Jérôme Plain

Enhancement and Quenching Regimes in Metal−Semiconductor Hybrid Optical Nanosources

We report on the emission of hybrid nanosources composed of gold nanoparticles coupled with quantum dots. The emission relies on energy transfer from the quantum dots to gold nanoparticles which could be de-excited through radiative plasmon relaxation. The dependence of the emission efficiency is studied systematically as a function of the size of gold nanoparticles and interdistance between gold nanoparticles and quantum dots. We demonstrate a size-dependent transition between quenching and enhancement and a nonradiative energy transfer from the quantum dots to the gold nanoparticles.

Optimizing Electromagnetic Hotspots in Plasmonic Bowtie Nanoantennae

Sensitivity is a key factor in the improvement of nanoparticle-based biosensors. Bowtie nanoantennae have shown high sensitivity for both surface-enhanced Raman scattering (SERS)- and localized surface plasmon resonance (LSPR)-based biosensing. In this work, optical bowtie nanoantennae with varying geometries were simulated, fabricated, and characterized. We successfully fabricated sub-5 nm gaps between prisms. The gap between prisms, the prism size, and the radius of curvature of the prism corners were characterized for their effects on the optical and electromagnetic properties. Bowties were characterized using LSPR, SERS, and photochemical near-field imaging. The results indicate that the radius of curvature of the prism corners has an important effect on the SERS abilities of a nanoparticle array. The trends described herein can be utilized to intelligently design highly sensitive SERS and LSPR biosensing substrates.

Tuning of an Optical Dimer Nanoantenna by Electrically Controlling Its Load Impedance

Optical antennas are elementary units used to direct optical radiation to the nanoscale. Here we demonstrate an active control over individual antenna performances by an external electrical trigger. We find that by an in-plane command of an anisotropic load medium, the electromagnetic interaction between individual elements constituting an optical antenna can be controlled, resulting in a strong polarization and tuning response. An active command of the antenna is a prerequisite for directing light wave through the utilization of such a device.

Quantitative Analysis of Localized Surface Plasmons Based on Molecular Probing

We report on the quantitative characterization of the plasmonic optical near-field of a single silver nanoparticle. Our approach relies on nanoscale molecular molding of the confined electromagnetic field by photoactivated molecules. We were able to directly image the dipolar profile of the near-field distribution with a resolution better than 10 nm and to quantify the near-field depth and its enhancement factor. A single nanoparticle spectral signature was also assessed. This quantitative characterization constitutes a prerequisite for developing nanophotonic applications.

Fabrication of aluminium nanostructures for plasmonics

Metallic nanostructures are the building blocks for nanoplasmonics and for subsequent applications in nanooptics. For several decades, plasmonics have been almost exclusively studied in the visible region by using nanostructures made of noble metals exhibiting plasmonic properties in the near infrared to visible range. This notwithstanding, emerging applications will require the extension of nanoplasmonics toward higher energies, particularly in the UV range. Therefore, alternative metals, often described as poor metals are emerging to achieve that goal. Among all these metals, aluminium appears to be one of the most appealing for extending plasmonics towards ultraviolet energies. Aluminium is cheap, widely available, compatible with optoelectronic devices and exhibits plasmonic properties over a wide range of energies, from the infrared to the deep UV. Our aim is to present a review of current research centred on the fabrication of aluminium nanostructures. Mastering the geometry of aluminium nanostructures is extremely important in order to tune their plasmonic properties and target a given application. First we give an introduction to the nanofabrication of aluminium nanostructures within the context of plasmonics. The review then focuses on the possible geometries that such structures may take when fabricated with specific fabrication techniques. Each technique is detailed and the plasmonic properties of the aluminium nanostructures are briefly described. When possible, an example of an application is given. Finally, the future applications of aluminium plasmonics are highlighted and a conclusion with perspectives is given.

Localized surface plasmon resonances in the ultraviolet from large scale nanostructured aluminum films

We report on a straightforward preparation method to obtain a dense layer of quasi-spherical aluminum nanoparticles over a large area. The method is based on rapid thermal annealing of a thin aluminum film deposited on a super-repellent substrate. Diameters ranging from 2 to 15 nm are obtained by varying the film thickness. Aluminum nanoparticles exhibit well-defined localized surface plasmon resonances in the ultraviolet range as revealed by extinction measurements and confirmed by Mie theory.

High-resolution imaging and spectroscopy of multipolar plasmonic resonances in aluminum nanoantennas.

We report on the high resolution imaging of multipolar plasmonic resonances in aluminum nanoantennas using electron energy loss spectroscopy (EELS). Plasmonic resonances ranging from near-infrared to ultraviolet (UV) are measured. The spatial distributions of the multipolar resonant modes are mapped and their energy dispersion is retrieved. The losses in the aluminum antennas are studied through the full width at half-maximum of the resonances, unveiling the weight of both interband and radiative damping mechanisms of the different multipolar resonances. In the blue-UV spectral range, high order resonant modes present a quality factor up to 8, two times higher than low order resonant modes at the same energy. This study demonstrates that near-infrared to ultraviolet tunable multipolar plasmonic resonances in aluminum nanoantennas with relatively high quality factors can be engineered. Aluminum nanoantennas are thus an appealing alternative to gold or silver ones in the visible and can be efficiently used for UV plasmonics.

Spatially controlled synthesis of silver nanoparticles and nanowires by photosensitized reduction

The present paper reports on the spatially controlled synthesis of silver nanoparticles (NPs) and silver nanowires by photosensitized reduction. In a first approach, direct photogeneration of silver NPs at the end of an optical fiber was carried out. Control of both size and density of silver NPs was possible by changing the photonic conditions. In a further development, a photochemically assisted procedure allowing silver to be deposited at the surface of a polymer microtip was implemented. Finally, polymer tips terminated by silver nanowires were fabricated by simultaneous photopolymerization and silver photoreduction. The silver NPs were characterized by UV-visible spectroscopy and scanning electron microscopy.

Critical current enhancement in YBCO–Ag melt-textured composites: influence of microcrack density

Abstract A strong increase of the critical current density of YBa 2 Cu 3 O 7 (YBCO) melt-textured composites has been observed by adding Ag 2 O particles in the precursor mixture while the concentration of Y 2 BaCuO 5 (Y211) precipitates remains constant. Critical current density enhancement factors as high as 200% at 5 K ( J c ab (5 K, 0 T)∼2.5×10 6 A/cm 2 ) and 1000% at 77 K and 2 T ( J c ab (77 K, 2 T)∼2.2×10 4 A/cm 2 ) have been reached in samples with 20 wt.% of Ag 2 O. Critical current measurements at 77 K for H ∥ ab also confirm the increase of the J c enhancement factor with the magnetic field (∼100% at 0 T and 140% at 2 T). The improvement of the critical currents in the YBCO–Ag melt-textured composites is correlated with the reduction of the density of microcracks parallel to the ab plane, as observed by scanning electron microscopy (SEM). Results are interpreted in terms of a release of the current limiting factors and an improvement of flux pinning properties by preexisting defects.

Biological and chemical gold nanosensors based on localized surface plasmon resonance

In this paper, we discuss the performances of gold nanosensors based on Localized Surface Plasmon Resonance (LSPR) designed by Electron Beam Lithography (EBL) in the context of biological and chemical sensing. We demonstrate the sensitivity of our gold nanosensors by studying the influence of the concentration of 11-mercaptoundecanoic acid (MUA) on the shift of LSPR wavelength. Additionally, to study the selectivity of our nanosensors, the system Biotin/Streptavidin was used to detect very weak concentration of biomolecules. These results represent new steps for applications in chemical research and medical diagnostics.