National Institute Of Materials Physics - Romania

Quasi-static polarization induced by dc electric field was studied in a broad range of temperatures in epitaxial films of relaxor ferroelectric PbMg1/3Nb2/3O3 and PbSc1/2Nb1/2O3. The electric field was applied and the response was measured along the out-of-plane crystal direction of the epitaxial perovskite-structure (001) oriented films. The films remained in the relaxor state in zero-field cooling. A new polar state can be induced by electric field at a critical temperature below 100 K. The critical field and the induced polarization increased on cooling and reached the bulk-like values at 20 K. The orientational anisotropy of thin-film dipolar systems is discussed as a possible reason for the observed stable relaxor state.

ZnO crystallites were grown by electroless deposition on poly(methyl methacrylate) (PMMA) fiber mats prepared by an electrospinning technique. The electroless deposition involves three steps: sensitization, activation and deposition, which were performed by subsequently dipping the PMMA fiber mats in the appropriate solutions. After the deposition the PMMA fibers are uniformly coated with ZnO prisms which show hexagonal wurtzite structure and optical signatures (band-gap value and emission bands) typical for this semiconductor. By combining electroless deposition and electrospinning, different semiconductor coated polymer fibers can be obtained for a wide range of applications. Both methods are appropriate for large scale production, being scalable, cheap, efficient and suitable for large-area covering techniques. (C) 2014 Elsevier B.V. All rights reserved.

The electrochemical polymerization of diphenylamine (DPA) onto electrodes of Pt coated with highly separated metallic (98%) or semiconducting (99%) single-walled carbon nanotubes (SWCNTs) in the presence of H3PW12O40 was performed by cyclic voltammetry in order to obtain composite materials based on polydiphenylamine (PDPA) doped with heteropolyanions of H3PW12O40 and carbon nanotubes. Our data demonstrate that the photoluminescence quenching effect of the PDPA doped with H3PW12O40 heteropolyanions in the presence of SWCNTs is due to the metallic component. Under UV irradiation of SWCNTs highly separated in metallic and semiconducting tubes functionalized with PDPA doped with heteropolyanions of H3PW12O40 new photochemical reactions are evidenced by photoluminescence studies. These reactions lead to a shortening of the macromolecular chain of PDPA. The photochemical process is more intense in the case semiconducting SWCNTs functionalized with PDPA doped with heteropolyanions in comparison to metallic SWCNTs functionalized with PDPA in doped state, it being a consequence of an additional chemical interaction between the DPA dimer doped with H3PW12O40 heteropolyanions and semiconducting SWCNTs. (C) 2014 Elsevier Ltd. All rights reserved.

We report on thin film deposition by matrix-assisted pulsed laser evaporation of simple hydroxyapatite (HA) or silver (Ag) doped HA combined with the natural biopolymer organosolv lignin (Lig) (Ag:HA-Lig). Solid cryogenic target of aqueous dispersions of Ag:HA-Lig composite and its counterpart without silver (HA-Lig) were prepared for evaporation using a KrF* excimer laser source. The expulsed material was assembled onto TiO2/Ti substrata or silicon wafers and subjected to physical-chemical investigations. Smooth, uniform films adherent to substratum were observed. The chemical analyses confirmed the presence of the HA components, but also evidenced traces of Ag and Lig. Deposited HA was Ca deficient, which is indicative of a film with increased solubility. Recorded X-ray Diffraction patterns were characteristic for amorphous films. Lig presence in thin films was undoubtedly proved by both X-ray Photoelectron and Fourier Transform Infra-Red Spectroscopy analyses. The microbiological evaluation showed that the newly assembled surfaces exhibited an inhibitory activity both on the initial steps of biofilm forming, and on mature bacterial and fungal biofilm development. The intensity of the antibiofilm activity was positively influenced by the presence of the Lig and/or Ag, in the case of Staphylococcus aureus, Pseudomonas aeruginosa and Candida famata biofilms. The obtained surfaces exhibited a low cytotoxicity toward human mesenchymal stem cells, being therefore promising candidates for fabricating implantable biomaterials with increased biocompatibility and resistance to microbial colonization and further biofilm development.

Although Raman spectra reveal, as a signature of double-walled carbon nanotubes (DWCNTs), two radial breathing mode (RBM) lines associated with the inner and outer tubes, the specification of their nature as metallic or semiconducting remains a topic for debate. Investigating the spectral range of the RBM lines, we present a new procedure of the indexing of the semiconducting or metallic nature of the inner and outer shell that forms the DWCNT. The procedure exploits the difference between the intensities of recorded anti-Stokes Raman spectrum and the anti-Stokes spectrum calculated by applying the Boltzmann formulae to the recorded Stokes spectrum. The results indicate that the two spectra do not coincide with what should happen in a normal Raman process, namely, that there are RBM lines of the same intensity in both spectra, as well as RBM lines of higher intensity that are observed in the calculated spectrum. This discrepancy results from the surface-enhanced Raman scattering mechanism that operates differently on metallic or semiconducting nanotubes. In this context, the analysis of the RBM spectrum can reveal pairs of lines associated with the inner/outer shell structure of DWCNT, and when the intensities between the recorded and calculated spectra coincide, the nanotube is metallic; otherwise, the nanotube is semiconducting. Copyright (c) 2014 John Wiley & Sons, Ltd.

xEu(2)O(3)-(1-x)alpha-Fe2O3 (x=0.1, 0.3, 0.5, and 0.7) nanoparticle system was successfully synthesized by mechanochemical activation of Eu2O3 and alpha-Fe2O3 mixtures for 0-12 h of ball milling time. The investigations aimed at exploring the formation of magnetic ceramic nanostructures, which are of crucial importance for catalysis and sensing applications. X-ray powder diffraction (XRD),as well as Fe-57 and Eu-151 Mossbauer spectroscopy and thermal analysis by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) was used to study the phase evolution of xEu(2)O(3)-(1-x)alpha-Fe2O3 nanoparticle system under the mechanochemical activation process. Rietveld refinement of the XRD patterns yielded the values of the particle size as a function of composition and milling times and indicated the formation of the EuFeO3 perovskite for large x values and long milling times. The Fe-57 Mossbauer studies showed that the spectrum of the mechanochemically activated composites evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with europium oxide. The Eu-151 Mossbauer investigations showed that the isomer shift decreased with increasing milling time for all molar concentrations employed. These results correlate well with the DSC/TGA analysis, which shows the consumption of hematite and the formation of EuFeO3 in the system under investigation. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

xIrO(2)-(1-x)alpha-Fe2O3(x=0.1, 0.3 and 0.5) nanoparticle systems were successfully synthesized by mechanochemical activation of IrO2 and alpha-Fe2O3 mixtures for 0-12 h of ball milling time. The study aims at exploring the formation of magnetic oxide semiconductors at the nanoscale, which is of crucial importance for catalysis, sensing and electrochemical applications. X-ray powder diffraction (XRD), Mossbauer spectroscopy, magnetic measurements and simultaneous differential scanning calorimetry (DSC) and thermal gravirnetric analysis (TGA) were used to study the phase evolution of xIrO(2)-(1-x)alpha-Fe2O3 nanoparticle systems under the mechanochemical activation process. Rietveld refinement of the XRD patterns yielded the values of the particle size and lattice parameters as function of composition and milling times and indicated the presence of Ir-substituted hematite and Fe-doped iridium oxide for large x values and long milling times. The Mossbauer studies showed that the spectrum of the mechanochemically activated composites evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with iridium oxide. Magnetic measurements recorded at 5 K in an applied magnetic field of 40,000 Oe showed that the saturation magnetization of the milled samples increased with ball milling time while preserving a multidomain magnetic structure. The unmilled sample at 5 K showed a spinflop type metarnagnetic transition around 30,000 Oe. The Morin transformation was evidenced by zero-field cooling field cooling (ZFC-FC) measurements in 200 Oe and 1 T and the transformation characteristic temperatures were shifted to lower values. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Ribbons of Fe-Pd ferromagnetic shape memory alloys were prepared by rapid solidification via the melt-spinning technique. The effect of moderate and high temperature heat treatments on the martensitic transformation and the related changes of the magnetic behavior was analyzed by X-ray diffraction, differential scanning calorimetry and temperature, and field-dependent magnetometry. In addition, information about magnetic easy axis and magnetically field-induced strains (MFIS) were achieved from linear thermal expansion measurements performed under cooling at different applied fields. The observed low values of MFIS in the as-prepared ribbons are due, besides to the small size and random orientation of the grains, to the high atomic disorder inside the crystalline grains. The anisotropy field is enhanced by the reduced atomic disorder, as reflected by the increased MFIS values after thermal treatments.

The charge storage properties of Ge nanocrystals-based MOS-like capacitors with tunnel and gate HfO2 are studied. HfO2/Ge/HfO2/Si trilayer structures were prepared by magnetron sputtering (in Ar) and subsequent rapid thermal annealing (650 degrees C). HfO2/Si structures were also prepared, some under similar conditions, while others were deposited in Ar:O-2. TEM investigations and C-V measurements were performed. TEM on annealed trilayers evidences the formation of ordered and precisely positioned array of Ge nanocrystals embedded in crystalline HfO2. The annealed Al/HfO2/Ge/HfO2/p-Si/Al capacitors present counterclockwise C-V hysteresis (0.8 V memory window) mainly given by Ge nanocrystals, with negligible contribution from crystallized-HfO2 traps.

ZnO complex microstructures were deposited onto interdigitated metallic electrodes by electrospraying. Simple methods, such as wet chemical precipitation and optical lithography, were used for the synthesis of flower-like and snowflake-like ZnO structures and for the preparation of interdigitated metallic electrodes, respectively. The electrosprayed ZnO particles preserve the structural, optical and morphological properties of the chemically synthesized ZnO powders. During the electrospraying process, the ZnO microstructures form bridges between the interdigitated metallic electrodes leading to electrical contacting. Changes in the electron transport through the ZnO microstructures are evidenced by their exposure to ammonia or their passivation with poly(methyl methacrylate). Merging such easy-scalable and low-cost techniques, devices based on electrosprayed complex ZnO structures can be designed.