Numerical and Comparative Study of the Agility of Planar Transmission Lines printed on a Ferroelectric Thin Film

International audienceIn this paper, we report on simulation results at 10 GHz of planar transmission lines (TL) printed on a ferroelectric thin film deposited on sapphire and lanthanum aluminate substrates. The ferroelectric film permittivity is supposed to vary from 700 to 500. First, the main properties of microstrip (MS), coplanar waveguide (CPW) and coplanar strips (CS) namely their effective permittivity, characteristic impedance and insertion loss are computed as a function of the physical and electrical parameters. Then their tunability and figure of merit are defined and compared. CPW and CS lines present a tunability (eff/eff_max) of about 16 % for a gap value g = 30 μm. The MS lines show a much less tenability of 2%. Moreover, the figure of merit of CPW and CS configurations are of 6.3 and 12.2 %/dB for a gap value of 30 μm, respectively. By increasing the gap, these figures of merit can be improved up to the limiting values of 8.7 and 15.4 %/dB, respectively

Randomly organized and self-assembled Na0.5Bi0.5TiO3 nanodots elaborated by sol-gel and pulsed laser deposition routes

International audienceThis work reports for the first time on the elaboration, by both chemical (sol-gel) and physical (pulsed laser deposition) routes, of lead-free ferroelectric Na0.5Bi0.5TiO3 nanodots deposited on bare c-sapphire single crystal substrates presenting a 5° miscut angle along the [110] direction. Prior to any deposition, the sapphire substrates were treated at 1350 °C, during 24 h in air, in order to increase the height of the surface steps, reaching by this way ~8 nm. The experimental parameters adjusted for the growth of Na0.5Bi0.5TiO3 dots were the concentration of sols and the number of laser pulses (50 and 100) for the sol-gel and pulsed laser deposition routes, respectively. Whereas the sol-gel route leads to randomly organized Na0.5Bi0.5TiO3 nanodots in respect to the surface steps, the pulsed laser deposition route provokes the self-assembly for some important proportion of these dots along the same surface steps. Despite the lack of organization for the sol-gel dots, the latter present a much more regular distribution in size (~100 and ~10-20 nm as an average lateral dimensions and height, respectively) compared to dots deposited by laser ablation, where three different populations of grains can be observed. In each case, the dots do not seem to be epitaxially grown

Cистемна організація уваги та загальні принципи її корекції як засіб оптимізації учбової та професійної діяльності

У статті викладено результати літературних та експериментальних досліджень, у яких розкриваються основні напрямки, котрі стосуються феномени уваги:механізми її виникнення, типи уваги, функції контролю та управління. Розглянуто ряд методів, котрі можуть бути використані для тренінгів, з метою збільшення об’єму уваги, ступеня її концентрації, швидкості, ступеня зосередження, переключення і розподілу

Substrate-controlled allotropic phases and growth orientation of TiO2 epitaxial thin films

International audienceTiO2 thin films were grown by pulsed laser deposition on a wide variety of oxide single-crystal substrates and characterized in detail by four-circle X-ray diffraction. Films grown at 873 K on (100)-oriented SrTiO3 and LaAlO3 were (001)-oriented anatase, while on (100) MgO they were (100)-oriented. On (110) SrTiO3 and MgO, (102) anatase was observed. On M-plane and R-plane sapphire, (001)- and (101)-oriented rutile films were obtained, respectively. On C-plane sapphire, the coexistence of (001) anatase, (112) anatase and (100) rutile was found; increasing the deposition temperature tended to increase the rutile proportion. Similarly, films grown at 973 K on (100) and (110) MgO showed the emergence, besides anatase, of (110) rutile. All these films were epitaxically grown, as shown by ' scans and/or pole figures, and the various observed orientations were explained on the basis of misfit considerations and interface arrangement

Sr1-xBaxSnO3 system applied in the photocatalytic discoloration of an azo-dye

International audienceSemiconductor materials have received substantial attention as photocatalysts for controlling water pollution. Among these materials, perovskite-structured SrSnO3 is a promising candidate for this application, whereas BaSnO3 exhibits very low activity. In the present work, Sr1−xBaxSnO3 (x = 0, 0.25, 0.50, 0.75 and 1) was synthesized by solid-state reaction and was applied in the photocatalytic discoloration of the organic dye Remazol Golden Yellow. The perovskite structure was obtained for all compositions of the solid solutions with both Sr2+ and Ba2+ present in the lattice. A remarkable change in the short-range symmetry was observed as the amount of Ba2+ increased, and this change led to a decrease in the band gap of the material. Although the BaSnO3 was not active toward water photolysis, the discoloration induced by this perovskite was twice that induced by SrSnO3. The two materials appear to feature different mechanisms of photodegradation: the direct mechanism prevails in the case of BaSnO3, whereas the indirect mechanism appears to play a key role in the case of SrSnO3

Zinc-gallium oxynitride powders: effect of the oxide precursor synthesis route

International audienceZinc-gallium oxynitride powders (ZnGaON) were synthesized by nitridation of ZnGa2O4 oxide precursor obtained by polymeric precursors (PP) and solid state reaction (SSR) methods and the influence of the synthesis route of ZnGa2O4 on the final compound ZnGaON was investigated. Crystalline single phase ZnGa2O4 was obtained at 1100 oC / 12 h by SSR and at 600 oC / 2 h by PP with different grain sizes and specific surface areas according to the synthesis route. After nitridation, ZnGaON oxynitrides with a GaN würtzite-type structure were obtained in both cases, however at lower temperatures for PP samples. The microstructure and the specific surface area were strongly dependent on the oxide synthesis method and on the nitridation temperature (42 m2g-1 and 5 m2g-1 for PP and SSR oxides treated at 700 °C, respectively). The composition analyses showed a strong loss of Zn for the PP samples, favored by the increase of ammonolysis temperature and by the higher specific surface area

Intercomparison of Permittivity Measurement Techniques for Ferroelectric Thin Layers

International audienceThe dielectric properties of a KTa0.65Nb0.35O3 (KTN) ferroelectric composition for a submicronic thin layer were measured in the microwave domain using different electromagnetic characterization methods. Complementary experimental techniques (broadband methods versus resonant techniques, waveguide versus transmission line) and complementary data processing procedures (quasi-static theoretical approaches versus full-wave analysis) were selected to investigate the best way to characterize ferroelectric thin films. The measured data obtained from the cylindrical resonant cavity method, the experimental method that showed the least sources of uncertainty, were taken as reference values for comparisons with results obtained using broadband techniques. The error analysis on the methods used is discussed with regard to the respective domains of validity for each method; this enabled us to identify the best experimental approach for obtaining an accurate determination of the microwave dielectric properties of ferroelectric thin layers

Preparation of niobium based oxynitride nanosheets by exfoliation of Ruddlesden-Popper phase precursor.

International audienceA new oxynitride Ruddlesden-Popper phase K1.6Ca2Nb3O9.4N0.6 .1.1H2 O was synthesized by the topochemical ammonolysis reaction at 700 °C from the oxide Dion-Jacobson phase KCa2Nb3O10 in the presence of K2CO3. The oxynitride showed good stability with a little loss of nitrogen, even after a few months of exposure to air. Its crystal structure was solved by Rietveld refinement of X-ray powder diffraction data in space group P4/mmm and considering a two-phase mixture, due to the difference in the degree of hydration, with a = 3.894(2) Å and c = 17.90(8) Å for the most hydrated phase and a = 3.927(6) and c = 17.09(2) for the less one. Optical band gaps were measured by diffuse reflectance UV-Vis indicating a red shift of Eg to the visible region. The oxynitride layered perovskite was then protonated and exfoliated into nanosheets. TEM images and SAED patterns of the nanosheets proved that exfoliation was successful, showing lattice parameters quite compatible with the Rietveld refinement

Élevage : des performances mises à l’index…

Élevage : des performances mises à l’index

Effect of the Microstructure of ZnO Thin Films Prepared by PLD on Their Performance as Toxic Gas Sensors

International audienceIn 2008, the modified European Restriction of Hazardous Substances (RoHS) directive prohibited the use of hazardous substances such as lead, cadmium, and mercury. As such, an urgent need for lead-free components emerged in Europe. In this frame, we have decided to study the microstructure influence of zinc oxide thin films on the detection of hydrogen sulfide (H2S). Zinc oxide thin films were deposited by PLD on silicon substrates under different conditions to modify the microstructure. In order to compare our demonstrators to current commercial semiconductor gas sensors, measurements under H2S were also performed with sensors from Figaro and Winsen corporations. Gas sensors were therefore implemented by using commercial cases in view to test them with Simtronics gas detector DG477. The good sensitivity values measured at T = 400 degrees C under 100 ppm H2S, and response times as low as 30 s, definitely confirm that ZnO thin films could be developed for commercial sensors