National Institute Of Materials Physics - Romania

We have developed a thin film structure with a maximum magnetoresistance effect (MRE) at room temperature, which is one of the operating requirements for many applications. It is shown that La0.67Ba0.33Ti0.02Mn0.98O3 epilayers obtained by pulsed laser deposition onto (001) SrTiO3 single crystal substrates exhibit the highest MRE, Delta R/R(H) approximate to 150% or Delta R/R(0) approximate to 60% under 5 T, at 300 K, a temperature near to the corresponding Curie temperature (T-C). Both doping with a tiny amount of titanium and induced stress due to lattice mismatch between the thin film and the substrate contribute to a decrease in T-C as compared to the pristine compound and therefore to the decrease in the temperature where the highest MRE is recorded. Published by AIP Publishing.

A series of flexibly linked bis-imidazolium salts with alkyl sulfate anions having different chain lengths (10, 12, 14) was designed and prepared starting from 1,1'-(alpha,omega-alkanediyl)-bisimidazole and alkyl bromides (14 or 16 carbon atoms) followed by metathesis with the corresponding sodium salts. These compounds were investigated because of their liquid crystalline properties using a combination of differential scanning calorimetry (DSC), polarized optical microscopy (POM) and temperature dependent powder X-ray diffraction (XRD). All nine bis-imidazolium compounds with alkyl sulfate anions show liquid crystalline properties which were influenced by flexible spacer length, alkyl tail length and, finally, the length of alkyl chains attached to sulfate groups. Broader mesophase ranges were found for compounds with a shorter spacer (six carbon atoms), about 70 degrees C. For compounds with a spacer of ten carbon atoms, higher mesophase ranges and clearing temperatures were found for longer alkyl tails (sixteen carbon atoms). Increasing the length of alkyl chains attached to sulfate anions resulted in higher clearing temperatures for compounds with the longer spacer. The variation in the carbon atom number of the alkyl sulfate anion for bis-imidazolium compounds with the shorter spacer has almost no impact on their SmA phase stability.

Bi1.5-xZn0.92-yNb1.5O6.92-delta (BZN) thin films were grown by pulsed laser deposition on two different Pt-covered substrates, namely textured {111} Pt/TiO2/SiO2/(100) Si substrate (Pt/Si) and epitaxial {111} Pt/R-plane sapphire substrate (Pt/sapphire). In both cases, the BZN films present {111} and {100} out-of-plane orientations, in relative ratios of 65: 35 on Pt/Si and 80: 20 on Pt/sapphire, respectively. The film grown on Pt/Si is textured, while the film deposited on Pt/sapphire presents epitaxial-like relationships with the substrate, for both out-of-plane orientations. Dielectric measurements were taken on both types of thin films, using Pt/BZN/Pt planar capacitor structures. The BZN/Pt/sapphire film presents higher dielectric constant (245 at 100 kHz) and higher tunability (12% at 600 kV/cm) than the BZN/Pt/Si film (200; 6%), while the dielectric losses values are nearly same (similar to 0.05).

Hydroxyapatite is a calcium phosphate intensively proposed as a bone substitution material because of its resemblance to the constituents of minerals present in natural bone. Since hydroxyapatite's properties are mainly adequate for nonload bearing applications, different solutions are being tested for improving these properties and upgrading them near the target values of natural bone. On the other hand, starch (a natural and biodegradable polymer) and its blends with other polymers have been proposed as constituents in hydroxyapatite mixtures due to the adhesive, gelling, and swelling abilities of starch particles, useful in preparing well dispersed suspensions and consolidated ceramic bodies. This article presents the perspectives of incorporating starch and starch blends in hydroxyapatite materials. Based on the role of starch within the materials, the review covers its use as (i) a polymeric matrix in hydroxyapatite composites used as adhesives, bone cements, bone waxes, drug-delivery devices or scaffolds and (ii) a sacrificial binder for fabrication of porous hydroxyapatite scaffolds. The suitability of these materials for bone reconstruction has becomes a reachable aim considering the recent advancements in ceramic fabrication and the current possibilities of controlling the processing parameters.

A new family of cyclometalated palladium(II) complexes with the non-symmetric dimeric liquid crystal Schiff base alpha-(4-cyanobipheny1-4'-yloxy)-omega-(4-n-decyloxyanilinebenzylidene-4'-oxy) hexane and alkoxysubstituted N-benzoyl thiourea (BTU) derivatives as auxiliary ligands was designed and prepared with the aim to study the influence of increasing the number of aliphatic chains on the molecular organization in the liquid crystal phase. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction. A transition from the lamellar (complex 3a with two aliphatic chains on BTU ligand) to columnar organization (complexes 3b and 3c having three and four chains on BTU ligand, respectively) was evidenced for these palladium(II) complexes, which was correlated with the increase of the number of terminal chains at molecular periphery. (C) 2017 Elsevier B.V. All rights reserved.

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.