Anne-Marie Haghiri-Gosnet

λ3/1000 Plasmonic Nanocavities for Biosensing Fabricated by Soft UV Nanoimprint Lithography

Arrays of plasmonic nanocavities with very low volumes, down to λ(3)/1000, have been fabricated by soft UV nanoimprint lithography. Nearly perfect omnidirectional absorption (3-70°) is demonstrated for the fundamental mode of the cavity (λ ≃ 1.15 μm). The second-order mode exhibits a sharper resonance with strong angular dependence and total optical absorption when the critical coupling condition is fulfilled (45-50°, λ ≃ 750 nm). It leads to high refractive index sensitivity (405 nm/RIU) and figure of merit (∼21) and offers new perspectives for efficient biosensing experiments in ultralow volumes.

Microstructure and magnetic properties of strained La0.7Sr0.3MnO3 thin films

The lattice deformation of dense strained La0.7Sr0.3MnO3 (LSMO) films is shown to control the easy direction of the magnetization. Optimized pulsed laser deposited conditions allow the fabrication of dense LSMO thin films which present an exceptional flatness with a peak–valley roughness (Rp–v) of 1 A, associated to epitaxial grains as large as 1 μm. Electron microscopy coupled with x-ray diffraction have been used to study the unit cell distortion of both tensile and compressive dense LSMO films as a function of the thickness. No relaxation of the lattice distortion imposed by substrate has been observed in the thickness range 10–60 nm. The Curie temperature is not significantly affected by the nature of the substrate: a TC of 350 K is observed for both SrTiO3 (STO) and LaAlO3 (LAO) substrates, i.e., close to the bulk material (369 K). In contrast, the easy direction of magnetization depends on the substrate. For tensile films deposited on the STO substrate, the unit cell is elongated along the film’s pl...

Spectacular decrease of the melting magnetic field in the charge-ordered state of Pr0.5Ca0.5MnO3 films under tensile strain

An insulator to metal transition below 240K is induced by applying a 7T magnetic field in Pr0.5Ca0.5MnO3 thin films grown by the Pulsed Laser Deposition technique on (100) SrTiO3 substrates. This value of the melting magnetic field, much lower that the one required in bulk (20T), is assumed to be an effect of the tensile stress. These results confirm the importance of the bandwidth in the control of the physical properties of this compound and open the route to get colossal magnetoresistive properties by using strain effects.

Spectacular decrease of the melting magnetic field in the charge-ordered state of tensile Pr0.5Ca0.5MnO3 films

An insulator to metal transition below 240K is induced by applying a 7T magnetic field in Pr0.5Ca0.5MnO3 thin films grown by the Pulsed Laser Deposition technique on (100) SrTiO3 substrates. This value of the melting magnetic field, much lower that the one required in bulk (20T), is assumed to be an effect of the tensile stress. These results confirm the importance of the bandwidth in the control of the physical properties of this compound and open the route to get colossal magnetoresistive properties by using strain effects.

Substrate effect on the magnetic microstructure of La0.7Sr0.3MnO3 thin films studied by magnetic force microscopy

Colossal magnetoresistive La0.7Sr0.3MnO3 thin films have been grown under tensile strains on (100)-SrTiO3 substrates and compressive strains on (100)-LaAlO3 and (110)-NdGaO3 substrates by pulsed laser deposition. Using magnetic force microscopy (MFM), a “feather-like” magnetic pattern, characteristic of films with an in-plane magnetization, is observed for films deposited on both SrTiO3 and NdGaO3 while a “bubble” magnetic pattern, typical of films with an out-of-plane magnetization, is recorded for LaAlO3. We show that the shape of the magnetic pattern imaged by MFM is fully correlated to the easy direction of the magnetization in the film.

Electropreconcentration with charge-selective nanochannels.

We report on the systematic investigation of electropreconcentration phenomena in hybrid micro/nanofluidic devices. The competition between the electroosmotic dragging force and the highly nonlinear electrophoretic forces induced by the polarization effect is responsible for four preconcentration regimes within such structures that can arise at both cathodic and anodic sides of the nanochannel. Numerical calculations on the spatiotemporal concentration of charged molecules confirm such a classification, showing a general agreement with the reported experimental data at low and moderate ionic strengths. The results also suggest that both the mobility and the valence of the species of interest are important parameters in the determination of the preconcentration rates.

A multicolor microfluidic droplet dye laser with single mode emission

A digital microfluidic dye laser that integrates a Fabry–Perot cavity with two fiber-based mirrors is shown to exhibit a single mode emission. In addition, fast switching is achieved via the alternation of droplet streams that contain two different dyes. Single-longitudinal-mode emission is observed for each dye wavelength (at 565 and 586 nm) with a linewidth narrower than 0.12 nm. This system appears thus well suited for on-chip spectroscopy and flow cytometry.

Large domain wall magnetoresistance up to room temperature in La0.7Sr0.3MnO3 bridges with nanoconstrictions

To obtain low field magnetoresistance (MR) in manganites, we have introduced a geometrically constrained magnetic domain wall (DW) in La0.7Sr0.3MnO3 micrometric devices. Nanoconstrictions artificially induced using high resolution e-beam lithography are shown to effectively reduce the DW width leading to strongly enhanced DW resistance. Sharp and large resistance switches result from the appearance and annihilation of the DWs. Room temperature sharp resistance switches, with a MR of 16%, are evidenced in a manganite-based device.

Single particle demultiplexer based on domain wall conduits

The remote manipulation of micro and nano-sized magnetic particles carrying molecules or biological entities over a chip surface is of paramount importance for future on-chip applications in biology and medicine. In this paper, we present a method for the on-chip demultiplexing of individual magnetic particles using bifurcated magnetic nano-conduits for the propagation of constrained domain walls (DWs). We demonstrate that the controlled injection and propagation of a domain wall in a bifurcation allow capturing, transporting, and sorting a single magnetic particle between two predefined paths. The cascade of n levels of such building blocks allows for the implementation of a variety of complex sorting devices as, e.g., a demultiplexer for the controlled sorting among 2n paths.

Pressure-assisted selective preconcentration in a straight nanochannel.

We investigate the preconcentration profiles of a fluorescein and bovine serum albumin derivatized with this fluorescent tag in a microfluidic chip bearing a nanoslit. A new preconcentration method in which a hydrodynamic pressure is added to both electroosmotic and electrophoretic contributions is proposed to monitor the location of the preconcentration frontline. A simple predictive model of this pressure-assisted electropreconcentration is proposed for the evolution of the flow profile along this micro/nano/microfluidic structure. We show with a small analyte such as fluorescein that the additional hydrostatic pressure mode enables to stabilize the concentration polarization (CP) effect, resulting in better control of the cathodic focusing (CF) peak. For BSA (bovine serum albumin), we exhibit that the variation of the hydrodynamic pressure can have an even more drastic effect on the preconcentration. We show that, depending on this hydrodynamic pressure, the preconcentration can be chosen, either in the cathodic side or in the anodic one. For the first time, we prove here that both anodic focusing (AF) and cathodic focusing (CF) regimes can be reached in the same structures. These results also open new routes for the detection and the quantification of low abundance biomarkers.