Electron emission during pulsed polarization switching of ferroelectric ceramics

It is shown that in the pulsed polarization switching of polycrystalline ferroelectrics in high fields the external field is damped by the electronic subsystem associated with the crystallite boundaries. Therefore, the reorganization of a ferroelectric system with a high density of surface states at the crystallite boundaries is not irreversible, and the system returns to its former state after the polarization-switching voltage is removed. Because of this, electron emission from the surface of a ferroelectric ceramic can be brought about by unipolar pulses. Zh. Tekh. Fiz. 69, 49–52 (July 1999)     

Low-voltage nonstationary electron emission from single-walled carbon nanotubes as exoelectron emission

Low-voltage nonstationary electron emission from single-walled carbon nanotubes after the passage of high autoemission current has been observed. This emission is assumed to be exoelectron emission associated with mechanical stresses and defects appearing in nanotubes due to electrostatic forces acting on nanotubes in a strong electric field.     

The switchable component of ferroelectric ceramics polarization and pulsed emission of electrons

The switchable component of the polarization of ferroelectric ceramics subjected to a pulse electric field was found with the use of the Preisach model. The model parameters were found for PLZT-9/65/35 ceramics from an experimentally found hysteresis loop. The threshold field strength for the switchable component was established to be close to the threshold strength of electron emission.     

Energetic electron emission from a ferroelectric sample during incomplete surface discharge

In this paper, the results of simplified analytical modeling and particle-in-cell numerical simulations of plasma formation and propagation along the surface of a ferroelectric sample under the application of a negative driving pulse to the rear solid electrode are presented. These models allow one to reproduce the main characteristics of the incomplete discharge. In particular, it is shown that the experimentally observed energetic electrons are related to the secondary emission electron acceleration in the sheath between the plasma and the ferroelectric surface. Also, simulation results show that secondary electron emission significantly decreases the surface plasma density while increasing its propagation velocity and that high desorption rate of the neutrals is required to sustain surface plasma formation.     

短脉冲强激光驱动磁重联过程的靶后电势分布特征

超短超强激光因其极端的物理参数范围以及可用于研究相对论等离子体等特征,成为当前激光驱动磁重联物理的研究热点.通常采用两路激光与平面靶相互作用实现激光驱动磁重联,然而在实验诊断中,由于激光等离子体自身的复杂性导致很难辨别磁重联的物理特征.本文对两路短脉冲激光驱动平面靶磁重联进行了数值模拟,重点分析了靶后电势分布特征和磁重联之间的关系.模拟结果显示,靶后电势分布可以直接影响被加速离子在探测面上的空间分布,因此可用来直接诊断短脉冲激光驱动磁重联实验.     

Absorption current in a loaded ferroelectric ceramic material

This paper reports on the results of measurements of absorption currents in a ferroelectric ceramic material without external mechanical load and after bending. The revealed changes in the time dependence of the current are compared with those obtained by simulating the domain wall motion. The experimental results are in satisfactory agreement with the model dependence with due regard for the change in the character of domain motion.     

Nanosecond-time-resolution thermal emission measurement during pulsed excimer-laser interaction with materials

A nanosecond-time-resolution pyrometer has been developed for measuring the transient surface temperature of a solid material heated by pulsed excimer-laser irradiation. Fast germanium diodes are employed to capture the transient thermal emission signals in the wavelength range between 1.2 and 1.6 pm. The surface temperature is derived from the measured spectral thermal emission. The directional spectral emissivity is determined in situ by measuring the transient directional spectral reflectivity and applying Kirchhoffs law. The experimental results are in good agreement with numerical thermal modeling predictions. The pyrometric thermal emission measurement also yields the solid/liquid interface temperature during the pulsed excimer-laser-induced melting. The relation between the measured interface superheating temperature and the interface velocity reveals the melting kinetic relation during the high-power, short-pulse laser-induced phase-change processes.     

Nanosecond-time-resolution thermal emission measurement during pulsed excimer-laser interaction with materials

A nanosecond-time-resolution pyrometer has been developed for measuring the transient surface temperature of a solid material heated by pulsed excimer-laser irradiation. Fast germanium diodes are employed to capture the transient thermal emission signals in the wavelength range between 1.2 and 1.6rwm. The surface temperature is derived from the measured spectral thermal emission. The directional spectral emissivity is determined in situ by measuring the transient directional spectral reflectivity and applying Kirchhoff's law. The experimental results are in good agreement with numerical thermal modeling predictions. The pyrometric thermal emission measurement also yields the solid/liquid interface temperature during the pulsed excimer-laser-induced melting. The relation between the measured interface superheating temperature and the interface velocity reveals the melting kinetic relation during the high-power, short-pulse laser-induced phase-change processes.     

Thermoluminiscence and exoelectron emission of KCl phosphors,activated by mercury-like ions

An experimental investigation is made of thermostimulated electronic emission and luminescence in potassium halide crystals activated with mercury-like ions. These phosphors were excited with X-rays or ultra-violet light in the activator absorption bands. The transfer of activator excitation to the host lattice, the creation of colour centres by these processes and the mechanism of exoelectron emission are discussed.Physics and Astronomy Institute of the Estonian Academy of Sciences, Tartu, Est.S.S.R. The experimental part of the work was completed in October–November 1962, during H. Käämbre's stay at the Institute of Solid State Physics, Prague.     

Measurement of the statistics and spatial distribution of pulsed amplified spontaneous emission

The statistical and spatial distribution of a source of pulsed A.S.E. working in the linear regime are found to agree with those of spontaneous emission in a time short compared with a transition lifetime, as predicted by Allen et al.     

Thermally stimulated exoelectron emission of BeO: Excitation by low energy electron impact

The thermally stimulated exoelectron emission (TSEE) of oxide films on polycristalline Be substrates can be excited by extremely low energy electron bombardment (primary energies below 5 eV). The emission intensity as a function of primary energy is different for the two groups of high and low temperature glow peaks. A threshold of excitation for the glow maxima below 400°C cannot be measured down to excitation energies of 1 eV, whereas a resonance in the excitation function is found around 3.5 eV for the peaks above that temperature. These excitation functions are discussed in connection with the present emission concepts of BeO.     

Thermally stimulated exoelectron emission (TSEE) of BeO: Work function dependence

The TSEE of oxide films on Be foils has been investigated in ultrahigh vacuum with the facility of preparing clean oxide layers by argon sputtering and oxidation in situ. There is the possibility of monitoring the chemical state of the surfaces investigated by Auger spectroscopy via chemical effects in the Be-KVV line. Only surfaces oxidized in wet oxygen turn out to be TSEE-active and extremely stable emitters. Measurements of the thermionic work function demonstrate that low electron affinity values of the oxide surfaces are necessary to observe exoelectron emission. Clean oxide surfaces are found to be TSEE-inactive.Dedicated to Prof. Dr. Dr. Ing. E.h. W. Hanle on occasion of his 75th birthday.Part of thesis (D 26).     

The effect of injected-charge spatial distribution on the x-ray induced electron emission intensity in ferroelectric electrets

The nonmonotonic behavior of electron emission intensity induced in a surface layer of a ferroelectric electret by soft x-ray irradiation with an injected charge depth is predicted using a model of an accelerating electric field. The predicted behavior is in agreement with the results of the model experiments.     

Colossal magnetoresistance in pulsed laser-deposited thin ceramic films

Films of La_100−xCa_xMnO_z, where x = 34, 40 and 50, with perovskite structure, have been prepared by pulsed laser deposition. The films are non-epitaxial, polycrystalline and have cubic crystal structure at room temperature. The temperature variation of resistivity shows no evidence of an electrical phase transformation. The highest CMR observed is near 1800% at 55 K in a maximum applied field of 70 kOe (5600 kA/m). The results of temperature variation of susceptibility, hysteresis, resistivity and CMR properties follow a self-consistent behaviour.     

结构紧凑陶瓷电容器型脉冲调制器

设计了一种结构紧凑的陶瓷电容器型脉冲调制器,对其电路进行了理论计算,分析了主要参数对调制器输出波形的影响,并用PSpice软件建立电路模型进行验证,模拟结果与理论计算结果相符较好。该调制器能够产生上升前沿小于10 ns、脉宽30～40 ns、幅度为100～200 kV的可调高电压脉冲。该调制器用陶瓷电容器作为储能器件,用SF6作为绝缘介质,是一种无液体的脉冲调制器,具有结构紧凑、体积小、重量轻等特点。     

Lead-free ferroelectric thin films obtained by pulsed laser deposition

Na_0.5Bi_0.5TiO₃-BaTiO₃ (NBT-BT) thin films grown by pulsed laser deposition have been investigated by X-ray diffraction, scanning electron microscopy, and dielectric spectroscopy in order to clarify the role of substrate temperature on crystalline structure, grain morphology, and dielectric properties. We have shown that the structural and dielectric properties of NBT-BT thin films with composition at morphotropic phase boundary (6% BT) critically depend on the substrate temperature: small variations of this parameter induce structural changes, shifting the morphotropic phase boundary toward tetragonal or rhombohedral side. Higher deposition temperature (1000 K) favor the formation of rhombohedral phase, films deposited at 923 K and 973 K have tetragonal symmetry at room temperature. Grains morphology depends also on the deposition temperature. Atomic force micrographs show grains with square or rectangular shape in a compact structure for films grown at lower temperatures, while grains with triangular shape in a porous structure are observed for films grown at 1000 K. Dielectric spectroscopy measurements evidenced the phase transition between ferroelectric and antiferroelectric phase at 370 K. Films grown at 1000 K shown low electrical resistivity due to their porous structure. High dielectric constant values (about 800 at room temperature and 2700 at 570 K) have been obtained for films grown at temperatures up to 973 K.