Direct measurement of the effective infrared dielectric response of a highly doped semiconductor metamaterial.

We have investigated the effective dielectric response of a subwavelength grating made of highly doped semiconductors (HDS) excited in reflection, using numerical simulations and spectroscopic measurement. The studied system can exhibit strong localized surface resonances and has, therefore, a great potential for surface-enhanced infrared absorption (SEIRA) spectroscopy application. It consists of a highly doped InAsSb grating deposited on lattice-matched GaSb. The numerical analysis demonstrated that the resonance frequencies can be inferred from the dielectric function of an equivalent homogeneous slab by accounting for the complex reflectivity of the composite layer. Fourier transform infrared reflectivity (FTIR) measurements, analyzed with the Kramers-Kronig conversion technique, were used to deduce the effective response in reflection of the investigated system. From the knowledge of this phenomenological dielectric function, transversal and longitudinal energy-loss functions were extracted and attributed to transverse and longitudinal resonance modes frequencies.

Plasmonic mode interferences and Fano resonances in Metal-Insulator-Metal nanostructured interface.

Metal-insulator-metal systems exhibit a rich underlying physics leading to a high degree of tunability of their spectral properties. We performed a systematic study on a metal-insulator-nanostructured metal system with a thin 6 nm dielectric spacer and showed how the nanoparticle sizes and excitation conditions lead to the tunability and coupling/decoupling of localized and delocalized plasmonic modes. We also experimentally evidenced a tunable Fano resonance in a broad spectral window 600 to 800 nm resulting from the interference of gap modes with white light broad band transmitted waves at the interface playing the role of the continuum. By varying the incident illumination angle shifts in the resonances give the possibility to couple or decouple the localized and delocalized modes and to induce a strong change of the asymmetric Fano profile. All these results were confirmed with a crossed comparison between experimental and theoretical measurements, confirming the nature of different modes. The high degree of control and tunability of this plasmonically rich system paves the way for designing and engineering of similar systems with numerous applications. In particular, sensing measurements were performed and a figure of merit of 3.8 was recorded ranking this sensor among the highest sensitive in this wavelength range.

Noble metal nanocrystals at the surface of nitride semiconductors: synthesis, deposition and surface characterization.

Currently an extensive range of noble metal colloidal nanocrystals (NCs) can be readily produced by diverse chemical methods. These nanomaterials present novel physical properties and can be regarded as building blocks to the nanofabrication of smaller, energy efficient and faster devices. Moreover, when these NCs are deposited on the surface of luminescent semiconductors, as it is the case of GaN-based heterostructures, exciton coupling with the metal plasmons may occur. In this work we report on the deposition of noble metal NC at the surface of InGaN/GaN multiple quantum wells (MQW), with efficient light emission in the visible range. We investigate the surface organization of Ag and Au NCs with sizes ranging from 5-30 nm as a function of deposition conditions. Scanning Electron Microscopy and Atomic Force Microscopy clearly showed that the metallic nanoparticles were successfully incorporated within the MQWs of the nitride semiconductors.