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Electrically-contacted optical gap antennas are nanoscale interface devices enabling the transduction between photons and electrons. This new generation of devices captures visible to near infrared electromagnetic radiation and converts the incident energy in a direct-current (DC) electrical signal. The nanoscale rectenna is usually constituted of metal elements (e.g. gold). Light absorption by the metal contacts may lead to additional thermal effects which need to be taken into account to understand the complete photo- response of the device. The purpose of this communication is to discuss the contribution of laser-induced thermo-electric effects in the photo-assisted electronic transport., Comment: 9 figures

International audience; We aim at controlling the spatial distribution of nonlinear photoluminescence in a shaped micrometer-size crystalline gold flake. Interestingly, the underlying surface plasmon modal landscape sustained by this mesoscopic structure can be advantageously used to generate nonlinear photoluminescence (nPL) in remote locations away from the excitation spot. By controlling the modal pattern, we show that the delocalized nonlinear photoluminescence intensity can be redistributed spatially. This is first accomplished by changing the polarization orientation of the pulsed laser excitation in order to select a subset of available surface plasmon modes within a continuum. We then propose a second approach to redistribute the nPL within the structure by implementing a phase control of the plasmon interference pattern arising from a coherent two-beam excitation. Control and engineering of the nonlinear photoluminescence spatial extension is a prerequisite for deploying the next generation of plasmonic-enabled integrated devices relying on hot carriers.

26 p.; International audience; This paper explores the nonlinear photoluminescence emitted by Indium Tin Oxide (ITO) thin layers patterned by focused gallium ion beam milling. Using tightly focused near-infrared femtosecond pulsed laser excitation, a broad up-converted luminescence spanning the visible spectrum is detected. The intensity of the luminescence follows a non-monotonous relationship with milling doses and can be related to the modification of the ITO electronic band structure by the implantation of Ga ions. The shape and the power dependence of the spectrum share strong similarities with nonlinear photoluminescence arising from metals. The results are consistent with a nonlinear luminescence process originating from the radiative decay of photo-generated hot carriers. The ther-1 mal coefficient relating the hot carrier temperature to the laser intensity is determined as a function of milling dose.

International audience; In this contribution, we report that conforma-tional changes of molecules that are often buried in a wide-distributed Gaussian distribution can be discerned by analyzing the dynamics of specific Raman lines. We investigate the pertinence of the auto-and cross-correlation functions applied to the dynamics of three Raman lines of an amino acid, the tryptophan. The cross-correlation between intensity and the Raman band is an indicator of the charge transfer during the diffusion limited reaction of tryptophan and the gold surface. The Pećlet number Pe can provide a valuable indicator of the convective and/or diffusive features of each Raman band. Adsorption induced conformation changes can be identified using the autocorrelation of the multiples states within the Raman band centered at 1550 cm −1 .

Processing information with conventional integrated circuits remains beset by the interconnect bottleneck: circuits made of smaller active devices need longer and narrower interconnects, which have become the prime source of power dissipation and clock rate saturation. Optical interchip communication provides a fast and energy-saving option that still misses a generic on-chip optical information processing by interconnect-free and reconfigurable Boolean arithmetic logic units (ALU). Considering metal plasmons as a platform with dual optical and electronic compatibilities, we forge interconnect-free, ultracompact plasmonic Boolean logic gates and reconfigure them, at will, into computing ALU without any redesign nor cascaded circuitry. We tailor the plasmon mode landscape of a single 2.6 μm

Hot electron-based devices are quite promissing for ultrafast photodetection and to set off enhanced physicochemical reactions [1] . Controlling their generation at the nanoscale within plasmonic devices is a key for the future development of hybrid hot-electrons technologies. Indeed, Surface Plasmon-Polaritons (SPPs) can be exploited to confine light and enhance the number of excited hot carriers [2] . We aim at studying the excitation and dynamics of hot electrons, enhanced by plasmonics, with two different approaches.

International audience; Rare-earth doped nanocrystals possess optical transitions with significant either electric or magnetic dipole characters. They are of considerable interest for understanding and engineering light-matter interactions at the nanoscale with numerous applications in nanophotonics. Here, we study the 5 D 0 → 7 F 1 transition dipole vector in individual NaYF 4 : Eu 3+ nanorod crystals by Fourier and confocal micro-scopies. A single-crystal host matrix leads to narrow emission lines at room temperature that permit separation of the Stark sublevels resulting from the crystal-field splitting. We observe a fully magnetic transition and low variability of the transition dipole orientation over several single nanorods. We estimate the proportion of the dipole transitions for the Stark sublevels. We also determine an effective altitude of the rod with respect to the substrate. The narrow emission lines characteristic of NaYF 4 : Eu 3+ ensure well-defined electric or magnetic transitions, and are thus instrumental for probing locally their electromagnetic environment by standard confocal microscopy.

International audience; Processing information with conventional integrated circuits remains beset by the interconnect bottleneck: circuits made of smaller active devices need longer and narrower interconnects, which have become the prime source of power dissipation and clock rate saturation. Optical interchip communication provides a fast and energy-saving option that still misses a generic on-chip optical information processing by interconnect-free and reconfigurable Boolean arithmetic logic units (ALU). Considering metal plasmons as a platform with dual optical and electronic compatibilities, we forge interconnect-free, ultracompact plasmonic Boolean logic gates and reconfigure them, at will, into computing ALU without any redesign nor cascaded circuitry. We tailor the plasmon mode landscape of a single 2.6 μm2 planar gold cavity and demonstrate the operation and facile reconfiguration of all 2-input logic gates. The potential for higher complexity of the same logic unit is shown by a multi-input excitation and a phase control to realize an arithmetic 2-bit adder.

We report a quantitative analysis of the wavevector diagram emitted by nonlinear photoluminescence generated by a tightly focused pulsed laser beam and distributed along Au nanowire via the mediation of surface plasmon polaritions. The nonlinear photoluminescence is locally excited at key locations along the nanowire in order to understand the different contributions constituting the emission pattern measured in a conjugate Fourier plane of the microscope. Polarization-resolved measurements reveal that the nanowire preferentially emits nonlinear photoluminescence polarized transverse to the long axis at close to the detection limit wavevectors with a small azimuthal spread in comparison to the signal polarized along the long axis. We utilize finite element method to simulate the observed directional scattering by using localized incoherent sources placed on the nanowire. Simulation results faithfully mimic the directional emission of the nonlinear signal emitted by the different portions of the nanowire., 8 pages, 8 figures

International audience; We investigate the influence of a static electric field on the incoherent nonlinear response of an unloaded electrically contacted nanoscale optical gap antenna. Upon excitation by a tightly focused near-infrared femtosecond laser beam, a transient elevated temperature of the electronic distribution results in a broadband emission of nonlinear photoluminescence (N-PL). We demonstrate a modulation of the yield at which driving photons are frequency up-converted by means of an external control of the electronic surface charge density. We show that the electron temperature and consequently the N-PL intensity can be enhanced or reduced depending on the command polarity and the strength of the control static field. A modulation depth larger than 100% is observed for activation voltages of a few volts.

International audience; A priori, la question peut surprendre ; son reflet doré est si caractéristique. Pourtant, ce métal précieux peut diffuser une réponse chromatique variée si on l’observe sous une forme nano-structurée. Mieux, si on l’éclaire avec une impulsion lumineuse ultra-brève, l’or génère une variété de phénomènes non-linéaires qui enrichissent spectralement la palette de longueurs d’onde émise par le métal.

We propose a new concept of localized surface plasmon polariton (SPP) mode excitation in a spherical nanoparticle, which utilizes a collective mechanism of dissipative instability in an adjacent 2D plasma carrying a DC electric current. We show that 2D DC current becomes unstable at optical frequencies when the drift velocity exceeds the speed of sound in the 2D plasma. Dissipative instability emerges as a result of self-consistent 2D plasma oscillations coupled to the electromagnetic modes of the nanosphere, the material of which is absorbing at given frequency (i.e., the dielectric permittivity Ime > 0), and instability is absent in the case of transparent material. We derive the dispersion equation for this dissipative instability by a self-consistent solution of the Maxwell equations for the electromagnetic modes and the hydrodynamic equations for the 2D plasma current. Our estimates demonstrate attainment of very high instability increments Imω ~ 1015 s−1, which makes the proposed concept very promising for excitation of plasmonic nanoantennas.

Hot electrons generated within plasmonic structures possess a high kinetic energy that can be employed to drive and catalyze a huge range of physicochemical processes at the metallic interface. Up to now, these photogenerated hot carriers were mainly generated within simple plasmonic nanoparticles where hot carrier localization coincides spatially with the position optical excitation. A current challenge for the development of future plasmonic-based hot electron devices requires the ability for a delocalized hot carrier production to control on a large-distance their spatial distribution. Here, we demonstrate the remote generation of hot electrons by launching a propagative surface plasmon on a gold waveguide. Such hot carriers can be produced at distances of several microns from the excitation. Moreover, using far- and near-field hyperspectral microscopy, we show that hot carriers present spatial and energy distributions driven by the propagating plasmon field distribution itself. This opens the door to ...

We observe anomalous visible to near-infrared electromagnetic radiation emitted from electrically driven atomic-size point contacts. We show that the number of photons released strongly depends on the quantized conductance steps of the contact. Counter-intuitively, the light intensity features an exponential decay dependence with the injected electrical power. We propose an analytical model for the light emission considering an out-of-equilibrium electron distribution. We treat photon emission as bremsstrahlung process resulting from hot electrons colliding with the metal boundary and a find qualitative accord with the experimental data., Main manuscript plus supplementary information

When gold nanowires are excited with a tightly focused femtosecond laser a distributed nonlinear photoluminescence (N-PL) develops throughout the entire structure. A complete spaced-resolved analysis of the spectral signature of the nanowire nonlinear response is carried out to understand the origin of the distributed nonlinear response. We discuss various mechanisms to explain the experimental data and unambiguously demonstrate that the spatial and spectral extension of the N-PL in the nanowire are mainly dictated by the propagation of a surface plasmon excited at the pump wavelength. We also present experimental signature of near-field excitation of a broadband continuum of surface plasmons excited locally throughout the N-PL emission spectrum.

In this contribution, we provide new insights on the temporal fluctuations of surface enhanced Raman spectra (SERS) of large single molecules such as proteins. Because they can only fit partly into small active volume, SERS analysis is referred to spectral pointillism where only protein subdomains are shined and the whole protein landscape is built from the dynamics of successive individual spectra. By applying our approach on bovine serum albumin, we show that single protein subdomains are mostly comprised of three distinct amino acids. Surface amino acids such as lysine are preferentially detected in the open form of the protein. The investigation of the tryptophan Fermi doublet in the single protein regime is highly instructive on the protein conformation. We finally demonstrate that spectral pointillism enables to correlate individual amino acids with structural information.

In biomedicine and biophysics, the discrimination of protein conformations is of critical importance for identifying the unfolding states in the diagnosis of neurodegenerative diseases. We develop a dynamic Raman spectroscopic approach based on a statistical analysis of the time series of spectral fingerprints of single protein. We show that the unfolded state of bovine serum albumin can be identified in the time series using the fluctuations of the Raman bands of some amino acids, tryptophan, tyrosine, leucine, and histidine, acting as biomarkers. The statistical analysis induces also the sorting between physisorption and chemisorption events. This is confirmed by the spectral analysis of the different characteristic spectra highlighted based on the amino acids fingerprints following, notably, the hydrophobicity

We operate micron-sized CdSe/CdS core–shell quantum dot (QD) clusters deposited onto gold patches as integrated light sources for the excitation of photonic waveguides. The surface plasmon mode launched by the QD fluorescence at the top interface of the gold patches are efficiently coupled to photonic modes sustained by titanium dioxide ridge waveguides. We show that, despite a large effective index difference, the plasmonic and the photonic modes can couple with a very high efficiency provided the vertical offset between the two kinds of waveguides is carefully controlled. Based on the effective index contrast of the plasmonic and the photonic modes, we engineer in-plane integrated hybrid lenses. The hybrid lenses are obtained by shaping the contact interface between the plasmonic and the photonic waveguides. We demonstrate a 2-fold enhancement of the coupling efficiency for tapers equipped with a hybrid lens. Our results are expected to be useful for the development of low-cost, integrated light sources...

Directional harmonic generation is an important property characterizing the ability of nonlinear optical antennas to diffuse the signal in well-defined region of space. Herein, we show how sub-wavelength facets of an organic molecular mesowire crystal can be utilized to systematically vary the directionality of second harmonic generation (SHG) in the forward scattering geometry. We demonstrate this capability on crystalline diamonoanthraquinone (DAAQ) mesowires with subwavelength facets. We observed that the radial angles of the SHG emission can be tuned over a range of 130 degrees. This angular variation arises due to spatially distributed nonlinear dipoles in the focal volume of the excitation as well as the geometrical cross-section and facet orientation of the mesowire. Numerical simulations of the near-field excitation profile corroborate the role of the mesowire geometry in localizing the electric field. In addition to directional SHG from the mesowire, we experimentally observe optical waveguiding of the nonlinear two-photon excited fluorescence (TPEF). Interestingly, we observed that for a given pump excitation, the TPEF signal is isotropic and delocalized, whereas the SHG emission is directional and localized at the location of excitation. All the observed effects have direct implications not only in active nonlinear optical antennas, but also in nonlinear signal processing., Accepted in Applied Optics

We show that the rate of stimulated emission by electron, passing through nanoscale constriction, can beenhanced substantially (by several orders) with proper tailoring of the constriction shape.

Hot carriers are energetic photoexcited carriers driving a large range of chemicophysical mechanisms. At the nanoscale, an efficient generation of these carriers is facilitated by illuminating plasmonic antennas. However, the ultrafast relaxation rate severally impedes their deployment in future hot-carrier based devices. In this paper, we report on the picosecond relaxation dynamics of hot carriers in plasmonic monocrystalline gold nanoantennas. The ultrafast dynamics of the hot carriers is experimentally investigated by interrogating the nonlinear photoluminescence response of the antenna [1]. From this investigation, we reveal some leverages to control the dynamics of such hot carriers within nano antenna. In particular, an increase by a factor up to five of this dynamics (from 0.5 ps to 2.5 ps) is observed for resonant nanoantenna compared to off-resonance antenna and when excitation power increases. By a two temperature model we model quantitatively the dynamics of hot carriers and we demonstrate the nonlinear generation of these carriers. The control over the carrier dynamics should allow to employ their energy more effieciently within physico-chemical processes. In a second part, we investigate the hot carrier dynamics with a spectrally resolved two-pulse correlation configuration, and demonstrate that the relaxation of the photoexcited carriers depends of their energies relative to the Fermi level. We find a 60% variation in the relaxation rate for electron−hole pair energies ranging from ca. 0.2 to 1.8 eV. The quantitative relationship between hot-carrier energy and relaxation dynamics is an important finding for optimizing hot-carrier-assisted processes and shed new light on the intricacy of nonlinear photoluminescence in plasmonic [2]. [1] O. Demichel et al, ACS Photonics 3, 791 (2016) [2] R. Mejard et al, ACS Photonics 3, 1482 (2016)

Electrically driven optical antennas can serve as compact sources of electromagnetic radiation operating at optical frequencies. In the most widely explored configurations, the radiation is generated by electrons tunneling between metallic parts of the structure when a bias voltage is applied across the tunneling gap. Rather than relying on an inherently inefficient inelastic light emission in the gap, we suggest to use a ballistic nanoconstriction as the feed element of an optical antenna supporting plasmonic modes. We discuss the underlying mechanisms responsible for the optical emission and show that, with such a nanoscale contact, one can reach quantum efficiency orders of magnitude larger than with standard light-emitting tunneling structures.

Background: Electrically controlled optical metal antennas are an emerging class of nanodevices enabling a bilateral transduction between electrons and photons. At the heart of the device is a tunnel junction that may either emit light upon injection of electrons or generate an electrical current when excited by a light wave. The current study explores a technological route for producing these functional units based upon the electromigration of metal constrictions.Results: We combine multiple nanofabrication steps to realize in-plane tunneling junctions made of two gold electrodes, separated by a sub-nanometer gap acting as the feedgap of an optical antenna. We electrically characterize the transport properties of the junctions in the light of the Fowler–Nordheim representation and the Simmons model for electron tunneling. We demonstrate light emission from the feedgap upon electron injection and show examples of how this nanoscale light source can be coupled to waveguiding structures.Conclusion: Electromigrated in-plane tunneling optical antennas feature interesting properties with their unique functionality enabling interfacing electrons and photons at the atomic scale and with the same device. This technology may open new routes for device-to-device communication and for interconnecting an electronic control layer to a photonic architecture.

The Raman intensity fluctuations are the initial source of a lack of accuracy or reproducibility of SERS based nanosensors to reliably estimate the molecular concentration in microfluidics. Here, we show that the statistical analysis of the weighting of Raman scattering of the probed molecules compared to the photoluminescence of gold nanoparticles is particularly effective as a concentration indicator in a single molecule regime. We present a novel approach in the Fourier domain that is not limited by a multipoint precalibration or even the knowledge of the enhancement factor of the transducer. The analysis of pink noise in the frequency domain reveals a subdiffusion motion of individual adsorbed molecules in the hot-spot. The cutoff frequency between the white and pink noise is used to determine the in-line molecular concentration over a wide range between 10–11 and 10–6 M.

International audience; On-chip optoelectronic and all-optical information processing paradigms require compact implementation of signal transfer for which nanoscale surface plasmons circuitry offers relevant solutions. This work demonstrates the directional signal transmittance mediated by 2D plasmonic eigenmodes supported by crystalline cavities. Channel devices comprising two mesoscopic triangular input and output ports and sustaining delocalized, higher-order plasmon resonances in the visible to infra-red range are shown to enable the controllable transmittance between two confined entry and exit ports coupled over a distance exceeding 2 μm. The transmittance is attenuated by > 20dB upon rotating the incident linear polarization, thus offering a convenient switching mechanism. The optimal transmittance for a given operating wavelength depends on the geometrical design of the device that sets the spatial and spectral characteristic of the supporting delocalized mode. Our approach is highly versatile and opens the way to more complex information processing using pure plasmonic or hybrid nanophotonic architectures.

International audience

Aluminum nanostructures have recently been at the focus of numerous studies due to their properties including oxidation stability and surface plasmon resonances covering the ultraviolet and visible spectral windows. In this article, we reveal a new facet of this metal relevant for both plasmonics purpose and photo-thermal conversion. The field distribution of high order plasmonic resonances existing in two-dimensional Al structures is studied by nonlinear photoluminescence (nPL) microscopy in a spectral region where electronic interband transitions occur. The polarization sensitivity of the field intensity maps shows that the electric field concentration can be addressed and controlled on-demand. We use a numerical tool based on the Green dyadic method to analyze our results and to simulate the absorbed energy that is locally converted into heat. The polarization-dependent temperature increase of the Al structures is experimentally quantitatively measured, and is in an excellent agreement with theoretical predictions. Our work highlights Al as a promising candidate for designing thermal nanosources integrated in coplanar geometries for thermally assisted nanomanipulation or biophysical applications., 8 pages 6 figures main article; 7 pages 9 figures supporting informations

The large field enhancement generated at the surface of a resonant plasmonic nanoparticle, or optical antennas, is the key mechanism that eventually led to the development of nonlinear plasmonics [1-2]. While the resonance may boost the nonlinear yield of an adjacent structure or surrounding medium, it was soon realized that optical antennas possess nonlinear coefficients comparable or exceeding those of standard nonlinear optical materials [3]. We discuss here two nonlinear optical processes — incoherent multi-photon luminescence (MPL) and coherent second-harmonic generation (SHG) — emitted from gold rod optical antennas upon local illumination with a tightly focused femtosecond near-infrared laser beam.

Electrically Driven Optical Antennas represent promising issues for integrated plasmonic nanosources. However, their low quantum efficiency (QE) remains a major hurdle. To address this issue, we analyze the different light emission mechanisms in planar nanoscale devices. We found that the electrical properties of the device are dictating the processes at play. For low device conductance, photons are essentially emitted by inelastic tunneling events and the applied voltage sets the highest photon energy. For high conductance gap antennas, we show that the spectrum released by the device originates from the spontaneous emission of out-of-equilibrium electronic distribution. We then propose a novel route for increasing the QE. Estimation shows that if the nanoantennas are excited by electrons passing ballistically through mesoscopic contacts constituting the antenna, the excitation QE may reach ∼ 0.01–0.1. Finally, we explore an alternative approach based on charge injection in semiconductor Mie resonators.

Surface plasmon modes propagating in metal nanowires are conveniently excited by focusing a laser beam on one extremity of the nanowire. We find that the precise positioning of the nanowire inside the focal region drastically influences the excitation efficiency of the different SPP modes sustained by the plasmonic waveguide. We demonstrate a spatially selective excitation of bound and leaky surface plasmon modes with excitation maps that strongly depend on the orientation of the incident linear polarization. We discuss this modal selection by considering the inhomogeneous distribution of the field components inside the focus. Our finding provides a way to discriminate the effective indices of the modes offering thus an increased coupling agility for future nanowire-based plasmonic architectures.

Electrically driven optical antennas are attracting much attention, in particular, due to necessity to develop integrated electrical source of surface plasmons for future plasmonic nanocircuitries. By default, this term denotes a metal nanostructure, in which electromagnetic oscillations at optical frequencies are excited by electrons, tunneling between metallic parts of the structure when a bias voltage is applied between them. Instead of relying on an inefficient inelastic light emission in a tunnel gap, we are suggesting to use ballistic nanoconstrictions as the feed element of an optical antennas in order to excite electromagnetic plasmonic modes. Similarly to tunneling structures, the voltage applied at the constriction falls over the contact of nanoscale length. Electron passing through the contact ballistically can gain the energy provided by the bias ~1eV and exchange it into an mode of the optical antenna. We discussed the underlying mechanisms responsible for the optical emission, and show that with nanoscale contact, one can reach quantum efficiency orders of magnitude larger than with standard tunneling structures.

In this contribution, we report the identification of the principal reference Raman spectra of a single cystein molecule. To that purpose, we design an active Surface Enhanced Raman Spectroscopy (SERS) template based on surfactant-less Chebyshev nanoparticles operating in a microfluidic platform. A principal component analysis is obtained from fluctuating spectra to sort the reference spectra of cystein. The assignment of Raman bands brings new insight into the conformation of an amino acid adsorbed onto gold nanoparticle.

Standard gold in the field of plasmonics is obtained by evaporation or sputtering and therefore is polycrystalline. Yet, this gold presents numbers of drawbacks such as roughness, grains and ill-defined electronic band diagrams in addition to the lack of reproducibility from one instrument to another. It is, thus, beneficial to turn to a metal production that can enable well-defined and controlled gold parameters. To that end, we have explored the wet synthesis of gold nanoplates which represents a simple and robust means of obtaining single-crystal gold (Guo Z, Zhang Y, DuanMu Y, Xu L, Xie S, Gu N, Colloids Surf A 278:33–38, 2006). The synthesized nanoplates are from 50 to less than 100 nm in thickness and can span over micrometers in lateral dimensions corresponding to areas of several hundreds of μm2. They can thus be considered as thin film material perfectly suitable for plasmonic applications.

The Purcell factor $F_p$ is a key quantity in cavity quantum electrodynamics (cQED) that quantifies the coupling rate between a dipolar emitter and a cavity mode. Its simple form $F_p\propto Q/V$ unravels the possible strategies to enhance and control light-matter interaction. Practically, efficient light-matter interaction is achieved thanks to either i) high quality factor $Q$ at the basis of cQED or ii) low modal volume $V$ at the basis of nanophotonics and plasmonics. In the last decade, strong efforts have been done to derive a plasmonic Purcell factor in order to transpose cQED concepts to the nanocale, in a scale-law approach. In this work, we discuss the plasmonic Purcell factor for both delocalized (SPP) and localized (LSP) surface-plasmon-polaritons and briefly summarize the expected applications for nanophotonics. On the basis of the SPP resonance shape (Lorentzian or Fano profile), we derive closed form expression for the coupling rate to delocalized plasmons. The quality factor factor and modal confinement of both SPP and LSP are quantified, demonstrating their strongly subwavelength behaviour., Comment: Journal of Optics (in press)

We investigate spontaneous light emission by electrons passing through a nanoscale metal constriction and find that the Purcell-enhanced emission is engendered by two distinct mechanisms. In the first mechanism emission is caused by electron colliding with the effective potential of the mesoscopic contact while the second mechanism involves collisions of electrons with the walls of the constriction. We find that multiple collisions with the walls can lead to the orders-of-magnitude higher light emission probability in comparison to a single collision with the effective potential.

We propose a novel physical mechanism for the excitation of optical nanoantenna which utilizes the dissipative instability of DC electric current in the quantum well. Realization of this approach in nanoplasmonics can lead to a new device - nanoresotron.

A rigorous theory of photon emission accompanied inelastic tunnelling inside the gap of plasmonic nanoantennas has been developed. The disappointingly low efficiency of the electrical excitation of surface plasmon polaritons in these structures can be increased by orders of magnitude when a resonant tunnelling structure is incorporated inside the gap. Resonant tunnelling assisted surface plasmon emitter may become a key element in future electrically-driven nanoplasmonic circuits., 7 pages, 6 figures

Hot carriers are energetic photo-excited carriers driving a large range of chemico-physical mechanisms. At the nanoscale, an efficient generation of these carriers is facilitated by illuminating plasmonic antennas. However, the ultrafast relaxation rate severally impedes their deployment in future hot-carrier based devices. In this paper, we report on the picosecond relaxation dynamics of hot carriers in plasmonic monocrystalline gold nanoantennas. The temporal dynamics of the hot carriers is experimentally investigated by interrogating the nonlinear photoluminescence response of the antenna with a spectrally-resolved two-pulse correlation configuration. We measure time-dependent nonlinearity orders varying from 1 to 8, which challenge the common interpretation of multi-photon gold luminescence. We demonstrate that the relaxation of the photo-excited carriers depends of their energies relative to the Fermi level. We find a 60 % variation in the relaxation rate for electron-hole pair energies ranging from c.a. 0.2 to 1.8 eV. The quantitative relationship between hot carrier energy and relaxation dynamics is an important finding for optimizing hot carriers-assisted processes and shed new light in the intricacy of nonlinear photoluminescence in plasmonic structures.

We show that nanoscale metal contacts (constrictions) can serve as an efficient sources of plasmons for future nanoplasmonic integrated circuits. Electron, passing ballistically through nanoscale contact, can emit plasmons with the probability ∼0.1 due to multiple collisions with walls of the constriction.

Surface enhanced Raman scattering (SERS) spectroscopy becomes increasingly used in biosensors for its capacity to detect and identify single molecules. In practice, a large number of SERS spectra are acquired and reliable ranking methods are thus essential for analysing all these data. Supervised classification strategies, which are the most effective methods, are usually applied but they require pre-determined models or classes. In this work, we propose to sort SERS spectra in unknown groups with an alternative strategy called Fourier polar representation. This non-fitting method based on simple Fourier sine and cosine transforms produces a fast and graphical representation for sorting SERS spectra with quantitative information. The reliability of this method was first investigated theoretically and numerically. Then, its performances were tested on two concrete biological examples: first with single amino-acid molecule (cysteine) and then with a mixture of three distinct odorous molecules. The benefits of this Fourier polar representation were highlighted and compared to the well-established statistical principal component analysis method.

International audience; In this Letter, we demonstrate a reversible strong coupling regime between a dipolar surface plasmon resonance and a molecular excited state. This reversible state is experimentally observed on silver nanoparticle arrays embedded in a polymer film containing photochromic molecules. Extinction measurements reveal a clear Rabi splitting of 294 meV, corresponding to ∼13% of the molecular transition energy. We derived an analytical model to confirm our observations, and we emphasize the importance of spectrally matching the polymer absorption with the plasmonic resonance to observe coupled states. Finally, the reversibility of this coupling is illustrated by cycling the photochromic molecules between their two isomeric forms.

In the present work, the combination of chemical immobilization with electron beam lithography enables the production of sensitive and reproducible SERS-active areas composed of stochastic arrangements of gold nanoparticles. The number of nanoparticles was varied from 2 to 500. Thereby a systematic analysis of these SERS-active areas allows us to study SERS efficiency as a function of the number of nanoparticles. We found that the experimental parameters are critical, in particular the size of the SERS-active area must be comparable to the effective area of excitation to obtained reproducible SERS measurements. The sensitivity has also been studied by deducing the number of NPs that generate the enhancement. With this approach we demonstrates that the maximum enhancement, the best sensitivity, is obtained with the smallest number of nanoparticles that is resonant at a given excitation wavelength.

International audience; We report on the nanoscale optical characterization of gold nanorods irradiated out of their plasmonic resonance. Our approach is based on the reticulation of a photopolymerizable formulation locally triggered by enhanced electromagnetic fields. The tiny local field enhancement stems from the surface polarization charges associated with the electric field discontinuity at the metal/dielectric interface. This allows us to get a nanoscale signature of the spatial distribution of the surface charge density in metallic nanoparticles irradiated off-resonance.

We review our recent studies of electromagnetic coupling and associated temporal dynamics of molecular excitations with plasmonic resonances supported by either localized or extended planar geometries. We focus on coherent interactions between plasmon resonances and molecular excitations, which are experimentally challenging due to the very short (∼10–100 fs) coherence times of plasmons. Recent experimental results and theoretical analysis for observing and controlling coherences between molecular excitations and plasmonic polarizations are shown. Advances will explore new directions in ultrafast coherent control of molecular excited states and energy dissipation processes, as well as ultrafast addressing and switching in plasmonics-based circuit architectures.