National Institute Of Materials Physics - Romania

A multifrequency electron paramagnetic resonance (EPR) investigation of Nd3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (MF) 9.43 GHz, and at the 95, 190, and 285 GHz high frequencies was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective electron spin of one-half and to a tetragonal symmetry. For the magnetic field along the tetragonal axis, the g(-)factor and the hyperfine constant A of the lowest doublet of the ground multiplet decreases with frequency increase. For the magnetic field perpendicular to the tetragonal axis, the g(perpendicular to)-factor exhibits a small azimuthal angular dependence that increases with increasing the frequency due to the S-4 site symmetry. The azimuthal angular dependence allows to clearly distinguish between different local axial symmetries. These properties are interpreted as high field/frequency (HF) effects associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. We show that from the combined analysis of the multifrequency MF- and HF-EPR spectra and of the optical data, an accurate description of the ground multiplet of the Kramers rare earth ions in solid matrices can be derived.

Widely applicable nonaqueous solution routes have been employed for the syntheses of crystalline nanostructured tungsten oxide particles from a tungsten hexachloride precursor. Here, a systematic study on the crystallization and assembly behavior of tungsten oxide products made by using the bioligand deferoxamine mesylate (DFOM) (product I), the two chelating ligands hexadecyltrimethylammoniumbromide (CTAB) (II) and poly(alkylene oxide) block copolymer (Pluronic P123) (III) is presented. The mechanistic pathways for the material synthesis are also discussed in detail. The tungsten oxide nanomaterials and reaction solutions are characterized by Fourier transform IR, H-1, and C-13 NMR spectroscopies, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The indexing of the line pattern suggests WO3 is in its monoclinic structure with a=0.7297nm, b=0.7539nm, c=0.7688nm, and beta=90.91 degrees. The nanoparticles formed have various architectures, such as chromosomal shapes (product I) and slates (II), which are quite different from the mesoporous one (III) that has internal pores or mesopores ranging from 5 to 15 nm. The nanoparticles obtained from all the synthetic procedures are in the range of 40-60 nm. The investigation of the gas-sensing properties of these materials indicate that all the sensors have good baseline stability and the sensors fabricated from material III present very different response kinetics and different CO detection properties. The possibility of adjusting the morphology and by that tuning the gas-sensing properties makes the preparation strategies used interesting candidates for fabricating gas-sensing materials.

TiO2 nanopowders, doped with Fe3+ and Eu3+ were obtained by high-energy ball milling and their physical properties were investigated as a function of the doping content and ball milling time. A noticeable red shift and high photoactivity in the degradation and catalytic oxidation reactions of styrene and phenol were found for all doped specimens.

The X (9.8 GHz)-band electron paramagnetic resonance (EPR) properties of substitutional Mn2+ ions in high quality cubic ZnS single crystals grown from PbCl2 flux have been thoroughly investigated. Accurate spin Hamiltonian (SH) parameters: g = 2.002 25 +/- 0.000 06; a = (7.987 +/- 0.008) x 10(-4) cm(-1) and A = -(63.88 +/- 0.02) x 10(-4) cm(-1) were obtained by simulation and fitting to the experimentally allowed transitions recorded for the magnetic field aligned within +/- 0.25 degrees along the main crystal axes. The normally forbidden hyperfine M = + 1/2 <->-1/2, Delta m = +/- 1 transitions were also observed. Their position was found to be in agreement, within the experimental accuracy of Delta H = +/- 0.01 mT, with calculations using the same SH parameters. The angular variation of the ratios of the intensities of the central forbidden to the allowed transitions could be accounted for only by including an additional constant contribution. The observed line broadening of the M = +/- 1/2 <->+/- 3/2 and +/- 3/2 <->+/- 5/2 fine structure transitions and their line width variation in a (110) plane have been quantitatively described by considering a random distribution of lattice strains at the Mn2+ impurity ions. The influence of the forbidden transitions and line broadening on the EPR spectra line shape of the Mn2+ ions in cubic ZnS crystalline powders is also examined.

This paper presents the investigation of electrical properties of carbon nanotubes (CNT). A sandwich configuration, quartz substrate/Cr/Al/CNT (partially immersed in SiN)/Cr/Al was investigated. The CNT are mainly oriented parallel with the electrodes. Current - voltage characteristics were taken at 20 K and room temperature and a current - temperature characteristic was taken at constant voltage (20 mV). The I - V characteristics are almost linear, while the G - V characteristics present some peaks and dips, interpreted as voltage percolation thresholds. The I - T and R - T characteristics are also linear (except at low temperatures). The investigated structures have a high electrical polarizability.

We report the synthesis, by a surfactant-assisted liquid-liquid reaction, of nanocrystalline ZnS doped with 0.2 mol% Mn2+ ions self-assembled in a mesoporous structure. The XRD measurements demonstrate the formation of a sponge-like mesoporous material with a tight distribution of pores of 1.8 nm mean diameter built from cubic ZnS nanocrystals of 1.8 nm average size. TEM investigation confirms the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from nanocrystallites of cubic ZnS. The ordering effect of self-assembling, which is reflected in the tight size distribution of crystallites and pores, might be also responsible for the well resolved EPR spectra, attributed to the presence of three types of isolated Mn2+ paramagnetic centers. (C) 2008 Elsevier Ltd. All rights reserved.

The paper reports on the main findings issued from studying the formation of adsorbed micelle-like clusters of ionic surfactant (sodium dodecyl sulfate and hexadecyl trimethylammonium bromide) onto molecule of collagenous polypeptide (collagen hydrolyzates and calfskin collagen type 1). Capillary viscometry, UV-circular dichroism, transmission electron microscopy and surfactant titration method were used to characterize the macromolecular component of the studied systems. To highlight the critical aggregation concentration (cac) and the critical saturation concentration (T-2) in the investigated polypeptide-surfactant systems, the steady-state fluorescence of pyrene (1(1)/1(3) rule) and the surface tension measurements (the droplet volume method) were availed. The study revealed a significant decrease of the effective micelle concentration of surfactant (cue) in the presence of polypeptide irrespective of pH and a critical concentration T-2 depending on the system composition and pH.

The interactions by which ions lose their energy in silicon are investigated at the microscopic level. this theoretical study put in evidence that the ionization could also represent a source of structural defects, and, contrary to the processes initiated by elementary particles, could generate extended primary defects, as, e.g. four-fold coordinated defects, due to the simultaneous breaking of bond for more neighbouring atoms in the lattice in a single interaction, in the ionisation core. The average energy transferred per atom is calculated, and also the energy spent by ionisation. The time dependence of the temperature in the ionisation core is derived in some simplifying assumptions. These contributions not considered yet in the studies of degradation of silicon detectors in radiation fields and could account for the discrepancies observed between models and measurements at microscopic versus device level for hadrons and ions. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The aim of this study was to provide and characterize nanostructured TiO2 films for application in the depollution of the contaminated water against Escherichia coli (E. coli). The nanometric size of particles and the porosity of the films have been correlated with the technological parameters of the deposition process. For this aim three-layer TiO2 films were deposited by sol-gel and dip-coating method on SiO2/glass substrate. Iron (1 and 7%) and polyethylene glycol (PEG(600)) (0.014-0.110 M) were added to the coating solutions to study their effect on the porosity of the samples and respectively on the amorphous to anatase phase transition, as well as on the antibacterial activity. The samples were characterized using different complementary methods such as X-ray Diffraction (XRD), Spectroscopic Ellipsometry (SE), Atomic Force Microscopy (AFM), dynamics (growth and adherence) of E. coli development versus nanofilm composition (where the amount of bacterial inoculums used was closer to those Found in wasted waters). The obtained films have shown low toughness (values bellow 0.74 nm) and the particle size in nanometric range. The direct optical band gap values increases with the Fe content tip to 2.64 eV (470 nm), leading to an active photocatalyst tinder visible light (in our case under natural illumination condition). The inhibitory effect towards the E. Coli is Correlated with PEG and Fe concentration and was found to he the strongest for the sample containing 0.069 M PEG.