Structure and magnetic properties of the Co x Pt100−x nanowire arrays

The development of photocathodes materials has become an important task for X-ray free electron laser and new generation of particle accelerator. The choice of the optimum cathode type and its further improvement is a fundamental issue for the progress in radio-frequency photoinjectors. Metallic photocathodes offer several advantages over the semiconductor ones, e.g. long lifetime and prompt response time on the photoemission. This paper reviews the requirements and the current status of metallic photocathodes prepared by pulsed laser ablation deposition technique. Magnesium, yttrium and lead are proposed as good alternative to copper photocathode which is generally used in radio-frequency photoinjectors. Parametric studies of the irradiation conditions are demanded to optimize the metallic thin film deposition. The main achievements on the morphology and structure characterization as well as photoemission testing of metallic photocathodes are presented and discussed.     

Structure and magnetic properties of Fe96−x Zr x B4 nanowire arrays

Fe96-xZrx B4(1相似文献   

Synthesis and piezoelectric properties of?well-aligned ZnO?nanowire arrays via a?simple solution-phase approach

An effective, low cost and catalyst-free solution-phase approach was demonstrated for achieving a tailored length and controlled surface-to-volume ratio of aligned ZnO nanowire (NW) arrays. By a slight variation of the solution concentration and growth time, significant changes in length and surface-to-volume ratio of the obtained ZnO NW arrays have been controlled, respectively. The morphology and microstructure of the synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Also the growth mechanism was discussed. For the study of the piezoelectric property of aligned ZnO NW arrays, some measuring models of nanogenerators (NGs) were fabricated with two pieces of grown ZnO NW array structures stacking together and penetrating into each other. One of the pieces was coated with Au film as the conductive nanotip (NTP) array. The NG was driven by an ultrasonic wave. The piezoelectric output current was gained and characteristic curves have been illustrated for different measuring results. The curves show that increasing the length and surface-to-volume ratios of ZnO NW arrays can enhance the output power of the NGs, respectively. It can be seen that the NGs fabricated with size-controlled ZnO NW arrays provide a feasible technology for building high-power output or power-controlled NGs for applications where a smaller size or appointed power output NGs are required. However, no relationship was found between the piezoelectric current output and the driving frequency of ultrasonic waves from 10 to 50 kHz.     

Magnetic properties of Co–Cu nanowire arrays fabricated in different conditions by SC electrodeposition

Magnetic Co–Cu alloy nanowires with low Cu content were prepared by SC electrodeposition in pores of anodic aluminum oxide templates. The as-deposited Co–Cu nanowires, with a diameter of 15 nm, show distinctive magnetic anisotropy as an applied magnetic field parallel to the axis of nanowires. With increase in the molar ratio of Co and Cu, the coercivity along nanowire axis increases and reaches a maximum value of 1977.5 Oe at the Co/Cu molar ratio of 60:1, but the maximum value of coercivity increases to 1743.6 Oe with the decrease of frequency to 2 Hz.     

Electrochemical fabrication and characterization of lepidocrocite (γ-FeOOH) nanowire arrays

We report on the fabrication of γ-phase iron oxyhydroxide (γ-FeOOH, lepidocrocite) nanowire (nw) arrays within the alumina pores by electrodeposition. An aqueous solution, friendly to alumina matrix, was generated and applied in this study for uniform deposition of γ-FeOOH nw arrays directly through the alumina barrier layer using an alternating current (ac) mode. As-deposited nanowired products were characterized using ⁵⁷Fe Mössbauer spectroscopy (MS), atomic absorption spectrophotometry analysis, field-emission scanning electron microscopy, UV-vis transmission spectroscopy, transmission electron microscopy and X-ray diffraction. The formation of pure lepidocrocite nw arrays in the alumina pores with the average Ø_pore of 45 and 150 nm was verified by transmission MS at cryogenic temperatures.     

Vibrational and Light-Emitting Properties of Si/Si1−xSnx Heterostructures

Multilayer heterostructures Si/Si_1−xSn_x grown by molecular beam epitaxy on Si (001) substrates have been studied by Raman and photoluminescence spectroscopy. Raman spectra exhibit peaks corresponding to the vibrations of Si-Sn and Sn-Sn bonds; the vibrations of Sn-Sn bonds imply the presence of tin nanocrystals in heterostructures. Two photoluminescence bands at 0.75 eV (1650 nm) and 0.65 eV (1900 nm) have been observed in heterostructures at low temperatures. The former band can be attributed to optical transitions in quantum wells in the type II heterostructure Si/Si_1−xSn_x. The latter band can be associated with excitons localized in tin nanocrystals.

     

Knight shift in PbTe and Pb1−xSnx Te

The importance of various contributing mechanisms to the Knight shift (K) in PbTe and Pb_1−xSn_xTe is analyzed using a perturbation theory and a general experession for K which includes the spin (K_s), orbital (K_o) and spin-orbit (K_so) contributions to the Knight shift. It is found that K_s is the dominant contribution. However, with increase in the carrier concentration, the strength of K_so increases, and becomes of the same order as K_s at high density of carriers. K_o is found to be small throughout the range of the carrier density considered. Further, it is seen that the electron-electron exchange enhancement parameter increases with increase in the carrier density. We have also considered the effect of temperature. The results and the trends obtained in our calculation are in overall agreement with the experiment for the range of the carrier density considered.     

Hydrothermal-induced oriented growth of Fe–Co alloy and Sm-substituted magnetite nanowire composites

Fe–Co alloy and Sm³⁺-substituted magnetite nanowire composites (Co_xFe_1−x/Co_yFe_1−ySm_zFe_2−zO₄) have been synthesized via a hydrothermal method without using surfactants or templates. The effects of substitution on structure and morphology were investigated by powder X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy (TEM). The TEM image shows that the average diameter of the magnetite nanowires is about 40 nm and the length is several micrometers. The z=0.1 composite shows relatively high saturation magnetization (92.3 emu/g) detected by a vibrating sample magnetometer. The possible growth mechanism of the nanowires is discussed on the basis of the crystal structure of the materials. From the perspective of thermodynamics, we explain the postulated mechanism of the hydrothermal reaction.     

Synthesis and superconductivity properties of Ba1−xKxBiO3

Ba_1?xK_xBiO₃ with x from 0.315 to 0.6 were successfully synthesized by molten salts method and characterized by XRD and magnetic susceptibility measurements. It is found that Ba_1?xK_xBiO₃ powders could directly be precipitated from KOH melts. Superconductivity has been observed in all samples and the highest superconducting transition temperature was found to be T_c = 30.6 K with x = 0.4. The lattice constant linearly depended on the potassium content in accord with the equation of a = 4.3548–0.1743x, and the decrease of the mole ratio of Bi³⁺/Bi⁵⁺ resulted in the increase of the potassium content, which suggested the disproportionation of Bi valence.     

Elastic and vibrational properties of Mg2Si1−xSnx alloy from first principles calculations

The structural, elastic and phonon properties of Mg₂Si_1?xSn_x alloy are investigated by performing density functional theory and density functional perturbation theory calculations. The calculated lattice parameter increases with the increase of Sn content obeying Vegard’s Law that is in good agreement with available experimental data. Shear modulus, Young’s modulus and sound velocities are determined from the obtained elastic constants. Phonon dispersion curves show a pronounced softening with increasing of Sn content. The softening mechanism has been discussed based upon the element mass and bond strength. Besides, phonon contribution to the Helmholtz free energy, the entropy and the constant-volume heat capacity are calculated within the harmonic approximation based on the calculated phonon density of states. Results show Mg₂Si_1?xSn_x is thermodynamically more stable with higher Sn content.     

Synthesis and magnetic properties of Co–Zn magnetic fluid

Co_1−xZn_xFe₂O₄ (with x varying from 0 to 0.7) nanoparticles to be used for ferrofluid preparation were prepared by chemical co-precipitation method. The fine particles were suitably dispersed in transformer oil using oleic acid as the surfactant. The magnetization (M_s) and the size of the particles were measured at room temperature. The magnetization (M_s) was found to decrease with the increase in zinc substitution. The magnetic particle size (D_m) of the fluid was found to vary from 11.19 to 4.25 nm decreasing with the increase in zinc substitution.     

The realization of ion-implanted Hg1−xCdxTe photovoltaic arrays

A review of the main aspects of the realization of PV Hg_1−xCd_xTe arrays is presented. Results obtained on coating this material are reported and related to the carrier concentration of the bulk. Changes in the electrical properties, produced by ion implantation, are also reported and discussed.     

High-temperature background of internal friction in (Co45Fe45Zr10) x (Al2O3)100 − x , Co x (CaF2)100 − x , and Co x (PZT)100 − x nanocomposites

The elastic (G) and inelastic (Q ^?1) properties of (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 ? x} , Co _x (CaF₂)_{100 ? x} , and Co _x (PZT)_{100 ? x} (x = 23–76 at %) nanocomposites obtained by ion-beam sputtering are studied in the temperature range 300–900 K. A significant rise in the Q Q ^?1 (T) curve is observed at temperatures above 650 K, which is attributed to thermally activated migration of point defects under the conditions of confined geometry.     

Structural and magnetic properties of Ga-substituted Co2−W hexaferrites

Precursor powders of BaCo₂Fe_16-xGa_xO₂₇ with 0.0 ≤ x ≤ 0.8 were prepared using high-energy ball milling, and the effects of chemical composition on the structural and magnetic properties of the powders sintered at 1300 °C were investigated using x-ray diffractometer (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). XRD patterns of all samples indicated crystallization of pure BaCo₂−W (BaCo₂Fe₁₆O₂₇) hexaferrite phase. SEM measurements revealed large step-like formations with hexagonal crystallites. The magnetic data revealed small fluctuations of the saturation magnetization below the value 72.56 emu/g corresponding to the unsubstituted sample. The coercive field H_c of all samples ranged between 70 Oe and 130 Oe, indicating soft magnetic phase. Curie temperature determined from the thermomagnetic curves of the samples decreased from 485 °C at x = 0.0 down to 451 °C at x = 0.6. Also, the thermomagnetic curves revealed the presence of a minority magnetic phase with enhanced superexchange interaction, and the occurrence of complex magnetic phase transitions associated with spin reorientation transitions above room temperature.     

Magnetic properties and reduction characteristics of Fe–Co–B catalysts

Hyperfine Interactions - The effect of the amount of boron on the magnetic properties and the reduction characteristics of Fe–Co–B catalysts have been studied by Thermal Programmed...     

Synthesis,microstructure and dielectric properties of (1−x)PSN−xPLuN

Ceramic lead niobates and their solid solutions PSN–PLuN (pure lutecium niobate) were synthesized by solid state reactions. The sequence of phases formed at PSN–PLuN synthesis has been studied by X-ray analysis. Their symmetry changed from rhombohedral for PSN to pseudo-monoclinic for the 0.75PSN–0.25PLuN compositions. The performed EDS investigations revealed that the samples PSN–PLuN are perfectly sintered. They contain a little glassy phase and their grains are well shaped. The increase of lutecium content in the examined solid solution caused downward shift of the temperature of the phase transition. The decrease of the achieved permittivity values ? was observed as well.