Montecarlo and boltzmann calculations of electron energy distributions in RF fields

Summary Detailed comparisons between Montecarlo and Boltzmann calculations of electron energy distributions in gases acted upon by RF fields are presented. Attention is turned to model gases of special theoretical interest but various calculations have also been made for real gases such as pure CO and He−CO mixtures. The analysis has shown that large discrepancies exist between energy distributions obtained with the two mentioned techniques under conditions of particular physical interest. The discrepancies are found to be the consequence of the two-term approximation and are expected to disappear if an appropriate multiterm solution of the Boltzmann equation is adopted.     

Low energy electron transport in furfural

We report on an initial investigation into the transport of electrons through a gas cell containing 1 mTorr of gaseous furfural. Results from our Monte Carlo simulation are implicitly checked against those from a corresponding electron transmission measurement. To enable this simulation a self-consistent cross section data base was constructed. This data base is benchmarked through new total cross section measurements which are also described here. In addition, again to facilitate the simulation, our preferred energy loss distribution function is presented and discussed.     

Relativistic calculations of fine-structure energy levels of He-like Ar in dense plasmas

The fine-structure energy levels of 1s2s and 1s2p atomic states for the He-like Ar ion immersed in dense plasmas are calculated. The ion sphere model is used to describe the plasma screening effect on the tested ion. The influences of the hard sphere confinement and plasma screening on the fine-structure energy levels are investigated respectively. The calculated results show that the confined effect of the hard sphere on the fine-structure energy levels increases with decreasing hard sphere radius, and the plasma screening effect on the fine-structure energy levels increases with the increase of free electron density. In dense plasmas, the confined effect of the hard sphere on the fine-structure energy levels can be neglected generally, compared with the contribution from free electron screening. An interesting phenomenon about the energy level crossing is found among 1s2s(~1S_0) and 1s2p(~3P_(0,1)) atomic states. The results reported at the present work are useful for plasma diagnostics.     

Real-space calculations for electron transport properties of nanostructures

Recent developments in the fabrication and investigation of conductors of atomic dimensions have stimulated a large number of experimental and theoretical studies on these nanoscale devices. In this paper, we introduce examples presenting the efficiencies and advantages of a first-principles transport calculation scheme based on the real-space finite-difference (RSFD) formalism and the overbridging boundary-matching (OBM) method. The RSFD method does not suffer from the artificial periodicity problems that arise in methods using plane-wave basis sets or the linear dependence problems that occur in methods using atomic basis sets. Moreover, the algorithm of the RSFD method is suitable for massively parallel computers and, thus, the combination of the RSFD and OBM methods enables us to execute first-principles transport calculations using large models. To demonstrate the advantages of this method, several applications of the transport calculations in various systems ranging from jellium nanowires to the tip and surface system of scanning tunneling microscopy are presented.     

Ab-initio electron transport calculations of carbon based string structures

First-principles calculations show that monatomic strings of carbon have high cohesive energy and axial strength, and exhibit stability even at high temperatures. Because of their flexibility and reactivity, carbon chains are suitable for structural and chemical functionalizations; they also form stable ring, helix, grid, and network structures. Analysis of electronic conductance of various infinite, finite, and doped string structures reveal fundamental and technologically interesting features. Changes in doping and geometry give rise to dramatic variations in conductance. In even-numbered linear chains, strain induces a substantial decrease of conductance. The double covalent bonding of carbon atoms underlies their unusual chemical, mechanical, and transport properties.     

Calculation of the optimum electron energy in an Ar+-laser plasma

Using newly available values for the relevant cross sections the electron energy at maximum laser power at 488 nm was calculated to ∼6 eV, independent of discharge current. Agreement exists between theory and a re-evaluation of experiments. To check the calculations also other Ar-laser plasma parameters were determined and compared with experiments. In the papers of Herziger and SeeligkT _e is called mean electron energy. For comparison with our results a factor 3/2 has to be considered.     

4 OPW calculations of electronic transport coefficients of aluminium containing point defects

The scattering of conduction electrons on dilute point defects in aluminium was investigated, for zero temperature, by pseudopotential calculations considering the realistic form of the Al Fermi surface (FS) and band structure. The 4-OPW wavefunctions, band velocities and FS curvatures were calculated for 1,300 pointsk on 1/48 (cubic symmetry element) of the FS. The scattering potentials were obtained as follows: for the impurities Ge, Mg, Zn, and Ga tabulated pseudopotentials were used and rescreened for the electron density of Al, the vacancy was treated as a missing Al atom and the [100] dumbbell interstitial as two Al atoms with a vacancy in between (always with strain field corrections). The scattering matrixP _kk was obtained in first order Born approximation. The linearized Boltzmann equation was solved numerically by iteration, for zero magnetic field and for a reduced set of 109 points on 1/48 FS, to yield the anisotropic transport relaxation times _k and lifetimes _k ⁰ .The _k were interpolated for the 1,300 points again and inserted into low-field FS integrals for the galvanomagnetic coefficients which depend sensitively on the details of the FS and the anisotropy of _k . Without any free parameter, our results agree very well with experimental data for the case of Ge, Mg, and Zn impurities, and less so for the homovalent Ga impurities and for the self-defects. The diffusion thermopower was also calculated.Auszug aus der vom Fachbereich Physik der Techn. Universität München genehmigten Dissertation über Berechnung von elektrischen Transporteigenschaften von Aluminium mit der Pseudopotentialmethode des Dipl.-Phys. Klaus Pfändner. Tag der Promotion: 29. 11. 1977This work was supported by the German Bundesministerium für Forschung und Technologie     

氩直流辉光放电等离子体中电子运动及能量的模拟

采用自动调节时间步长的蒙特卡罗模拟,对平行板放电系统中的氩气直流辉光放电系统中的等离子体区内电子的运动过程进行了跟踪和抽样。统计结果表明:在我们的实验条件下,等离子体中的电子在电场作用下出现明显的轴向漂移;在40000次抽样中,出现能量为E的电子数目随能量E增大呈下降趋势,场强增大将引起能量分布展宽和电子平均能量增加;即使场强达到15V·cm-1,等离子体激发和电离仍是很少的;场强和气压都能明显改变电子的平均自由程。     

Flux-limited nonequilibrium electron energy transport in warm dense gold

An abrupt change in energy transport has been observed in femtosecond laser heated gold when the absorbed laser flux exceeds ~7×10(12) W/cm(2). Below this value, the absorbed flux is carried by ballistic motion of nonthermal electrons produced in interband excitation. Above this value energy transport appears to include ballistic transport by nonthermal electrons and heat diffusion by thermalized hot electrons. The ballistic component is limited to a flux of ~7×10(12) W/cm(2). This offers a unique benchmark for comparison with theory on nonequilibrium electron transport.     

Angular and energy distributions of low energy electrons from backscattered-conversion electron Mössbauer spectroscopy

Angular and energy distributions of backscattered-low energy resonant and nonresonant electrons from iron films are studied both theoretically and experimentally. The results indicate that relatively few emerging resonant or nonresonant electrons are observed/predicted between 600 eV and 50 eV kinetic energy. A significant fraction of the total electron signal emerges, however, below 50 eV, which is shown to result from low energy Auger cascades, low energy shake-off electrons and secondary electrons attributed to higher energy events. The large number of low energy electrons permits relatively short acquisition times (ca. 1h) and enhanced surface sensitivities. They may be especially useful in future depth-deconvolution efforts.     

Realistic calculations of parity distributions and densities of exciton states at high excitation energy

Effects of the density-dependence of theα-particle-bound nucleon effective interaction on single-folding models of inelasticα-particle scattering are studied, in particular in view of corrections of the isoscalar transitions rates extracted by implicit folding procedures. Thel-dependent corrections factorsC _l are calculated and tubulated for applications.     

Electronic method for direct display of the electron energy distributions in plasma

Direct display of the electron energy distribution function has been performed with the aid of the analog computer MEDA 41 TA.     

流注放电低温等离子体中电子输运系数计算的蒙特卡罗模型

流体或者粒子-流体混合数值仿真是研究流注放电基本物理机制的常用手段,而精确的电子输运系数是保证其仿真正确性的必要前提.鉴于现有电子输运系数求解工具存在一定缺陷,本文开发了采用蒙特卡罗方法求解低温等离子体中电子输运系数的仿真工具,测试表明其准确性和精确度均较高.研究了氮氧气体混合比及大气压下三体碰撞吸附对电子输运系数的影响.氮气中流注放电仿真表明,流体仿真中采用本模型改进后的电子输运系数可显著改善流注通道内部的等离子体参数分布.     

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用高密度等离子体模型可以计算出一整套输运参数,并且在很宽的等离子体温度和密度范围内有合理的精度,可广泛应用于Z箍缩等离子体、激光聚变和磁约束聚变等领域,并将这个模型计算出的各种输运参数拟合成了实用的公式。     

Scaling in second order electron correlation calculations of potential energy curves and spectroscopic constants

The determination of potential energy curves and spectroscopic constants using the method of scaling in second order electron correlation calculations is investigated. An application to the ground state of the fluorine molecule is described using full fourth order many-body perturbation theory within two basis sets.     

On the activation energy of the electron liquid in Hg0.8Cd0.2Te

Recently we have shown that a magnetic field induced electron (Wigner) condensation takes places in Hg_0.8Cd_0.2Te. The correlated electrons behave like a viscous liquid with activated mobility [1]. We present the activation energy of the mobility at magnetic fields up to B = 20 T. The experimental data show that the strong increase of the activation energy with B at low fields slow down and even seems to saturate at magnetic fields above 20 T. Qualitatively this behaviour is expected for a magnetic field induced electron liquid.