National Institute Of Materials Physics - Romania

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.

Barium titanate (BaTiO3) has been doped in situ with 5 mol% thulium by a sol-gel method. The as-prepared gel powder consists of nanosized grains (20-30 nm) and crystallizes on the cubic BaTiO3 lattice, at 700 degrees C. Ba0.95Tm0.05TiO3 ceramics derived from this powder have tetragonal perovskite structure and contain a small amount of Tm2Ti2O7 pyrochlore phase. These ceramics exhibit dielectric constants of 4282-3240 and dielectric loss (tan delta) of 0.1077-0.0161 at Curie temperature T-c=132 degrees C and at 10 Hz-100 kHz, respectively. For a drive voltage of 400 V, the hysteresis loop recorded at the frequency of 100 Hz shows a remnant polarization (P-r) value of 76 mu C/cm2 and a coercive field (E-c) of 124 V and for 1 kHz a remnant polarization (P-r) value of 58 mu C/cm2 and a coercive field (E-c) of 116 V.

Transmission electron microscopy and X-ray photoelectron spectroscopy analyses are performed to investigate Ge nanoparticles embedded in an amorphous SiO2 matrix. GeSiO thin films are prepared by two methods, sol-gel and radio frequency magnetron sputtering. After the deposition, the sol-gel films are annealed in either N-2 (at 1 atm and 800 A degrees C) or H-2 (at 2 atm and 500 A degrees C), and the sputtered films in H-2 (at 2 atm and 500 A degrees C), to allow Ge segregation. Amorphous Ge-rich nanoparticles (3-7 nm size) are observed in sol-gel films. Crystalline Ge nanoparticles in the high pressure tetragonal phase (10-50 nm size) are identified in the sputtered films. The size of the nanoparticles increases with Ge concentration in the volume of the film. At the film surface, the Ge concentration is much larger that in the volume for both sol-gel and sputtered films. At the same time, at the film surface, only oxidized Ge is observed.

Yttria doped ceria reinforced with yttria doped alumina compound for IT-SOFC applications has been prepared by sol-gel method and sintered at 1300 degrees C, 1400 degrees C, 1500 degrees C. XRD, and SEM show the presence of a needle-like cerium-magnetoplumbite (CeAl11O17) phase in the compound; the oxygen deficient phase grows from the alumina phase by using ceria from the surrounding matrix and releasing oxygen ions As the sintering temperature is increased, the alumina phase is gradually transformed into CeAl11O17. Compared to the yttria doped ceria without reinforcement, the obtained compounds with ceria-magnetoplumbite show only a slight decrease of the Young elasticity modulus. However, the samples become brittle after backing in oxygen atmosphere (1000 degrees C, and 1500 degrees C).

Effect of an antibacterial drug, sulfacetamide, IUPAC name N-[(4-aminophenyl) sulfonyl] acetamide (APSA) on the corrosion of carbon steel in 1.0 M HCl solution has been investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and XPS analysis. The electrochemical measurements indicated that the presence of APSA in 1.0 M HCl solution decreases the corrosion current (i(corr)) and increases the polarization rezistance (R-p). XPS surface analysis showed at this stage, in the absence of APSA, that the main product of corrosion is a non-stoichiometric Fe3+ oxide/oxide-hydroxide, consisting of a mixture of Fe2O3 and FeO(OH), where FeO(OH) is the main phase. Moreover, in presence of inhibitor the surface layer consists of FeO(OH) rather than pure oxide, adsorbed molecules of sulfacetamide and inorganic compounds such as: sulfides, carbonates, sulphates, nitrates, which were obtained by electrochemical degradation of APSA. UV-Vis spectrophotometry and HPLC technique were performed to determine the medium composition before and after corrosion. The results showed a decrease of the inhibitor concentration in 1.0 M HCl solution after carbon steel corrosion, indicating an adsorption process between organic compound molecules from aqueous phase and the electrode surface and/or the electrochemical degradation of APSA.

This paper presents the very first surface physics experiment performed in ultrahigh vacuum (UHV) in Romania, using a new molecular beam epitaxy (MBE) installation. Cleaning of a Si(001) wafer was achieved by using a very simple technique: sequences of annealing at 900-1000 degrees C in ultrahigh vacuum: low 10(-8) mbar, with a base pressure of 1.5 x 10(-10) mbar. The preparation procedure is quite reproducible and allows repeated cleaning of the Si(001) after contamination in ultrahigh vacuum. The Si(001) single crystal surface is characterized by low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), and Auger electron spectroscopy (AES). The latter technique is utilized in order to investigate the sample contamination by the residual gas in the UHV chamber, as determined by a residual gas analyzer (RGA). Unambiguous assignment of oxidized and unoxidized silicon is provided; also, an important feature is that the LVV Auger peak at 90-92 eV cannot be solely attributed to clean Si (i.e. Si surrounded only by Si), but also to silicon atoms bounded with carbon. Even with a sum of partial pressures of oxygen and carbon containing molecules in the range of 5 x 10(-10) mbar, the sample is contaminated very quickly, having a (1/e) lifetime of about 76 minutes.

Ultrathin ferromagnetic Fe layers on Si(001) have recently been synthesized using the molecular beam epitaxy (MBE) technique, and their structural and magnetic properties, as well as their interface reactivity have been investigated. The study was undertaken as function of the amount of Fe deposited and of substrate temperature. The interface reactivity was characterized by Auger electron spectroscopy (AES). The surface structure was characterized by low-energy electron diffraction (LEED). The magnetism was investigated by magneto-optical Kerr effect (MOKE). A higher deposition temperature stabilizes a better surface ordering, but it also enhances Fe and Si interdiffusion and it therefore decreases the magnetism. Despite the rapid disappearance of the long range order with Fe deposition at room temperature, the material exhibits a significant uniaxial in-plane magnetic anisotropy. For the Fe deposition performed at high temperature (500 degrees C), a weak ferromagnetism is still observed, with saturation magnetization of about 10 % of the value obtained previously. MOKE studies allowed inferring the main properties of the distinct formed layers.