National Institute Of Materials Physics - Romania

Tungsten trioxide (WO3) thin films were grown by pulsed laser deposition (PLD) with the aim to be applied in gas sensors. The films were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and profilometry. To study the gas sensing behavior of these WO3 films, they were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was applied to analyze their gas sensitivity. Synthesis of tetragonal-WO3 films starting from a target with predominantly monoclinic WO3 phase was observed. The films deposited at 300 degrees C presented a surface topology favorable for the sorption properties, consisting of a film matrix with protruding craters/cavities. QCM prototype sensors with such films were tested for NO2 sensing. The PLD grown WO3 thin films show good sensitivity and fast reaction at room temperature, even in as-deposited state. With the presented technology, the manufacturing of QCM gas sensors is simple, fast and cost-effective, and it is also suitable for energy-effective portable equipment for on-line monitoring of environmental changes. (C) 2017 Elsevier B.V. All rights reserved.

A hysteresis loop with three polarization states is obtained in the case of a symmetric epitaxial ferroelectric-interlayer-ferroelectric structure with bottom and top SrRuO3 electrodes. The ferroelectric layers are of PbZr0.2Ti0.8O3, while the interlayer is CoFe2O4. It is shown that the three polarization states can be separately accessed, suggesting that this type of structure can be used as building element for a three-state nonvolatile ferroelectric random-access memory (FERAM). The presence of the three-state memory effect is explained through a simple phenomenological model based on Landau-Ginzburg-Devonshire theory. The findings of this study can pave the way to multistate all-oxide FERAM devices, resulting in a 50% increase in the storage density compared to actual nonvolatile memories.

The positions of the low energy electron diffraction (LEED) spots from ferroelectric single crystal films depend on its polarization state, due to electric fields generated outside of the sample. Onemay derive the surface potential energy, yielding the depth where the mobile charge carriers compensating the depolarization field are located (delta). On ferroelectric Pb(Zr, Ti)O-3(001) samples, surface potential energies are between 6.7 and 10.6 eV, and d values are unusually low, in the range of 1.8 +/- 0.4 angstrom. When delta is introduced in the values of the band bending inside the ferroelectric, a considerably lower value of the dielectric constant and/or of the polarization near the surface than their bulk values is obtained, evidencing either that the intrinsic 'dielectric constant' of the material has this lower value or the existence of a 'dead layer' at the free surface of clean ferroelectric films. The inwards polarization of these films is explained in the framework of the present considerations by the formation of an electron sheet on the surface. Possible explanations are suggested for discrepancies between the values found for surface potential energies from LEED experiments and those derived from the transition between mirror electron microscopy and low energy electron microscopy.

Epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin films were grown by pulsed laser deposition on two slightly different types of single crystal substrates, namely SrTiO3 (STO) buffered with a thin layer of conductive SrRuO3 (SRO), and SrTiO3 doped with 0.5% Nb (STON). Although self-poling effect was expected in both cases, due to the compressive strain imposed by the substrate, it was found that the pyroelectric response of as grown samples is with about two orders of magnitude larger for the PZT film deposited on SRO/STO compared to the one deposited on STON substrate. In order to explain the finding, the electrical properties were investigated and it was found that the quantities involved in the equation giving the magnitude of the pyroelectric signal, namely dielectric constant and electrical resistivity, have about the same values Therefore, the different pyroelectric response in the as-grown samples was explained by different structure of ferroelectric domains induced by the different carrier concentration in the two substrates: 90 degrees domains for PZT on SRO/STO and 180 degrees domains for PZT on STON. It appears that the resistivity of the substrate and its ability to compensate the depolarization field affect the domain structure, with impact on the pyroelectric response, although the strain conditions are similar in both cases. The trying to increase the pyroelectric response for the PZT film deposited on STON substrate by applying a poling process was not successful, as the 180 degrees domain structure restores shortly after removing the poling field. (C) 2017 Elsevier Ltd. All rights reserved.

The stability of thin films of lead zirco-titanate (PZT) under intense soft X-ray beams is investigated by time-resolved photoelectron spectromicroscopy with a lateral resolution below 1 micrometer. Surface dissociation is observed when samples are irradiated with intense (5 x 10(23) photons per s per m(2)) soft X-rays, with promotion of reduced lead on the surface. On areas exhibiting outwards polarization (P(+)), the reduced lead is formed at the expense of P(+)-PZT. On areas presenting co-existing P(+) states with areas without out-of-plane polarization (P-(0)), the reduced lead is formed at the expense of the P-(0)-PZT component, while the P(+)-PZT remains constant. The main dissociation mechanism was found to be triggered by 'hot' electrons in the conduction band, with energies exceeding the surface dissociation energies. Dissociation occurs basically when the electron affinity is larger than the dissociation energy of PbO (for P(+) areas) or PbO- (for P-(0) areas). Such mechanisms may be adapted for dissociation of other molecules on surfaces of ferroelectric thin films or for quantifying the stability of ferroelectric surfaces interacting with other radiation, with applications in the fields of photocatalysis or photovoltaic devices.

We report on the synthesis by Pulsed Laser Deposition of simple and Ti doped hydroxyapatite thin films of biological (ovine dentine) origin. Detailed physical, chemical, mechanical and biological investigations were performed. Morphological examination of films showed a surface composed of spheroidal particulates, of micronic size. Compositional analyses pointed to the presence of typical natural doping elements of bone, along with a slight non-stoichiometry of the deposited films. Structural investigations proved the monophasic hydroxyapatite nature of both simple and Ti doped films. Ti doping of biological hydroxyapatite induced an overall downgrade of the films crystallinity together with an increase of the films roughness. It is to be emphasized that bonding strength values measured at film. Ti substrate interface were superior to the minimum value imposed by International Standards regulating the load-bearing implant coatings. In vitro tests on Ti doped structures, compared to simple ones, revealed excellent biocompatibility in human mesenchymal stem cell cultures, a higher proliferation rate and a good cytocompatibility. The obtained results aim to elucidate the overall positive role of Ti doping on the hydroxyapatite films performance, and demonstrate the possibility to use this novel type of coatings as feasible materials for future implantology applications. (C) 2017 Elsevier B.V. All rights reserved.

The magnetic properties, in the 5 K-350 K temperature range, were investigated in relationship with the structure and morphology of Zn1-xFexO (x = 0, 0.01, 0.03) powders prepared by hydrothermal route. The magnetization measurements reveal that all powders are ferromagnetic at room temperature, with Curie temperature TT, higher than 350 K. The coercivity Hc takes values between 58 Oe and 107 Oe at 300 K and, between 217 Oe and 613 Oe at 5 K. The weak magnetization of the un-doped ZnO powder is temperature independent and was associated with the high surface to volume ratio of the powder particles (or the number of surface defects). The saturation magnetization M-s, was substantially enhanced (up to a factor of about 20 at 300 K and of about 200 at 5 K) at all temperatures as Fe concentration increased, in spite of reduction of the surface to volume ratio of the powder particles. The Hc vs. Tand FC/ZFC curves for the un-doped ZnO show typical ferromagnetic behavior, whereas for the Fe doped powders exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) - like and spin-glass-like behavior. The observed magnetic phenomena in Fe doped ZnO can be explained on the basis of "donor defects concentration magnetic cations concentration" phase diagram for dilute magnetic semiconductors. (C) 2017 Elsevier B.V. All rights reserved.

Measurements of the magnetocapacitance effect in epitaxial La0.7Sr0.3MnO3/Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterostructures have been performed using a quasi-static method. Through capacitance-voltage measurements carried out under variable magnetic field it has been found that the magneto-capacitance depends on the orientation of the ferroelectric polarization. The value of magneto-capacitance can be as high as 1% in the voltage range near the ferroelectric coercive field. This has been attributed to a variation of the apparent built-in voltage of the PZT-LSMO Schottky barriers on applied magnetic field.

Bi3+, Pb2+ and Bi3+-Pb2+-containing aluminophosphate glasses were obtained by unconventional wet method, the molar formula of the glasses being: i) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3Bi(2)O(3); ii) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3PbO and iii) 6LiPO(3), 3Al(PO3)(3), 1Ba(PO3)(2), 10Bi(PO3)(3), 80Pb(PO3)(2). The glass samples were investigated to determine the density, the thermal expansion coefficients and the chemical stability. The magnetic measurements for Bi and Pb-single doped glasses revealed a diamagnetic behavior and those of Bi-Pb-containing glass disclosed a diamagnetic behavior superposed a small paramagnetic contribution, observed in low magnetic fields that can be attributed to the impurities presented in the matrix. The Verdet constant for the analyzed glasses appeared to have positive values proving a diamagnetic behavior of the investigated material. (C) 2016 Published by Elsevier B.V.

We report on the fabrication of silicon-reinforced carbon (C: Si) structures by combinatorial pulsed laser deposition to search for the best design for a new generation of multi-functional coated implants. The synthesized films were characterized from the morphological, structural, compositional, mechanical and microbiological points of view. Scanning electron microscopy revealed the presence, on top of the deposited layers, of spheroid particulates with sizes in the micron range. No microcracks or delaminations were observed. Energy dispersive x-ray spectroscopy and grazing incidence x-ray diffraction pointed to the existence of aC to Si compositional gradient from one end of the film to the other. Raman investigation revealed a relatively high sp(3) hybridization of up to 80% at 40-48 mm a part from the edge with higher Ccontent. Si addition was demonstrated to significantly increase C: Si film bonding to the substrate, with values above the ISO threshold for coatings to be used in high-loading biomedical applications. Surface energy studies pointed to an increase in the hydrophilic character of the deposited structures along with Si content up to 52 m Nm(-1'). In certain cases, the Si-reinforced Ccoatings elicited an antimicrobial biofilm action. The presence of Si was proven to be benign to HEp-2 cells of human origin, without interfering with their cellular cycle. On this basis, reliable C: Si structures with good adherence to the substrate and high efficiency against microbial biofilms can be developed for implant coatings and other advanced medical devices.