Xavier Castel

Development of new localized surface plasmon resonance interfaces based on gold nanostructures sandwiched between tin-doped indium oxide films.

This article reports on the fabrication and characterization of plasmonic interfaces composed of a sandwiched structure comprising a tin-doped indium oxide (ITO) substrate, gold nanostructures (Au NSs), and a thin ITO film overcoating. The change in the optical characteristics of the ITO/Au NSs/ITO interfaces as a function of the ITO overlayer thickness (d(ITO) = 0-200 nm) was followed by recording UV-vis transmission spectra. The influence of the thickness of the ITO overcoating on the position and shape of the plasmonic signal is discussed. The possibility to functionalize the ITO/Au NSs/ITO interfaces chemically is demonstrated by covalently linking ethynyl ferrocene to azide-terminated ITO/Au NSs/ITO interfaces. The resulting interfaces were characterized using X-ray photoelectron spectroscopy (XPS), electrochemical (cyclic voltammetry and differential pulse voltammetry) techniques, and UV-vis transmission spectroscopy.

Optical and electrochemical properties of tunable host–guest complexes linked to plasmonic interfaces

This article describes the use of localized surface plasmon resonance (LSPR) interface to detect complexation/decomplexation steps of a controllable host–guest system at the solid–liquid interface. The LSPR interfaces consist of a sandwiched structure comprising a tin-doped indium oxide (ITO) substrate, gold nanostructures (Au NSs) and a thin ITO film overcoating. “Click” chemistry was used to covalently link an alkyne-functionalized π-electron deficient tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+) unit to an azide-terminated LSPR interface. The modified interfaces were characterized using X-ray photoelectron spectroscopy (XPS), cyclic voltammetry and UV-vis transmission spectroscopy. Tetrathiafulvalene (TTF) was used as a model guest molecule to demonstrate the possibility to follow the complexation/decomplexation events by monitoring the change in the LSPR signal. The results demonstrate that redox controlled host–guest complexation at the surface can be monitored effectively using LSPR.

Cooperative communications between vehicles and intelligent road signs

CAPTIV is a research program proposing new low-cost and energy-efficient mobile communications solutions to ease and make safer road traffic conditions. Considering ¿intelligent¿ road signs and vehicles, i.e. equipped with an autonomous radio communication system, drivers will be able to receive at any time various information about traffic fluidity or road sign identification. In order to reduce deployment cost and increase lifetime of the whole system, Multi-Input Multi-Output (MIMO) signal processing techniques are used. Considering each crossroads as a communication node, the possible cooperation between road signs allows energy-efficient communications between crossroads. MIMO channels characterization and modeling, specific antennas conception, associated with signal processing techniques allow to further optimize the energy consumption between nodes. A driving simulator is used in order to both validate the communication system and protocols between vehicles and road signs and evaluate the effect of the additional information on the driver behavior. Supported by the Brittany Regional Council, CAPTIV is a highly applicative program. A first prototype of such a communicating crossroads will be presented in the Vehipole in Saint-Brieuc (technological site devoted to ITS experimentations).

Loss reduction technique in ferroelectric tunable devices by laser micro-etching. Application to a CPW stub resonator in X-band

Ferroelectric materials are known to be lossy at microwaves. A local microetching technique based on laser ablation is implemented here to reduce the insertion loss of highly tunable devices fabricated on KTa1-xNbxO3 (KTN) ferroelectric thin films. The relevance of this approach is studied in X-band by comparing numerically and experimentally the performance of a frequency-tunable coplanar waveguide stub resonator before and after KTN microetching. The experimental data demonstrate a large loss reduction (by a factor 3.3), while keeping a high-frequency tunability (47%) under a moderate biasing static electric field (80 kV/cm). This approach paves the way for the design of ferroelectric reconfigurable devices with attractive performance in X-band and even beyond.