| 1. |
- Verre, Ruggero, 1985, et al.
(författare)
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Quasi-isotropic Surface Plasmon Polariton Generation through Near-Field Coupling to a Penrose Pattern of Silver Nanoparticles
- 2014
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 8:9, s. 9286-9294
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Tidskriftsartikel (refereegranskat)abstract
- Quasicrystals are structures that possess long-range order without being periodic. We investigate the unique characteristics of a photonic quasicrystal that consists of plasmonic Ag nanodisks arranged in a Penrose pattern. The quasicrystal scatters light in a complex but spectacular diffraction pattern that can be directly imaged in the back focal plane of an optical microscope, allowing us to assess the excitation efficiency of the various diffraction modes. Furthermore, surface plasmon polaritons can be launched almost isotropically through near-field grating coupling when the quasicrystal is positioned close to a homogeneous silver surface. We characterize the dispersion relation of the different excited plasmon modes by reflection measurements and simulations. It is demonstrated that the quasicrystal in-coupling efficiency is strongly enhanced compared to a nanopartide array with the same particle density but only short-range lateral order. We envision that the system can be useful for a number of advanced light harvesting and optoelectronic applications.
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| 2. |
- Ogier, Robin, 1987, et al.
(författare)
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Macroscopic Layers of Chiral Plasmonic Nanoparticle Oligomers from Colloidal Lithography
- 2014
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 1:10, s. 1074-1081
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Tidskriftsartikel (refereegranskat)abstract
- Optical near-field coupling between closely spaced plasmonic metal nanoparticles is important to a range of nanophotonic applications of high contemporary interest, including surface-enhanced molecular spectroscopy, nanooptical sensing, and various novel light-harvesting concepts. Here we report on monolayers of chiral heterotrimers and heterotetramers composed of closely spaced silver and/or gold nanodisks of different heights fabricated through facile hole-mask colloidal lithography. These quasi-three-dimensional oligomers are interesting for applications because they exhibit "hot" gaps and crevices of nanometric dimensions, a pronounced circular dichroism, and optical chirality in the visible to near-infrared wavelength range, and they can be produced in large ensembles (>109) of identical orientation. We analyze the optical properties of the samples based on simulation results and find that the circular dichroism is due to strong near-field coupling and intricate phase retardation effects originating in the three-dimensional character of the individual oligomers.
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| 3. |
- Wersäll, Martin, 1985, et al.
(författare)
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Directional Nanoplasmonic Antennas for Self-Referenced Refractometric Molecular Analysis
- 2014
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:36, s. 21075-21080
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Tidskriftsartikel (refereegranskat)abstract
- Localized surface-plasmon resonance (LSPR) sensors are typically based on tracing resonance peak shifts that precisely follow changes in the local refractive index. Such measurements usually require a spectrometer, a stable light source, and an accurate LSPR position tracing technique. As a simple but efficient alternative, we investigated a self-referenced single-wavelength sensing scheme based on angle-dependent and highly directional radiation patterns originating from a monolayer of asymmetric gold nanodimers. We found that one could easily trace a model biotinneutravidin recognition reaction as well as minute bulk refractive index changes, by measuring the intensity ratio between the light scattered in two different directions with respect to the dimers. The refractometric resolution of the methodology was estimated to be on the order of Delta n approximate to 10(-5) RIU. These results may be particularly useful for label-free biosensing applications that require a combination of simple and cost-effective optical readout with a reasonable sensitivity.
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| 4. |
- Svedendahl, Mikael, 1984
(författare)
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Tinkering with Light at the Nanoscale using Plasmonic Metasurfaces and Antennas: From Fano to Function
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface plasmons are charge density oscillations that can couple strongly to light and be excited in, for instance, thin metal films and metal nanoparticles. The plasmonic excitation squeezes the light down to nanometric length scales, far smaller than the wavelength of the light. This localization of light can be utilized in several surface-enhanced spectroscopies, for photothermal therapy, in optical trapping methodologies and in refractometric sensing schemes. This thesis focuses on various excitation schemes and spectroscopic measurements of surface plasmons and their sensitivity to the dielectric surrounding the metal.Plasmonic excitations in metal films and nanoparticles have several common features, although only the former has successfully been commercialized as a refractometric biosensing platform. In a direct comparison of the two, both platforms performed equally well, from a sensitivity point-of-view. However, there are two significant advantages of nanoparticle plasmonic sensing schemes: The much relaxed excitation conditions and the miniscule size of the nanoparticle sensors. In a combination of these features, hundreds of individual nanoparticles were simultaneously interrogated in order to approach the few to single molecule detection limit. The data were obtained using a hyperspectral imaging methodology in combination with an enzymatic precipitation reaction that enhanced the plasmonic response from individual adsorbed molecules. The results demonstrated a sensitivity in the single molecule range, but a number of inhomogeneous broadening effects prevented counting the exact number of molecules per particle. In a different line of research, plasmonic nanoparticles placed in a large two dimensional array with small interparticle spacing and supported with a glass substrate were interrogated. The nanoplasmonic layer then act as a metamaterial that can support strongly asymmetric resonances, dispersive modes and even complete light absorption. These effects are due to a so-called Fano interference between the plasmon excitation and the reflection from the dielectric boundary. Complete absorption enhances the optical near-fields, which can be utilized in, for instance, surface enhanced spectroscopy techniques. However, minimizing the reflection has another interesting feature: A rapid phase jump of the reflected light. The phase is shown to vary about one order of magnitude faster than the reflected intensity and, therefore, also provides around one order of magnitude higher sensitivity to molecular adsorption. Altogether, the results presented in this thesis provides a basis for several interesting sensing schemes, as well as insight into some fundamentally intriguing phenomena regarding absorption, nanoscale coherence and light localization.
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