Abdelhanin Aassime

Giant coupling effect between metal nanoparticle chain and optical waveguide.

We demonstrate that the optical energy carried by a TE dielectric waveguide mode can be totally transferred into a transverse plasmon mode of a coupled metal nanoparticle chain. Experiments are performed at 1.5 μm. Mode coupling occurs through the evanescent field of the dielectric waveguide mode. Giant coupling effects are evidenced from record coupling lengths as short as ~560 nm. This result opens the way to nanometer scale devices based on localized plasmons in photonic integrated circuits.

Soft UV nanoimprint lithography-designed highly sensitive substrates for SERS detection

AbstractWe report on the use of soft UV nanoimprint lithography (UV-NIL) for the development of reproducible, millimeter-sized, and sensitive substrates for SERS detection. The used geometry for plasmonic nanostructures is the cylinder. Gold nanocylinders (GNCs) showed to be very sensitive and specific sensing surfaces. Indeed, we demonstrated that less than 4 ×106 avidin molecules were detected and contributed to the surface-enhanced Raman scattering (SERS) signal. Thus, the soft UV-NIL technique allows to obtain quickly very sensitive substrates for SERS biosensing on surfaces of 1 mm 2.

Integration of short gold nanoparticles chain on SOI waveguide toward compact integrated bio-sensors

We demonstrate the integration of short metal nanoparticle chains (L ≈700 nm) supporting localized surface plasmons in Silicon On Insulator (SOI) waveguides at telecom wavelengths. Nanoparticles are deposited on the waveguide top and excited through the evanescent field of the TE waveguide modes. Finite difference time domain calculations and waveguide transmission measurements reveal that almost all the TE mode energy can be transferred to nanoparticle chains at resonance. It is also shown that the transmission spectrum is very sensitive to the molecular environment of nanoparticles, thus opening the way towards ultra-compact sensors in guided plasmonics on SOI. An experimental demonstration is reported with octadecanthiol molecules for a detection volume as small as 0.26 attoliter.

Low-field magnetoresistance in a nanopatterned manganite track

We have measured the contribution of magnetic domain walls (DWs) to the electric resistance in epitaxial manganite films patterned by electron-beam lithography into a track containing a set of notches. We find a DW resistance-area (RA) product of ~2.5 10^(-13) Ohm/m^2 at low temperature and bias, which is several orders of magnitude larger than the values reported for 3d ferromagnets. However, the current-voltage characteristics are highly linear which indicates that the DWs are not phase separated but metallic. The DWRA is found to increase upon increasing the injected current, presumably reflecting some deformation of the wall by spin-transfer. When increasing temperature, the DWRA vanishes at ~225K which is likely related to the temperature dependence of the film anisotropy.

Conventional and Un-Conventional Lithography for Fabricating Thin Film Functional Devices

Thin film devices are conquering many aspects of today’s life, and continuous shrinking of building block dimensions of these structures enhances their performances and makes them economically attractive. This chapter is an overview of some conventional and unconventional lithography techniques used to fabricate thin film functional structures. Several aspects of pattern transfer were addressed with emphasis on the limits of these lithography techniques. We have thus highlighted the issue of pitch resolution for optical lithography and discussed some aspect of proximity effects for electron beam lithography. Pattern transfer from resist image to the wafer was also discussed. Considered as unconventional, we discussed several aspects linked to thin film fabrication using nanoimprint and nanosphere lithography techniques.

Light propagation in metallic nanoparticle chains on SOI waveguide

In this work, we demonstrate successful interfacing between metallic nanoparticle (MNP) chain supporting localized surface plasmons (LSP) and silicon-on-insulator (SOI) waveguides. We show that the optical energy carried by a TE SOI waveguide mode at telecom wavelengths can be efficiently transferred into MNP chains deposited on the waveguide top, whatever the number of metallic particles (from 5 to 50). Especially in short chains, most of the energy can be transferred into the fourth or fifth MNP of the chains. Predictions from theoretical models are fully corroborated by transmission and near-field measurements.

Localized surface plasmon evanescent excitation at telecom wavelength

Size reduction of optical components can be achieved by manipulating light at sub-wavelength scales. Of practical interest, metallic nanoparticle (MNP) chains supporting localized surface plasmons (LSP) can transmit light below the diffraction limit [1] and thus realize ultra-compact couplers [2]. However, their insertion in photonic integrated circuits requires the optimization of their optical coupling to conventional dielectric waveguides. In the present configuration (inserts of Fig. 1(a–b)), the MNP chain is deposited on the top of a dielectric waveguide, and its excitation occurs via the evanescent field of the waveguide. We use a 3D finite-difference time-domain calculation method (FDTD Solutions Lumerical) to investigate the coupling of the MNP chain to two types of slab dielectric waveguides (Si3N4 and SOI (silicon on insulator)) at telecom wavelengths. The NP dimensions are chosen in such a way that the MNP chain can be excited in this wavelength range. The LSP resonance wavelength is fixed at 1410 nm. Since this resonance strongly depends on the optical index environment of the NP, the optimal NP size is different for the two waveguide structures. In each case, the MNP chain is composed of 50 rod-shaped gold nanoparticles deposited on the slab waveguide.