Publications (34)139.75 Total impact
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Article: Mechanisms of Fano Resonances in Coupled Plasmonic Systems.
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ABSTRACT: Fano resonances in hybridized systems formed from the interaction of bright modes only are reported. Despite precedent works, we demonstrate theoretically and experimentally that Fano resonances can be obtained by destructive interference between two bright dipolar modes out of phase. A simple oscillator model is provided to predict and fit the far-field scattering. The predictions are verified with numerical calculations using a surface integral equation method for a wide range of geometrical parameters. The validity of the model is then further demonstrated with experimental dark-field scattering measurements on actual nanostructures in the visible range. A remarkable set of properties like crossings, avoided crossings, inversion of subradiant and superradiant modes and a plasmonic equivalent of a bound state in the continuum are presented. The nanostructure, that takes advantage of the combination of Fano resonance and nanogap effects, also shows high tunability and strong near-field enhancement. Our study provides a general understanding of Fano resonances as well as a simple tool for engineering their spectral features.ACS Nano 04/2013; · 10.77 Impact Factor -
Article: Engineering Metal Adhesion Layers That Do Not Deteriorate Plasmon Resonances.
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ABSTRACT: Adhesion layers, required to stabilize metallic nanostructures, dramatically deteriorate the performances of plasmonic sensors, by severely damping the plasmon modes. In this article, we show that these detrimental effects critically depend on the overlap of the electromagnetic near-field of the resonant plasmon mode with the adhesion layer and can be minimized by careful engineering of the latter. We study the dependence of the geometrical parameters such as layer thickness and shape on the near-field of localized plasmon resonances for traditional adhesion layers such as Cr, Ti, and TiO2. Our experiments and simulations reveal a strong dependence of the damping on the layer thickness, in agreement with the exponential decay of the plasmon near-field. We developed a method to minimize the damping by selective deposition of thin adhesion layers (<1 nm) in a manner that prevents the layer to overlap with the hotspots of the plasmonic structure. Such a designed structure enables the use of standard Cr and Ti adhesion materials to fabricate robust plasmonic sensors without deteriorating their sensitivity.ACS Nano 03/2013; · 10.77 Impact Factor -
Article: Plasmonic Radiance: Probing Structure at the Ångström Scale with Visible Light.
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ABSTRACT: Plasmonic modes with long radiative lifetimes combine strong nanoscale light confinement with a narrow spectral linewidth carrying the signature of Fano resonances, making them very promising for nanophotonic applications such as sensing, lasing and switching. Their coupling to incident radiation, also known as radiance, determines their optical properties and optimal use in applications. In this work, we theoretically and experimentally demonstrate that the radiance of a plasmonic mode can be classified into three different regimes. In the weak coupling regime, the lineshape exhibits remarkable sensitivity to the dielectric environment. We show that geometrical displacements and deformations at the \AA ngstr\"om scale can be detected optically by measuring the radiance. In the intermediate regime, the electromagnetic energy stored in the mode is maximal, with large electric field enhancements that can be exploited in surface enhanced spectroscopy applications. In the strong coupling regime, the interaction can result in hybridized modes with tunable energies.Nano Letters 12/2012; · 13.20 Impact Factor -
Article: Biosensor based on chemically-designed anchorable cytochrome c for the detection of H(2)O(2) released by aquatic cells.
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ABSTRACT: A novel third generation biosensor was developed based on one-shot adsorption of chemically-modified cytochrome c (cyt c) onto bare gold electrodes. In contrast to the classic approach which consists of attaching cyt c onto an active self-assembled monolayer (SAM) priory chemisorbed on gold, here short-chain thiol derivatives (mercaptopropionic acid, MPA) were chemically introduced on cyt c protein shell via its lysine residues enabling the very fast formation (<5min) of an electroactive biological self-assembled monolayer (SAM) exhibiting a quasi-reversible electrochemical behavior and a fast direct electron transfer (ET). The heterogeneous ET rate constant was estimated to be k(s)=1600s(-1), confirming that short anchors facilitate the ET via an efficient orientation of the heme pocket. In comparison, no ET was observed in the case of native and long-anchor (mercaptoundecanoic acid, MUA) modified cyt c directly adsorbed on gold. However, in both cases the ET was efficiently restored upon in-bulk generation of gold nanoparticles which acted as electron shuttles. This observation emphasizes that the lack of electroactivity might be caused by either an inappropriate orientation of the protein (native cyt c) or a critical distance (MUA-cyt c). Finally, the sensitivity of the bare gold electrode directly modified with MPA-cyt c to hydrogen peroxide (H(2)O(2)) was evaluated by amperometry and the so-made amperometric biosensor was able to perform real-time and non-invasive detection of endogeneous H(2)O(2) released by unicellular aquatic microorganisms, Chlamydomonas reinhardtii, upon cadmium exposure.Biosensors & bioelectronics 11/2012; 42C:385-390. · 5.43 Impact Factor -
Article: Molecule-Dependent Plasmonic Enhancement of Fluorescence and Raman Scattering near Realistic Nanostructures.
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ABSTRACT: The enhancement of fluorescence and Raman scattering by plasmonic nanostructures is studied theoretically with special focus on the effects of the observed molecule's properties and the realistic geometry of the plasmonic nanostructure. Numerical experiments show that the enhancement factor may vary by many orders of magnitude depending on a fluorophore's transition rates or intrinsic quantum yield. For different molecules, boosting fluorescence enhancement means optimizing different factors, leading to a different ideal geometric and spectral configuration. This framework, coupled with powerful new simulation tools, will facilitate the design and characterization of fluorescence-enhancing plasmonic nanostructures as well as yield experimental access to the intrinsic properties of the molecules under study.ACS Nano 09/2012; · 10.77 Impact Factor -
Article: A zeptoliter volume meter for analysis of single protein molecules.
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ABSTRACT: A central goal in bioanalytics is to determine the concentration of and interactions between biomolecules. Nanotechnology allows performing such analyses in a highly parallel, low-cost, and miniaturized fashion. Here we report on label-free volume, concentration, and mobility analysis of single protein molecules and nanoparticles during their diffusion through a subattoliter detection volume, confined by a 100 nm aperture in a thin gold film. A high concentration of small fluorescent molecules renders the aqueous solution in the aperture brightly fluorescent. Nonfluorescent analytes diffusing into the aperture displace the fluorescent molecules in the solution, leading to a decrease of the detected fluorescence signal, while analytes diffusing out of the aperture return the fluorescence level. The resulting fluorescence fluctuations provide direct information on the volume, concentration, and mobility of the nonfluorescent analytes through fluctuation analysis in both time and amplitude.Nano Letters 12/2011; 12(1):370-5. · 13.20 Impact Factor -
Article: Influence of electromagnetic interactions on the line shape of plasmonic Fano resonances.
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ABSTRACT: The optical properties of plasmonic nanostructures supporting Fano resonances are investigated with an electromagnetic theory. Contrary to the original work of Fano, this theory includes losses in the materials composing the system. As a result, a more general formula is obtained for the response of the system and general conclusions for the determination of the resonance parameters are drawn. These predictions are verified with surface integral numerical calculations in a broad variety of plasmonic nanostructures including dolmens, oligomers, and gratings. This work presents a robust and consistent analysis of plasmonic Fano resonances and enables the control of their line shape based on Maxwell's equations. The insights into the physical understanding of Fano resonances gained this way will be of great interest for the design of plasmonic systems with specific spectral responses for applications such as sensing and optical metamaterials.ACS Nano 11/2011; 5(11):8999-9008. · 10.77 Impact Factor -
Article: Relation between near-field and far-field properties of plasmonic Fano resonances.
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ABSTRACT: The relation between the near-field and far-field properties of plasmonic nanostructures that exhibit Fano resonances is investigated in detail. We show that specific features visible in the asymmetric lineshape far-field response of such structures originate from particular polarization distributions in their near-field. In particular we extract the central frequency and width of plasmonic Fano resonances and show that they cannot be directly found from far-field spectra. We also address the effect of the modes coupling onto the frequency, width, asymmetry and modulation depth of the Fano resonance. The methodology described in this article should be useful to analyze and design a broad variety of Fano plasmonic systems with tailored near-field and far-field spectral properties.Optics Express 10/2011; 19(22):22167-75. · 3.59 Impact Factor -
Article: Ab initio theory of Fano resonances in plasmonic nanostructures and metamaterials
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ABSTRACT: An ab initio theory for Fano resonances in plasmonic nanostructures and metamaterials is developed using Feshbach formalism. It reveals the role played by the electromagnetic modes and material losses in the system, and enables the engineering of Fano resonances in arbitrary geometries. A general formula for the asymmetric resonance in a non-conservative system is derived. The influence of the electromagnetic interactions on the resonance line shape is discussed and it is shown that intrinsic losses drive the resonance contrast, while its width is mostly determined by the coupling strength between the non-radiative mode and the continuum. The analytical model is in perfect agreement with numerical simulations.05/2011; -
Article: Excitation and reemission of molecules near realistic plasmonic nanostructures.
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ABSTRACT: The enhancement of excitation and reemission of molecules in close proximity to plasmonic nanostructures is studied with special focus on the comparison between idealized and realistically shaped nanostructures. Numerical experiments show that for certain applications choosing a realistic geometry closely resembling the actual nanostructure is imperative, an idealized simulation geometry yielding significantly different results. Finally, a link between excitation and reemission processes is formed via the theory of optical reciprocity, allowing a transparent view of the electromagnetic processes involved in plasmon-enhanced fluorescence and Raman-scattering.Nano Letters 02/2011; 11(2):482-7. · 13.20 Impact Factor -
Article: Accurate and versatile modeling of electromagnetic scattering on periodic nanostructures with a surface integral approach.
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ABSTRACT: A surface integral formulation for light scattering on periodic structures is presented. Electric and magnetic field equations are derived on the scatterers' surfaces in the unit cell with periodic boundary conditions. The solution is calculated with the method of moments and relies on the evaluation of the periodic Green's function performed with Ewald's method. The accuracy of this approach is assessed in detail. With this versatile boundary element formulation, a very large variety of geometries can be simulated, including doubly periodic structures on substrates and in multilayered media. The surface discretization shows a high flexibility, allowing the investigation of irregular shapes including fabrication accuracy. Deep insights into the extreme near-field of the scatterers as well as in the corresponding far-field are revealed. This method will find numerous applications for the design of realistic photonic nanostructures, in which light propagation is tailored to produce novel optical effects.Journal of the Optical Society of America A 10/2010; 27(10):2261-71. · 1.56 Impact Factor -
Article: Symmetry and selection rules for localized surface plasmon resonances in nanostructures
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ABSTRACT: We describe a general theoretical framework based on the Bergman spectral representation to study how a nanostructure interacts with an external electromagnetic field. The selection rules for localized surface plasmon resonances (LSPRs) are obtained by implementing the group theory upon the electric vector field. The influence of symmetry breaking on the splitting of degenerated modes and the switching of dark modes by specific illuminations are discussed. These results emphasize the fact that the selection rules for a vector field are different from the case of a scalar field and essentially induced by the geometry of the structure. Finally, this work not only points out that measurements of LSPRs may result in very different results with different external fields, but also provides a strategy to selectively excite specific LSPRs of plasmonic structures.Phys. Rev. B. 06/2010; 81(23). -
Article: Distance-controlled scattering in a plasmonic trap
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ABSTRACT: Light scattered by a dielectric object when it is trapped in the field of a plasmonic nanostructure is studied theoretically and experimentally using both dielectric spheres and S. cerevisiae cells. A dramatic enhancement of the scattered light is observed for short separation distances between scatterer and plasmonic trap. It is shown that this effect can serve to selectively image cells after their immobilization and distinguish them from a turbid background. The high sensitivity of the scattered light to the separation distance and lateral displacement also provides additional insights in the configuration of the cell within the trap.Applied Physics Letters 03/2010; · 3.84 Impact Factor -
Article: Trapping and sensing 10 nm metal nanoparticles using plasmonic dipole antennas.
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ABSTRACT: The optical trapping of Au nanoparticles with dimensions as small as 10 nm in the gap of plasmonic dipole antennas is demonstrated. Single nanoparticle trapping events are recorded in real time by monitoring the Rayleigh scattering spectra of individual plasmonic antennas. Numerical simulations are also performed to interpret the experimental results, indicating the possibility to trap nanoparticles only a few nanometers in size. This work unveils the potential associated with the integration of plasmonic trapping with localized surface plasmon resonance based sensing techniques, in order to deliver analyte to specific, highly sensitive regions ("hot spots").Nano Letters 02/2010; 10(3):1006-11. · 13.20 Impact Factor -
Article: Integration of plasmonic trapping in a microfluidic environment.
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ABSTRACT: Near field generated by plasmonic structures has recently been proposed to trap small objects. We report the first integration of plasmonic trapping with microfluidics for lab-on-a-chip applications. A three-layer plasmo-microfluidic chip is used to demonstrate the trapping of polystyrene spheres and yeast cells. This technique enables cell immobilization without the complex optics required for conventional optical tweezers. The benefits of such devices are optical simplicity, low power consumption and compactness; they have great potential for implementing novel functionalities for advanced manipulations and analytics in lab-on-a-chip applications.Optics Express 05/2009; 17(8):6018-24. · 3.59 Impact Factor -
Article: Surface integral formulation for 3D simulations of plasmonic and high permittivity nanostructures.
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ABSTRACT: Among the most popular approaches used for simulating plasmonic systems, the discrete dipole approximation suffers from poorly scaling volume discretization and limited near-field accuracy. We demonstrate that transformation to a surface integral formulation improves scalability and convergence and provides a flexible geometric approximation allowing, e.g., to investigate the influence of fabrication accuracy. The occurring integrals can be solved quasi-analytically, permitting even rapidly changing fields to be determined arbitrarily close to a scatterer. This insight into the extreme near-field behavior is useful for modeling closely packed particle ensembles and to study "hot spots" in plasmonic nanostructures used for plasmon-enhanced Raman scattering.Journal of the Optical Society of America A 05/2009; 26(4):732-40. · 1.56 Impact Factor -
Article: Channel and wedge plasmon modes of metallic V-grooves with finite metal thickness.
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ABSTRACT: We investigate numerically the effect of a finite metal film thickness on the propagation characteristics of the channel Plasmon polariton (CPP) and wedge plasmon polariton (WPP) modes, both in a symmetric and asymmetric environment. We observe that decreasing the metal thickness results in an improvement of the field localization near the groove tip and an increase of the losses for both types of mode. This behavior stems from the typical symmetric charge distribution of both modes across the metal film. When considering an asymmetric dielectric environment, the CPP mode is found to evolve into short range Plasmon modes propagating along the groove walls, in contrast to the WPP mode which remains essentially confined at the tip apex. These results can be useful to tailor the properties of such plasmon modes, using the metal thickness as the variable parameter.Optics Express 03/2009; 17(4):2364-74. · 3.59 Impact Factor -
Article: Retardation-induced plasmonic blinking in coupled nanoparticles.
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ABSTRACT: We study how retardation leads to interference effects in radiatively coupled plasmonic nanoparticles. We show that inclined illumination through a glass substrate on two plasmonic particles results in either an enhanced field or an attenuated field localized at the position of the first particle. Periodic intensity blinking of the first particle is observed as a function of the particle separation. This phenomenon is nonsymmetric, and almost no blinking is observed on the second particle. The effect is strongest when the illumination angle is chosen such that the optical retardation path in the substrate coincides with the particle distance. Implications of this plasmonic blinking for near-field measurements are discussed.Optics Letters 03/2009; 34(3):368-70. · 3.40 Impact Factor -
Article: Reversal of the optical force in a plasmonic trap.
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ABSTRACT: We study in detail the optical forces generated by a plasmonic trap on a plasmonic nanoparticle. The permittivity of the trapped particle is tuned using a Drude model. The interplay between the plasmon resonances of the trap and of the particle can produce different regimes leading to attractive or repulsive forces. Hence a particle will be trapped or repulsed depending on its permittivity. Such a physical system should provide new functionalities for lab-on-the-chip applications.Optics Letters 01/2009; 33(24):3001-3. · 3.40 Impact Factor -
Article: Engineering the optical response of plasmonic nanoantennas.
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ABSTRACT: The optical properties of plasmonic dipole and bowtie nanoantennas are investigated in detail using the Green's tensor technique. The influence of the geometrical parameters (antenna length, gap dimension and bow angle) on the antenna field enhancement and spectral response is discussed. Dipole and bowtie antennas confine the field in a volume well below the diffraction limit, defined by the gap dimensions. The dipole antenna produces a stronger field enhancement than the bowtie antenna for all investigated antenna geometries. This enhancement can reach three orders of magnitude for the smallest examined gap. Whereas the dipole antenna is monomode in the considered spectral range, the bowtie antenna exhibits multiple resonances. Furthermore, the sensitivity of the antennas to index changes of the environment and of the substrate is investigated in detail for biosensing applications; the bowtie antennas show slightly higher sensitivity than the dipole antenna.Optics Express 07/2008; 16(12):9144-54. · 3.59 Impact Factor
Top co-authors
Top Journals
- Optics Express (5)
- Nano Letters (4)
- ACS Nano (4)
- Optics Letters (3)
- Applied Physics Letters (1)
Institutions
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2005–2012
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École Polytechnique Fédérale de Lausanne
- Laboratoire de nanophotonique et métrologie
Lausanne, VD, Switzerland
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