Intraband luminescence spectra of insulators and semiconductors excited by pulsed electron beams or electric fields

The features of the intraband luminescence spectrum of wide-gap insulators (KI, KBr, CsCl, etc.) and semiconductors (GaP, CdS, α-SiC, and ZnS) are studied in the temperature interval 80–760 K. The spectra of the intraband luminescence are compared with the spectra of the pre-breakdown electroluminescence of GaP and α-SiC surface-barrier diode structures and of a ZnS thin-film electroluminescence indicator. In alkali halide crystals the short-wavelength boundary hν _m of the intraband luminescence is less than the band gap E _g and is governed by complex excitonic processes. In semiconductors with indirect transitions hν _m>E _g. The differences in the spectra of the intraband luminescence and the intraband pre-breakdown electroluminescence can be explained by differences in the distributions of the hot charge carriers over levels of the allowed bands and in the maximum energies of the carriers involved in the formation of the spectra. Fiz. Tverd. Tela (St. Petersburg) 39, 613–617 (April 1997)     

Point sources and rays in the phase-space representation of random electromagnetic fields

Random stationary electromagnetic fields can be modeled in terms of point sources disposed onto two distinct layers, named the radiant and the virtual layers. It allows describing the propagation of the power and the states of spatial coherence and polarization of the field by means of separate phase-space ray-maps. Spatial coherence of the field, correlation of the polarization angles and achievement of the Fresnel-Arago laws within the structured spatial coherence supports are the necessary conditions that determine the electromagnetic point sources in the virtual layer. The contributions of these sources produce two types of modulations on the electromagnetic field at the observation plane, one of them of scalar type is the interferometric power modulation, and the other one of vector type is de modulation of the polarization state provided by the radiant point sources, according to the Stokes' parameters. Some examples are presented.     

Influence of defects on the ordering degree of nanopores made from anodic aluminum oxide

Anodic aluminum oxide (AAO) templates with highly ordered nanoporous structure were fabricated by means of the electrochemical anodization under the constant anodic voltage and electrolyte temperature. The dependence of the ordering degree of nanopores on the point defects, dislocation configuration and grain boundary of aluminum is qualitatively analyzed. Experiment results show that the size of the ordered region of nanopores depends strongly on the point defects, dislocation cell configuration.     

High resolution x-ray study of microstructural changes in semiconductors and insulators subject to high electric fields

Using a high-resolution X-ray diffractometer, microstructural changes have been observed in Si-, LiF- and CdS-crystals subject to high d.c. and a.c. fields. At high fields the diffraction peaks are unstable due to inhomogeneous distribution of the electric current in the specimen. The inhomogeneous regions have been directly observed in high-resolution topographs. A correlation between current fluctuations and the diffracted beam intensity has been observed. Changes in peak shapes as a result of field have been observed.     

Dynamic drag of edge dislocation by circular prismatic loops and point defects

Motion of edge dislocation in the presence of prismatic loops and point defects is studied analytically. It is shown that at certain conditions, the velocity dependence of the drag force has two maximums and two minimums.     

Influence of periodie and random two-dimensional nuclei distribution on the recrystallization kinetics

The recrystallization process is modeled by using both a periodic lattice and a random array of nuclei for the two-dimensional, instantaneous nucleation case. Recrystallization kinetics is obtained with analytical expressions for the periodic model and computer-generated results for the random situation. The resulting kinetics shows some disagreement with the classical Johnson-Mehl-Avrami-Kolmorogav kinetics, and stresses the fact that there is a finite time for the completion of the whole process. The time for completion is calculated for the two-dimensional and three-dimensional cases.     

Influence of external electric and magnetic fields on magnetoelectric interaction in ferromagnets

A gap in the spectrum of spin and ferroelectric waves is investigated versus magnetic and electric fields. It is demonstrated that the magnetoelectric interaction is amplified with increasing external magnetic field and is weakened with increasing external electric field. This allows the interaction between the spin and ferroelectric subsystems to be controlled by external fields. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 43–47, February, 2009.     

Dipolar response and hydrogen-bond kinetics in liquid water in square-wave time-varying electric fields

Non-equilibrium molecular dynamics simulations of liquid water have been performed at 298 K in the presence of external time-varying electric fields, approximating a square wave, of varying peak intensity (0.005–0.1 V/Å) in the microwave to far-infrared frequency range (20–500 GHz). Significant non-thermal field effects were noted in terms of dipolar response and acceleration of hydrogen-bond kinetics. The coupling between the total dipole moment and the external field has been investigated and autocorrelation functions (ACFs) of both the total dipole moment and the average of the individual molecular dipole moment along the laboratory axis of the applied fields exhibited coupling, with the former showing a stronger coupling and the latter showing coupling to lower magnitude fields. The maximum alignment achieved has been computed as a function of field intensities and frequencies: the lower frequencies show a greater maximum alignment as the system had more time within each field cycle to respond. The normalised probability distribution and the hydrogen-bond ACFs have been computed: the ACF showed a clear effect over shortening the hydrogen-bond relaxation time. The field effects over the molecules’ transitions from four to five hydrogen bonds have been computed. There was an enhancement of fewer molecules undergoing transitions and a dampening for a larger proportion of molecules, depending on the external fields’ periods.     

Influence of an electric field and a high excitation density on the luminescence of epitaxial GaN films

The influence on the recombination luminescence spectra of a field applied to the Schottky barrier and a high excitation density GaN epitaxial films grown by metalorganic chemical-vapor deposition (MOCVD) is investigated. It is discovered that quenching of the luminescence takes place under a reverse bias, while an increase in its intensity occurs under a forward bias. The effect observed is attributed to thickness variation of the space-charge layer under the effects of the applied voltage. The appearance of a new band caused by exciton-exciton collisions is observed under the conditions of a high excitation density. Fiz. Tverd. Tela (St. Petersburg) 40, 936–937 (May 1998)     

Influence of electric and magnetic fields on the shock wave configuration at the diffuser inlet

The possibility is investigated of influencing the shock wave configuration in a xenon plasma flow at the inlet of a supersonic diffuser by applying electric and magnetic fields. Flow patterns resulting from interaction of the plasma with external fields in the entire diffusor volume and its different sections are compared. The patterns are obtained by the Schlieren method using two recording regimes: individual frames or a succession of frames. The study focuses on the normal shock wave formation process under strong MHD interaction over the whole diffuser volume. Basic factors affecting the plasma flow velocity in the diffuser under externally applied fields are compared, namely, the ponderomotive force and the Joule heating of the gas by the electric field, which decelerate the supersonic flow, and the heat removal to the external electric circuit producing the opposite effect. It has been shown that the external fields are most effective if applied to the inlet part of the diffuser, while the flow in the diffuser section, where there is a large density of dissipative structures, is not readily responsive to external factors. It is suggested that the measure of response can be estimated by the energy that goes to the shock wave formation as a result of the flow interaction with the diffuser walls.     

真空绝缘子脉冲表面电场在线测量系统的实现

基于Kerr电光效应,建立了用以对纳秒脉冲高电压作用下的真空绝缘子表面电场进行在线测量的实验系统。该测量系统由快脉冲高电压源、YAG激光器、同步控制系统、被测中空薄壁绝缘子及Kerr效应单元、光学相位差检测系统等部分构成。利用YAG激光器输出的激光脉冲,触发导通快脉冲高压源中的高压气体开关,使其给被测绝缘子试品上施加一个脉宽100 ns的高压脉冲方波。利用同步控制,使得探测激光在试品上的脉冲方波达到幅值后,入射到Kerr腔体中对Kerr效应进行探测。从而实现了对绝缘子表面电场的在线测量,并给出了初步的测量结果。     

Effect of surface fields on luminescence of ZnS and ZnO crystals

It is shown that changes in luminescence characteristics of zinc sulfide and oxide in the presence of external effects that alter the surface charge are associated with a change in the parameters of surface barriers and can be explained within the framework of a model that takes into account separation of recombining partners in the Schottky barriers. We suggest a barrier mechanism for the effect of the surface region of a crystal on experimentally measured luminescence parameters and show that errors occuring in the measurement of these parameters can reach 10% and greater, depending on the depth of penetration of light. Moscow State University of Railways, 15 Obraztsov Str., Moscow, 103055, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 804–808, November–December, 1999.     

Influence of heterojunction interface on exciplex emission from organic light-emitting diodes under electric fields

In this paper, electroluminescence from organic light-emitting diodes based on 2-(4^′-biphenyl)-5-(4^′′-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and N,N^′-diphenyl-N,N^′-bis(3-methylphenyl)-(1,1^′-biphenyl)-4,4^′-diamine (TPD) is reported. Based on the exciplex emission from the TPD/PBD interface under high electric fields, the influence of the TPD/PBD interface on exciplex emission was investigated by increasing the number of TPD/PBD interfaces while keeping both the total thickness of the TPD layer and the PBD layer constant in the multiple quantum-wells (MQW) device ITO/TPD/[PBD/TPD]_n/PBD/Al (n is the well number that was varied from 0 to 3). Our experimental data shows that exciplex emission can be enhanced by suitably increasing the well number of this kind of MQW-like device. PACS 78.60.Fi; 78.55.Kz; 73.61.Ph     

真空绝缘子脉冲表面电场在线测量系统的实现

基于Kerr电光效应,建立了用以对纳秒脉冲高电压作用下的真空绝缘子表面电场进行在线测量的实验系统。该测量系统由快脉冲高电压源、YAG激光器、同步控制系统、被测中空薄壁绝缘子及Kerr效应单元、光学相位差检测系统等部分构成。利用YAG激光器输出的激光脉冲,触发导通快脉冲高压源中的高压气体开关,使其给被测绝缘子试品上施加一个脉宽100ns的高压脉冲方波。利用同步控制,使得探测激光在试品上的脉冲方波达到幅值后,入射到Kerr腔体中对Kerr效应进行探测。从而实现了对绝缘子表面电场的在线测量,并给出了初步的测量结果。     

Influence of a forming process and electric fields on the insulator-conductor transition in thin films of polyheteroarylenes

The results of experiments on initiation of the high-conductivity state of a metal/polymer/metal system by varying the boundary conditions with allowance for the possible influence of diffusion of the electrode material into the polymer film are presented. It is established that forming does not occur in poly(phthalidylidenebiphenylylene) and that the transition to the high-conductivity state can occur without an external source of electric voltage. Zh. Tekh. Fiz. 69, 85–87 (March 1999)     

表面改性对绝缘子真空沿面闪络特性的影响

在不同温度下对交联聚苯乙烯绝缘子进行了表面氟化处理,在脉宽0.5 s的脉冲电压下对绝缘子的真空沿面闪络性能进行测试。结果表明：在50~60 ℃下对交联聚苯乙烯进行表面氟化能将绝缘子沿面闪络电压提高40%~60%。通过在绝缘子表面层规律地嵌入多个薄膜导电层,制备了新型结构的高梯度绝缘子,新型高梯度绝缘子沿面闪络电压较相同材料的普通绝缘子提高40%~50%,并保持了较好的力学及加工性能。