Publications

Low-loss dielectrics with various microstructure and, consequently, different extrinsic losses were investigated by using terahertz time-domain spectroscopy. The losses have been extrapolated and compared with those measured at microwave frequencies. The results showed that extrinsic factors have a considerably contribution in microwave domain. The intrinsic limit of dielectric loss of low absorption polycrystalline materials have been estimated by terahertz spectroscopy.

Mixed manganese iron oxides (Mn/Fe/O) as heterogeneous catalysts were prepared by hydrothermal treatment and citrate methods to be tested in the oxidation of p-xylene (PX) using as oxidation agent molecular oxygen, hydrogen peroxide, and tert-butyl hydroperoxide. Preparation of mixed Mn-Fe oxide by the citrate method releases materials with smaller particle size and lower degree of crystallinity as compared with the hydrothermal one, which further leads to a higher activity toward the oxidation of PX. A conversion of PX of 98% and a yield in p-toluic acid of 93% were obtained in the presence of Mn/Fe/O prepared by the citrate method using tert-butyl hydroperoxide as an oxidizing agent. (C) 2017 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Super paramagnetic iron oxide nanoparticles such as maghemite have been shown to exhibit antimicrobial properties [1-5]. Moreover, the iron oxide nanoparticles have been proposed as a potential magnetically controllable antimicrobial agent which could be directed to a specific infection [3-5]. The present research has focused on studies of the surface and structure of iron oxide dextran (D-IO) composite layers surface and structure. These composite layers were deposited on Si substrates. The structure of iron oxide dextran composite layers was investigated by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) while the surface morphology was evaluated by Scanning Electron Microscopy (SEM). The structural characterizations of the iron oxide dextran composite layers revealed the basic constituents of both iron and dextran structure. Furthermore, the in vitro evaluation of the antifungal effect of the complex layers, which have been shown revealed to be active against C. albicans cells at distinct intervals of time, is exhibited. Our research came to confirm the fungicidal effect of iron oxide dextran composite layers. Also, our results suggest that iron oxide dextran surface may be used for medical treatment of biofilm associated Candida infections.

This paper presents electric and electro-optic studies conducted on a new composite, namely hydroxypropylcellulose network with liquid crystal fillings. The composite was manufactured using the electrospinning method, and deposited on indium tin oxide glass. In terms of electric characterization, the samples were subjected to impedance spectroscopy, their equivalent circuit model was deduced, and the corresponding electric parameters were computed based on the Cole-Cole diagrams and frequency plots of the two impedance components. In terms of electro-optic studies, the optical transmission of the sample under a varying steady-state alternative regime voltage was recorded, and the saturation threshold field was determined. Also, the switching times of the sample with respect to a step signal were determined.

We studied the effect of short term furnace annealing over the photoconductive properties of tristacked layer i.e. TiO2/(SiGe/TiO2)(3). The structure was prepared by depositing alternate layers of TiO2 and SiGe films, using direct-current magnetron sputtering technique. A transmission electron microscopy and grazing incidence spectroscopy was used to analyze the morphology of the structure. Photoconductive properties were studied by measuring photocurrent spectra at different applied voltages and temperatures. Tristack layers were obtained with 5-10 nm SiGe nanocrystals (NCs) by annealing at 600 degrees C for 5 min. No sign of SiO2 formation was found inside stacked layers. A maximum in the photocurrent spectra was observed at 994 nm at 300 K but it red-shifted gradually to 1045 nm with decrease in temperature to 100 K. This transition in peak maxima is attributed to SiGe NCs, due to lattice vibration and to contribution of non-radiative recombination at low temperatures.

In the recent years a special attention has been granted to the generation and characterization of hydroxyapatite-polydimethylsiloxane layers especially due to their biomedical applications. In this context, in this paper, we analyzed the influence of X ray radiation delivered in medical dose on the morphological mid chemical structure of hydroxyapatite-polydimethylsiloxane layers deposited on Ti substrates. The damage effects produced by the ionizing radiation on the surface and structure of hydroxyapatite-polydimethylsiloxane layers were identified by Scanning Electron Microscopy (SEM) and Glow Discharge Optical Emission Spectroscopy (GDOES). The antibacterial activity of the irradiated and non irradiated samples was also evaluated.

The progress of nanotechnology made possible the use of nanomaterials as adsorbents and magnetic iron oxides represents one of the first generations of nanoscale materials used in environment technologies [1]. A systematic characterization of commercial magnetite (Fe3O4) is presented in this research. The commercial (Fe3O4) magnetic adsorbents were characterized by various characterizations methods such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX). This study was also focused on the study of adsorption isotherms and the kinetics evaluation. X-ray studies indicated that As3+ and Cu2+ removed by Fe3O4 did not seem to alter the structure of Fe3O4 but they were highlighted in the EDX analysis. In addition, the SEM studies were consistent with the XRD results. The rate of adsorption of contaminants, in contaminated solutions decreases when the amount of contaminant increases in all experiments performed. The results revealed that Fe3O4 nanoparticles are promising candidates which could be used as sorbents for the removal of arsenic from the marine environment, for site remediation and groundwater treatment.

The working life of a bearing depends on the aging characteristics of the lubricant. Aging produces physical, structural and rheological modifications in the grease that have rarely been studied from an overall stand-point. Also, analysis of used greases can be a valuable source of information on the mechanisms involved when a bearing is lubricated with grease. From this point of view, it is very useful to establish a few criteria for the grease life time, as follows: modification of the physical and chemical properties of the greases, modification of the rheological parameters, modification of the global electrical resistance of the grease film and modification of the microscopically grease structure and apparition of the wear particles. The paper proposes a comparative study of greases in the fresh state and after use in ball bearings, analysing the modification of the rheological and structural properties. The mechanical aging test was carried out on an experimental stand and the grease structure was studied using a scanning electron microscope. The rheological properties were studied on a cone and plate Brookfield viscometer.

Sodium dodecyl sulfate (SDS) effects at the electrified p- and n-GaAs(100)/H2SO4 interfaces were investigated by EIS, XPS and AFM. XPS data revealed that under the open circuit conditions, SDS adsorption on GaAs(100) results in a protective overlayer which prevents the further oxidation in air of both types of semiconductor surfaces. The dopant nature is, however, decisive for the way of bonding the surfactant molecule to the surface. At the p-doped substrate, SDS adsorbs mainly at As sites by its hydrocarbon tail and by the anion head to the Ga sites at the n-doped one. Although the surfactant behaves as a dipole under the applied potential control, the dopant type plays a key role in the SDS interaction with GaAs(100) electrodes too. EIS data evidenced that SDS interaction with n-GaAs(100) electrode brings a pronounced decrease of the capacitive contribution of the surface states and a shift of the flatband potential to less negative values, unlike the p-doped one, where no significant change in its electronic properties was observed. These results were rationalized in terms of surface states- and field-effects operating at the electrified interfaces under discussion. (C) The Author(s) 2017. Published by ECS.

GeSi NCs / TiO2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of TiO2 /(GeSi/TiO2)x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 degrees C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / TiO2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T-1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (similar to 770 and similar to 1060 nm).