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We present a new method to pattern assemblies of gold nanorods (GNRs) on substrates and a study of the near-field coupling induced by the aggregation of the nanoparticles. The combination of deep-UV lithography and controlled deposition of functionalized GNRs generates complex GNR assemblies. Near-field coupling is investigated by photoemission electron microscopy (PEEM) on single, dimer, and elongated aggregates of GNRs. This comparative study exhibits different kinds of near-field coupling efficiency that occur depending of the incident light polarization, interparticle gaps and angles between the nanorods. Hot spots of the near-field are associated with the interparticle gap regions.

The analysis of the local distribution of the electric field, induced by localized surface plasmon resonance (LSPR), is crucial for selecting the morphology of gold nanoparticles (AuNPs) for specific applications. The reported study is based on an LSPR-induced near-field two-photon photopolymerization (NF2P) reaction. The initiation of NF2P is triggered by LSPR-enhanced near-field light, while in the far-field, oxygen inhibits this reaction. The spatial extent of the NF2P reaction is compared to the local electric field distribution depending on AuNP morphologies, established by numerical simulations. Overall, our results demonstrate that the photopolymerization is not only driven by the local near-field enhancement but also strongly depends on the topologies of nano-object, and the photopolymerization extension was more confined in anisotropic and sharp structures compared to isotropic ones. Additionally, we showcased its capability to confine polymerization reactions within nanoscale volumes with the possibility of controlling the localization of polymer lobes at a single triangle apex, for instance, via light polarization.

A simple group theory approach is proposed to predict the charge distribution of low order localized surface plasmon resonances (LSPRs) of finite metallic particles of basic geometries. As an illustration, the case of randomly oriented Au colloidal particles of cubic C4vsymmetry excited at dipolar resonance is presented. The symmetry approach is confirmed by numerical simulations carried out by the boundary element method. Experimental validation is achieved by high-resolution subwavelength near-field mapping conducted by photoemission electron microscopy.

The two-photon luminescence (TPL) of small 10 nm × 40 nm colloidal gold nanorods (GNR) is investigated at the single object level, combining polarization-resolved TPL and simultaneously acquired topography. A very high dependence of the TPL signal with both the nanorods longitudinal axis and the incident wavelength is observed, confirming the plasmonic origin of the signal and pointing to the limit of the analogy between GNRs and molecules. The maximum two-photon brightness of a single GNR is measured to be a few millions higher than the two-photon brightness of fluorescein molecules. The spectral analysis of the TPL evidence two emission bands peaks: in the visible (in direct connection with the gold band structure) and in the infrared (IR). In both bands, the TPL signal is observed to vary quadratically with the excitation beam; the signal emitted in either the visible or the IR exhibits, however, different polarization properties. We show that the important TPL observed in these small gold nanorods results from resonance effects both at the excitation and emission level: local field enhancement at the longitudinal surface plasmon resonances (LSPR) first results in an increase of the electron–hole generation. Further relaxation of electron–hole pairs then mostly leads to the excitation of the GNR transverse plasmon mode and its subsequent radiative relaxation.

An opal plasmonic sample, constituted by a hexagonal arrangement of metallized silica spheres, presents remarkable optical properties due to the mixing of periodic arrangement and singularities at the sphere touching points. It is therefore an interesting candidate for exploiting the excitation of both localized and propagating surface plasmons. Several channels of excitation based on these properties or exploiting a certain level of disorder are evidenced, opening new routes for the efficient excitation of plasmons on a wide spectral range. The versatility of such a hybrid system is evidenced in the context of two complementary experiments: specular reflective spectrometry and photoemission electron microscopy. Both techniques offer different points of view on the same physical phenomenon, and the link between them is discussed. Such experiments evidence the opportunities offered by these two-dimensional hybrid materials in the context of nanophotonics.

The plasmonic properties of single Au triangular nanoprisms are investigated using photoemission electron microscopy with particular emphasis on polarization dependence. Two localized surface plasmon resonances (LSPRs) are studied, namely, the in-plane dipolar and quadrupolar plasmon excitations. Experimental maps of the near-field spatial distribution upon polarization and wavelength of the exciting field are interpreted in the framework of a group theory description and finite difference time domain simulations. This work demonstrates the selective excitations, by lifting of degeneracy, of the different LSPR eigenmodes at the single object level and opens ways for the active control of the angular radiation patterns of optical nanoantennas. This approach is general and applies to any nano-object, whatever its initial shape symmetry.

We report on a simple way to mark and track individual molecules self-assembled on a surface by scanning tunneling microscopy. The tracer mechanism consists in a minimal one-atom chemical substitution. While this substitution leads to significant modifications in the STM signature of the molecules, no substantial changes of the physics of self-assembling are observed when using the modified or unmodified molecular building blocks. This allows us to follow the intrinsic dynamical properties of the self-assembled molecular patterns.

Localized surface plasmon-induced photopolymerization of free-radical acrylate monomers is an efficient, smart, and versatile method for preparing metal/polymer hybrid nanoparticles (NPs) with accurate control of the thickness and spatial distribution of the polymer on the NP surface. Despite a growing number of practical demonstrations, the mechanism leading to polymerization of the acrylate monomer by localized surface plasmon resonance (LSPR) is still controversial. It could be related to either a photochemical mechanism enhanced by electromagnetic hot spots (enhanced near field) or thermoplasmonic (photothermal heating) or electrochemical (viahot-carrier injection) mechanisms, as proposed in different studies. After developing a high-resolution characterization method based on transmission electron microscopy and by tuning the photopolymer composition and the irradiation conditions, the LSPR-induced physicochemical mechanism is revealed. We demonstrate that the photochemical pathway is the main mechanism under the mild irradiation conditions chosen for this process. In a more general way, photopolymerization proves to be a powerful tool to investigate the coupling between metal nanostructures and organic moieties.