In this paper, Y 2 O 3 -Lu 2 O 3 co-doped molybdenum secondary emission material were prepared by spark plasma sintering at 1480 °C for 5 minutes. the penetration depth of the primary electron were studied using Monte Carlo methods. Using first principles calculations based on the density functional theory, the secondary emission mechanism of the cathode were analyzed.
Bismuth ferrite nanopowders were hydrothermally synthesized with and without NH4Cl for comparison. The effects of NaOH concentration, reaction temperature and reaction time on the product phases and morphologies were studied in detail. Pure BiFeO3 was synthesized in a wide hydrothermal condition with the help of NH4Cl. Especially, it can be synthesized at low temperature of 140 degrees C. X-ray diffraction and Fourier transform infrared spectra revealed the BiFeO3 products had a perovskite structure. Scanning electron microscopy images showed that different BiFeO3 morphologies were formed under different hydrothermal conditions. NH4Cl played a key role in the BiFeO3 formation and BiFeO3 morphologies. Part BiFeO3 samples exhibited weak magnetic properties.
(Fe50Co50)(1-x)-Gdx thin films (30 nm) with x<15% deposited on silicon substrates by magnetron sputtering were investigated by X-ray diffraction, vibrating sample magnetometer, and ferromagnetic resonance. Theoretical fittings of the angular dependent ferromagnetic resonance field of the FeCoGd films have been performed using the Landau-Lifshitz equation It is found that the ferromagnetic resonance experimental data is well fitted by the theory and various magnetic properties have been extracted in accordance. The saturation magnetization decreases from 22750 Oe at x = 0% to 14079 Oe at x = 14% in the FeCo-Gd film, and the perpendicular magnetic anisotropy has changed from an easy film plane to an easy film normal geometry. The gyromagnetic ratio, as well as the Landé g factor, are found increased also with increasing Gd content, i.e. from g = 2.08 at x = 0% to g = 2.29 at x = 14%. An enhancement of the L-S coupling in the presence of a low Gd content has been concluded based on an observable increase from 0.011 at x = 12% up to 0.015 at x = 14% in the Gilbert damping.
With the rapid development of broadcasting, communication and aviation industry, the study of vacuum electron devices has become the key issue of the researchers around the world. Being the heart of electron tubes and magnetrons, the cathode plays an important role in these devices. Two kinds of cathodes, rare earth oxide-Mo cermet (RE2O3-Mo in brief) secondary emission materials and Scandia doped tungsten matrix impregnated thermionic emission materials have been studied.
Sodium-doped LaMnO3 samples were prepared by the urea combustion method and the structure of the samples was determined by X-ray diffraction experiments. The local structure of the samples was measured with extended X-ray absorption fine structure of the MnK-edge. The resistance of the samples (with and without applied magnetic field) shows a metal-insulator transition that implies the competition between large structural disorder and charge ordering. The sample with the largest Debye-Waller factor has the highest insulator-metal transition temperature (TIM) but the smallest magnetoresistance (MR) ratio. This indicates the different roles of disorder that plays onMRratio and TIM in sodium-doped LaMnO3 materials. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
In this paper, we propose a purely electrical scheme to generate the spin-polarized current with arbitrary spin polarization degree. Two parallel quantum dots are inserted in an asymmetry Rashba ring and subject to two time-dependent microwave fields, which is expected to pump out a sizable current in principle.
In this study, nanofluid heat transfer research has been divided by fluid conditions of laminar flow and turbulent flow. All parameter are compared to measure convective heat transfer coefficients altogether in entrance region. The effect of some factors such as mass fraction, temperature, and various velocity were selected and the effects of these parameters on the convective heat transfer coefficients in the water based fluids are discussed. Distilled water and Multi-walled carbon nanotubes were used to produce nanofluids.
High temperature annealing and Cs, O activation is the formations of NEA GaN photocathode of external incentives, GaN material performance of the cathode of the internal factors are fundamental. In this paper, aiming at the difference of the uniform-doping and gradient-doping NEA GaN photocathode in structure, combined with the cathode active changes of the optical current and activated after the success of the spectral characteristics of the uniform-doping and gradient-doping performance of NEA photocathode similarities and differences. Experiments show that: compared to the uniform-doping cathode, graded-doping cathode activated with radiation in the current slow growth rate, activation time is relatively long, successful activation of higher quantum efficiency. Using field-assisted photocathode emission model can explain the differences existing between the two, built-in electric field gradient doping structure to increase the presence of electronic drift to the cathode surface movement; the electron reaches the cathode surface to improve the escape probability of electronic.
In this paper, the structures and field emission properties of energetic C ion irradiated SiNWs have been investigated and influence of ion irradiation on structures and properties has been discussed. Vertically SiNW arrays are synthesized by using Ag-assisted electroless-chemical etching at room temperature, as reported in literatures. The process mainly comprises three steps: 1) surface cleaning of polished silicon wafers; 2) immersion of the cleaned silicon wafers into HF-based aqueous solution containing silver nitrate to synthesize Ag catalyst; 3) chemical etching of the Ag catalyst-covered silicon wafers in HF-base aqueous solution containing oxidant (H2O2). After throughout above processes, SiNW arrays have been synthesized. Then, the samples are immersed in 50% HNO3 solution to dissolve Ag catalyst. The as-grown SiNWs are irradiated by energetic carbon ion with an average energy of 20 keV and various doses. FE-SEM, EDS and XPS are employed to characterize the morphology and chemical structures of samples. The field emission measurement is carried out in an ultrahigh vacuum chamber with a bi-diode system, in which the base pressure is lower than 3x10-7 Pa.
Zinc oxide is a wide band gap semiconductor (WBGS). Its band bending, which usually favors field emission by lowering surface barrier and bringing more electrons to the bottom of conduction band, can be quite dramatic under high field. In the last few years, different kinds of ZnO nano-materials has been synthesized and applied as the cathode materials for field emission. For better application of ZnO in commercial field emission devices, long-term current stability is one of the most important aspects to be ensured. So in this paper, the field emission behavior of screen printing tetrapod ZnO will be studied by exposing to CO, which is the main residual gas in sealed tetrapod ZnO (T-ZnO) field emission device.
The authors have developed a new method to fabricate patterned W18O49 nanowire arrays by combination of thermal evaporation and lift-off technology. It is found that the phosphoric acid processing of the lift-off technology has strong effect on the field emission property of W18O49 nanowires.
Ca3Co2O6 has a rhombohedral structure composed of Co2O6 chains running along the hexagonal c-axis, separated by Ca2+ ions. Each chain is surrounded by six equally spaced chains, forming a triangular lattice in the ab plane. Because the intra-chain ferromagnetic coupling is much stronger than the inter-chain antiferromagnetic interaction, as T decreases, each ferromagnetic chain would behave like a rigid magnetic moment. Regarding each spin chain as a rigid giant spin, the three-dimensional compound may be simplified into a 2D triangular lattice. Therefore, in the present work, Monte Carlo simulation is performed on a 2D triangular lattice with classical Heisenberg spins. We focus on the influence of single-ion anisotropy to the magnetic property in this system. The results obtained are helpful to understand the stepwise magnetic behavior observed in Ca3Co2O6.
Summary form only given. The influence of alkali-metal adsorption positions and defects positions on work functions of (5, 5) single-walled carbon nanotubes (CNTs) with a capped edge had been investigated by first-principles calculations. An single-walled armchair (5, 5) CNT with a capped edge was assumed. A single vacancy defect was created by removing a carbon atom from different atomic layers (which were labeled as T1-T4 in FIG. 1(a)). The alkali-metal adatoms (Li/Na/Cs) were located above the center of the pentagons or hexagons (which were labeled as P1-P4 in Fig. 1(b)) on the caps for the perfect CNT (P-CNT), while they were associated with defective CNTs (D-CNTs) on the vacancy defects. After Li/Na/Cs adsorption, the work functions of the Pand D-CNTs along the Z-axis and the X-axis (X-WF) decrease significantly. Compared with adsorption of one Li/Na atom, the work functions of CNTs in axial or radial directions decreased more obviously after Cs adsorption. For comparison purpose, FIG. 1(c) summarizes the work functions of P-CNTs and D-CNTs (Ti) with alkali-metal adatoms on the top, plotted against the electronegativity of Li, Na and Cs. All the axial and radial work functions of (5, 5) Pand D-CNTs with Li/Na/Cs on P1 increase linearly with the electronegativity. The curves for the axial or radial work functions are almost parallel to each other. We plot the work functions of the (5, 5) P-CNT with alkali-metal adatoms on different positions in FIG. 1(d)-(e). For the adatom-P-CNT systems, there is no significant difference between the work functions in radial direction (except lower work functions in P3), while the work functions in axial direction actually depend on the adsorption position of alkali-metal atoms. The adatom-P-CNT systems have the lowest work functions with alkali-metal adatoms on P1 in axial direction and on P3 in radial direction. The work functions of different D-CNTs and adatom-D-CNTs systems with one vacancy defect in different atomic layers are shown in FIG. 1(f)-(g). One vacancy defect could raise the work functions of the CNTs. For the adatom-D-CNTs systems, there is no visible trend between the work functions in axial direction, while the work functions in radial direction show a monotonously decrease from T1 to T4. The adatom-D-CNTs systems have the lowest work functions with the Li adatom on T4 and the Na/Cs adatom on T2 in axial direction and with alkali-metal adatoms on T3 in radial direction. Since the electronegativity of Li/Na/Cs is less than carbon, the Li/Na/Cs adatoms on the CNTs are easily ionized. The charge density redistributions or charge transfer will lead to increase of the Fermi levels of the Pand D-CNT. The variation of work functions can be induced by either an enhanced (reduced) surface dipole moments, or a lowering (rising) of its intrinsic bulk Fermi levels [1]. Our results show that the changes of the work functions mainly come from the shifts of Fermi levels. The induced dipole moments lead to a minor decrease in the work functions.
Research of negative electron affinity GaN ultraviolet photocathode performance parameters on the effect of quantum efficiency is reported. Electronic surface escaping probability is one of the important parameters in comprehensive measure the level of the preparation of GaN optoelectronic cathode.
Metallic metamaterials with magnetic resonance have attracted a lot of interest during the passed decades due to their potential applications on realizing artificial magnetism from zero frequency to optical spectrum. Since nonmagnetic natural materials, such as Cu, are lack of magnetic response at microwave frequencies, magnetic metamaterials usually contain a resonant structure to provide artificial permeability. As for the resonator, various structures such as split ring and cut-wire pair, were proposed to explore the resonant magnetic properties with paramagnetic or diamagnetic response in similar to natural magnetic materials. In previous work we calculated the transmission spectra and effective permeability of a double square ring of Cu and observed the antibonding magnetic response (i.e., a pair of antiparallel magnetic dipolar moments for each double-ring unit cell). Such an antibonding magnetic resonance is interesting not only for its transient magnetic moments distribution just like an oscillation version of the static antiferromagnetism, but also for its Fano-type resonance. In this paper, we simplify the double-ring to a ring-plate structure, and investigate the modified artificial permeability for this antibonding magnetic resonance by introducing asymmetric geometry.
In this paper, a study on quick spark plasma sintering (SPS) method for synthesizing the polycrystalline CeB<;sub>6<;/sub> bulk is presented. CeB<;sub>6<;/sub> is the material of choice for high current density cathode. However, in fact, because of the long sintering time and high temperature, the traditional hot pressure sintering preparation of polycrystalline CeB<;sub>6<;/sub> bulk causes coarse grains and low density which decrease the emission property. The pulsed voltage method was used to test the electron emission of the CeB6. The pulse thermionic emission density was measured with increasing voltages up to 1000 V at various cathode temperatures from 1500 K to 1863 K, at pressure of 2x10-4 Pa, a pulse width of 20 μs and repetition frequency of 120 Hz.
It is of special interest to obtain a single nanodimensional emitting protrusion on the surface of a tungsten carbide emitter, which would serve as an ideal point source of electrons and ions. However, it is difficult to grow a single nanodimensional protrusion on the surface of a tungsten carbide emitter. In this study, the task was solved as follows. In the course of a field crystal growth, each nanoprotrusion reach a stationary state when the stretching electrostatic field forces pressure PF = F2/8π equal to the compressing surface tension forces pressure Pγ = 2γ/r (γ - the coefficient of surface tension) [5]. The pressure PF creates a grow and sharpening of a protrusion and the pressure Pγ creates a blunting and disappearance of a protrusion. If the PF value is gradually decreased (by reducing the applied voltage U), the value of Pγ will became greater than PF at first for the sharpest nanoprotrusion. As a result, this protrusion will be became blunt and cease to emit. By further reducing the applied voltage U we can gradually eliminate the emission from other protrusions until a single emitting nanoprotrusion survives.
