Jean-Pierre Abid

Hyper-Rayleigh scattering of gold nanorods and their relationship with linear assemblies of gold nanospheres

The surface plasmon enhanced hyper-Rayleigh scattering light collected from an aqueous solution of gold nanorods is reported. A non negligible part of the signal is attributed to a photoluminescence background attributed to the electron hole recombination following multiphoton excitation of d-valence band electrons into the sp-conduction band. This radiative relaxation process is likely favored by the presence of the organic species adsorbed at the surface of the nanorods. The absolute value for the hyperpolarisability of nanorods is also compared by the external reference method to that of para-nitroaniline and found to be rather large although an absolute value cannot be given because the exact number density of the gold nanorods is unaccessible. This value is however compared with values reported for linear assemblies of gold spherical nanoparticles and further support the simple model of gold metal ellipsoids to describe the hyper-Rayleigh light intensities. The polarisation analysis of the hyper-Rayleigh scattering light is also determined for gold nanorods and compared to the expected one for gold nanospheres. For the latter spheres, the weakness of the signal intensities precludes a definite comparison with the model. On the opposite, for the nanorods, the polarisation dependence of the hyper-Rayleigh scattered light clearly deviates from the one expected for nanospheres.

Selective structure changes of core-shell gold-silver nanoparticles by laser irradiation: homogeneisation vs. silver removal

A method involving laser irradiation is shown to lead to selective modification of core–shell gold–silver nanoparticles.

Ferromagnetism at Room Temperature on Electrodeposited Co2 + -Doped ZnO Thin Film

Predicted by the theory, ferromagnetism is expected in Co-doped ZnO. Recently, ferromagnetism above room temperature was reported in thin films as well as in bulk samples made of cobalt-doped zinc oxide. In this study, we report the preparation of ZnO doped with 5% of Co Zn1−xCoxO, x = 0.05 by electrodeposition. Sample characterization using X-ray diffraction, highresolution transmission electron microscopy, and X-ray photoelectron spectroscopy shows that the dopant is substitutional. Moreover, the magnetic properties of Co-doped ZnO samples electrodeposited as a function of field and temperature exhibit clearly ferromagnetism with Curie temperature above 400 K.

Pure surface plasmon resonance enhancement of the first hyperpolarizability of gold core–silver shell nanoparticles

We report the optical second harmonic (SH) response from gold core-silver shell nanoparticles supported at a liquid-liquid interface in the spectral region where the second harmonic generation (SHG) frequency is resonant with the surface plasmon (SP) resonance excitation of the nanoparticles. We compare these results with that obtained by classical linear optical absorption spectroscopy and show that the nonlinear optical response is dominated by the SP resonance enhancement with negligible contributions from the interband transitions. As a result, the SH spectrum exhibits two clear SP resonance bands attributed to the two SP resonances of the composite nanostructure formed by the gold core-silver shell nanoparticles. Absolute values of the hyperpolarizabilities are measured by hyper Rayleigh scattering (HRS) and compared that of pure gold nanoparticles. The hyperpolarizability measured at a harmonic energy of 3.0 eV, enhanced through excitation of the high energy SP resonance of the nanoparticle, increases with the silver content whereas the hyperpolarizability measured at a harmonic energy of 2.4 eV, enhanced through the excitation of the low energy SP resonance of the nanoparticle, decreases because of the shift of this resonance away from the harmonic frequency. The hyperpolarizability determined by HRS and the square root of the SHG intensities, scaling with the nanoparticle hyperpolarizability, have similar trends with respect to the silver content indicative of closely related adsorption properties yielding similar surface concentrations at the liquid-liquid interface.

Nanomosaic Network for the Detection of Proteins Without Direct Electrical Contact

A nanomosaic network of metallic nanoparticles for the detection of ultralow concentrations of proteins is reported, which uses two planar microelectrodes embedded in a microchip that permit generation of capacitive coupling to the nanomosaic system without the need for direct electrical contact with the channel. By tailoring the microchannel surface using a sandwich configuration of polyethylene terephthalate/gold nanoparticles/poly(L-lysine), the surface charge can be modified following biomolecular interactions and monitored using a noncontact admittance technique. This nanodevice system behaves like a tunable capacitor and can be employed for the detection of any kind of molecule. The femtomolar detection of an anionic protein, such as beta-lactoglobulin in phosphate-buffered saline medium, is taken as an example.