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The explosive behavior of neo-classical double tearing mode (NDTM) is numerically investigated by a reduced four-field-drift-magnetohydrodynamic code [Ye et al., Nuclear Fusion 59, 096044 (2019)] with the bootstrap current effect. It is numerically observed that the explosive burst of NDTM can be absolutely suppressed by diamagnetic drift flow. The dependence of the critical value of diamagnetic drift flow V 0 * c for avoiding the explosion on typical plasma parameters is numerically studied in detail. It is found that V 0 * c decreases with increasing Δ r s , while it increases with an increasing bootstrap current fraction. The plasma viscosity and resistivity can raise the threshold through their effects on the rotation of magnetic islands and the instability of system, respectively. Furthermore, the perpendicular transport and parallel transport, which are significant to the driven effects of the bootstrap current, have the opposite effects on V 0 * c . The underlying mechanisms are discussed. [ABSTRACT FROM AUTHOR]

ZnTiO3 thin films were prepared by radio frequency cosputtering of ZnO and TiO2. It was found the as-prepared film is amorphous and the cubic phase ZnTiO3 films form after annealing at temperature above 500 °C. The absorption spectra indicate that the optical band gap of the crystalline ZnTiO3 film is about 3.70 eV. A strong photoluminescence band centered at 355 nm consisting of two emission peaks was observed in 800 °C annealed ZnTiO3 thin film, and the peak positions of these two emission move to short wavelength with increasing annealing temperature. It was found the emission peak at ultraviolet zone is resulted from O2- vacancy and that in the blue zone is attributed to Zn2+ vacancy. [ABSTRACT FROM AUTHOR]

The microstructure and optical properties of MgO–TiO2 composite thin films prepared by radio frequency magnetron sputtering were studied. The composite films have an amorphous structure and the growth rate of the composite film increases with increasing Mg content. The refractive index almost linearly decreases with increasing Mg content in the composite films at wavelength larger than 300 nm and can be adjusted in the wide range between the refractive index of TiO2 and that of MgO. The extinction coefficient decreases with Mg content and is nearly zero at visible light region. The optical band gap of the composite films determined from the absorption spectra increases with Mg content, and has a good agreement with that obtained from spectroscopic ellipsometry simulation. A broad photoluminescence band in the visible region was observed in the composite films with high Mg content and was considered resulted from the oxygen vacancies. [ABSTRACT FROM AUTHOR]

Presents a study which deposited crack-free transparent ferroelectric lanthanum-doped lead zirconate titanate (PLZT) thin films on silicon substrates using the sol-gel deposition technique. Method and materials used in preparing silicon wafer samples; Approach used in the wet chemical etching of the samples; Observation on the wave guiding properties of the PLZT.

Plasma toroidal rotation acceleration in the co-current direction introduced by the n = 1 (toroidal mode number) static resonant magnetic perturbation (RMP) has been observed in the EAST tokamak. It strongly depends on the RMP coil configuration, which is manifested by its dependence on δ ϕ U L (phase difference between upper and lower coils) and RMP current. Modeling results from NTVTOK based on the linear plasma response modeled by MARS-F shows that the Neoclassical Toroidal Viscosity (NTV) torque is in the co-current direction because of the dominant contribution from electrons with the condition that the electron normalized collisionality is much lower than that of ions in this experiment. The modeled dependence of core integrated NTV torque modulated by the magnitude of core magnetic perturbation on δ ϕ U L is consistent with the experimental observations. Threshold condition related to normalized collisionality to achieve the transition from rotation braking to acceleration is obtained in the NTV modeling and agrees well with experimental observations. It is shown in the modeling that the discharges with rotation acceleration are located at the regime that electron contribution to NTV is dominant and the torque is in co-current direction, while others with rotation braking are located at the regime that ion contribution to NTV torque is dominant and the torque is in countercurrent direction. Though the modeling results are in qualitative agreement with the experimental results, there is quantity difference between the modeled NTV torque based on linear plasma response and the experimental values. Possible reason is that the 3D fields are underestimated by linear modeling, particularly in the case of RMP field penetration, as demonstrated by the RMP current threshold for the rotation acceleration observed in the experiments. [ABSTRACT FROM AUTHOR]

The discharge chemistry of CHF3 in 27/2, 60/2, and 60/13.56 MHz dual-frequency capacitively coupled plasmas (DF-CCPs) is studied with actinometric optical emission spectroscopy and mass spectrometry. The frequency effect on the generation of reactive species was investigated. The reactive radicals and the density ratio of F/CF2 could be controlled by the 2 MHz rf power in 27/2 and 60/2 MHz DF-CCPs. The density ratios of F/CF2 in 27/2 and 60/2 MHz DF-CCPs are observed to increase with an increase in low-frequency power. However, this control could not be obtained in 60/13.56 MHz DF-CCP. [ABSTRACT FROM AUTHOR]

The photoluminescence properties of nitrogen-incorporated SnO2 thin films on Si (100) substrates deposited by reactive magnetron sputtering have been studied. A strong photoluminescence band centered at 3.696 eV with full width at half maximum of 0.2 eV has been observed at room temperature. The peak position of the emission shifts to higher energy with increasing excitation intensity or decreasing temperature. The emission is considered due to the localized exciton recombination, and the observed exciton localization and band-tail states are believed to originate from the potential fluctuation induced by spatial distribution fluctuations of nitrogen concentration and/or grain boundary defects in the nanocrystalline film. [ABSTRACT FROM AUTHOR]

Investigates trap levels in sol-gel derived polycrystalline Pb(Zr,Ti)O[sub 3] thin films using deep level transient spectroscopy (DLTS). Fabrication of metal-ferroelectric-metal capacitor structures using a constant voltage DLTS system; Observation of prominent peaks associated with a single trap level; Measurement of the activation energy.

In this work, the thermal stability of annealed Ag/Nb multilayers was investigated as the individual layer thickness (h) varies from 1 nm to 100 nm. The lamellar structures remain unchanged after annealing at 500 °C for 1 h, and the hardness at all scales remains undiminished after annealing. The results show that two low energy interfaces are responsible for the superior thermal stabilities. The coherent interface is formed when h < 20 nm, and the amorphous interface is formed when h ≥ 20 nm, respectively. The evolution of interfacial structures and the process of solid state amorphization are discussed accordingly. [ABSTRACT FROM AUTHOR]

Focuses on a study conduted using simplified kinetic models to investigate the mechanism of negative differential conductivity (NDC) in an electron-beam sustained gas discharge of pure xenon (Xe). Calculation of the drift velocity of electrons in Xe; What model calculations involves; Definition of NDC; Discussion on the influence of the uncertainty in the momentum transfer cross sections and the small impurity of Xe on NDC observation.

In direct-drive–ignition designs, preheat by fast electrons created by the two-plasmon–decay or stimulated Raman instabilities can increase the adiabat in the fuel layer and reduce compression and neutron yields. Since eliminating the preheat entirely is a major challenge, it is necessary to understand the levels of preheat that preclude ignition in a direct-drive target. Two 1-D ignition-scale target designs serve as the basis for examining the effects of synthetically increasing the levels of fast electrons using the 1-D radiation–hydrodynamic code LILAC, which include two models of fast-electron transport. The first is an ignition design adapted from a 2-D polar-direct-drive design for the National Ignition Facility. The second is a variant of the first with identical dimensions and compositions but using a laser pulse that generates stronger shocks and a higher fuel adiabat. This more stable design approaches ignition and achieves yield multiplication as a result of alpha heating. The designs are then re-optimized to recover performance. The igniting design, when fast-electron transport was modeled with diffusion, was found to tolerate 50% more fast-electron preheat of the cold (sub-50 eV) deuterium-tritium (DT) ice layer when the laser pulse was optimized using the optimizer Telios. When a straight-line fast-electron transport model was used, the effects of optimization were negligible. For the subignition design, an increase of over a factor of at least 3 in the tolerable level of fast-electron preheat was obtained for both transport models. [ABSTRACT FROM AUTHOR]

The interaction of Na impurities and O vacancies (VO) in ZnO was studied in theory and experiment. The VO facilitated substitutional Na (NaZn/NaZn-) acceptors with inhibiting interstitial Na (Nai/Nai+) donors, which may benefit the p-type conductivity. The formed (NaZn-VO)+/0 complexes induced the change of band structures of ZnO, with the broadening of gap energies and disappearance of the VO2+-related impurity level, which confirmed by the blue shift of the near-band-edge (NBE) UV emission and the decay of the visible emission in PL spectra. The strong and dominant NBE UV emission suggested acceptable luminescence behaviors of Na-doped ZnO. [ABSTRACT FROM AUTHOR]

The influence of annealing on the morphological, structural, and optical properties of ZnO:Tb thin films on Si substrate grown by magnetron cosputtering is investigated. It has been found that the ZnO:Tb thin films with structures of tetrapod and screwlike nanorod are formed after annealing at temperature of 950 °C. X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and Raman analyses prove that the tetrapod-aiguille zinc oxide (T-A-ZnO) and the screwlike nanorods are composed of Zn, Tb, and O elements. The photoluminescence spectra of the ZnO:Tb thin films with the T-A-ZnO structure and the screwlike nanorods are featured with two ultraviolet emission peaks and one strong green emission band, and the photoluminescence intensity increases with increasing annealing temperature. The surface defects in the T-A-ZnO structure and the screwlike nanorods are considered to be responsible for enhanced green emission in the annealed ZnO:Tb thin films. [ABSTRACT FROM AUTHOR]

The valence band offset (VBO) of a n-ZnO/p-MgxNi1-xO heterojunction grown by pulsed laser deposition was investigated by x-ray photoelectron spectroscopy. From the directly measured VBO of 1.64 ± 0.05 eV, a -2.26 ± 0.05 eV conduction band offset was derived. This indicates that the ZnO/MgxNi1-xO heterojunction has a type-II (staggered) band alignment. The conduction band minimum (CBM) of the n-ZnO/p-MgxNi1-xO heterojunction shifts to higher energy with Mg doping relative to the n-ZnO/p-NiO heterojunction. Thus, the position of the CBM can be controlled by the Mg concentration. [ABSTRACT FROM AUTHOR]

A series of 10-period ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) with well widths varying from 2.2 to 5.6 nm have been grown on r-plane sapphire substrates by pulsed laser deposition. A good periodic structure with clear interfaces was observed by transmission electron microscopy. In a-plane ZnO/Zn0.9Mg0.1O MQWs, the luminescence was dominated by localized exciton emissions at low temperatures, while the free exciton (FE) transition was dominating emissions at temperatures above 100 K. The thermal quenching behavior of exciton emission has been analyzed. A rate equation assuming two nonradiative recombination channels is used to describe the quenching of the transitions observed. Moreover, the FE emission energy in the MQWs shows a systematic blueshift with decreasing well width, which is consistent with a quantum confinement effect. [ABSTRACT FROM AUTHOR]

The N2 atmosphere postannealing is introduced to improve the interfacial quality and the dielectric properties of HfO2 films prepared by pulsed laser deposition. The disappearance of interface layer between HfO2 film and Si substrate and the decrease of leakage current densities after annealing are further confirmed by high-resolution cross-sectional transmission electron microscopy investigation and electrical measurement. Electric conduction analysis results show that the dominant leakage current conduction mechanisms of the annealed HfO2 film are the Schottky emission at low electric field, the trap-assisted tunneling, and space-charge-limited current at high electric field for the gate and substrate injections, respectively. [ABSTRACT FROM AUTHOR]

Hollow cadmium selenide (CdSe) tetrapods were synthesized on a large scale. The directional growth of twins led the tetrapod nanostructure to be formed. The silicon powder was responsible for the growth of the hollow tetrapods. The UV-visible absorption spectra of the hollow CdSe tetrapods display an absorption edge at about 765 nm. There is a redshift of 53 nm of the absorption edge, in comparison with that of bulk CdSe at 712 nm. In the Raman spectra, two new anomalous modes at 250.91 and 493.42 cm-1 are observed. This might originate from the enhanced internal stress of hollow structures. [ABSTRACT FROM AUTHOR]

The optical properties of δ-Bi2O3 thin films were investigated using spectroscopic ellipsometry and optical absorption spectrum. δ-Bi2O3 thin films were grown on Si and quartz substrates under different oxygen flow ratios (OFR) by radio frequency reactive magnetron sputtering. The Tauc-Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films. The optical bandgap was obtained by three different methods. It was found that refractive index and extinction coefficient decrease, and the optical bandgap has a slight blue shift with increasing the OFR. Factors influencing the optical constants and optical bandgap are discussed. [ABSTRACT FROM AUTHOR]

A series of Al-doped amorphous silicon oxide films have been grown on p-type silicon (100) substrates by a dual ion beam cosputtering method. Visible electroluminescence (EL) from the devices, made by films with different contents of Al, can be seen with the naked eye under forward bias and reverse bias for films containing sufficient amounts of Al. The EL spectra are found to have a luminescence band peaked at 510 nm (2.4 eV), which is the same result as that obtained from silicon oxide films. With the increase in the amounts of Al, the peak position does not shift, the onset of the bias decreases, and the intensity of EL peak increases. Experiment results show that the doping of Al is beneficial to improving the conduction condition of films while the structure of the films associated with luminescence centers is affected hardly at all. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Thin films of the high Tc superconducting Y-Ba-Cu metal oxide have been prepared for the first time by plasma-assisted organometallic chemical vapor deposition using β-diketonate chelates of Y, Ba, and Cu, Y(C11H19O2)3, Ba(C11H19O2)2, and Cu(C11H19O2)2 as starting materials, followed by post-annealing under a reduced pressure of oxygen stream. X-ray diffraction spectra indicate that the films deposited on the yttria-stabilized zirconia (YSZ) substrate have a significant preferential orientation of the crystallite c axis being perpendicular to the substrate surface. Four-probe resistivity measurements reveal the temperature of the onset of superconductivity at 91.6 K and zero resistance by 78.5 K. [ABSTRACT FROM AUTHOR]