Publications

In the last years oxide materials for electronics show significant progress. However, many details regarding technology control of the properties have to be solved. For electronics, thin films and heterestructures are important taking advantage of integration and synergetic concepts leading to new types of devices and functionalities. It is notable that, while fabrication of new devices and materials showing new phenomena are booming, the growth principles and concepts are somehow developing slowly within this general trend. This is because in many cases, growth of materials is very personalized. Understanding of the bi-directional relationship between the general and particular principles deserves attention. The immediate benefit is that knowledge on growth for one material can be transferred to another one. In our work we have analyzed such relationships for some oxide multicomponent perovskites. Materials used in our examples are Bi-Sr-Ca-Cu-O and YBa2Cu3O7, (Ca, Sr)CuO2, (Ca, Ba)CuO2 and Bi4Ti3O12. Presented thin films or heterostructures are with c-axis and non-c-axis orientations and based on these examples we discuss some of the growth principles.

In this article, we present and discuss how the stress influences the trapping phenomena in both the bulk Si and nanostructures based on Si. For this, we use single crystal Si irradiated with 28 MeV iodine ions of fluence (5 +/- 0.5) x 10(11) ions/cm(2) and 2D Si based nanostructures of (nc-Si/CaF2)(50) multilayers. The method of thermally stimulated discharge currents without bias was employed to investigate the trapping phenomena and the modeling of the discharge current curves was carried out. In the case of irradiated Si, we have modeled the discharge currents considering six trapping levels and a supplementary stress electric field independent of temperature superposed on the frozen-in electric field produced by the charged traps at low temperature. The stress electric field is due to the stopped iodine ions which are heavier than those of Si host. Six traps are evidenced and their parameters are calculated. In the (nc-Si/CaF2)(50) multilayer structures, we experimentally evidenced traps which produce in the discharge current maxima with two shapes. Three maxima have normal shape and the others five maxima are narrow and sharp looking like spikes. We modeled the discharge current curves taking for the concentration a power temperature dependence law, and for the cross section a Gaussian temperature dependence.

This paper analyses and discusses the effect of Ge/Si atomic ratio and annealing temperature on the conduction mechanisms governing the electrical behavior of Ge-SiO2 films containing Ge nanoparticles embedded in amorphous SiO2 matrix. For this, the experimental conductance-temperature curves are modeled in correlation with the microstructure findings for two types of films. One type of films has a lower Ge/Si ratio of 0.73 and was obtained by magnetron sputtering followed by annealing in H-2, at 500 degrees C, while the second one has a higher ratio of 1.86 and was obtained also by sputtering, but was annealed in N-2, at 800 degrees C. Both types of films show an electrical behavior with a T-1/4 conductance dependence on temperature, typical for hopping mechanism.

The dispersion and the polar independent contributions to the surface free energy in the case of fused quartz plates were evaluated by contact angle measurements against a series of liquids like water, glycerol, ethylene glycol, dimethyl sulfoxide and a nematic mixture NP5 of azoxybenzene type compounds. The smooth fused quartz plates were thermally pretreated at 240 degrees C and 1000 degrees C to decrease the number of surface hydroxyl groups; their surface was characterized by X-ray photoelectron spectroscopy. The contact angle data were further processed applying either the approach of Owens-Wendt with geometric mean or the Wu's approach of harmonic mean of nonpolar and polar interactions. The liquids were chosen thus to fulfill Della Volpe and Siboni's criterion namely that these have the condition number of system matrix low enough. The values obtained for the components of surface free energy were discussed in comparison with the results obtained in literature for crystalline quartz or for other silica forms as bulk or films. The study has shown a decrease of the polar component of the surface tension by increase of the pretreatment temperature.

We report on the synthesis of advanced nanostructured hydroxyapatite (HA) thin films onto 3D titanium (Ti) mesh substrates by Pulsed Laser Deposition method. Morphological and structural investigations as well as pull-out tests proved the stoichiometric transfer of crystalline HA films along with their good adherence. In vivo tests were performed on 12 patients (six with simple Ti mesh, six with Ti mesh biofunctionalized with HA). The tomodensitometry analysis of the cranial control scans evidenced the process of osseogenesis. For four patients with implanted HA/Ti mesh structures, the modification of the value obtained on Hounsfield scale was observed at the level of implant, proving the progress of osseointegration. We conclude that the structures exhibit excellent bonding strength and functionality, and are suitable for neurosurgical applications.

This study aims to present the manufacture of polymer photonic crystals (PCs) and the study of the influence of PbS quantum dots on their optical properties. Monodisperse latexes resulting from the polymerization of styrene and acrylic acid were obtained by a soap-free emulsion copolymerization process and their optical response was modified using PbS high refractive index nanoparticles. A stop-band modulation was achieved by controlling the nanoparticles concentration that resulted in the altering of the self-assembly process. Thus, at low PbS concentrations, a blue-shift of the band-gap was registered, whereas at high concentrations, a red-shift was measured. The hybrid materials were investigated by DLS, SEM, HRTEM, UV-VIS and XRD analyses.

The presence and structure of paramagnetic point defects in C-13 and O-17 implanted ultrapure Si single-crystal material, two impurities which seem to play a major role in the detectors performance degradation and radiation resistance enhancement, respectively, are reported before and after irradiation with 6 MeV electrons. The investigation, performed by Q-band electron spin resonance spectroscopy in the 300 - 10 K temperature range, included also reference ultrapure and O-16 doped single-crystal Si-platelets. It resulted in the observation of points defects associated with lattice defects as dangling bonds and impurities.

Single crystal ZnO nanowires grown by pulsed laser deposition (PLD) and vapour-liquid-solid (VLS) technique respectively, were in-situ and ex-situ covered with additional ZnO shell layers. Luminescence investigation revealed significant luminescence spectra shift from UV to blue emission band of the obtained structures while changing the deposited shell layer film thickness. But with no monotone variation with the deposited film thicknesses. While the luminescence changes are generally considered as being determined by the ratio between core emission lines intensity and shell 'defects' lines intensity, the strongest changes in the photoluminescence spectra were obtained in our experiments for the nanometer order shell layer thicknesses. The comparison between luminescence results and luminescence studies on 50 nm ZnO nanoparticles clusterization, together with HRTEM investigations of the ZnO shell layer suggest that the nanoparticle-nanowire interface, respectively the coupling between the ZnO single crystal core and ZnO nanostructured shell layer, might play a significant role in the luminescence spectra changes.

A new green method for the synthesis of reduced graphene oxide-gold nanoparticle (rGO-AuNP) hybrids in aqueous solution that exploits the ability of ascorbic acid (AA) to operate as an effective dual agent for both graphene oxide (GO) and gold ion reduction is reported. Through careful investigation of the production of rGO-AuNP hybrids stabilized with polyvinylpyrrolidone (PVP), several versatile routes were devised with the aim of controlling the size, shape and distribution of AuNPs anchored onto the graphene sheets as well as the GO reduction. Particularly, when rGO is used as a platform for Au ion nucleation, a relative sparse distribution of AuNPs of size ranging from 20 nm to 50 nm is noticed. In contrast, when gold ions are added to the solution prior to any GO reduction, the density of large AuNPs is rather low relative to the uniformly packed small sized AuNPs (3-12 nm). The progress of GO reduction is explained by considering the contribution of the catalytic activity of AuNPs, besides the reducing activity of AA. Finally, a plausible mechanism for the nucleation and distribution of AuNPs onto the graphenic surface is assumed, highlighting the significance of oxygen moieties. The green method developed here is promising for the fabrication of gold-graphene nanocomposites with tunable surface "decoration", suitable for surface-enhanced Raman spectroscopy (SERS).

The aim of this study was to evaluate the biological properties of iron oxide nanoparticles (IO-NPs) obtained in the aqueous suspension. The iron oxide nanoparticles were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The biocompatibility of the iron oxide was demonstrated by the in vitro quantification of HeLa cells viability using propidium iodide (PI) and fluorescein diacetate (FdA) and the MTT colorimetric assay. The toxicity of small size iron oxide nanoparticles was also evaluated by means of histological examination on male Brown Norway rats after intraperitoneal injection. At the tested concentrations, the nanoparticles proved to be not cytotoxic on HeLa cells. The rat's behavior, as well as the histopathological aspect of liver, kidney, lung, and spleen tissues at 48 h after intraperitoneal injection did not present any modifications. The in vivo and in vitro assays suggested that the IO-NPs could be further used for developing new in vivo medical applications.