Publications

The 2,2'-bipyridine effects on iron monosulfide (FeS) oxidative dissolution rates have been examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The adsorption of 2,2'-bipyridine to synthetic FeS was investigated by batch adsorption experiments, SEM, energy-dispersive X-ray analysis and Raman spectroscopy. The experiments were performed in air-saturated solutions at pH 5, 25 degrees C and an ionic strength of I = 0.004 M NaCl. Correlation between oxidative dissolution rates and 2,2'-bipyridine adsorption suggests that FeS oxidative dissolution is the result of two antagonistic processes: (i) the inhibiting adsorption of 2,2'-bipyridine on mineral surface and (ii) the promoting effect of 2,2'-bipyridine on the iron dissolution from FeS surface. Copyright (C) 2014 John Wiley & Sons, Ltd.

The porous alumina (Al2O3) layer obtained at the interface between polydimethylsiloxane/hydrogen peroxide medium and aluminum substrate under charged and neutral species injection produced in negative corona discharges in air at atmospheric pressure is analyzed by different methods in this paper. The scanning electron microscopy investigations showed the uniform distribution of the pores formed in the alumina layer and their columnar structures. Both energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) measurements indicate that during the anodization process of the aluminum in the polydimethylsiloxane/hydrogen peroxide medium in corona discharge the incorporation of silicon in the structure of the alumina layer is possible.

The goal of this study was to synthetize and characterize a porous material based on tetraethyl orthosilicate (TEOS) coated hydroxyapatite (HApTh) after removal experiments of Pb2+ ions from aqueous solutions. In order to study the morphology and composition, the samples obtained after removal experiments of Pb2+ ions from aqueous solution with the initial Pb2+ ion concentrations of the aqueous solutions were 0.1g.L-1 (HApTh-50) and 0.9g.L-1 (HApTh-450) have been investigated by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). Removal experiments of Pb2+ ions were carried out in aqueous solutions with controlled concentration of Pb2+. After the removal experiment of Pb2+ ions from solutions, porous hydroxyapatite nanoparticles were transformed into HApTh-50 and HApTh-450 due to the adsorption of Pb2+ ions followed by a cation exchange reaction. The obtained results show that the porous HApTh nanopowders could be used for Pb2+ ions removal from aqueous solutions.

Oxide materials are becoming of increasing interest due to their large variety of physical properties such as dielectric, magnetism, superconductivity, conductivity, ferroelectricity, multiferroism, etc. In addition, interfacing oxides with other materials is conferring new or better device functionalities. The main physical properties of oxides interfaces and their impact on the electrical properties of interest for microelectronic applications are presented. Further on, this subchapter is also devoted to the investigation and understanding of interface effects observed in heterostructures containing linear (SiO2) and non-linear (ferroelectrics) dielectrics in combination with wide-band gap semiconductor materials (e.g. ZnO and SiC) with special emphasis on size effects, interface quality and the opportunity to control the emergent phenomena in Metal-Oxide-Semiconductor (MOS) and Metal-Ferroelectric-Semiconductor (MFS) materials systems.

A series of bis(imidazolium) salts with different mesogenic groups (cyanobiphenyl or cholesteryl) and their silver carbene complexes with Br- anion has been designed and prepared. The liquid crystalline behaviour of these ionic liquids and their corresponding silver-carbene complexes was investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The silver complexes are thermally stable on a broad temperature range with accessible transition temperatures close to ambient temperature. The compounds with cholesteryl groups show higher transition temperatures than the compounds possessing cyanobiphenyl mesogenic groups, but their thermal stability is limited by a slight decomposition before reaching the isotropic state. Interestingly, the bis(imidazolium) salt with two cyanobiphenyl groups at each side shows an enantiotropic nematic phase on a short range, being one of the few examples of ILC displaying nematic phase.

The results of the investigation of vanadium and its oxides based nanocomposite structures interaction with the water are brought in this paper. It was established, that at the non-contact interaction of the nanocomposite structures with the water, its activation occurs, which is revealed in a change in the sign of the redox potential of the water from the initial positive to the negative one. Besides, the activation effect is interconnected, i.e. the activation both of the water as well as of nanocomposite structures occurs. The observed effect is explained in the frame of the resonance interaction of the oscillating dipoles theory (the conductive clusters uniformly distributed in V2O5 dielectric matrix with the water molecule dipoles. On the basis of the experimental results, one can affirm that the vanadium and its oxides based nanocomposite structures are a biologic activators and can be used in a modern biomedicine.

We report on the synthesis by PLD of bioactive glass (BG) films onto ultra high molecular weight polyethylene acetabular cups, and their preliminarily characterization after immersion in simulated body fluid. Fourier Transform Infrared spectra evidenced the strong depolymerization of the BG coatings. Scanning Electron Microscopy evidenced that the typical PLD film surface was converted after soaking in SBF to a rough one consisting of acicular crystals. Energy Dispersive Spectroscopy analysis demonstrated a remarkable conservation of the targets stoichiometry. The functionalization of acetabular cups with BG films by PLD should allow for the fabrication of implant coatings with improved osteoinductive characteristics.

The interplay between magnetic properties and structure and interdifussion at interfaces is analyzed mainly by surface science methods and by core level spectroscopies (based on X-ray absorption XAS and X-ray photoelectron spectroscopy XPS) on model systems implying deposition of magnetic metals (Fe, Co, Sm) on usual semiconductors (Si, GaAs, InAs). The Chapters begins with a review of the core level spectroscopies and of derived techniques, such as X-ray photoelectron diffraction (XPD) from XPS and X-ray magnetic circular dichroism (XMCD) from XAS, together with a brief description of other surface science techniques employed, such as low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), magneto-optical Kerr effect (MOKE), and with some basics of the molecular beam epitaxy (MBE) method. The examples are organized in pairs, namely one analyzes comparatively (i) interfaces formed by Fe or by Sm on Si(001), (ii) by Fe on GaAs(001) and on InAs(001), (iii) and by Co on bare GaAs(011) and on GaAs(011) passivated with Sb, in order to outline how small changes of the nature of the metal deposited, of the substrate (though identical from the chemical point of view) and of its initial state may result in strong deviations concerning both the quality of structures obtained and their magnetic properties. For instance, it is shown that Sb/Si(001) yields better properties than Fe/Si(001), Fe/InAs(001) exhibits lower reactivity and enhanced Fe magnetic moments than Fe/GaAs(001), and that passivation with antimony of GaAs(011) substrates yields to a reduced As out-diffusion into the metal layer, yielding lower tetragonal distortion and enhanced Co magnetic moments.

The high intensity and high repetition rate of the European X-Ray Free Electron Laser, presently under construction in Hamburg, will require pixel sensors which can stand X-ray doses up to 1 GGy for 3 years of operation. Within the AGIPD Collaboration the Hamburg group has systematically studied X-ray damage in silicon sensors for the dose range between 1 kGy and 1 GGy using strip sensors and test structures fabricated on high-ohmic n-type silicon from four different vendors. The densities of oxide charges, interface traps and surface current as function of dose and annealing conditions have been determined. The results have been implemented in TCAD simulations, and the radiation performance of strip sensors and guard-ring structures has been simulated and compared to experimental results. Finally, with the help of detailed TCAD simulations, the layout and technological parameters of the AGIPD pixel sensor have been optimized. It is found that the optimization for silicon sensors exposed to high X-ray doses is significantly different from that for non-irradiated sensors, and that the specifications of the AGIPD sensor can be met. (C) 2013 Elsevier B.V. All rights reserved.

Thin films composed of graphene-based materials exhibit promising functional properties for the development of high-performance devices in a wealth of applications. However, there are significant technological challenges which force one to search for alternative pathways of materials production and deposition. This paper reports the deposition of graphene oxide (GO) flakes on quartz substrates by using the ultraviolet matrix-assisted pulsed laser evaporation (MAPLE) technique in vacuum or controlled nitrogen gas environment. Water, which is highly transparent to UV radiation, was used as matrix solvent for the preparation of the MAPLE targets. The results reveal that GO platelets can be successfully transferred by MAPLE technique. Besides, the GO material experiences a significant deoxygenating process during deposition, leading to the formation of reduced GO. Numerical simulations also show that the thickness of GO platelets highly influences the deposition process and the structure of the immobilized material. Thick enough aggregates can reach temperatures of thousands of degrees and undergo a large degradation in their structure.