Anne-Laure Baudrion

Controlling matter with nanoscale spatial selectivity is a key hurdle for plasmonic applications such as nanophotonics, sensing, and catalysis. Plasmon-assisted nanolithography has recently emerged as a powerful strategy to address this challenge by exploiting the highly confined electromagnetic fields and hot carriers generated during plasmon excitation to confine organic or inorganic layers at the nanoscale. Among the surface chemistries compatible with this approach, aryl diazonium salts are particularly attractive because their reduction produces highly reactive aryl radicals that form robust covalent bonds with metallic surfaces under mild conditions. Under light excitation, the plasmon-induced reduction of aryl diazonium salts enables the rapid and site-selective grafting of functional organic layers confined to plasmonic hot spots. The resulting functional films provide versatile chemical handles for further modification. However, to date, the use of plasmon-mediated diazonium grafting as a spatially controlled primer layer to direct the site-selective immobilization of colloidal nanoparticles remains unexplored. We address this gap by using lithographic gold nanodisc arrays as optically programmable templates. Under plasmon excitation, these nanostructures enable the formation of positively charged nanoscale anchoring domains at plasmonic hot spots, derived from diazonium salts bearing amine groups. These localized charged domains can then guide the spatial organization of negatively charged colloidal gold nanoparticles. The geometrical parameters of the plasmonic arrays, including nanodisc diameter and interparticle spacing, were carefully tuned to access different plasmon excitation regimes around the 633 nm laser wavelength, enabling blue-shifted, near-resonant, and red-shifted conditions, and expanding the variety of achievable hybrid patterns. Complementary characterization using SEM, UV−vis spectroscopy, and FDTD simulations demonstrates that this approach provides a straightforward and versatile strategy to direct the assembly of colloidal nanoparticles on lithographic nanostructures via optical excitation.

Hot carrier and heat generation in plasmonic nanoparticles are critically important in plasmon-assisted chemistry and catalysis, sensing, and optoelectronic applications. The selective control of these effects plays a key role in determining the efficiency of chemical processes and the performance of associated devices. A major challenge lies in distinguishing and precisely controlling these effects under experimental conditions, particularly since most applications rely on continuous-wave (CW) irradiation, where both phenomena occur simultaneously. In this work, we investigate the polymerization of diazonium salts on gold nanocubes under CW and femtosecond (fs) irradiation as a probe for evaluating the efficiency of hot-electron generation and heat production. Our findings reveal that continuous excitation of the quadrupole plasmonic mode promotes a hot-electron-driven process, owing to the absorptive character of the quadrupole resonance. Conversely, excitation of the dipole mode under CW irradiation results in chaotic polymer growth, driven by lattice heat generation. However, fs excitation of the dipole mode induces polarization-dependent polymerization precisely at plasmonic hot spots. We attribute this phenomenon to the synergistic effect of vibrational heating of adsorbate molecules occurring on the picosecond scale due to energy transfer from hot electrons, which leads to the formation of the first polymer layers on the nanocube corners, followed by a lattice-heating-driven reaction that proceeds more rapidly at the created anchoring sites. These results offer insights into the ultrafast processes occurring in gold nanoparticles upon irradiation and pave the way for designing energetically efficient chemical reactions and optoelectronic devices.

We report a silicon nitride photonic structure that enhances and directs emission from nitrogen-vacancy centers in nanodiamonds, aiming at scalable integration into photonic integrated circuits. The design consists of two parallel ridge waveguides separated by a subwavelength air gap, supporting a confined optical mode that increases the local density of optical states, thereby enhancing spontaneous emission via the Purcell effect. A Bragg reflector is included to recover emissions that would otherwise radiate out of plane, directing it toward the output waveguide. Controlled localization of nanodiamonds within lithographically defined regions is achieved through lithographic masks. Fluorescence lifetime measurements reveal a ninefold emission rate enhancement, with Purcell factors up to 8.9 and simulated β-factors of up to 13.7%. This approach provides a compact platform that combines slot-waveguide emission enhancement with lithography-assisted nanodiamond localization for integration with photonic integrated circuits and compatibility with other solid-state quantum emitters.

Plasmonic nanoparticles support localized surface plasmon resonances (LSPR), exhibiting broad spectral features determined by nanoparticle geometry and material. When periodically arranged, they enable diffractive modes linked to Rayleigh anomalies (RA). The coupling between LSPR and RA produces surface lattice resonances, which combine strong field confinement, enhanced scattering, and high resonance quality with broad applications in sensing and light emission. While monometallic arrays have been extensively studied, bimetallic systems remain largely unexplored. This work investigates checkerboard arrays of gold and aluminum nanoparticles and demonstrates broadband surface lattice modes arising from hybridization of their distinct plasmonic responses. Simulations and experiments show that gold and aluminum dipolar resonances couple via the same RA in the near-infrared, extending beyond aluminum's usual plasmonic range. This previously unreported mechanism opens new routes toward broadband, high-performance plasmonic arrays for sensing, photonics, and telecommunications.

Plasmon‐enhanced sensing based on localized resonances conventionally relies on the variation of the mode frequency of a nano‐resonator, owing to its dependence on the local dielectric environment. In this work, a novel approach to optical refractometric sensing is introduced, using second‐harmonic emission from metagratings of plasmonic nanoantennas. Leveraging the angular shift of the nonlinear emission patterns induced by changes in the local refractive index, a directional sensing strategy complementary to plasmonic resonance‐based detection is demonstrated. This approach is first assessed on periodic metagratings, where the effects of the resonance spectral shift and the variation of the emission pattern are disentangled through Fourier‐space imaging. A graded aperiodic metagrating layout is then introduced to enable the direct measurement of the angular shift in the emission. In this configuration, a comparable performance between angular and spectroscopic sensing is obtained, highlighting the potential of emission directionality as an independent and synergistic mechanism for enhanced nonlinear optical sensing.

Aluminum (Al) is a cost-effective alternative to noble metals for plasmonics, particularly in the ultraviolet (UV) and visible regions. However, in the near-infrared (NIR) region, its performance is hindered by interband transitions (IBTs) at around 825 nm, leading to increased optical losses and broad resonances. Surface lattice resonances (SLRs) offer a promising solution by enhancing the plasmonic quality factor (Q-factor) through coherent coupling of localized surface plasmon (LSP) modes with Rayleigh anomalies. Although high-Q SLRs have been demonstrated in homogeneous environments, achieving similar enhancements in asymmetric media such as air remains a challenge. This study presents a novel approach for improving the Q factor of aluminum in air by utilizing SLRs in aluminum nanoparticle (NP) arrays fabricated via electron beam lithography (EBL) on a high refractive index indium tin oxide (ITO) substrate. The ITO substrate enhances long-range coupling between NPs, reinforcing coherent interactions. Using absorption micro-spectrometry and finite-difference time-domain (FDTD) simulations, we demonstrate Q factors reaching 110 in air, significantly exceeding typical values in IR in an asymmetrical surrounding medium. Our results establish aluminum as a viable low-cost material for high-performance plasmonic applications in sensing, telecommunications, and optoelectronics.

We study numerically and experimentally the second‐harmonic generation (SHG) from rectangular metagratings of V‐shaped gold nanoantennas. We show that by carefully engineering the array pitch to steer the diffraction orders toward the single antenna emission, the extracted signal is maximized. This enhancement is attributed to the angular overlap between the radiation pattern and array factor and is comparable to the improvement yielded by the coupling of surface lattice resonances (SLRs) with local modes. Moreover, we demonstrate a simple technique to experimentally reconstruct the emission diagram of an antenna from measurements of the collective grating response as a function of the excitation angle. Excellent agreement is obtained with simulations when the sample is immersed either in air or in water, which is crucial in view of future sensing application. Thanks to the high signal‐to‐noise ratio and low dependence on the statistical particle dispersity, this method constitutes an effective alternative to back‐focal plane imaging when very weak signals such as SHG are involved.

Hyperbolic metaparticles have emerged as the next step in metamaterial applications, providing tunable electromagnetic properties on demand. However, coupling of optical modes in hyperbolic meta-antennas has not been explored. Here, we present in detail the magnetic and electric dipolar modes supported by a hyperbolic bowtie meta-antenna and clearly demonstrate the existence of two magnetic coupling regimes in such hyperbolic systems. The coupling nature is shown to depend on the interplay of the magnetic dipole moments, controlled by the meta-antenna effective permittivity and nanogap size. In parallel, the meta-antenna effective permittivity offers fine control over the electrical field spatial distribution. Our work highlights new coupling mechanisms between hyperbolic systems that have not been reported before, with a detailed study of the magnetic coupling nature, as a function of the structural parameters of the hyperbolic meta-antenna, which opens the route toward a range of applications from magnetic nanolight sources to chiral quantum optics and quantum interfaces.

The development of advanced plasmonic applications is centered on the achievement of active devices. Active plasmonic nanostructures exhibiting tunable resonances have the potential to provide smart materials with a wide range of applications in optoelectronics, including sensing and logic operations. Here, we use finite-difference time-domain simulations to compare the optical properties of nanocones and nanocylinders embedded in two different states of a photochromic medium, first considering a plane wave illumination and then a point dipole one. We show that the photochromic transition induces strong coupling behavior for both illuminations, and it allows a nanocone to effectively enhance one emitter’s emission at one wavelength and quench another emitter at a different wavelength.

Metallic or dielectric nano-objects change the photon local density of states of closely placed emitters, particularly when plasmon or Mie resonances are present. Depending on the shape and material of these nano-objects, they may induce either a decrease or an increase in decay rates of the excited states of the emitter. In this work, we consider the reduction of the probability of optical transitions in emitters near high-refractive index dielectric (silicon and zinc selenide) nanoparticles. We tune the spectral positions of magnetic and electric modes of nanocylinders to obtain the largest overlap of the valleys in the total decay rate spectra for differently oriented dipoles and, in this way, find the highest inhibition of about 80% for randomly oriented emitters. The spectral positions of these valleys are easy to control since the wavelengths of the modes depend on the height and diameter of nanocylinders. The inhibition value is robust to the distance between the emitter and the nanoparticle in the range of nearly 50 nm, which is crucially important for the applications, such as selective optical transition engineering and photovoltaics.