Showing papers by "Olivier J. F. Martin published in 2017"
TL;DR: It is demonstrated that topographic features comprising lithographed funnelled traps and auxiliary sidewalls on a solid substrate can deterministically direct the capillary assembly of Au nanorods to attain simultaneous control of position, orientation and interparticle distance at the nanometre level.
Abstract: Predetermined and selective placement of nanoparticles onto large-area substrates with nanometre-scale precision is essential to harness the unique properties of nanoparticle assemblies, in particular for functional optical and electro-optical nanodevices. Unfortunately, such high spatial organization is currently beyond the reach of top-down nanofabrication techniques alone. Here, we demonstrate that topographic features comprising lithographed funnelled traps and auxiliary sidewalls on a solid substrate can deterministically direct the capillary assembly of Au nanorods to attain simultaneous control of position, orientation and interparticle distance at the nanometre level. We report up to 100% assembly yield over centimetre-scale substrates. We achieve this by optimizing the three sequential stages of capillary nanoparticle assembly: insertion of nanorods into the traps, resilience against the receding suspension front and drying of the residual solvent. Finally, using electron energy-loss spectroscopy we characterize the spectral response and near-field properties of spatially programmable Au nanorod dimers, highlighting the opportunities for precise tunability of the plasmonic modes in larger assemblies.
253 citations
TL;DR: This study employs metal-insulator-metal sandwich nanodisks that support enhanced in-phase electric dipole modes, which are blue-shifted with respect to a single metal disk, which enables the generation of short wavelength colors with larger nanostructures.
Abstract: Plasmonic effects associated with metallic nanostructures have been widely studied for color generation. It became apparent that highly saturated and bright colors are hard to obtain, and very small nanostructures need to be fabricated. To address this issue, in this study, we employ metal–insulator–metal sandwich nanodisks that support enhanced in-phase electric dipole modes, which are blue-shifted with respect to a single metal disk. The blue shift enables the generation of short wavelength colors with larger nanostructures. The radiation modes hybridize with the Wood’s anomaly in periodic structures, creating narrow and high-resonance peaks in the reflection and deep valleys in the transmission spectra, thus producing vivid complementary colors in both cases. Full colors can be achieved by tuning the radius of the nanodisks and the periodicity of the arrays. Good agreement between simulations and experiments is demonstrated and analyzed in CIE1931, sRGB, and HSV color spaces. The presented method has p...
172 citations
TL;DR: This work demonstrates a narrowband metasurface that relies on Fano resonances to control the propagation of light and creates a phase modulation along the surface within a narrow spectral range.
Abstract: Controlling the phase of an electromagnetic field using plasmonic nanostructures provides a versatile way to manipulate light at the nanoscale. Broadband phase modulation has been demonstrated using inhomogeneous metasurfaces with different geometries; however, for many applications such as filtering, hyperspectral imaging and color holography, narrowband frequecy selectivity is a key functionality. In this work, we demonstrate, both theoretically and experimentally, a narrowband metasurface that relies on Fano resonances to control the propagation of light. By geometrically tuning the sub-radiant modes with respect to a fixed super-radiant resonance, we can create a phase modulation along the surface within a narrow spectral range. The resulting anomalous reflection measured for such a Fano-resonant metasurface exhibits a 100 nm bandwidth and a color routing efficiency of up to 81% at a central wavelength of λ=750 nm. The design flexibility provided by this Fano-assisted metasurface for color-selective light manipulation is further illustrated by demonstrating a highly directional color-routing effect between two channels, at λ=532 and 660 nm, without any crosstalk.
84 citations
TL;DR: A dehydration treatment is developed which alters the morphology of the deposited silver, leading to an improved chemical and thermal stability of the Ag nanostructures and films, which then remain stable for more than 14 weeks under ambient laboratory conditions.
Abstract: Silver (Ag) nanostructures and thin films are advantageous plasmonic materials as they have significantly lower losses than gold (Au). Unfortunately, Ag nanostructures suffer from poor chemical and thermal stability, which limit their applications. Here, the mechanisms leading to the deterioration of Ag nanostructures are clarified. It is first shown that oxygen alone cannot oxidize Ag nanostructures. Then, experiments using X-ray photoelectron spectroscopy reveal that the amount of sulfur in ambient air is too low for efficient tarnishing of the Ag surface. Finally, water is found to be the most critical factor for the degradation of Ag nanostructures and thin films. At high relative humidity, adsorbed water forms a thin film enabling the migration of Ag ions at the Ag/air interface, which deteriorates the Ag nanostructures. A dehydration treatment is developed which alters the morphology of the deposited silver, leading to an improved chemical and thermal stability of the Ag nanostructures and films, which then remain stable for more than 14 weeks under ambient laboratory conditions. In addition, dehydration also improves significantly the root-mean-square roughness for Ag thin films deposited on a glass substrate.
55 citations
TL;DR: In this paper, the role of the mode coupling in the enhancement of second harmonic generation was investigated in detail, and it was clearly demonstrated that second-harmonic generation is enhanced when the coupling between the quadrupole and...
Abstract: Multiresonant plasmonic nanoantennas have recently gained a lot of attention due to their ability to enhance nonlinear optical processes at the nanoscale. The first nanostructure designed for this purpose was an aluminum antenna composed of three arms, designed to be resonant at both the fundamental and the second harmonic frequencies. It was demonstrated that second harmonic generation induced by its resonances at both the fundamental and second harmonic wavelengths is higher than the one from a simple dipolar nanoantenna supporting a resonance at the fundamental wavelength only. However, the underlying mechanisms leading to this strong nonlinear signal are still unclear. In this study, both advanced simulations and experiments are combined to investigate in details the role of the mode coupling in the enhancement of second harmonic generation. By varying the length of the nanoantenna arms, it is clearly demonstrated that second harmonic generation is enhanced when the coupling between the quadrupole and...
54 citations
TL;DR: An improved fabrication method is reported that enables precise tuning of the heterodimer geometry, with interparticle distances made down to a few nanometers between Au-Ag and Au-Al nanoparticles, which facilitates the development of plasmonic heterostructures with tailored responses, beyond the possibilities offered by homodimers.
Abstract: While plasmonic antennas composed of building blocks made of the same material have been thoroughly studied, recent investigations have highlighted the unique opportunities enabled by making compositionally asymmetric plasmonic systems. So far, mainly heterostructures composed of nanospheres and nanodiscs have been investigated, revealing opportunities for the design of Fano resonant nanostructures, directional scattering, sensing and catalytic applications. In this article, an improved fabrication method is reported that enables precise tuning of the heterodimer geometry, with interparticle distances made down to a few nanometers between Au–Ag and Au–Al nanoparticles. A wide range of mode energy detuning and coupling conditions are observed by near field hyperspectral imaging performed with electron energy loss spectroscopy, supported by full wave analysis numerical simulations. These results provide direct insights into the mode hybridization of plasmonic heterodimers, pointing out the influence of each...
43 citations
TL;DR: The vdW MoS2/VO2 heterojunction combines the excellent blocking capability of an n-n junction with a high conductivity in on-state, and it can be turned into a Schottky rectifier at high applied voltage or at temperatures higher than 68 °C, exploiting the metal state of VO2.
Abstract: Junctions between n-type semiconductors of different electron affinity show rectification if the junction is abrupt enough. With the advent of 2D materials, we are able to realize thin van der Waals (vdW) heterostructures based on a large diversity of materials. In parallel, strongly correlated functional oxides have emerged, having the ability to show reversible insulator-to-metal (IMT) phase transition by collapsing their electronic bandgap under a certain external stimulus. Here, we report for the first time the electronic and optoelectronic characterization of ultra-thin n-n heterojunctions fabricated using deterministic assembly of multilayer molybdenum disulphide (MoS2) on a phase transition material, vanadium dioxide (VO2). The vdW MoS2/VO2 heterojunction combines the excellent blocking capability of an n-n junction with a high conductivity in on-state, and it can be turned into a Schottky rectifier at high applied voltage or at temperatures higher than 68 °C, exploiting the metal state of VO2. We report tunable diode-like current rectification with a good diode ideality factor of 1.75 and excellent conductance swing of 120 mV/dec. Finally, we demonstrate unique tunable photosensitivity and excellent junction photoresponse in the 500/650 nm wavelength range.
36 citations
TL;DR: This work shows that the design of extrinsic chiral surfaces can be optimized with complex multipolar resonances in order to twist the fluorescence emission from nearby molecules and lead to the development of polarization- and angle-resolved ultracompact optical devices.
Abstract: Plasmonic antennas and planar structures have been undergoing intensive developments in order to control the scattering and absorption of light. One specific class, extrinsic chiral surfaces, that does not possess 2-fold rotational symmetry exhibits strong asymmetric transmission for different circular polarizations under obliquely incident illumination. In this work, we show that the design of those surfaces can be optimized with complex multipolar resonances in order to twist the fluorescence emission from nearby molecules. While this emission is usually dipolar and linearly polarized, the interaction with these resonances twists it into a multipolar radiation pattern with opposite helicity in different directions. The proposed structure maximizes this effect and provides control over the polarization of light. Splitting of left- and right-handed circularly polarized light is experimentally obtained in the backward direction. These results highlight the intricate interplay between the near-field absorpt...
35 citations
TL;DR: By isolating and reproducing self-similar features in long silver strip antennas, the edge modes present in the Koch snowflake fractals are identified and it is demonstrated that the fractal response can be obtained by the sum of basicSelf-similar segments called characteristic edge units.
Abstract: We investigate the plasmonic behavior of Koch snowflake fractal geometries and their possible application as broadband optical antennas. Lithographically defined planar silver Koch fractal antennas were fabricated and characterized with high spatial and spectral resolution using electron energy loss spectroscopy. The experimental data are supported by numerical calculations carried out with a surface integral equation method. Multiple surface plasmon edge modes supported by the fractal structures have been imaged and analyzed. Furthermore, by isolating and reproducing self-similar features in long silver strip antennas, the edge modes present in the Koch snowflake fractals are identified. We demonstrate that the fractal response can be obtained by the sum of basic self-similar segments called characteristic edge units. Interestingly, the plasmon edge modes follow a fractal-scaling rule that depends on these self-similar segments formed in the structure after a fractal iteration. As the size of a fractal s...
32 citations
TL;DR: In this article, the energy conservation law with full-wave electromagnetic computations based on a surface integral equation method was used to derive the electron energy loss spectra directly from two dissipative processes, namely, absorption and scattering.
Abstract: Electron energy loss spectroscopy is a method of choice for the characterization of both the spatial and spectral properties of localized surface plasmon resonances. The energy lost by the impinging electrons is commonly explained by the Lorentz force acting on their motion. Here, we adopt another point of view to compute the electron energy loss spectra. Coupling the energy conservation law with full-wave electromagnetic computations based on a surface integral equation method, we derive the electron energy loss spectra directly from two dissipative processes, namely, absorption and scattering. This antenna-based approach is applied to nanostructures with different sizes and materials, showing an excellent agreement with experimental observation and computations based on the evaluation of the Lorentz force. This formalism permits the easy separation of absorption losses in the nanostructures forming a coupled system and reveals the subtle interplay between absorption and scattering, which are controlled ...
26 citations
TL;DR: This work investigates the optical second harmonic generation from plasmonic metasurfaces composed of aligned gold nanopillars with a pronounced out-of-plane tilt using a flexible nonlinear Fourier microscope and shows that the nonlinear response can vary by almost two orders ofmagnitude when the incidence angle is changed.
Abstract: Electromagnetic metasurfaces with strong nonlinear responses and angular selectivity could offer many new avenues for designing ultrathin optics components. We investigated the optical second harmonic generation from plasmonic metasurfaces composed of aligned gold nanopillars with a pronounced out-of-plane tilt using a flexible nonlinear Fourier microscope. The experimental and computational results demonstrate that these samples function as wavevector-selective nonlinear metasurfaces, that is, the coherent second harmonic signal does not only depend on the polarization and wavelength of the excitation beam, but also of its direction of incidence, in spite of the subwavelength thickness of the active layer. Specifically, we observe that the nonlinear response can vary by almost two orders-of-magnitude when the incidence angle is changed from positive to negative values compared to the surface normal. Further, it is demonstrated that these metasurfaces act as a directional nonlinear mirrors, paving the way for new design of directional meta-mirrors in the nonlinear regime.
TL;DR: In this paper, a beam steering device was proposed to enable selective color filtering and redirection of a white light source (such as a white LED) using a waveguide gratings.
Abstract: Resonant waveguide gratings (RWGs) are subwavelength structures of great interest for biosensors, optical filters and optical security applications. We demonstrate and characterize a beam steering device, where the in-coupling and out-coupling processes make use of different RWGs that share the same ultrathin dielectric waveguide. This device enables selective color-filtering and redirection of a white light source (such as a white LED). Furthermore, this structure is compatible with up-scalable fabrication processes such as roll-to-roll replication, and is relevant for high-volume production. Because of its color selectivity and its use in low coherence illumination conditions, such a beam steering device could be implemented in a variety of optical applications such as optical security, multifocal or monochromatic lenses, biosensors, and see-through optical combiners for near-eye displays.
TL;DR: In this paper, the authors investigate the generation of second-harmonic light by gold nanorods and demonstrate that the collected nonlinear intensity depends upon a phase interplay between different modes available in the nanostructure.
Abstract: In this work, we investigate the generation of second-harmonic light by gold nanorods and demonstrate that the collected nonlinear intensity depends upon a phase interplay between different modes available in the nanostructure. By recording the backward and forward emitted second-harmonic signals from nanorods with various lengths, we find that the maximum nonlinear signal emitted in the forward and backward directions is not obtained for the same nanorod length. We confirm the experimental results with the help of full-wave computations done with a surface integral equation method. These observations are explained by the multipolar nature of the second-harmonic emission, which emphasizes the role played by the relative phase between the second-harmonic modes. Our findings are of particular importance for the design of plasmonic nanostructures with controllable nonlinear emission and nonlinear plasmonic sensors as well as for the coherent control of harmonic generations in plasmonic nanostructures.
TL;DR: A new optical biosensor allowing sensitive and dynamic measurements of H2O2 in real-time using multiscattering enhanced absorption spectroscopy is focused on, based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous FeII and ferric FeIII.
Abstract: Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs raise concerns about their safety for the environment and humans. There is growing evidence showing that if engineered nanomaterials are released into the environment, there is a possibility that they could cause harm to aquatic microorganisms. Among the divers effects triggering their toxicity the ability of ENMs to generate reactive oxygen species (ROS) capable of oxidizing biomolecules is currently considered a central mechanism of toxicity. Therefore, development of sensitive tools for quantification of the ROS generation and oxidative stress are highly sought. After briefly introducing ENMs-induced ROS generation and oxidative stress in the aquatic microorganisms (AMOs), this overview paper focuses on a new optical biosensor allowing sensitive and dynamic measurements of H2O2 in real-time using multiscattering enhanced absorption spectroscopy. Its principle is based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous FeII and ferric FeIII. For biological applications cytochrome c was embedded in porous random media resulting in an extended optical path length through multiple scattering of light, which lowers the limit of detection to a few nM of H2O2. The sensor was also integrated in a microfluidic system containing micro-valves and sieves enabling more complex experimental conditions. To demonstrate its performance, abiotic absorption measurements of low concentrations of dye molecules and 10 nm gold particles were carried out achieving limits of detection in the low nM range. Other biologically relevant reactive oxygen species can be measured at sub-μM concentrations, which was shown for glucose and lactate through enzymatic reactions producing H2O2. In ecotoxicological investigations H2O2 excreted by aquatic microorganisms exposed to various stressors were measured. Pro-oxidant effects of nano-TiO2 and nano-CuO towards green alga Chlamydomonas reinhardtii were explored in various exposure media and under different light illuminations. Dynamics of Cd2+ induced effects on photosynthetic activity, sensitisation and recovery of cells of C. reinhardtii was also studied.
TL;DR: A highly sensitive analysis of cyclic RGD (cRGD) peptide ligands of cells using surface enhanced Raman spectroscopy (SERS) using single dimer nanogap antennas in aqueous environment shows good agreement between characteristic peaks of the SERS and theRaman spectra of bulk c(RGDfC) with its peptide's constituents.
Abstract: The cyclic RGD (cRGD) peptide ligands of cells have become widely used for treating several cancers. We report a highly sensitive analysis of c(RGDfC) using surface enhanced Raman spectroscopy (SERS) using single dimer nanogap antennas in aqueous environment. Good agreement between characteristic peaks of the SERS and the Raman spectra of bulk c(RGDfC) with its peptide's constituents were observed. The exhibited blinking of the SERS spectra and synchronization of intensity fluctuations, suggest that the SERS spectra acquired from single dimer nanogap antennas was dominated by the spectrum of single to a few molecules. SERS spectra of c(RGDfC) could be used to detect at the nanoscale, the cells' transmembrane proteins binding to its ligand. SERS of cyclic RGD on nanogap antenna.
TL;DR: In this paper, a topographically templated assembly of single-crystal colloidal gold nanorods into trimers, with a dolmen geometry, is presented, which enables the precise positioning of high-quality nanorod, with gaps as small as 1.5 nm, which permits a gradual and controlled symmetry breaking by tuning the arrangement of these strongly coupled nanostructures.
Abstract: Plasmonic antennas have enabled a wealth of applications that exploit tailored near-fields and radiative properties, further endowed by the bespoke interactions of multiple resonant building blocks. Specifically, when the interparticle distances are reduced to a few nanometers, coupling may be greatly enhanced leading to ultimate near-field intensities and confinement along with a large energy splitting of resonant modes. While this concept is well-known, the fabrication and characterization of suitable multimers with controlled geometries and few-nanometer gaps remains highly challenging. In this article, we present the topographically templated assembly of single-crystal colloidal gold nanorods into trimers, with a dolmen geometry. This fabrication method enables the precise positioning of high-quality nanorods, with gaps as small as 1.5 nm, which permits a gradual and controlled symmetry breaking by tuning the arrangement of these strongly coupled nanostructures. To characterize the fabricated structur...
01 Mar 2017
TL;DR: Swiss National Science Foundation (NRP 64 Project No. 406440-131280/1) as discussed by the authors, NRP 64 is a project of the Swiss National Research Program (SNRP 64).
Abstract: Swiss National Science Foundation (Swiss National Research Program NRP 64 Project No. 406440-131280/1)
TL;DR: In this article, a coupled oscillator model with the transfer matrix method was proposed to analyze and engineer the phase of the light reflected from a Fano-resonant metasurface.
Abstract: We introduce a general formalism combining the coupled oscillator model with the transfer matrix method to analyze and engineer the phase of the light reflected from a Fano-resonant metasurface. This method accounts for periodicity and the presence of substrates, and we demonstrate that these factors can be used to tune the reflected phase at will. Utilizing these effects and adjusting the coupling strength of the underlying unit cell, we achieve zero reflection at the dark resonance of the metasurface. We show that the resulting phase singularity can dramatically increase the sensitivity of phase-based detection schemes. The phase bifurcation unveiled in this work can be used to design plasmonic metasurfaces that explore the unusual phase behavior of light.
31 Aug 2017
TL;DR: In this paper, a novel thin-film single-layer structure based on resonant waveguide gratings (RWGs) allows to engineer selective color filtering and steering of white light.
Abstract: A novel thin-film single-layer structure based on resonant waveguide gratings (RWGs) allows to engineer selective color filtering and steering of white light. The unit cell of the structure consists of two adjacent finite-length and cross-talking RWGs, where the former acts as in-coupler and the latter acts as out-coupler. The structure is made by only one nano-imprint lithography replication and one thin film layer deposition, making it fully compatible with up-scalable fabrication processes. We characterize a fabricated optical security element designed to work with the flash and the camera of a smartphone in off-axis light steering configuration, where the pattern is revealed only by placing the smartphone in the proper position. Widespread applications are foreseen in a variety of fields, such as multifocal or monochromatic lenses, solar cells, biosensors, security devices and seethrough optical combiners for near-eye displays.
TL;DR: In this paper, the authors demonstrate the role of the surface of a plasmonic nano-antenna and show that increasing the number of layers and hence increasing the total accessible surface of the antenna, results in an enhanced scattering cross section and a redshift which indicates that lower energy photons are required to couple to the metal electrons.
Abstract: Surface plasmons are excited at a metal/dielectric interface, through the coupling between conduction electrons and incident photons. The surface plasmon generation is therefore strongly determined by the accessibility of the surface to the incoming electromagnetic field. We demonstrate the role of this surface for plasmonic nanoantennas with identical volumes and resonant lengths. An antenna is stratified parallel to the plane of its main dipolar resonance axis and the influence of the number of layers and the spacing between them on the optical properties of the antenna are investigated experimentally. We show that increasing the number of layers and, hence, increasing the total accessible surface of the antenna, results in an enhanced scattering cross section and a redshift which indicates that lower energy photons are required to couple to the metal electrons. In particular, the far-field enhancement observed for double-layer nanostructures suggests that standard single-layer metal deposition can be easily and advantageously substituted with metal/dielectric/metal deposition to boost light scattered by a plasmonic antenna.
TL;DR: In this article, the influence of Fano resonances on the nonlinear response of hybrid plasmonic nanostructures is theoretically investigated using the combination of a surface integral equation method and an analytical model.
Abstract: The influence of Fano resonances on the nonlinear response of hybrid plasmonic nanostructures, i.e., nanoantennas loaded with a nonlinear optical material, is theoretically investigated using the combination of a surface integral equation method and an analytical model. The results demonstrate that a suitable design of the field enhancement enables the observation of optical bistability for incident conditions that would be impossible for a bare nanoantenna. This study provides new insights into the possibilities offered by Fano resonances to control the nonlinear response of hybrid plasmonic systems.
01 Jun 2017
TL;DR: In this paper, the second harmonic generation from plasmonic centrosymmetric nanostructures is controlled by two main properties: first, SHG is forbidden in the bulk of centroid symmetric structures in the dipolar approximation, and second, a dipolar excitation at the fundamental frequency induces SH modes with vanishing dipole moments.
Abstract: Second harmonic generation (SHG) is an important tool for the study of plasmonic nanostructures and can open up important sensing applications since the second harmonic (SH) signal has an increased sensitivity to nanostructures shape and environment in comparison with the linear scattering [1,2]. SHG from plasmonic centrosymmetric nanostructures is controlled by two main properties. First, SHG is forbidden in the bulk of centrosymmetric structures in the dipolar approximation, meaning that nanostructures made of metals like gold and silver generate a SH signal coming mainly from their surfaces, where the symmetry is effectively broken. Second, because of the same symmetry reason, a dipolar excitation at the fundamental frequency induces SH modes with vanishing dipole moments [3]. In the case of plasmonic dimers, with the large intensity enhancement occurring in the gap, the SH emission is limited due to out-of-phase SH sources with destructive interferences in the far-field region. Consequently, new strategies must be developed to overcome this limitation.