National Institute Of Materials Physics - Romania

The research describes the synthesis, optical, photocatalytic, electrochemical and photoelectrocatalytical properties of highly defected, low surface area, tubular SiO2. High surface density of light-absorbing defects is obtained by conducting the synthesis at low temperature (0 degrees C) and by optimizing the ratios between reactants. The calcined tubular SiO2 is characterized by intense and broad absorption band centered at approximate to 320 nm, spanning from deep UV to green. The formation of Si3+ surface defects by calcination is accompanied by a substantial intensification of light absorbing characteristics. The annealing leads also to appearance of intense photoluminescence bands centered at around 433 and 533 nm for excitation wavelengths 320-380 nm. The photocatalytic generation of H-2 and CO2 from water-methanol mixture under solar (AM 1.5) and visible (lambda > 390 nm) irradiation is performed to probe the capability of light-absorbing defects of SiO2 to work as active sites and to gather indirect information on nature of active sites. The electrochemical and photoelectrochemical activity of tubular SiO2 are highlighted by employing [Ru(bpy)(3)]Cl-2 complex as electron transfer witness. According to our results, highly defected nanotubular SiO2 exhibit uncommon optical, light harvesting, electronic and electrochemical properties with great potential for practical applications in numerous fields. (C) 2016 Elsevier B.V. All rights reserved.

Synthetic physiological fluids are currently used as a first in vitro bioactivity assessment for bone grafts. Our understanding about the interactions taking place at the fluid-implant interface has evolved remarkably during the last decade, and does not comply with the traditional International Organization for Standardization/final draft International Standard 23317 protocol in purely inorganic simulated body fluid. The advances in our knowledge point to the need of a true paradigm shift toward testing physiological fluids with enhanced biomimicry and a better understanding of the materials' structure-dissolution behavior. This will contribute to "upgrade" our vision of entire cascades of events taking place at the implant surfaces upon immersion in the testing media or after implantation. Starting from an osteoinductive bioglass composition with the ability to alleviate the oxidative stress, thin bioglass films with different degrees of polymerization were deposited onto titanium substrates. Their biomineralization activity in simulated body fluid and in a series of new inorganic-organic media with increasing biomimicry that more closely simulated the human intercellular environment was compared. A comprehensive range of advanced characterization tools (scanning electron microscopy; grazing-incidence X-ray diffraction; Fourier-transform infrared, micro-Raman, energy-dispersive, X-ray photoelectron, and surface-enhanced laser desorption/ionization time-of-flight mass spectroscopies; and cytocompatibility assays using mesenchymal stem cells) were used. The information gathered is very useful to biologists, biophysicists, clinicians, and material scientists with special interest in teaching and research. By combining all the analyses, we propose herein a step forward toward establishing an improved unified protocol for testing the bioactivity of implant materials.

This contribution is a review of recent aspects connected with photoelectron spectroscopy of free ferroelectric surfaces, metals interfaced with these surfaces, graphene-like layers together with some exemplifications concerning molecular adsorption, dissociations and desorptions occurring from ferroelectrics. Standard photoelectron spectroscopy is used nowadays in correlation with other characterization techniques, such as piezoresponse force microscopy, high resolution transmission electron spectroscopy, and ferroelectric hysteresis cycles. In this work we will concentrate mainly on photoelectron spectroscopy and spectro-microscopy characterization of ferroelectric thin films, starting from atomically clean ferroelectric surfaces of lead zirco-titanate, then going towards heterostructures using this material in combination with graphene-like carbon layers or with metals. Concepts involving charge accumulation and depolarization near surface will be revisited by taking into account the newest findings in this area.

Iron and nitrogen doped TiO2 nanoparticles were synthesized and investigated with the aim to obtain photocatalytic systems with enhanced visible light efficiency. In a first step, commercially available Degussa P25 was impregnated with iron (0.3, 0.5, and 1 at. %) and nitrogen under hydrothermal conditions. In the second step, Fe-N doped TiO2 was synthesized by a hydrothermal route starting with TiCl3, FeCl3 center dot 6H(2)O and Urea, at 200 degrees C for 2 h. All samples were post annealed at 400 degrees C for 2h. The X-ray diffraction (XRD) revealed a two phase nanoscaled composition (Anatase and Rutile) of Degussa P25 and a single phase-nanoscaled Anatase content of the hydrothermally synthesized (1at.%) Fe-N doped TiO2 sample. The presence of Fe and nitrogen in samples was confirmed by Mossbauer and X-ray photoelectron spectroscopy measurements (XPS). Transmission electron microscopy (TEM) revealed the structure, particle dimension and morphology. The photocatalytic measurements (based on degradation of Methylene Blue) evidenced the most efficient composition in TiO2 Degussa P25 series as corresponding to 1 at.% Fe, in both UV and visible spectrum. At the same time, the hydrothermal synthesized sample (1at.%) Fe-N doped TiO2 exhibits the best activity in visible spectral region. The nanoscaled systems were synthesized in view of tests on textile materials.

Capacitance-voltage (C-V) hysteresis of metal-ferroelectric-semiconductor (MFS) structure based on a-In2GaZnO5.5 and Pb0.2Zr0.8TiO3 layers are recorded in the 350-470 K range. The structure is grown on FTO/glass to obtain a transparent MFS. The memory functionality of the heterostructure is proved through C-V and P-V characteristics. The memory window is dependent on the temperature, the largest value of 2.5 V being obtained at 470 K, where the contribution of the ferroelectric-semiconductor interface defect states is minimized. The direction of C-V hysteresis is clockwise at 350 K, and it turns counterclockwise at higher temperatures where the ferroelectric polarization has the main contribution.

We report on the selection by combinatorial pulsed laser deposition of Silver-doped Carbon structures with reliable physical-chemical characteristics and high efficiency against microbial biofilms. The investigation of the films was performed by scanning electron microscopy, high resolution atomic force microscopy, energy dispersive X-Ray Spectroscopy, X-ray diffraction, Raman spectroscopy, bonding strength "pull-out" tests, and surface energy measurements. In vitro biological assays were carried out using a large spectrum of bacterial and fungal strains, i.e., Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Enterococcus faecalis and Candida albicans. The biocompatibility of the films obtained was evaluated on MG63 mammalian cell cultures. The optimal combination with reasonable physical-chemical properties, efficient protection against microbial colonization and beneficial effects on human cells was found for Silver-doped Carbon films containing 2 to 7 at.% silver. These mixtures can be used to fabricate safe and efficient coatings of metallic implants, with the goal to decrease the risk of implant associated biofilm infections which are difficult to treat and often responsible for implant failure. (C) 2016 Elsevier B.V. All rights reserved.

Be/W and W/Be bilayers, of interest in regard to the specific behavior of plasma facing components (PFCs) were deposited on Si substrates by thermionic vacuum arc, with Fe, Fe-Cr and Fe-Cr-Al interlayers. The interlayers, with compositions approaching the one of the reduced activation steels used in supporting PFCs, were subsequently annealed in hydrogen atmosphere. The multilayers were characterized with respect to morphologic, structural, diffusional and atomic intermixing aspects via XRD, XRR, X-ray photoemission spectroscopy and Mossbauer spectroscopy. All as-prepared samples present partially amorphous structures. A main alpha-Fe phase is observed, as well as (superparamagnetic) secondary Fe oxides, metallic Fe with Si, Cr, W and Be neighbors, Be-rich Fe-Be and Fe-Si phases. High amounts of tungsten and tungsten oxides were also evidenced in the Fe layer. The strong atomic intermixing of W and Be layers was indirectly supported by the unusual densities of Wand Be layers and Fe-57 Mossbauer spectroscopy results. (C) 2016 Elsevier B.V. All rights reserved.

We report the evolution of structural, dielectric, ferroelectric and ferromagnetic properties in novel (Pb1 - 3x/2Ndx) (Ti0.98 - yFeyMn0.02)O-3 perovskite ceramics (x = 0.08, 0 < y < 0.05). We found room-temperature ferroelectric polarization and ferromagnetism for higher amount of iron ions(y >= 0.04). The paraelectric-ferroelectric phase transition occurred between 650 and 670 K for 0 <= y <= 0.05. Ferromagnetic hysteresis was measured at different temperatures on samples with y >= 0.04. Detailed structural analysis evidenced the variation of unit cell parameters with y increasing, confirming the substitution of the iron element in the lattice. Fe-57 Mtissbauer spectroscopy evidenced that iron ions occupy Ti positions in the perovskite lattice, with the oxidation state Fe3+ and two coordination types. X-ray photoelectron spectroscopy confirmed the presence of iron only as Fe3+ and, moreover, evidenced the presence of a substantial amount of Ti3+ ions in the structure. The presence of both Fe3+ (spin 5/2) in different coordinations as well as Ti3+ (spin 1/2) magnetic ions in B-site positions drives the occurrence of magnetic properties from low temperature to above room temperature, through superexchange Fe3+-O-Fe3+, Fe3+-O-Ti3+ and Ti3+-O-Ti3+ interactions. The finding of coexistent ferroelectric and ferromagnetic properties in these compounds ground the route to facile synthesis of multiferroics by simply doping a classical perovskite ferroelectric material like PbTiO3 with an adequate amount of transition magnetic ions. (C) 2016 Elsevier Ltd. All rights reserved.

We investigate band bending effects occurring at the interface between atomically clean Ge(001) and molecular beam epitaxy (MBE) deposited copper and platinum. Low energy electron diffraction(LEED) confirmed the crystallinity of the surface, evidenced the formation of (2 x 1) and (1 x 2) reconstructions, and revealed that it is strongly affected with metal deposition. X-ray photoelectron spectroscopy (XPS) data let us assume a Stranski-Krastanov growth mechanism and confirmed that the observed band bending is associated to an ohmic contact in both cases. For the platinum contact, the high values of the apparent inelastic mean free path (IMFP) derived from the evolution of the XPS intensities indicate a prevalence of mixture of Pt with Ge nearby the interface. Pt deposited on Ge(001) does not behave like a Schottky contact, as one may have expected due to the higher work function of platinum. The observed effect is similar to the ease where interfacial Pt had a lower work function by 2.25/1.96 eV than that of metallic Pt. We propose a model to explain this fact by the effective mass variation or to the conduction band broadening due to the strong intermixing of platinum with germanium under the surface. (C) 2016 Elsevier B.V. All rights reserved.