National Institute Of Materials Physics - Romania

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.

Thin films of Mg (x) Zn1-x O and Mg (x) Zn1-x O doped with nitrogen were deposited by Radio Frequency plasma beam assisted Pulsed Laser Deposition (RF-PLD) in oxygen or oxygen-nitrogen discharge with different nitrogen/oxygen ratios. A Nd:YAG laser working at a wavelength of 266 nm, having a 10 Hz repetition rate was used for the depositions. The energy density of the incident beam was 3 J/cm(2) and the RF power was set to 100 W for all the samples. X-ray Diffraction (XRD) and Spectroscopic Ellipsometry (SE) were employed to investigate the samples. The degree of crystallinity is fount to decrease with increasing the Mg concentration, while the solubility of Mg in ZnO increases by 30% in the N-doped Mg (x) Zn1-x O thin films grown by RF-PLD. Segregation of MgO phase at a Mg concentration of 30% for Mg (x) Zn1-x O thin film is detected both by XRD and SE. The band gap of the samples increases from 3.37 up to 3.57 eV with increasing the Mg concentration and the nitrogen/oxygen ratio for each Mg concentration. A dependence of the dielectric function (refractive index) on both stoichiometry and degree of crystalinity is also found, the refractive index having values between 1.7 and 2 in visible spectral range.

In this study, we present the deposition of ZnPc, Alq3, and PTCDA thin films using Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. We also report the realisation of multilayer structures, made by the successive application of MAPLE. The films have been characterized by spectroscopic (UV-VIS and Photoluminescence) and microscopic (SEM and AFM) methods, and the effect of different deposition conditions such as fluence, number of pulses, and target concentration on the properties has been analysed. This paper also presents some investigations on the electrical conduction in sandwich type structures ITO or Si/organic layer/Au or Cu and ITO/double organic layer/Cu, emphasising the dominant effect of the height of the energetic barriers at the inorganic/organic and organic/organic interfaces.

The relaxation of the irreversible magnetic moment m(t) in YBa(2)Cu(3)O(7) (YBCO) films was investigated as a function of temperature T and the external magnetic field H along the c axis applied in zero-field cooling conditions, for the determination of vortex creep parameters. The data analysis was performed using the T and current density dependence of the normalized vortex creep activation energy, or by the fit of the m(t) data with the well known interpolation formula in the framework of the general vortex creep equation. It was found that (i) even for specimens with strong static pinning the characteristic pinning energy remains small in the low-T range, where the vortex creep appearing in standard magnetization measurements is elastic, (ii) the observed strong increase of the time scale for creep and the decrease of the creep exponent with increasing H beyond the theoretical predictions can be attributed to the crossover elastic-creep-plastic-creep generated by the macroscopic currents induced in the specimen during magnetization measurements, and (iii) the creep parameters extracted with the interpolation formula are highly affected by the m(t) data registered at short t, which may lead to unphysical creep parameter values.