Hot electrons in nonparabolic bands with acoustic and polar optical phonon scattering

Most compound semiconductors have nonparabolic energy bands, and in pure material the dominant scattering mechanisms are usually by acoustic and polar optical phonons. In this paper, general expressions for the high-field transport properties of such materials are derived, using the balance-of-energy method and assuming a drifted Maxwellian distribution function. Under certain conditions the resultant drift velocity-field curves show a single-band negative differential resistance, arising not only from the increase in effective mass with carrier energy, but also from the change in relative scattering efficiencies of the two mechanisms as the applied field is increased. This effect is more marked at low temperatures. The model gives good agreement with previously reported experimental results on n-type PbTe at 77°K.     

蒙特卡罗方法模拟薄膜电致发光器件中碰撞离化的作用

基于经验赝势法得到的能带结构数据，采用分段多项式拟合获得ZnS能带结构的解析表达式 ，建立解析能带模型.使用建立的模型计算得到各能谷的态密度和总的散射速率,并与文献 的计算结果进行了对比，验证该解析能带模型既具有非抛物型多能谷能带模型运算速度快、 使用方便的优势,又具有与采用全导带模型相近的计算精度.进一步利用该模型进行蒙特卡罗 模拟，得到第一导带和第二导带中电子数随电场强度的变化、不同电场中能量分布函数以及 包含与不包含碰撞离化情况下电子能量随时间变化的曲线.讨论在外加电场下，电子在导带 内各个能谷间和 关键词： 蒙特卡罗模拟 解析能带模型 多项式拟合 碰撞离化     

Thermal analysis for transient radiative cooling of a conducting semitransparent layer of ceramic in high-temperature applications

A method is developed for obtaining transient temperature distribution in a cooling semitransparent layer of ceramic. The layer is emitting, absorbing, isotropically scattering and heat conducting with a refractive index ranging from 1 to 2. The solution involves solving simultaneously the energy equation and the integral equation for the radiative flux gradient. The energy equation is solved using an implicit finite volume scheme and the integral equation of radiative heat transfer is solved using the singularity technique and Gaussian integration. The effects of scattering are investigated. It is shown that scattering has a significant effect on the transient temperature distribution and the transient mean temperature of the layer.     

质子散射角分布的蒙特卡罗模拟

利用Monte Carlo模拟软件Fluka2006.3b.2,模拟计算质子经单膜散射后粒子角分布及能量分布.讨论质子束能量、散射体材料及厚度对散射角分布的影响.结果表明：薄的高原子序数材料适合做散射体. 关键词： 质子治疗 束流扩展 单膜散射法 散射角     

Energy bands in the presence of an external force field—II Anomalous velocities

The theory of field-modified energy bands is extended to include the effect of weak scattering forces on the energy band structure. The modified current operator is found to contain terms giving anomalous currents of a type previously treated by and (Phys. Rev. 95, 1154 (1954) in connection with electrical conduction in ferromagnets. The physical meaning of these currents is discussed, and they are shown to be analogous to spin-dependent currents in Dirac's theory of the electron. They may be regarded formally as resulting from a non-commutability of the components of the coördinates. It is shown that such currents, proportional to the acceleration, are caused by every accelerating mechanism, including scattering mechanisms. A classical transport theory including the anomalous currents is derived, valid for scattering mechanisms for which the momentum transfer per collision is small, and a very simple problem carried through by way of example. A formal theory including the anomalous transport currents is given for the general case of arbitrary scattering mechanism and overlapping bands. Finally, a critique is given of some recent theories of the spontaneous Hall effect in ferromagnetics.     

Temperature dependence of phonon energy spectra with nuclear resonant scattering of synchrotron radiation

Summary The phonon energy spectra of a polycrystalline α-Fe foil were observed at 150 K and 300 K by using the nuclear resonant scattering of synchrotron radiation. In each spectrum, inelastic scattering was observed at both sides of the elastic peak. It was found that the ratio of the elastic-scattering component and the asymmetry of the intensity of the side bands observed at 150 K are larger than those observed at 300 K, respectively. The observed temperature-dependent spectra are in good agreement with the spectra calculated from the phonon energy distribution function. One of the advantageous features of this method is that the excitation of only a specific element is possible. Our results show that this method is applicable to the study of lattice dynamics and opens a new field of the nuclear resonant scattering spectroscopy. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

High field transport properties in a GaN/AlGaN heterostructure

The drift velocity, electron temperature, electron energy and momentum loss rates of a two-dimensional electron gas are calculated in a GaN/AlGaN heterojunction (HJ) at high electric fields employing the energy and momentum balance technique, assuming the drifted Fermi–Dirac (F–D) distribution function for electrons. Besides the conventional scattering mechanisms, roughness induced new scattering mechanisms such as misfit piezoelectric and misfit deformation potential scatterings are considered in momentum relaxation. Energy loss rates due to acoustic phonons and polar optical phonon scattering with hot phonon effect are considered. The calculated drift velocity, electron temperature and energy loss rate are compared with the experimental data and a good agreement is obtained. The hot phonon effect is found to reduce the drift velocity, energy and momentum loss rates, whereas it enhances the electron temperature. Also the effect of using drifted F–D distribution, due to high carrier density in GaN/AlGaN HJs, contrary to the drifted Maxwellian distribution function used in the earlier calculations, is brought out.     

Quark Energy Loss and Shadowing in Nuclear Drell-Yan Process

The energy loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of three kinds of quark energy loss parameterizations given in literature and the nuclear parton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Drell-Yan production cross sections are analyzed for 800 GeV proton incident on a variety of nuclear targets from FNAL E866. It is shown that our results with considering the energy loss effect are much different from those of the FNAL E866, who analyzes the experimental data with the nuclear parton distribution functions obtained by using the deep inelastic IA collisions and pA nuclear Drell-Yan data. Considering the existence of energy loss effect in Drell-Yan lepton pairs production, we suggest that the extraction of nuclear parton distribution functions should not include Drell-Yan experimental data.     

Quark Energy Loss and Shadowing in Nuclear Drell-Yan Process

The energy loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Dre11-Yan process. By means of three kinds of quark energy loss parameterizations given in literature and the nuclear parton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Dre11-Yan production cross sections are analyzed for 800 GeV proton incident on a variety of nuclear targets from FNAL E866. It is shown that our results with considering the energy loss effect are much different from those of the FNAL E866, who analyzes the experimental data with the nuclear parton distribution functions obtained by using the deep inelastic IA collisions and pA nuclear Drell-Yan data. Considering the existence of energy loss effect in Drell-Yan lepton pairs production, we suggest that the extraction of nuclear parton distribution functions shoul““““d not include Dre11-Yan experimental data.     

Theory of ion scattering from single crystals

The scattering of He⁺, Ne⁺ and Ar⁺ ions at 600 eV from Ni(110) in the [11̄0] direction is modeled using classical dynamics. The distributions of final scattering angles of the primary ions are displayed as contour plots over the surface impact zone. From the contour plots the regions of the surface that give rise to scattering at specific angles can be isolated. The majority of the inplane scattering arises from collisions of the primary ion with second layer or “valley” atoms. However, to correctly reproduce the experimental energy distribution curves of Heiland and Taglauer (J. Vacuum Sci. Technol. 9 (1971) 620), we must include a simple collision time correction to account for neutralization of the ion beam. This analysis predicts that the ions which collide with second layer atoms of the solid are preferentially neutralized. The energy distributions due to first layer collisions agree well with experiment. We find that a full molecular three dimensional model is needed to describe all of the ion scattering events since for most of the collisions, the ion is simultaneously interacting with at least two atoms of the solid. However, in agreement with other workers we find only a single collision is responsible for the “binary” peak in the energy distribution. In addition the relative scattering intensity at different angles is dependent on having a three-dimensional solid.     

Multiple scattering theory of the density of states in semiconductors

A method for calculating the electronic density of states of a semiconductor in the presence of impurity scattering is given. The approach is based on a low density multiple scattering expansion. The calculation treats the density of states of the conduction band, shifts of the band edge, and the profiles of the impurity bands. It is performed for a simple model, using a spherical well potential for the individual impurity centers, but could be extended to any scattering potential. The first impurity band forms when the potential is sufficiently strong that one center can bind an electron. The impurity bands are of finite width, have a flat upper edge, and an asymmetrically broadened tail on the low energy side.     

Passage of beta particles through dielectrics in presence of an electric field

The effect of an electric field on the passage of thallium-204 beta particles through polymethyl methacrylate, polystyrene, polyethylene terephthalate (Lavsan), and polyethylene targets was investigated. The number of transmitted beta particles and their angular and energy distributions were determined. The transmission curves were obtained with a SBT-7 counter. The angular distribution was investigated in a specially designed scattering chamber, and the energy distribution was determined with a scintillation beta spectrometer incorporating the USD-1 and AI-100 instruments. It was found that the relative change in the number of transmitted beta particles depends on the size of the entrance solid angle, depends linearly on the potential difference applied to the dielectric, and is practically independent of the dielectric material if its thickness is expressed in mass units. It was also found that the relative change in angular distribution up to 60° with potential differences of not more than 10 kV is independent of the scattering angle. The energy distribution is not only shifted on the energy scale, but its shape is also altered. The results are attributed to the effect of the electric field on both the energy of the particles and the direction of their momentum. A simple method of calculating the effect of the field on the number of transmitted beta particles is proposed. The results of calculation agree with the experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 9, pp. 113–118, September, 1973.     

Electron emission from surfaces of alkali halides under the impact of metastable helium and neon atoms

Energy distributions of the electrons ejected from the evaporated film surfaces of LiF, LiCl, LiBr, NaF and NaCl by the impact of metastable He and Ne atoms have been measured. The observed distribution curves have two distinct structures: one peak is identified as the valence band structure caused by Penning ionization, while the other peak is ascribed to scattered electrons. The positions of the valence band peaks are shifted to lower ionization energy from the corresponding photoelectron peaks (by 0.1–1.5 eV depending on the substance). In contrast to the photoelectron spectra, the structure attributable to conduction bands appears only very weakly. The relative intensity of the peak caused by scattered electrons is either strong or weak depending on the combination of the metastable atom and the sample. The interpretation of this observation is that the scattered electron peak is enhanced when the energy of the metastable atom exceeds twice the band gap energy, i.e. when the electron—electron scattering of Penning electrons in the solid is feasible.     

Die Winkelverteilung im Bereich 30 bis 155° von elastisch an Golddampf gestreuten Elektronen mit Energien zwischen 150 und 1900 eV

The angular distribution of electrons scattered elastically by gold atoms has been investigated over the angular range from 30 to 155° and with electron energies between 150 and 1900 eV. The scattering curves obtained resemble closely the corresponding curves for mercury atoms. The theoretically expected energy dependence of the 90°-scattering is in poor agreement only with the results obtained experimentally in this work.     

气溶胶激光散射信号的特征分析

本文应用Mie散射理论对微球体粒子光散射的性质进行了理论分析与数值计算,得出了散射光分布与微球体尺度参数、复折射率之间的关系。结果表明:不同尺度参数的粒子的散射光强的分布相差极大,随着尺度参数的增加散射光强越来越集中于前向;复折射率的变化对散射光强影响不大。并且在边界层大陆乡村型霾的气溶胶模型下对大气气溶胶的体角散射系数进行了分析与数值计算,得出:气溶胶粒子的散射光强主要分布在前向,并且随着散射角的增加有规律的减小。由此提出了利用气溶胶粒子体散射系数的性质,通过测量散射点前向散射光强和延迟时间来实现激光束的近轴定位的方法。     

水下爆炸毁伤水下目标的能量分布特征

 针对某水下目标的抗水下爆炸实验数据,利用小波包良好的时频局部化性质,对被监测水下目标内部装置的冲击加速度信号进行了能量分析,得到了冲击信号的时频分布和不同频带上的能量分布。冲击信号的频带能量分布与目标毁伤的关系密切,选用冲击信号峰值、冲击信号主振频带能量、水下目标内部装置自振频率所在频带能量作为判别因子,建立距离判别模型,对水下目标毁伤情况进行了预测;利用回代估计法对模型的合理性进行了检验。研究结果表明,预测结果与实际结果相符,证明将频带能量作为水下爆炸毁伤水下目标的特征指标是合理的。     

Geometrical scaling at inelastic threshold

The possibility of geometrical scaling being a low energy phenomenon is investigated using phase shift data. For exotic reactions, in particular in K⁺p scattering, scaling is observed and the high energy (NAL-ISR)GS curve agrees with phase shift inelasticity η down to the inelastic threshold. For reactions with resonances the high energy curves average the phase shift inelasticities. The consequences of these results are discussed and predictions for ππ and Kπ scattering are presented.     

Investigation of fast neutron interaction with235U

The angular distribution of neutrons emitted by elastic, inelastic and fission processes on²³⁵U were measured at the incident neutron energies of 1.5, 1.9, 2.3, 4.0, 4.5, 5.0 and 5.5 MeV using nanosecond time-of-flight technique. The differential elastic scattering cross sections and their angular distributions at all the seven energies are presented. The total elastic scattering cross sections, angle and energy integrated cross sections for the inelastically scattered neutrons in energy bands of 200 keV, fission cross sections and the angular distributions of fission neutrons were extracted at 1.5, 1.9 and 2.3 MeV incident neutron energies. The energy distributions of the prompt fission neutrons and of the inelastically scattered neutrons are given at the incoming neutron energies of 1.5, 1.9 and 2.3 MeV; and the average fission neutron energies and the inelastic neutron evaporation temperatures were also evaluated at these energies.     

The inelastic electron tunneling spectroscopy of edge-modified graphene nanoribbon-based molecular devices

The inelastic electron tunneling spectroscopy(IETS) of four edge-modified finite-size grapheme nanoribbon(GNR)-based molecular devices has been studied by using the density functional theory and Green's function method. The effects of atomic structures and connection types on inelastic transport properties of the junctions have been studied. The IETS is sensitive to the electrode connection types and modification types. Comparing with the pure hydrogen edge passivation systems, we conclude that the IETS for the lower energy region increases obviously when using donor–acceptor functional groups as the edge modification types of the central scattering area. When using donor–acceptor as the electrode connection groups, the intensity of IETS increases several orders of magnitude than that of the pure ones. The effects of temperature on the inelastic electron tunneling spectroscopy also have been discussed. The IETS curves show significant fine structures at lower temperatures. With the increasing of temperature, peak broadening covers many fine structures of the IETS curves.The changes of IETS in the low-frequency region are caused by the introduction of the donor–acceptor groups and the population distribution of thermal particles. The effect of Fermi distribution on the tunneling current is persistent.     

用高能核子非弹性散射研究核力有效势

本文用扭曲波玻恩近似法及多体高能近似法,处理了原子核对高能核子的非弹性散射现象。在具有可靠的靶核激发态波函数的情况下,可利用这些理论处理方法研究核内两核子间的有效势,本文具体就碳核对185MeV入射核子的非弹性散射进行了计算。在计算中利用了粒子-空穴模型核波函数。在采用了具有各种交换性质并包含自旋轨道耦合项的有效势后,用一组合理的位阱参数,由多体高能近似法计算的理论值可与几个微分截面及极化实验曲线同时符合。