Solvothermal Synthesis of Molybdenum Disulfide Hollow Spheres Modified by Cyanex 301 in Water–Ethanol Medium

Hollow spherical molybdenum disulfide has been successfully synthesized via a solvothermal method using Cyanex 301 as sulfur source and modification agent. The hollow spheres are characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction and Energy-Dispersive X-ray analysis. The influences of reaction conditions are also discussed while a mechanism is proposed to explain the formation of the peculiar morphology.     

Saturation of a One-Sided Multipactor in Crossed Fields

We analyze the saturation mechanism of a vacuum resonance microwave discharge (multipactor) for systems in which a magnetostatic field returns electrons to the metal surface with secondary-emission multiplying. The steady-state model suggested earlier is improved essentially. In particular, we take into account the near-surface interaction of saturated electron bunches during the limited time of discharge-electron-surface impact. It is found that the Coulomb defocusing of electron bunches prevails over their microwave focusing (toward the resonance phase of the field), making it possible to extract superfluous secondary electrons when the electron bunches are reproduced on the discharge surface. Basic characteristics of the discharge, such as its existence conditions and proper fields and phase disposition of the resonance electron bunches, are determined as functions of the magnetostatic field and the secondary-emission coefficient. The results are discussed in comparison with the data of known experiments. An explanation of some differences related to both the observation conditions and the used analytical model is given.     

Excitation of surface plasmons by electrons in a parabolic beam

A theory is presented for the excitation of surface plasmons by an electron beam following a non-touching path above a metal surface in Born approximation. The metal is assumed to possess only surface plasmon excitations. Configurations involving deflection of the electron beam in a parallel plate condensor, and by scattering from a field emission tip are envisaged. The relation between experimental conditions and the validity of the semiclassical approximation is discussed. The region of space above the surface in which scattering occurs is calculated, but the feasability of the experiment depends on electron optical factors which are outlined.     

Problems of implementing SEMPA in experiments

A Mott analyzer of the spin polarization of secondary electrons was installed in a conventional scanning electron microscope (SEM). It can be used to study the magnetic states of the surfaces of ferromagnetic objects. The first results of experiments using scanning electron microscopy with analysis of the spin directions to obtain images with magnetic contrast are presented. Problems connected with the implementation of this procedure in the case of a conventional SEM with a relatively low vacuum are discussed, and factors affecting the choice of optimal experimental conditions are analyzed.     

Analytic conditions for the existence of localized electron states in a linear chain with an arbitrary number of impurities

The effective Hamiltonian and the negative eigenvalue theorem are used to obtain an analytic formula for the integrated density of electron states in a linear chain with an arbitrary number of impurities within the tight binding approximation. From this formula, the analytic conditions for the existence of localized electron states lying above or below the band of states of host atoms are obtained. The way of obtaining the energies of localized states and the form of eigenvectors are also discussed.     

Neue Kupferzentren in Zinkoxid

Electron spin resonance investigations of electron irradiated zinc oxide single crystals doped with copper have been performed. Beside the known Jahn-Teller spectrum of the Cu _ioct ⁰ centre the resonances of four new copper defects have been observed. The ESR parameters are explained assuming one unpaired electron in the otherwise filled 3d shell. The electron configurations are discussed under the conditions of the covalent ZnO bond.     

光合作用原初过程能量和电荷超快传递过程原理浅析

文章侧重于从物理的角度,介绍光合作用原初过程中能量和电荷超快传递过程的相关物理化学原理,如费米黄金规则,Frster及Dexter传能机制,Marcus电荷转移理论及激子理论.辨析相关原理的适用范围、共性及差异,并力图在上述相关原理的基础上阐述光合膜蛋结构与功能的关系,勾画出该研究方向的基本脉络.     

Theory of modified Busch method of determining specific charge of electrons

The conditions which have to be fulfilled for accurate determination of the specific charge of the electron, by the Busch equation are discussed. It is shown that in the modern modification of the method, where a plane divergent electron beam is produced by a sinusoidal voltage applied to horizontal deflecting plates, these conditions are not fulfilled Theoretical allowance for non-fulfillment of these conditions can be made by replacing the lengthl in the Busch equation by a certain reduced length. The reduced length is found for the case of strictly parallel nonferromagnetic deflecting plates.     

Features of electron transfer along heterogeneous atomic chains

The problem of electron transfer along a linear chain of atoms is discussed. The process under study occurs after the electron has transited from a hydrogen ion to an atomic chain. The wave packet propagation method not involving the perturbation theory was used for the calculations. Conclusions on the electron transfer behavior and necessary conditions are drawn. The approach can be applied to real physical systems where electron transition from a charged particle takes place.     

Peierls transition in a quasi-one dimensional system

We study the thermodynamics of a noninteracting electron system with a half filled strongly anisotropic tight binding band in the mean field approximation. This system may exhibit a structural transition dimerizing along the high conductivity direction. The conditions for the instability to occur are given as a function of the degree of anisotropy. The relationship to the behavior of TCNQ salts is discussed.     

Spectral and variational principles of electromagnetic field excitation in wave guides

Possible variational principles for excitation of an electromagnetic field in a wave guide are discussed. Our emphasis is not on the calculation of the modal shapes, which is common in previous art, but rather on the calculation of modal amplitude evolution, which are important in electron devices such as free electron lasers and gyrotrons. Variational principles have considerable importance in theoretical physics and are used among other things to derive numerical solution schemes, conservation laws via the Noether theorem and correct boundary conditions for the derived equations including the important effects of the backward waves amplitudes.     

Mr. Maxwell's journey into hadron country (electromagnetic currents in nuclei)

In these lectures an introduction is given into the main features of nuclear structure investigations by photoabsorption and electron scattering. After a brief review of the general structure of the electromagnetic interaction, the gauge conditions and low-energy theorems for the electromagnetic interaction operators are discussed. The various theoretical schemes for incorporating subnuclear degrees of freedom either as effective operators like the pion exchange current or explicitely like in the model of nuclear isobar configurations are reviewed. At the end, a few specific experiments are discussed as an illustration of what can be learned from such experiments.     

The discharge kinetics in molecular gases

Some problems of the conventional treatment applied to the molecular discharge plasma are discussed: the use of the two-term approximation of the electron distribution function, the inclusion of the second kind collisions in the Boltzmann equation and the influence of the boundary conditions for the rate equations on the concentration calculations.     

Laser induced electronic acceleration process in nano dot

A physical model of the laser induced electron transport in dielectric with small size is discussed. The model assumes that free electrons are originally existent or produced by impact detrapping. The free electrons transporting in low dimensional dielectrics interact with phonons and surface. When the laser electric field strength is high enough, the inelastic electron scattering such as impact ionization and cascade processes will play important roles. A small size effect has been found in electron absorbing laser energy under the conditions that the laser wavelength is in near infrared zone and the material has size in nanometer level. This is a very significative effect to enlighten us on preparing ultrahigh threshold laser films with new nano-structure.     

P-型半导体探测器在放射治疗中的剂量特性研究

电子束半导体探测器的测量精度易受到射线的能量、剂量率、入射方向和环境温度等条件的影响。此外,电子束测量射野中半导体探测器的存在将干扰均匀射野剂量场的正常分布。通过对P-型电子束半导体探测器在不同的电子束照射条件下的实际剂量测量,定量地评估了不同照射条件下电子束半导体探测器的剂量特性,以及它对电子束均匀照射野扰动的影响。The measurement accuracy of electron beam by using semiconductor detector is easily affected by beam energy, dose rate, beam incidence direction, environment temperature etc. Furthermore, the presence of the detectors on the patient surface perturbs the distribution of the radiation field. In the paper, the dose characteristics of semiconductor detector are quantitatively discussed. The perturbation of the symmetrical radiation field is investigated based on the measured results of P-type electron beam detector under different clinical conditions.     

Transmission electron microscopy study of defects in Sn-doped GaAs films grown by molecular beam epitaxy

Films of GaAs, heavily doped with Sn, which have been grown by molecular-beam epitaxy are found to contain single-crystal Sn particles situated in the nearsurface region of the epilayer GaAs. The morphology and chemical composition of the particles have been examined by using cross-section transmission electron microscopy combined with energy-dispersive x-ray spectroscopy. Different growth conditions were used to study the Sn-particle formation and high-resolution transmission electron microscopy was used to investigate microstructures. The observations are discussed in terms of several models previously proposed for these phenomena.     

Theory of renormalization and Compton scattering in quantum electrodynamics of coherent light of high intensity

The Feynman propagator of an electron interacting with an intense beam of monochromatic and linearly polarized light of low frequency is evaluated. The technique of Feynman-graph summation developed in a preceding paper is employed and Volkov boundary conditions are adopted. The mass- and momentum-shifts found previously are reexamined and the influence of spin, polarization and boundary conditions is discussed. The renormalization procedure is generalized such as to include also the modification of a true scattering vertex and as a specific application the intensity dependent amplitude of the Compton effect is calculated.     

Cyclotron-resonance maser with adiabatic magnetic pumping in a low-density plasma

The conditions under which the magnetic adiabatic compression of a plasma in a direct magnetic trap is accompanied by the accumulation of high energy in the hot anisotropic electron component are found. The basic instabilities resulting in the emission of the accumulated energy in the form of a pulse of stimulated electromagnetic radiation are analyzed. The possibility of creating terahertz radiation sources with the use of the magnetic compression of the plasma is discussed.     

Simplified calculations of a thermionic converter in the ignited mode

The charged particle transport in the plasma of a thermionic converter in the ignited mode is treated to be due to the charged particle density gradient and the electric field. The corresponding coefficients as well as the numerical treatment of the ionization and recombination processes are taken from the literature, the latter one in a suitable approximation. The electron temperature is assumed to be uniform within the gap. Taking account of the boundary conditions for the electron and ion currents and for the flux of the kinetic electron energy analytical solutions are found whose numerical evaluations can easily be performed. To make allowance for the Schottky effect and a double sheath at the emitter surface is shown to be necessary and possible with moderate effort for the calculation of I-V curves. The validity limit of the model is discussed.     

Optimization of Pulsed-DEER Measurements for Gd-Based Labels: Choice of Operational Frequencies, Pulse Durations and Positions, and Temperature

In this work, the experimental conditions and parameters necessary to optimize the long-distance (≥60 Å) double electron–electron resonance (DEER) measurements of biomacromolecules labeled with Gd(III) tags are analyzed. The specific parameters discussed are the temperature, microwave band, the separation between the pumping and observation frequencies, pulse train repetition rate, pulse durations and pulse positioning in the electron paramagnetic resonance spectrum. It was found that: (1) in optimized DEER measurements, the observation pulses have to be applied at the maximum of the electron paramagnetic resonance spectrum; (2) the optimal temperature range for K_a-band measurements is 14–17 K, while in W-band the optimal temperatures are between 6 and 9 K; (iv) W-band is preferable to K_a-band for DEER measurements. Recent achievements and the conditions necessary for short-distance measurements (<15 Å) are also briefly discussed.