionality can be controlled through the nanowire radius and its dielectric environment and the effect can be interpreted in terms of so-called leakage radiation from surface plasmons propagating in a single direction along a wire. We measure a forward-to-backward emission ratio exceeding 15 dB and an angular spread of 4 degrees for wires with radii of the order 150 nm on glass in air. These findings could pave the way for development of metal nanowires as subwavelength directors of light in solar, sensor, and spectroscopy applications.
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| 5. |
- El Daif, O., et al.
(författare)
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Silver nanodiscs for light scattering in thin epitaxial silicon solar cells: Influence of the disc radius
- 2011
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 0272-9172. - 9781627482110 ; 1391, s. 75-80
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Konferensbidrag (refereegranskat)abstract
- The effect of silver nanoparticles showing localised plasmonic resonances on the efficiency of thin film silicon solar cells is studied. Silver (Ag) nanodiscs were deposited on the surface of silicon cells grown on highly doped silicon substrates, through hole-mask colloidal lithography, which is a low-cost and bottom-up technique. The cells have no back reflector in order to exclusively study the effect of the front surface on their properties. Cells with nanoparticles were compared with both bare silicon cells and cells with an antireflection coating. We optically observe a resonance showing an absorption increase controllable by the disc radius. We also see an increase in efficiency with respect to bare cells, but we see a decrease in efficiency with respect to cells with an antireflection coating due to losses at wavelengths below the plasmon resonance. As the material properties are not notably affected by the particles deposition, the loss mechanism is an important absorption in the nanoparticles. We confirm this by numerical simulations.
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| 6. |
- Miljkovic, Vladimir, 1982
(författare)
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Simulations of directionality effects and optical forces in plasmonic nanostructures
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the rapid development of nanoscience and nanotechnology, surface plasmonics based on metal nanoparticles and nanostructures gain increasing interest, not only for fundamental scientific studies, but also for optical and sensor applications. At the nanoscale, the physical and chemical properties of metal particles, especially their optical properties, strongly depend on size and shape, as well as on the surrounding media and structures. By modifying those features, one may design novel functional materials and devices. This thesis deals with investigations of light-induced effects at the nanoscale, focusing on optically induced forces on plasmonic nanostructures and angular distribution of light due to the particle-substrate interactions. Nanoparticles trapped within an optically induced potential energy well (e.g. using optical tweezers) will interact with each other by mutual forces. This can lead tothe self-organization of the nanoparticles within the trap, an effect known as optical binding. In this thesis I have theoretically investigated the optical forces between the metal nanoparticles for different polarization configurations. In addition to the optical forces, there are other contributions to the total interaction forces betweenthe particles, such as the Coulomb repulsion and van der Waals attraction. These contributions have been investigated in the case of two strongly interacting gold particles through the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). The thesis also contains a study of optical manipulation (trapping, rotation and spinning) of elongated plasmonic particles, such as rods, dimers and micrometer long nanowires. The other main theme of the thesis is the angular distribution of light scattered from the nanoparticles and the nanowires. The scattering properties of these structures are strongly affected by the presence of the substrate. It is shown that the dipolar angular distribution of light scattered from a single dipolar emitter in a homogeneous medium is highly modified when the emitter is brought close to a glass substrate (and even more so when the emitter is brought close to a thin metal film).In addition to nanoparticles, the thesis deals with nanowires, structures that support plasmonic Fabry-Perot resonances due to multiple reflection of the plasmonspropagating along their interfaces. It is shown that nanowires can scatter light in a rather narrow angular distribution thanks to the phase retardation of the plasmonpropagating along the wire, which is dictated by the wire diameter, length and surrounding medium.
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| 7. |
- Tong, Lianming, 1981, et al.
(författare)
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Plasmon Hybridization Reveals the Interaction between Individual Colloidal Gold Nanoparticles Confined in an Optical Potential Well
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:11, s. 4505-4508
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Tidskriftsartikel (refereegranskat)abstract
- The understanding of interaction forces between nanoparticles in colloidal suspension is central to a wide range of novel applications and processes in science and industry. However, few methods are available for actual characterization of such forces at the single particle level. Here we demonstrate the first measurements of colloidal interactions between two individual diffusing nanoparticles using a colorimetric assay based on plasmon hybridization, that is, strong near-field coupling between localized surface plasmon resonances. The measurements are possible because individual gold nanoparticle pairs can be loosely confined in an optical potential well created by a laser tweezers. We quantify the degree of plasmon hybridization for a large number of individual particle pairs as a function of increasing salt concentration. The data reveal a considerable heterogeneity at the single particle level but the estimated average surface separations are in excellent agreements with predictions based on the classical theory of Derjaguin, Landau, Verwey, and Overbeek.
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