Publications

The goal of this study was the creation of a model to understand how solute properties influence the structure of nearby water. To this end, we used a two-dimensional cellular automaton model of aqueous solutions. The probabilities of translocation of water and solute molecules to occupy nearby sites, and their momentary distributions (including that of vacancies), are considered indicative of solute molecular mechanics and hydrophatic character, and are reflected in water molecules packing, i.e. 'organization'. We found that in the presence of hydrophilic solutes the fraction of water molecules with fewer neighbors was dominant, and inverse-proportionally dependent on their relative concentration. Hydrophobic molecules induced water organization, but this effect was countered by their own flexibility. These results show the emergence of cooperative effects in the manner the molecular milieu affects local organization of water, and suggests a mechanism through which molecular mechanics and crowding add a defining contribution to the way the solute impacts on nearby water.

We present the preparation, structure and physical properties of CoNb2O6 ceramics using spark plasma sintering technique. Magnetic data reveal the two antiferromagnetic transitions at 2.9 and 2 K. Microwave measurements gives epsilon(r) = 23.5 and a loss tangent of 29x10(-3).

Two series of icosahedral Al(100-x-y)Mn(x)Ln(y) alloys, first consisting of AlMnCe with variable Ce (x = 6 and y = 1, 2, 3, 4: Al93Mn6Ce, Al92Mn6Ce2, Al91Mn6Ce3, and Al90Mn6Ce4) or Mn (x = 8, 10; y = 1: Al89Mn10Ce and Al91Mn8Ce) concentration, and the second consisting of constant alloy composition (Al(91)Mn(6)Ln(3)), while varying the Ln nature (Gd, Dy, and Ho) were prepared. The icosahedral structure of the samples was confirmed by X-ray diffraction (XRD). As shown by EXAFS, the sample Al89Mn10Ce, with the lowest Ce/Mn ratio, display an advanced degree of disorder around the Ce atoms in the structure. Catalytic behavior highly depended on the alloys structure, the higher the degree of disorder around the rare-earth element in the structure, the higher catalytic activity. Replacing Ce with Gd, Dy or Ho in AlMnLn alloys does not result in a significant enhancement of the catalytic performances.

Embedding silver (Ag) into CaPs one could expect the enhancement of the antimicrobial performances of coatings for load bearing implants. The aim of this research was to evaluate whether the cellular morphology is influenced by the variation of Ag content, as well as by the solubility and morphological features of Ag-containing CaP coatings obtained by combinatorial pulsed laser deposition technique. In this view, we developed compositional libraries of either Ag and hydroxyapatite (HA) or Ag and beta-tricalcium phosphate (beta-TCP). The Ag content along the length of the combinatorial CaP coatings increased up to a maximum of similar to 1 at.%. SEM and AFM images evidenced the abundant presence of particulates typical for CaP coatings deposited by PLD. AFM histograms showed that the samples were rough with RMS values within 61-209 nm range. Ag content values up to 0.6 at. % into HA coatings were found nontoxic for mesenchymal stem cell (MSC) growth.

We have obtained by Spark Plasma Sintering (SPS), dense samples of MgB2 added with Ho2O3. Starting composition was (MgB2)(0.975)(HoO1.5)(0.025) and we used addition powders with an average particle size below and above 100 nm. For Mg, pristine and added MgB2 samples we measured potentiodynamic polarization curves in Phosphate Buffered Saline (PBS) solution media at room temperature. MgB2 based composites show corrosion/degradation effects. This behavior is in principle similar to Mg based alloys in the same media. Our work suggests that the different morphologies and phase compositions of the SPS-ed samples influence the interaction with corrosion medium; hence additions can play an important role in controlling the corrosion rate. Pristine MgB2 show a significant improvement of the corrosion resistance, if compared with Mg. The best corrosion resistance is obtained for pristine MgB2, followed by MgB2 with nano-Ho2O3 and mu-Ho2O3 additions.

In this manuscript we present interesting scientific results following the physical characterization of thin polyaniline polymer films achieved by means of Glancing Angle Deposition (GLAD) method. Aniline monomer was used as precursor in a cold plasma polymerization chamber and the resulting thin films were investigated by various physical techniques (Atomic Force Microscopy - AFM and Scanning Electron Microscopy - SEM), while also considering their conductive electrical properties.

N-type P-doped silicon single crystals with resistivity higher than 8000 Omega cm were irradiated with I-127(6+) ions of 28 MeV kinetic energy. The penetration of the ions through the target and the processes of energy loss were simulated using the CTRIM Monte Carlo code, and point defect production was calculated in the frame of our diffusion-reaction model. Trapping phenomena were investigated using the method of thermally stimulated currents without applied bias. The modeling of the current-temperature curves takes into consideration both point defects and stress-type trapping centers, produced by the ions stopped into the crystal.

Mossbauer spectroscopy has (one of its most important features) the ability to simultaneously undertake bulk and surface analyses. It is a non-destructive technique that can be applied in situ to investigate surfaces of varying thickness using the secondary radiation emitted after resonant absorption of a gamma ray. A short description of the technique is presented. It allows a detailed analysis of the chemical state of Mossbauer atoms within the material, including valence state and chemical compound. Some applications of electron Mossbauer spectroscopy (CEMS), obtained in National Institute of Materials Physics are given. The experimental devices for surface studies are presented.

Improvements in automatic processing of movie frames taken on commercial Drop Shape Analysis systems are presented, regarding the use of particular edge detection algorithms that account for optical peculiarities of the drop image formed on digital video camera sensors. These improvements can lead to better measurements of contact angles for drop images that present spots of reflected light close to edge and in the case of very low contact angles.

This paper reports on the conduction mechanisms in amorphous SiO2 films with embedded Ge nanoparticles. For this, measurements of current-temperature and current-voltage were employed and correlated with the microstructure results obtained from transmission electron microscopy (TEM). TEM images reveal that our films contain big Ge nanoparticles with low density and small Ge nanoparticles with high density, the last ones being the only responsible for the electrical transport. Two transport mechanisms were found at low and high temperature respectively, namely hopping on localized states in a band near Fermi level and charge excitation to the extended states at mobility edge.