Publications

The thermal stability of two amino acid-(tyrosine and tryptophan) coated magnetite and their corresponding precursors, [Fe-2(III) Fe-II(Tyr)(8)]center dot 9H(2)O and [(Fe2FeII)-Fe-III(Trp)(2)(OH)(4)](NO3)(2)center dot 8H2O (where tyrosine=Tyr and tryptophan=Trp), was analyzed in comparison with free amino acids. The complexes present a lower thermal stability relative to the free ligand, due to the catalytic effect introduced by the iron cation and the presence of NO3- groups. The presence of NO3- group determines also a different degradation's stoichiometry of the amino acid anion comparative with the one expressed by the free ligand molecule. The amino acid bonded to magnetite decomposes in two steps, its presence inducing an increasing of gamma-Fe2O3-->alpha Fe2O3 conversion temperature.

Intercalated PbI2 compounds were prepared by exposing crystalline films and crystalline powders of lead iodide to pyridine or iodine vapor at room temperature. Correlated studies of optical absorption, Raman scattering and low temperature photoluminescence (PL) reveal different properties in comparison with those of pure crystalline PbI2 powder. Depending of the nature of intercalated molecules (organic or inorganic) the basic semiconducting properties of PbI2 are dramatically modified. The main signature of iodine intercalated PbI2 consists in a luminescence band peaking at 2.24 eV appearing at 77 K under 350 nm excitation light. In the case of pyridine intercalated PbI2 a new intense band at about 3.3 eV in the absorption spectrum is observed. The the PL spectra of pyridine intercalated PbI2 at 77 K change substantially when the excitation wavelength. The Raman spectra confirm the presence of pyridine between the PbI2 layers.

PbZrO3 powders have been prepared by an alkoxide-based sol-gel route, starting from lead acetate, zirconium n-butoxide, and n-butanol as a solvent, and hydrolysed with different amounts of water in neutral and alkaline medium. The local environment of Zr and Pb atoms was pursued from the sol to the dried (150 degrees C) and heated (400 degrees C) powders, by extended x-ray absorption fine structure (EXAFS). The analysis of the sol revealed links between Pb and Zr, and even more links between Zr and Zr. The metal neighbourhoods in the dried powders are not influenced by the hydrolysis conditions. Pb-Zr correlations are gradually lost from the sol to the dried and heated powders, while the loss of Zr-Zr correlations is considerably lower.

in the last decade, considerable research effort was directed to the deposition of multilayer films with layer thicknesses in the nanometer range (superlattice coatings), in order to increase the performance of various cutting tools and machine parts. The goal of the present work was to investigate the main microstructural, mechanical and wear resistance characteristics of a superlattice coating, consisting of alternate multilayer ZrN/TiAIN films, with various bilayer periods (5 divided by 20 nm). The coatings were deposited by the cathodic arc method on Si, plain carbon steel and high speed steel substrates to be used as wear resistance surfaces. The multilayer structures were prepared by using shutters placed in front of each cathode (Zr and Ti + Al). The characteristics of multilayer structures (elemental and phase composition, texture, Vickers microhardness, thickness, adhesion, and wear resistance) were determined by using various techniques (AES, XPS, XRD, microhardness measurements, scratch, and tribological tests). A comparison with the properties of ZrN and TiAIN single-layer coatings was carried out.

The effect of ammonium polymolybdate (APM) on the corrosion of carbon steel in a solution of 1 M HCl was studied by weight loss and Mossbauer spectrometry. Inhibition efficiencies (P) have been obtained from weight measurement. The inhibition efficiencies increased with increase APM concentration. Mossbauer spectrometry shows that a superficial compound is formed on the electrode surface as a result of corrosion. (c) 2007 Elsevier B.V. All rights reserved.

This work describes the preparation of HfO2. thin films by the sol-gel method, starting with different precursors such as hafnium ethoxide, hafnium 2,4-pentadionate and hafnium chloride. From the solution prepared as mentioned above, thin films on silicon wafer substrates have been realized by 'dip-coating' with a pulling out speed of 5 cm min(-1). The films densification was achieved by thermal treatment for 10 min at 100 degrees C and 30 min at 450 degrees C or 600 degrees C, with a heating rate of 1 degrees C min(-1). The structural and optical properties of the films are determined employing spectroellipsometric (SE) measurements in the visible range (0.4-0.7 mu m), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The main objective of this paper was to establish a correlation between the method of preparation (precursor, annealing temperature) and the properties of the obtained films. The samples prepared from pentadionate and ethoxide precursors are homogenous and uniform in thickness. The samples prepared starting from chloride precursor are thicker and proved to be less uniform in thickness. Higher non-uniformity develops in multi-deposition films or in crystallized films. A nano-porosity is present in the quasi-amorphous films as well in the crystallized one. For the samples deposited on silicon wafer, the thermal treatment induced the formation of a SiO2 layer at the coating-substrate interface. (C) 2007 Elsevier B.V. All rights reserved.

The mixed oxide system 0.1SnO(2)-0-9 alpha-Fe2O3 (Sn1) was synthesized using the hydrothermal method and characterized using X-ray diffraction (XRD), Mossbauer spectroscopy and transmission electron microscopy (TEM). Sensing properties in both CH4 and CO were recorded as a function of temperature, humidity and concentration. The results were compared with those obtained for SnO2 (Sn10). It has been observed that Sn1 displays superior stability and sensitivity for methane as compared to Sn10. For both Sn1 and Sn10, the sensitivity to methane and carbon monoxide is influenced by temperature. In contradistinction to Sn10, Sn1 presents a reduced sensitivity to water vapors. A model based on the simultaneous evaluation of the electrical resistance and workfunction was elaborated to describe the selectivity of Sn1. (c) 2007 Elsevier B.V. All rights reserved.

The temperature dependence of the ferroelectric hysteresis and capacitance in PbZrO3 epitaxial films with (120)(O) and (001)(O) orientations was investigated in the 4.2-400 K temperature range. It was found that the films with (120)(O) orientation show a mixture of ferroelectric and antiferroelectric phases on the entire temperature range up to room temperature, with the ferroelectric phase more stable at low temperatures. Above room temperature the (120)(O) oriented films seem to behave only as an antiferroelectric material. By contrast, films with (001)(O) orientation show only ferroelectric behavior up to a temperature of about 60 K when the single hysteresis loop splits into a double loop characteristic for antiferroelectrics. Above this temperature the (001)(O) oriented films show only antiferroelectric behavior up to 400 K. The temperature dependence of capacitance and loss tangent clearly shows a maximum at around 16 K in the case of the (001)(O) oriented film. This might be associated with a low temperature ferroelectric-antiferroelectric phase transition. However, this transition is not visible in the (120)(O) oriented films. (C) 2008 American Institute of Physics.

This work reports on recently investigated structural and magnetic properties of three FexOy-SiO2 nanocomposites prepared by the alkoxide route of the sol-gel method. Depending on the presence or absence of catalyst and on its nature (acidic or basic), important differences among the samples have been observed from the point of view of their structure and properties. (c) 2007 Elsevier B.V. All rights reserved.

The capacitance of PbZrO(3)-Pb(Zr(0.8)TiO(0.2))O(3) epitaxial multilayers is significantly enhanced as the number of interfaces increases at the same total thickness of the structure. A possible explanation for this enhancement can be the increase of the dielectric susceptibility due to the presence of some interfacial polarization related, for instance, to trapped charges at the multilayer interfaces. The presented results suggest that capacitance tuning is achievable in antiferroelectric-ferroelectric epitaxial multilayers.