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[en] Co/ZnO films were deposited on glass substrates by magnetron sputtering at room temperature. The structure of the as-deposited films is studied by means of x-ray diffraction, x-ray photoelectron spectroscopy, and the zero-field-cooled and field-cooled magnetization curves. It is shown that the as-deposited samples consist of a mixture of regions of metallic Co and semiconducting ZnO. Large negative magnetoresistance of 26% and 11.9% are observed in the as-deposited Co/ZnO film with Co concentration of 50.7 at. % at 10 K and room temperature, respectively. Structural analysis, the temperature dependence of the conductivity and magnetoresistance reveal that the magnetoresistance is induced by spin-dependent tunneling between regions of conducting magnetic Co through the ZnO semiconducting barriers. The enhanced magnetoresistance in the low temperature regime may be related to the existence of higher-order tunneling processes between large Co regions mediated by small Co particles.
[en] The photostability and fluorescence properties of 1,3-diphenylisobenzofuran (DPBF), a popular singlet oxygen (1O2 or 1Δg) trapping-agent used in various solvents, are examined by UV-vis absorption, steady-state and time-resolved fluorescence techniques, as well as laser flash photolysis. DPBF is found to be easily photolyzed even if it is only exposed to the weak daylight in halogen-containing solvents in the absence of singlet oxygen. The photolysis is due to the addition of ·CCl3 (·CHCl2) to DPBF in the absence of oxygen, or ·OOCCl3 (·OOCHCl2) initiated chain polymerization of DPBF in the presence of oxygen. This result suggests that the reported singlet oxygen production in these solvents detected by DPBF was significantly higher than the true value. DPBF in DMF, DMSO, etc., on the other hand, is stable enough to enable fluorescence measurements. The fluorescence quantum yield of DPBF is very high in aprotic solvents and close to unity. The absorption, excitation and emission maxima are only slightly affected by the nature of solvents. The fluorescence lifetime is 5.0±0.3 ns. - Highlights: → We found that DPBF was easily photoxidized in CCl4 or CHCl3 without singlet oxygen. → The fluorescence quantum yield of DPBF is close to unity. → The photolysis is due to the addition of ·CCl3 (·CHCl2) to DPBF in the absence of oxygen. → The absorption, excitation and emission maxima are only slightly affected by solvents.
[en] Microstructure and oxidation behavior of modified Ni-16Mo-7Cr-4Fe alloys by yttrium microalloying were investigated by scanning electron microscopy, transmission electron microscopy, grazing incident Xray diffraction and synchrotron radiation X-ray fluorescence. M6C and Ni17Y2 phases were observed and the amount of Ni17Y2 increased with yttrium concentration. When the yttrium concentration increased to 0.43 wt.%, some Ni17Y2 chains and multi phase regions containing Ni17Y2, M6C and phase appeared, which is harmful for the oxidation resistance. The alloy containing 0.05 wt.% yttrium showed the best oxidation resistance, which derives its oxidation resistance from the adequate concentration of yttrium in the solid-solution ( phase), the formation of the protective layer of YCrO3 and chromia oxide and the strengthening effect of yttrium on oxide boundaries. (authors)
[en] Magnetic polyelectrolyte complex (PEC) based on chitosan and sodium ligninsulfonate as the support to stabilize Fe/Pd bimetallic particles (mPEC-Fe/Pd) were synthesized for the degradation and decolorization of organic pollutants in aqueous solution. The morphologies and structures of the as-obtained composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM). Various factors potentially influencing the decolorization performance of methyl blue (MB) and malachite green (MG) from aqueous solution (i.e., mPEC-Fe/Pd dosage, solution pH, initial dye concentration and reaction temperature) were investigated. mPEC-Fe/Pd exhibited higher catalytic activity towards the removal of MB and MG, which involved both adsorption of dye molecules on mPEC surface and reduction reaction by Fe/Pd particles. Nearly 99% and 91% of MB and MG were removed at initial dye concentration of 100 mg l−1 with 1.0 g l−1 of mPEC-Fe/Pd, respectively. The decolorization efficiency of MB and MG increased with the increase of solution pH and mPEC-Fe/Pd dosage but decreased with the increase of initial dye concentrations. mPEC-Fe/Pd could be recycled effectively, and the removal percentage of MB reached as high as 83.5% even at the eighth reuse. Furthermore, the catalytic performances were further investigated to remove other organic pollutants, in which 92.4% of oxytetracycline, 85.1% of Tetrabromobisphenol A, and 34.7% of norfloxacin were removed at 50 mg l−1 of aqueous solution using 1.0 g l−1 of mPEC-Fe/Pd. Due to high removal efficiency, rapid reaction rate, easy separation and good reusability, mPEC-Fe/Pd had the potential to become an environmental remediation material for the treatment of wastewater containing organic compounds. (paper)
[en] Nanostructured ZnO–Co and ZnO films with Pt, Cu, and Co as top electrodes, and Pt as bottom electrodes were grown by magnetron sputtering. Both ZnO–Co and ZnO films show bipolar resistive switching characteristics. The resistive switching properties of ZnO films are strongly dependent on the top electrode materials. The effect of top electrodes on resistive switching of ZnO–Co films is weakened due to the dominant roles of Co particles in the films. It is different with ZnO films that the ZnO–Co film shows a forming-free process. The calculation from the classical electromagnetism theory indicates that the existence of Co nanoparticles in the ZnO switching matrix can enhance the local electrical field to some extent, and decrease the operating voltages. So the device with a ZnO–Co film as a switching matrix can significantly reduce power consumption, weaken the dependence of the electrode materials, and optimize the resistive switching performance. (paper)
[en] The Si2Sb2Te5 phase change material has been studied by applying a nano-tip (30 nm in diameter) on an atomic force microscopy system. Memory switching from a high resistance state to a low resistance state has been achieved, with a resistance change of about 1000 times. In a typical I-V curve, the current increases significantly after the voltage exceeds ∼4.3 V. The phase transformation of a Si2Sb2Te5 film was studied in situ by means of in situ X-ray diffraction and temperature dependent resistance measurements. The thermal stability of Si2Sb2Te5 and Ge2Sb2Te5 was characterized and compared as well.
[en] The formation of L10 FePt nanoparticles by annealing of FePt/C multilayer films was studied. After annealing at 550 deg. C for 30 min, the superlattice peaks (0 0 1) and (1 1 0) found in the X-ray diffraction pattern of the FePt/C films indicate that the face-centered cubic disordered phase has been partially transformed into the L10 phase. FePt/C thin films became magnetically hard with a coercivity in the range 1.8-9.2 kOe due to the high anisotropy energy associated with the L10 ordered phase. The coercivity of the films decreased rapidly with increasing C layer thickness. With increasing C content, the grain size and intergrain interaction of the FePt/C multilayer films decreased. The coercivity not only depends on the C content, but also on the structure of the FePt/C mutilayer. The [FePt 3 nm/C 3 nm]10 sample shows a small dipolar interaction
[en] Fe xPt100-x(30 nm) and [Fe xPt100-x(3 nm)/ZrO2]10 (x = 37, 48, 57, 63, 69) films with different ZrO2 content were prepared by RF magnetron sputtering technique, then were annealed at 550 deg. C for 30 min. This work investigates the effect of ZrO2 doping on the microstructural evolution, magnetic properties, grain size, as well as the ordering kinetics of FePt alloy films. The as-deposited films behaved a disordered state, and the ordered L10 structure was obtained by post-annealing. The magnetic properties of the films are changed from soft magnetism to hard magnetism after annealing. The variation of the largest coercivities of [Fe xPt100-x/ZrO2]10 films with the Fe atomic percentage, x and differing amounts of ZrO2 content reveals that as we increase the ZrO2 content we must correspondingly increase the amount of Fe. This phenomenon suggests that the Zr or O atoms of ZrO2 preferentially react with the Fe atoms of FePt alloy to form compounds. In addition, introducing the nonmagnetic ZrO2 can reduce the intergrain exchange interactions of the FePt/ZrO2 films, and the interactions are decreased as the ZrO2 content increases, the dipole interactions are observed in FePt/ZrO2 films as the ZrO2 content is more than 15%
[en] The title compounds (Sr0.96-xBa0.04)Al12-yMgyO19:Tbx (0< x<0.4; 0< y<0.18) are single-phase magnetoplumbite determined by X-ray powder diffraction analysis. The characteristic emission lines of 5D3→7Fj (j=2, 3, 4, 5) and 5D4→7Fj (j=4, 5, 6) of Tb3+ are recorded under the VUV excitation. The intensive luminescence mainly comes from 5D3→7Fj transition when the concentration of Tb3+ is low. However, when the concentration of Tb3+ starts to increase from very low concentration, 5D4→7Fj transition is becoming dominant. Three broad excitation bands at 165, 193 and 233 nm have been observed. The band at 165 nm originates from the overlap between the host absorption and the charge transfer of Tb3+-O2-. The other two broad bands are the first spin-allowed and the spin-forbidden of 4f-5d transition, respectively. The experimental observation of the 4f-5d transition of Tb3+ is consistent well with the theoretical expectations
[en] In order to obtain a targeting drug carrier system, magnetic polylactic acid (PLA) microspheres loading curcumin were synthesized by the classical oil-in-water emulsion solvent-evaporation method. In the Fourier transform infrared spectra of microspheres, the present functional groups of PLA were all kept invariably. The morphology and size distribution of magnetic microspheres were observed with scanning electron microscopy and dynamic light scattering, respectively. The results showed that the microspheres were regularly spherical and the surface was smooth with a diameter of 0.55-0.75 μm. Magnetic Fe3O4 was loaded in PLA microspheres and the content of magnetic particles was 12 wt% through thermogravimetric analysis. The magnetic property of prepared microspheres was measured by vibrating sample magnetometer. The results showed that the magnetic microspheres exhibited typical superparamagnetic behavior and the saturated magnetization was 14.38 emu/g. Through analysis of differential scanning calorimetry, the curcumin was in an amorphous state in the magnetic microspheres. The drug loading, encapsulation efficiency and releasing properties of curcumin in vitro were also investigated by ultraviolet-visible spectrum analysis. The results showed that the drug loading and encapsulation efficiency were 8.0% and 24.2%, respectively. And curcumin was obviously slowly released because the cumulative release percentage of magnetic microspheres in the phosphate buffer (pH=7.4) solution was only 49.01% in 72 h, and the basic release of curcumin finished in 120 h. - Highlights: → We prepare magnetic polylactic acid microspheres loading curcumin. → The classical oil-in-water emulsion solvent-evaporation method is used. → The magnetic microspheres are regularly spherical with a diameter of 0.55-0.75 μm. → They show a certain sustained release effect on in vitro drug releasing.