National Institute Of Materials Physics - Romania

BaTi0.87Sn0.13O3 (BTS13) nanopowder was prepared by low-temperature aqueous synthesis (LTAS) method. The evolution of the structure and microstructure of the precursor precipitate, heated at temperatures up to 1000 degrees C was studied by TGA, FT-IR, SEM and XRD techniques. The dried precipitate showed a microstructure consisting of nano-sized grains (similar to 40 nm) with great tendency to agglomeration. BaTi0.87Sn0.13O3 single phase was obtained at 800 degrees C. The ceramics prepared from as-obtained BTS13 powders (60-70 nm) show good dielectric and ferroelectric characteristics. The dielectric constant was about 4800 and the dielectric loss (tan delta) was 0.229 at 1 kHz and at the Curie temperature (31 degrees C). The remanent polarization (P-r) and the coercive field (E-C) of Ba0.97Ho0.03TiO3 ceramics, at 1 kHz, were P-r = 13 mu C/cm(2) and E-C = 0.89 kV/cm. The ferroelectric parameters E-C and P-r decrease with increasing frequency in the domain 100 Hz to 10 kHz. (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.

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.

The corrosion inhibition of carbon steel in 1.0 mol L(-1) HCl in the presence of an antibacterial sulfa drug Sulfathiazole, IUPAC name 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide (TBSA) was investigated using mass loss and electrochemical measurements such as: potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). For the study of the surface morphology scanning electron spectroscopy (SEM) was used. The results showed that TBSA acts as a corrosion inhibitor in 1.0 mol L(-1) HCl solution by suppressing simultaneously the cathodic and anodic processes via adsorption on the carbon steel surface and that the inhibition efficiency increases with increasing concentration. XPS analysis revealed that the corrosion product consists of an oxyhydroxide/oxide mixture and that the iron oxyhydroxide proportion is higher than the iron oxide proportion.

Clean Si(001) single crystal surfaces provided different surface reconstructions: p(1 x 2) and c(n x 2) (n = 4, 6) at room temperature. The in situ oxidation of these surfaces was followed by Auger electron spectroscopy and by X-ray photoelectron spectroscopy. It is found that, in similar ultrahigh vacuum conditions, much faster contamination (about 500 times) occurs when the samples are investigated by AES than by XPS, owing to the interaction of the electron beam with the sample surface. With the sample subject to the AES investigation, the contamination occurs by forming >Si2C=O complexes based on the Si dimers. During XPS, reaction with water molecules from the residual gas should also be taken into account.

A new method, that involves Evanescent-Wave Cavity Ring-Down Spectroscopy (EW-CRDS), is presented. This method is useful for the study of thin films on optical solid surfaces. The new design of experimental set-up incorporates a semicylindrical prism with a plane surface where the Total Internal Reflection (TIR) effect appears. The antireflex (AR) coated cylindrical surface of the prism induces the stability of resonant cavity. The evanescent wave generated at the plane surface of the prism probes the absorption by matter in the vicinity of the prism. A general discussion of design criteria is presented to quantify intrinsic losses, and then absorption spectra for Rhodamine chloride R590 from 555 to 560 nm are presented to demonstrate the sensitivity of the system. The layer of R590 on BK7 surfaces is deposited from a solution of R590 in ethanol (92% purity) with 51 mg/l concentration. After vaporization of the ethanol the dye layer on surfaces is supposed to be uniform. This implementation of TIR surface in a resonant cavity provides a powerful new spectroscopic tool especially to angle-resolved diagnostic for interfaces and thin-films. The loss spectrum can be obtained for an angular range from the TIR critical angle to a maximum angle when the resonance of system is lost.

A highly durable and versatile micro scale biocatalytic reactor has been designed and investigated in the heterogeneous enzyme-catalytic oxidation of phenols. It consisted of optical or electron beam lithographic gold deposited layer with different thickness from nano- to micro-scale on a semiconductor surface. Horseradish peroxidase (H RP) enzyme was immobilized on the gold-surface using two different approaches (i.e., physical adsorption and self-assembled monolayer). Characterization of those HRP-gold surfaces was made using AFM (atomic force microscopy) coupled with ellipsometry measurements, SEM (scanning electron microscopy), STM (scanning tunneling microscopy) and spectrophotometric technique. The catalytic performances of the developed structures were investigated after their incorporation in microreactors using a recycling-flow system dedicated to phenols oxidation. In order to optimize the efficiency of the oxidation process it was checked the effect of the successively addition of the reagent, the influence of the reaction time, the stability and the reuse of the biocatalytic micro-system. Maximum phenol conversion was of 35.1%. In addition to phenol the system has also been investigated in oxidation of other phenolic compounds such as cathecol, hydroquinone, rezorcine, beta-naphtol, o/p-aminophenol and 4-metoxyphenol. (C) 2011 Elsevier B.V. All rights reserved.

The telomerization of 1,3-butadiene with homogeneous palladium/phosphine catalysts is an efficient method to transform biomass-based oxygenates into useful fine and bulk chemicals, e.g. surfaetants. Recovery and reuse of the expensive noble metal-based catalyst is highly desired for these systems and therefore a heterogeneous telomerization catalyst would be preferred. Layered double hydroxides (LDH) were investigated as supports for the heterogenization of the Pd/TPPTS (trisodium salt of 3, 3',3 ''-phosphanetriyl benzene sulfonic acid) telomerization catalyst. Turn over numbers (TONs) up to 1300 were obtained with heterogeneous (immobilized palladium and ligand) and pseudo-heterogeneous (immobilized ligand) catalysts in the telomerization of 1,3-butadiene with ethylene glycol (EG) and methanol (MeOH) under solvent- and base-free conditions; TONs are comparable to those obtained with the homogeneous catalysts under similar conditions. Importantly, the LDH support was found to induce a change in product selectivity. In addition to the expected C8 telomers, higher telomers with C16 or C24 chains were observed with rather high selectivities (up to 48% forEG and 77% for MeOH).

Clean Si(001) single crystal surfaces are obtained by cycles of long (30 mins.) annealings in ultrahigh vacuum (fairly below 1 x 10(-9) mbar). The surface reconstruction is investigated by low energy electron diffraction (LEED). This paper reports, in addition to the well-known p(2 x 1) reconstruction, the first observation of c(4 x 2) at room temperature and also the completely new c(6 x 2) reconstruction. The in situ oxidation of these surfaces was investigated by Auger electron spectroscopy (AES) and by X-ray photoelectron spectroscopy (XPS). It is found that, in similar ultrahigh vacuum conditions (6 x 10(-10) mbar), much faster contamination (about 500 times) occurs when the samples are investigated by AES than by XPS, owing mainly to the interaction of the electron beam with the sample surface. Also, much gentler surface bombardment with electrons, such as in LEED, still enhances sample oxidation. Therefore, XPS proves to be a much more convenient technique for non-destructive assessment of the surface composition. When the surface is subjected to the AES investigation, we found that the contamination occurs by forming >Si2C=O complexes based on the Si dimers.

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance. (C) 2011 Elsevier B.V. All rights reserved.