Advanced Materials Research Vols. 1120-1121

Abstract: Uniform LaPO₄ and LaPO₄:Ln³⁺ (Ln³⁺= Eu³⁺, Dy³⁺, Ce³⁺, Tb³⁺) microspheres have been selectively synthesized via a hydrothermal route, without using any catalyst, or template. X-ray diffraction, SEM, TEM, and photoluminescence spectroscopy were used to characterize the phase structure, morphology, and luminescence properties of the as-prepared samples. SEM results indicate that as-obtained samples have perfect spherical morphology with narrow size distribution. PL excitation and emission spectra demonstrated the LaPO₄:Ln³⁺ phosphors show strong light emissions with different colors coming from different activator ions under ultraviolet excitation, which might find potential applications in fields such as light phosphor powders and advanced flat panel displays.

Abstract: It has been studied that the impact of doping of Bi³⁺ on the luminescent properties of red phosphors Sr_3-xGaO₄F:xEu³⁺ prepared with high temperature solid-state reaction method followed by doping into certain amounts of Bi₂O₃. The resulting samples are characterized by XRD, Emission Spectrum and Excitation Spectrum. As a result, it is shown that the strongest emission peak caused by the forced electronic dipole transition of ⁵D₀-⁷F₂ is at 618 nm with solely doping of Eu³⁺. In addition, the luminescent intensity of the as-formed phosphor increases and the most intensive emission peak red-shifts with doping amount of Bi³⁺ while co-doping Eu³⁺ and Bi³⁺. Meanwhile, the relationship of energy transition of Eu³⁺ and Bi³⁺ is also discussed herein.

Abstract: Polycrystalline layered perovskite manganese oxides La_1.4Sr_1.6-xCa_xMn₂O₇ (x=0,0.2,0.4,0.8,1.0,1.4,1.6) samples is prepared using solid state reaction.The XRD analysis shows that La_1.4Sr_1.6-xCa_xMn₂O₇ (0 ≤ x ≤ 0.8) samples are Sr3Ti₂O₇-type tetragonal structure with space group I4/mmm and forms a layered perovskite structure; for the 1.0≤ x ≤1.6 series of samples the main phase is ABO₃ type orthorhombic structure with space group Pbnm.For small amount of Ca²⁺ ion-doped sample (x = 0.2,0.4), induce serious Jahn-Teller(J-T) distortion of MnO₆ octahedral.For a large number of doping (1.0≤ x ≤1.6) samples, ferromagnetic - paramagnetic transition occurs near the Curie temperature (T_c) from low to high temperatures.With increasing doping amount, the magnetization reached maximum at x=1.4 samples.Maximum magnetic entropy change of the three samples(x=1.0,1.4,1.6) reaches 0.84, 1.20 and 2.28 J kg^-1 K^-1 at 320,268 and 215K near the Curie temperature, respectively. The large magnetic entropy change effect under low magnetic field of the sample makes it an optimal candidate of room temperature magnetic refrigeration materials.

Abstract: Lanthanum oxide (La₂O₃) has been proposed as the promising gate dielectric material for future complementary metal-oxide-semiconductor (CMOS) technology. However, unlike the conventional homopolar materials such as silicon oxide or silicon nitride, La₂O₃ is more ionic and in particular at the La₂O₃/Si interface is less thermally stable. This work investigates the chemical and compositional variations of La₂O₃ thin film on the silicon substrate during rapid thermal annealing by using angle-resolved x-ray photoelectron spectroscopy (ARXPS) measurements. Results show that thermal annealing at temperatures above 500 °C would result in the incorporation of substrate Si atoms deep into the bulk of the La₂O₃ film and forming silicate phases both at the interface and in the bulk. These effects would result in the characteristic degradation of CMOS devices.

Abstract: In this paper, the hydrothermal-assisted liquid phase deposition (HT-LPD) method has been developed to prepare TiO₂ films. The crystalline structures and morphologies of as-prepared TiO₂ films were analyzed using an X-ray diffractometer (XRD) and scanning electron microscope (SEM). It was found that the HT-LPD TiO₂ film showed good crystallinity with preferrred orientation along c-axis. Moreover, the as-prepared TiO₂ films consisted of two layers, with the tiny nanoparticles as the underlying layer and the flower-like clusters as the upper layer. The photoelectrochemical measurements revealed that, when illuminated by the white light, the HT-LPD TiO₂ films exhibited a more negative photopotential value and an increased photocurrent value with elevated reaction temperature, excepting for the sample prerared at 150 °C. In summary, the TiO₂ films prepared by the improved LPD method could be served as the promising photoanode for the photoelectrochemical applications.

Abstract: In this paper, we studied the dependence of temperature and weak localization (WL) effect on the anomalous Hall effect (AHE) in strong disordered and poorly crystallized metal Co thin film deposited by high-pressure magnetron sputtering. The temperature coefficients of resistivity is positive at high temperatures and becomes negative at low temperatures, which is the typical characteristic of weak localization effect in dirty metal regime due to the strong disorder. The saturation anomalous Hall resistivity (ρ^A_xy) have no scaling relation between ρ_xy and ρ_xx in weak localization region with temperature below 50 K. In metal region, temperature ranged from 50 K to 300 K, the relation between ρ^A_xy and ρ_xx is ρ^A_xy=A+bρ²_xx, which indicates that the AHE in this Co thin film is scattering-independence at high temperature. The results also shows that the WL effect have a significant impact on the AHE of the Co thin film at low temperature.

Abstract: The optical and electric transport properties of the Al:ZnO(AZO) and (Cu, Al):ZnO (CAZO) films deposited by pulsed laser deposition (PLD) were investigated in this paper. The experiment found the optical band gap (OBG) of AZO films at room temperature increased from 3.378eV of ZnO to 3.446eV of ZnO:Al (2min) sample, but decreased as continue add Al to ZnO:Al (4min), which were attributes to the Burstein-Moss (B-M) effect. For CAZO films, there is obvious change about hall mobility, ν, and resistivity, ρ, after doped Cu. It can be found that the ν decreased from to and the ρ increased from to for AZO and CAZO, respectively, which is due to the scattering increasing between donor carriers and grain boundary as Cu²⁺ ions increase, meanwhile, it was also found the decrease of OBG, which are very help to further understand the electric transport properties and the OBG effect of AZO-based films as well as its devices potential application.

Abstract: In this work, n-type β-FeSi₂/intrinsic Si/p-type Si heterojunctions were prepared by facing-targets direct-current sputtering. We measured their current-voltage characteristics at low temperatures ranging from 300 K down to 50 K and investigated their ideality factor, saturation current and series resistance using thermionic emission theory and Cheung’s method. From thermionic emission theory, the ideality factor and saturation current density were calculated from the slope of the linear part from the forward lnJ-V and the straight line intercept of lnJ-V at zero voltage, respectively. When the temperature decreased from 300 K down to 50 K, the ideality factor increased from 1.12 to 11.13, whereas the saturation current density decreased from 2.09 × 10^-6 A/cm² to 1.06 × 10^-9 A/cm². Using Cheung’s method, we plotted the relations of dV/d(lnJ)-J and H(J)-J in order to estimate the series resistance from the slope of both plots. In addition, we estimated the ideality factor from a y-axis intercept of the dV/d(lnJ)-J plot. The series resistances from both plots were consistent with each other and increased with the decreasing temperature. The ideality factor estimated by Cheung’s method was in agreement with that obtained from estimation by thermionic emission theory.

Abstract: The glass forming ability and magnetic properties were investigated for adding neodymium to the Fe_71-xNb₄B₂₅Nd_x (x=0, 3, 5, 7,10) alloys prepared by copper suction casting. It was found that proper neodymium (x=5~10 at.%) could improve glass forming ability of Fe-Nb-B alloys effectively. Bulk amorphous Fe₆₆Nd₅B₂₅Nb₄ and Fe₆₄Nd₇B₂₅Nb₄ samples were obtained and presented high thermal stability and good soft magnetic properties. The value of activation energy of the first crystallization peak for the bulk amorphous alloy Fe₆₄Nd₇B₂₅Nb₄ is 683 kJ/mol.

Abstract: Organic light-emitting materials in Organic Light-emitting Diodes(OLED) reserch in a very important posotion, the quality of materials directly affect the level of luminous efficiency of the device. We chose benzene 2,6-alkynyl, respectively, and tetrakis (4-bromophenyl) silane, tetrakis (3-bromophenyl) silane synthesis of new cross-linked polymer, the structure was characterized by solid NMR, by fluorescence chromatography UV crosslinking compound characterization of chromatographic performance in photophysical aspects may choose to add a new organic light-emitting material.