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Tchiffo-Tameko C.,University of Orléans | Cachoncinlle C.,University of Orléans | Perriere J.,CNRS Nanosciences Institute of Paris | Nistor M.,NILPRP | And 4 more authors.
Applied Surface Science | Year: 2016

The effect of the co-doping with Nd and Nb on electrical and optical properties of TiOx films is reported. The role of oxygen vacancies on the physical properties is also evidenced. The films are grown by pulsed-laser deposition onto (001) sapphire and (100) silicon substrates. The substrate temperature was fixed at 700 °C. To obtain either stoichiometric (TiO2) or highly oxygen deficient (TiOx with x < 1.6) thin films, the oxygen partial pressure was adjusted at 10−1 and 10−6 mbar, respectively. 1%Nd-1%Nb, 1%Nd-5%Nb and 5%Nd-1%Nb co-doped TiO2 were used as bulk ceramic target. Composition, structural and morphological properties of films determined by Rutherford backscattering spectroscopy, X-ray diffraction and scanning electron microscopy, are correlated to their optical (UV–vis transmission and photoluminescence) and electrical properties (resistivity at room temperature). The most intense Nd3+ emission in the IR domain is obtained for stoichiometric films. Codoping Nd-TiOx films by Nb5+ ions is found to decrease the photoluminescence efficiency. The oxygen pressure during the growth allows to tune the optical and electrical properties: insulating and highly transparent (80% in the visible range) Nd/Nb codoped TiO2 films are obtained at high oxygen pressure, while conductive and absorbent films are grown under low oxygen pressure (10−6 mbar). © 2016 Elsevier B.V.

Le Boulbar E.,French National Center for Scientific Research | Millon E.,French National Center for Scientific Research | Mathias J.,French National Center for Scientific Research | Boulmer-Leborgne C.,French National Center for Scientific Research | And 4 more authors.
Applied Surface Science | Year: 2011

Pure and Nb-doped titanium oxide thin films were grown on sapphire substrates by pulsed-laser deposition in vacuum (10-7 mbar). The PLD growth leads to titanium oxide thin films displaying a high oxygen deficiency (TiO1.5) compared with the stoichiometric TiO2 compound. The structural and electrical properties (phase, crystalline orientation, nature and concentration of charge carriers, etc.) of these titanium oxide films were studied by XRD measurements and Hall effect experiments, respectively. The undoped TiO1.5 phase displayed a p-type semiconductivity. Doping this titanium oxide phase with Nb5+ leads to an n-type behaviour as is generally observed for titanium oxide films with oxygen deficiency (TiO x with 1.7 < x < 2). Multilayer homojunctions were obtained by the stacking of TiO1.5 (p-type) and Nb-TiO1.5 (n-type) thin films deposited onto sapphire substrates. Each layer is 75 nm thick and the resulting heterostructure shows a good transparency in the visible range. Finally, the I-V curves obtained for such systems exhibit a rectifying response and demonstrate that it is possible to fabricate p-n homojunctions based only on transparent conductive oxide thin films and on a single chemical compound (TiOx). © 2010 Elsevier B.V. All rights reserved.

Scarisoreanu N.D.,NILPRP | Craciun F.,CNR Institute for Complex Systems | Chis A.,NILPRP | Birjega R.,NILPRP | And 3 more authors.
Applied Physics A: Materials Science and Processing | Year: 2010

Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) thin films grown by pulsed laser deposition have been investigated by X-ray diffraction, scanning electron microscopy, and dielectric spectroscopy in order to clarify the role of substrate temperature on crystalline structure, grain morphology, and dielectric properties. We have shown that the structural and dielectric properties of NBT-BT thin films with composition at morphotropic phase boundary (6% BT) critically depend on the substrate temperature: small variations of this parameter induce structural changes, shifting the morphotropic phase boundary toward tetragonal or rhombohedral side. Higher deposition temperature (1000 K) favor the formation of rhombohedral phase, films deposited at 923 K and 973 K have tetragonal symmetry at room temperature. Grains morphology depends also on the deposition temperature. Atomic force micrographs show grains with square or rectangular shape in a compact structure for films grown at lower temperatures, while grains with triangular shape in a porous structure are observed for films grown at 1000 K. Dielectric spectroscopy measurements evidenced the phase transition between ferroelectric and antiferroelectric phase at 370 K. Films grown at 1000 K shown low electrical resistivity due to their porous structure. High dielectric constant values (about 800 at room temperature and 2700 at 570 K) have been obtained for films grown at temperatures up to 973 K. © 2010 Springer-Verlag.

Andrei A.,NILPRP | Scarisoreanu N.D.,NILPRP | Birjega R.,NILPRP | Dinescu M.,NILPRP | And 3 more authors.
Applied Surface Science | Year: 2013

Ferroelectric lead-free (Na0.5Bi0.5) 1-xBaxTiO3 thin films obtained by pulsed laser deposition have been structurally and electrically investigated for compositions, x = 0 and x = 0.06, in and out of the morphotropic phase boundary (MPB). Sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT), pure or in solid solution with other materials (like BaTiO3), is considered to be the best candidate material for lead-free ferroelectric and piezoelectric applications such as actuators and nonvolatile memory devices. Bulk solid solutions with BaTiO3 (BT), (1-x)NBT-xBT (NBT-x%BT) have been investigated widely, also due to a morphotropic phase boundary (MPB) with enhanced dielectric and ferroelectric properties between a rhombohedral and a tetragonal ferroelectric phase, at x = 0.06. Nonetheless, to transpose bulk properties to NBT-BT thin films is a major achievement. XRD technique has been used for structural characterizations of NBT-BT films. Dielectric spectroscopy measurements were performed at room temperature in the frequency range 100 Hz-1 MHz. The best films show pure perovskite phase and good crystalline structure, as a function of specific deposition conditions. Unusual characteristics, especially dielectric constant values higher than those for bulk, have been found for films with specific crystallographic orientations. © 2012 Elsevier B.V.

Monnereau O.,Aix - Marseille University | Tortet L.,Aix - Marseille University | Grigorescu C.E.A.,Romanian National Institute for Optoelectronics | Savastru D.,Romanian National Institute for Optoelectronics | And 8 more authors.
Journal of Optoelectronics and Advanced Materials | Year: 2010

The composition of Pulsed Laser Deposited thin films from Cr 8O21 targets has been investigated by Raman spectroscopy. To this purpose we have prepared the chromium oxides Cr8O 21, Cr2O5, CrO2 and Cr 2O3 in bulk form to provide standard Raman spectra for characterisation of the samples. The range of oxides has been prepared by thermal decomposition of CrO3 following the thermo-gravimetric analysis. CrO2 was obtained by two other specific ways, i.e. hot pressing of Cr8O21 and hydrothermal synthesis. Structural characterization was performed by X-ray diffraction, SEM, IR and Raman spectroscopy. Raman investigation is demonstrated to have the capacity to identify CrO2 as well as trace concentrations of secondary phases in the PLD thin films. The Raman measurements have led us also to the conclusion that PLD of Cr8O21 targets yields in thin films containing either mixtures of (Cr2O5, CrO2 and Cr2O3) or, under particular conditions of oxygen pressure and substrate temperature, of (CrO2 and Cr 2O3) only.

Ionita I.,University of Bucharest | Zamfirescu M.,NILPRP
2011 International Workshop on Biophotonics, BIOPHOTONICS 2011 | Year: 2011

We report here bone tissue ablation experiments performed with femtosecond laser. We determined ablation threshold value of human mandible which is the hardest bone of the skull. © 2011 IEEE.

Craciun F.,CNR Institute for Complex Systems | Galassi C.,CNR Institute of Science and Technology for Ceramics | Birjega R.,NILPRP
Journal of Applied Physics | Year: 2012

Complex dielectric susceptibility was used to investigate the relaxor properties and the ferroelectric phase transitions in (Na1/2Bi 1/2)1 - xBaxTiO3 (0 ≤ x ≤ 0.08) ceramics. XRD was used to characterize the ground states of poled and unpoled samples. Dielectric susceptibility vs. temperature studies allowed to obtain the relaxor properties and to identify the electric field-induced phase transitions in the morphotropic phase boundary (MPB) compositions (0.06 < x < 0.08) and the spontaneous relaxor-ferroelectric phase transitions in the rhombohedral compositions (x < 0.06). The frequency dispersion of the dielectric maximum at Tm was observed for all compositions, although of decreased extension for lower x. The relaxor properties have been analysed with Vogel-Fulcher law. The activation energy and attempt frequency for the MPB compositions are similar to those of classical relaxors like Pb(Mg 1/3Nb2/3)O3, while for rhombohedral compositions, they are similar to relaxor ferroelectrics with spontaneous relaxor-ferroelectric phase transitions, like Pb(Sc1/2Nb 1/2)O3. A relationship has been found between the relaxor dispersion degree and the hysteresis of the ferroelectric transition. © 2012 American Institute of Physics.

D'Amato R.,ENEA | Falconieri M.,ENEA | Gagliardi S.,ENEA | Popovici E.,NILPRP | And 3 more authors.
Journal of Analytical and Applied Pyrolysis | Year: 2013

Nanoparticles are the building blocks of many approaches for realizing nanostructured materials and devices. The technique of CO2 laser pyrolysis of gas- or vapour-phase precursors for the synthesis of nanoparticles has proven to be a very flexible and versatile technique which permits to cope with several challenges in different sectors of nanotechnology. Different kinds of pyrolytic nanopowders with average size in the range 5-60 nm and a narrow size distribution, have been produced and tested for the fabrication of structural materials and/or for functional applications in various fields. Here we report new results on the synthesis of SiC, TiO2 and SiO 2 nanoparticles for energetic applications and cultural heritage preservation. © 2013 Elsevier B.V. All rights reserved.

Filipescu M.,NILPRP | Stokker-Cheregi F.,NILPRP | Colceag D.,NILPRP | Nedelcea A.,NILPRP | And 3 more authors.
Applied Surface Science | Year: 2013

This paper reports on producing SiC based nanostructures (SiC, W-SiC, CNS-SiC) by pulsed laser deposition (PLD) and radio-frequency plasma assisted PLD. Simple and composite targets (SiC, 3/4 SiC + 1/4 tungsten and 3/4 SiC + 1/4 graphite) were irradiated by a 266 nm pulsed laser beam having a pulse duration of 7 ns. The silicon substrates were kept either at room temperature or heated up to 600 C. The depositions were performed in argon at various pressures, ranging from 0.05 mbar up to 2 mbar. The influence of deposition parameters on the structure, surface morphology and composition of different SiC based structures was studied by atomic force microscopy, scanning electron microscopy, secondary ion mass spectrometry, transmission electron microscopy and selected area electron diffraction. Fibers, tubes, nanoparticles and rolled sheets structures were obtained by varying laser fluence, substrate temperature, gas pressure and radio-frequency power. © 2012 Elsevier B.V. All rights reserved.

Cachoncinlle C.,University of Orléans | Hebert C.,CNRS Nanosciences Institute of Paris | Perriere J.,CNRS Nanosciences Institute of Paris | Nistor M.,NILPRP | And 2 more authors.
Applied Surface Science | Year: 2015

Low-dimensional semiconductor structures on nanometer scale are of great interest because of their strong potential applications in nanotechnologies. We report here optical and structural properties on UV lasing in ZnO thin films. The ZnO films, 110 nm thick, were prepared using pulsed-laser deposition on c-cut sapphire substrates at 500 °C under 10-2 oxygen pressure. The ZnO films are nearly stoichiometric, dense and display the wurtzite phase. The films are highly textured along the ZnO c-axis and are constituted of nanocrystallites. According to Hall measurements these films are conductive (0.11 Ω cm). Photoluminescence measurements reveals a so-called random lasing in the range 390 to 410 nm, when illuminating at 355 nm with a tripled frequency pulsed Nd-YAG laser. Such random lasing is obtained at rather low optical pumping, 45 kW cm-2, a value lower than those classically reported for pulsed-laser deposition thin films. © 2014 Elsevier B.V. All rights reserved.

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