Publications

A mesoporous structure of self-assembled nanocrystals of cubic ZnS doped with Mn2+ ions with a homogeneous distribution of pores of similar size was synthesized at room temperature by a surfactant-assisted liquid-liquid reaction. The component nanocrystals exhibit a high crystallinity and a tight size distribution centered at 2 nm, as well as the narrowest Electron Paramagnetic Resonance (EPA) spectra linewidth and the best resolution reported so-far, effects attributed to self-assembling. The observed EPA spectra consist of lines from the substitutional Mn2+(I) and surface Mn2+(II) and Mn2+(III) centers. Here we show that, in contrast with previous reports, our EPA spectra are highly sensitive to structural changes during pulse annealing in vacuum up to 500 degrees C. The changes are related to the transformation of the surface Mn2+ centers in new Mn2+ centers, attributed to an oxidation process in which the thermal decomposition of the Tween 20 additive, also observed by EPA, seems to be involved. We have also been able to observe, for the first time by EPR spectroscopy, the formation of the ZnO phase and the nanocrystals size increase, which occur during annealing up to 500 degrees C, structural changes confirmed by XRD and TEM observations on the samples previously investigated by EPR.

The first field for magnetic flux penetration H in Bi2Sr2CaCu2O8+delta (Bi-2212) single crystals near the critical temperature T-c was investigated from the local magnetic hysteresis loops registered for different magnetic field H sweeping rates by using a scanning Hall probe microscope (SHPM) with similar to 1 mu m effective spatial resolution. Evidences for a significant role of the surface barrier were obtained: the asymmetric shape of the magnetization loops and an anomalous change in the slope of H-p(T) close to T-c. (C) 2011 Elsevier B.V. All rights reserved.

Well-dispersed, uniform monometallic Pt and bimetallic Pt-Cu, and Pt-Ag nanoparticles protected with PVP have been synthesized by a modified-protocol alkaline polyol method. The nanoparticles were characterized by various methods (TEM, XPS, and XRD) to elucidate the relationship between morphology and preparation variables. The average of monodispersed nanoparticles ranged between 4.1 and 4.9 nm. Core-shell structure was obtained in the case of bimetallic nanoparticles. The core of bimetallic nanoparticles was found to be rich in platinum, whereas the shell contained mostly copper or silver. The final structure of bimetallic nanoparticles was found to be determined by the morphology particles resulted in the first reduction step. Explanations are advanced on the light of experimental results.

Simple and low cost biosensor based on screen-printed electrode for sensitive detection of some alkylphenols was developed, by entrapment of HRP in a nanocomposite gel based on single-walled carbon nanotubes (SWCNTs) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid. Raman and FTIR spectroscopy, CV and EIS studies demonstrate the interaction between SWCNTs and ionic liquid. The nanocomposite gel, SWCNT-[BMIM][PF6] provides to the modified sensor a considerable enhanced electrocatalytic activity toward hydrogen peroxide reduction. The HRP based biosensor exhibits high sensitivity and good stability, allowing a detection of the alkylphenols at an applied potential of -0.2 V vs. Ag/AgCl, in linear range from 5.5 to 97.7 mu M 4 for 4-t-octylphenol and respectively, between 5.5 and 140 mu M for 4-n-nonylphenol, with a response time of about 5s. The detection limit was 1.1 mu M for 4-t-octylphenol, and respectively 0.4 mu M for 4-n-nonylphenol (S/N = 3). (C) 2011 Elsevier B.V. All rights reserved.

Cotton/polyester woven fabrics were functionalized with ZnO thin films or nanoparticles by pulsed laser deposition, using a KrF* excimer laser source. Depending on the number of applied laser pulses, well-separated nanoparticles (for 10 pulses) or compact thin films (for 100 pulses) were deposited. The synthesized nanostructures were evaluated morphologically by scanning electron microscopy and atomic force microscopy, physico-chemically by x-ray diffraction and functionally by the contact angle method. By modifying the ambient gas nature and pressure in the deposition chamber, hydrophilic or hydrophobic surfaces were obtained. When using an oxygen flux, both the deposited thin films and nanoparticles were hydrophilic. After deposition in vacuum, the nanoparticles were hydrophobic, but the thin films were super-hydrophobic. This radical modification of wetting behavior was assigned to the differences in microstructure features and surface electrical charging in the two cases. (C) 2011 American Institute of Physics. [doi:10.1063/1.3639297]

A novel nanocomposite FePt-based exchange-coupled magnet has been synthesized and structurally and magnetically characterized. We report for the first time the direct formation of the L1(0) FePt phase without the need for post-synthesis annealing procedures in Fe-Pt-based melt-spun ribbons, obtained by a conventional melt spinning method. The structure and magnetic properties are investigated and the occurrence of the L1(0) ordered phase in the as-cast state of Fe-Pt-Ag-B melt-spun ribbons is confirmed by XRD and magnetic measurements. A microstructure consisting of fine, uniformly dispersed, 22-24 nm FePt grains dispersed within a soft magnetic matrix is observed by scanning transmission electron microscopy imaging. Coercive fields as high as 727 kAm(-1), saturation magnetization of about 1.2 T and energy product around 87 kJm(-3) are determined from 270 K hysteresis loops of the as-cast ribbons, making one of the best FePt-based nanocomposite magnet ribbons even without further annealing treatments.

The difficulties in synthesizing phase pure BaTiO3 doped-(Na0.5Bi0.5)TiO3 are known. In this work, we reporting the optimized pulsed laser deposition (PLD) conditions for obtaining pure phase 0.92(Na0.5Bi0.5)TiO3-0.08BaTiO(3), (BNT-BT0.08), thin films. Dielectric, ferroelectric and piezoelectric properties of BNT-BT0.08, thin films deposited by PLD on Pt/TiO2/SiO2/Si substrates are investigated in this paper. Perovskite structure of BNT-BT0.08 thin films with random orientation of nanocrystallites has been obtained by deposition at 600 degrees C. The relative dielectric constant and loss tangent at 100 kHz, of BNT-BT0.08 thin film with 530 nm thickness, were 820 and 0.13, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 22 mu C/cm(2) and a coercive field of 120 kV/cm. The piezoresponse force microscopy (PFM) data showed that most of the grains seem to be constituted of single ferroelectric domain. The as-deposited BNT-BT0.08 thin film is ferroelectric at the nanoscale level and piezoelectric. (C) 2011 Elsevier B.V. All rights reserved.

Abnormal anti-Stokes Raman emission (AASRE) is defined by an anti-Stokes/Stokes intensity ratio much greater than expected on the basis of the equilibrium population of excited vibration states provided by the Boltzmann law. Using nonlinear optical materials such as LiNbO(3) and CdS in powder form, we demonstrate that under continuous single beam excitation it presents AASRE whose properties are similar to a single beam pumped Coherent Anti-Stokes Raman Scattering. We explain AASRE as resulting from a wave-mixing mechanism of the incident laser light with a Stokes shifted Raman light produced by a spontaneous Raman light scattering process, both strongly scattered inside the sample. (C) 2011 American Institute of Physics. [doi:10.1063/1.3633936]

We show that the optical infrared magneto-refractive effect can be used to probe magneto-resistance effects in absolute terms. A spin valve sample with synthetic anti-ferromagnet has been studied using non-contact infrared reflection spectroscopy measurements. Direct experimental comparison shows excellent agreement between electrical and optical measurements in both shape of the magneto-resistance curves and absolute values. This opens the possibility of developing fast and efficient tests of magneto-resistive samples and sensors using an in situ, non-contact, non-destructive optical approach, without the need to determine a calibration factor between the electrical and optical measurements. [doi:10.1063/1.3631778]

Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1 : 1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.