Melting of silicon

Near the melting point of silicon, it is shown that the number of intrinsic defects increases drastically. This is further enhanced in the presence of an electron-hole plasma. Also, the migration energy of the vacancies is calculated to decrease near the melting point. This supports the basic assumptions of the dislocation theory of melting.     

Velocity gradient driven flute instabilities in plasmas

The effect of velocity gradient across the magnetic field on the low frequency flute modes is examined in detail, using the normal mode analysis. It is shown that some new type of instabilities driven primarily by the velocitygradient arise and these excited modes eventually attain the convective saturation. The onset of plasma turbulence due to these instabilities may possibly be one of the major contributors for anomalous heating process and enhanced plasma resistivity.     

Desorption of H ions from water chemisorbed on Si(100) by O 1s excitation - an Auger electron-photoion coincidence spectroscopy study

Auger electron-photoion coincidence (AEPICO) spectroscopy, which has been recently developed and proved to be a very powerful technique for investigating the dynamics of desorption induced by the core-level excitation, is applied to the investigation of Auger-stimulated ion desorption from the chemisorbed-water-Si(100) surface induced by O 1s excitation. It is shown that the fast relaxation of the excited state with a core hole and an excited electron takes place before the core hole decay, and that the desorption yield is enhanced by the shake-up (and/or shake-off) excitation. The relative cross-section for Auger-stimulated ion desorption is estimated, and is shown to increase as holes are created at deeper levels of the valence bands as the final state of the Auger decay. A comparison is also made with condensed H₂O.     

质子束尾波场中利用密度跃变实现电子捕获及加速的粒子模拟

 用2D3V粒子模拟程序研究了高能质子束驱动的尾波场加速电子的方案,及其在此方案中应用背景等离子体密度的跃变致使等离子体电子自注入加速相区的可能性。粒子模拟结果显示:密度跃变实现了电子的自注入,并且捕获的电子束处于加速相位,等离子体尾波场纵向电场对捕获的电子束起箍缩作用;捕获的电子束随着传输,表现为窄能谱分布;同时随着密度跃变大小的增大,可以增加等离子体电子的捕获。     

HL－1M感应与低杂波组合电流驱动研究

本文结合ＨＬ－１Ｍ的基本参数，利用准线性的低杂波电流驱动理论和等离子体的电回路方程．研究了在控制等离子体总电流不变情形下欧姆感应和低杂波注入组合驱动电流的问题。结果表明，这一组合驱动方案对ＨＬ－１Ｍ装置的运行是可行的，其驱动电流分布可以通过改变低杂波注入功率、波谱形状、等离子体电子温度、密度以及总等离子体电流等加以控制。组合驱动的电流分布将优于欧姆驱动的电流分布，并可能抑制诸如锯齿振荡等一些ＭＨＤ不稳定性。     

Electron-hole recombination induced desorption of excimers from solid Ar

Excimer desorption from solid Ar under selective excitation by photons in the range 10–35 eV at different temperatures is studied. An additional mechanism of exciton-induced desorption of excited dimers Ar*₂ is proposed. By combining photo-, cathodo- and thermoluminescence experiments the excimer desorption is shown to be enhanced by electron-hole recombination. The role of both participants of the recombination process is discussed.     

Nonlinear Evolution of Driven Electron Plasma Oscillations in Inhomogeneous Plasmas

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Modulation of terahertz generation in dual-color filaments by an external electric field and preformed plasma

Terahertz generation driven by dual-color filaments in air is demonstrated to be remarkably enhanced by applying an external electric field to the filaments. As terahertz generation is sensitive to the dual-color phase difference, a preformed plasma is verified efficiently in modulating terahertz radiation from linear to elliptical polarization. In the presence of preformed plasma, a dual-color filament generates terahertz pulses of elliptical polarization and the corresponding ellipse rotates regularly with the change of the preformed plasma density. The observed terahertz modulation with the external electric field and the preformed plasma provides a simple way to estimate the plasma density and evaluate the photocurrent dynamics of the dual-color filaments. It provides further experimental evidence of the photo-current model in governing the dual-color filament driven terahertz generation processes.     

Water vapor desorption and adsorbent regeneration for air conditioning unit using pulsed corona plasma

The dehumidifying action of a dehumidifier or air conditioner was employed to achieve a comfortable and desirable indoor comfort. Water vapor adsorbed on an adsorbent substance needs to be regenerated when the water vapor exceeds the adsorption capacity. The conventional process for adsorbent regeneration or moisture desorption uses the heat by means of the electric heater. In the present study, the water vapor desorption from the adsorbent material was investigated using a pulsed corona plasma for possible replacement of the electric heater. The water vapor desorption for a given power (defined as desorption efficiency) using the pulsed corona plasma was found to be superior over conventional thermal desorption. The gradient of desorption (desorption rate) was found to be significantly higher for plasma desorption, so that faster desorption can be achieved without excessive gas heating. In addition, the plasma desorption was not affected by the initial moisture content in an indoor environment, which leads to more economical, controllable, and flexible air conditioning system.     

Degradation of tungsten under the action of a plasma jet

The degradation of the surface and structure of single-crystal tungsten and sintered powder tungsten during the action of a pulsed plasma jet is studied. It is shown that the degradation of a tungsten target during the action of a plasma jet with an energy flux density of 0.25–1 MJ/m² is accompanied by surface evaporation and melting and the fracture of surface layers on scales of 150–250 μm. The results of a numerical simulation of the thermomechanical processes that occur in a tungsten target during the action of a plasma jet are presented. The degradation of tungsten during the action of a plasma jet is shown to proceed almost continuously from the action (evaporation, melting) to the times that are more than three orders of magnitude longer than the action time, which is caused by the thermomechanical processes occurring in the tungsten target. Moreover, the action of thermal stresses leads to structural and morphological changes throughout the sample volume, and these changes are accompanied by recrystallization in adiabatic shear bands.     

Mechanisms of molecular manipulation with the scanning tunneling microscope at room temperature: chlorobenzene/si(111)-(7 x 7)

We report a systematic experimental investigation of the mechanism of desorption of chlorobenzene molecules from the Si(111)-(7 x 7) surface induced by the STM at room temperature. We measure the desorption probability as a function of both tunneling current and a wide range of sample bias voltages between -3 V and +4 V. The results exclude field desorption, thermally induced desorption, and mechanical tip-surface effects. They indicate that desorption is driven by the population of negative (or positive) ion resonances of the chemisorbed molecule by the tunneling electrons (or holes). Density functional calculations suggest that these resonant states are associated with the pi orbitals of the benzene ring.     

Study of slag content and properties after plasma melting of incineration ash

The paper presents the investigation of plasma melting of the mixed bottom and fly incineration ash at various mixing ratios of the components. Chemical compound of the bottom and fly ash as well as the slag after its melting was analyzed by different methods, and the content of toxic components in them was determined. It is demonstrated that the direct disposal of the fly and bottom incineration ash may cause dioxin and heavy metal contamination of the environment. The influence of melted ash basicity on the resulting slag compound was studied. The mass balance of the melting process was defined. The tests were performed to determine the heavy-metals leaching from the ash and slag. It is also shown that the slag after plasma melting is dioxin-free and environmentally friendly.     

Local melting and drag for a particle driven through a colloidal crystal

We numerically investigate a colloidal particle driven through a colloidal crystal as a function of temperature. When the charge of the driven particle is larger or comparable to that of the colloids comprising the crystal, a local melting can occur, characterized by defect generation in the lattice surrounding the driven particle. The generation of the defects is accompanied by an increase in the drag force on the driven particle, as well as large noise fluctuations. We discuss the similarities of these results to the peak effect phenomena observed for vortices in superconductors.     

On the Boil-Off Time of Probe Surfaces in Plasmas

The time required for the melting of the surface of a glass-insulated probe inserted in a plasma is computed including the influence of plasma mass motion. This effect is relevant for probe measurements in moving current sheaths of electrical gas discharges. For dense plasma focus experiments, it is shown that the time of formation of a transition layer of evaporated material is shorter than the ion relaxation time in the plasma and the transit time of the current sheath by the probe position.     

The detection by SERS of resonantly excited desorption of pyridine from silver island films by IR laser absorption

We have shown that when a very thin film of pyridine about two or three monolayers thick on a silver island film is exposed to a pulsed CO₂ laser line whose frequency corresponds to that of a pyridine vibrational mode the physisorbed molecules within the pyridine film can be desorbed even at liquid He temperatures. It is interesting that this observation was first made using surface enhanced Raman scattering. Experimental results are presented from which it is concluded that the phenomenon can be described as resonantly excited desorption. The absorbed IR energy seems to be localized within the pyridine film and the silver film and thermallized to some degree causing some of the physisorbed molecules to desorb. Analysis of the SERS spectra before and after the resonantly excited desorption has enabled us to separate out the SERS spectra due to the physisorbed pyridine and the chemisorbed pyridine.     

Comparison of plasma chemistries for the dry etching of bulk single-crystal zinc-oxide and rf-sputtered indium-zinc-oxide films

The dry etching characteristics of bulk, single-crystal zinc-oxide (ZnO) and rf-sputtered indium-zinc-oxide (IZO) films have been investigated using an inductively coupled high-density plasma with different plasma chemistries. The introduction of interhalogens such as ICl, IBr, BI₃, and BBr₃ to the Ar plasma produced no enhancement of the ZnO and IZO etch rates with respect to physical sputtering in a pure argon atmosphere under the same experimental conditions. In these plasma chemistries, the etch rate of both materials increased with source power and ion energy, indicating that ion bombardment plays an important role in enhancing desorption of etch products. Except in Ar/CH₄/H₂ discharges, the ZnO etch rate was very similar to that of IZO, which indicates that zinc and indium atoms are driven by a similar plasma etching dynamic. CH₄/H₂-containing plasmas produced higher etch rates for IZO than for ZnO due to the preferential desorption of the group III etch products. Application of the CH₄/H₂/Ar plasma to the etching of deep features in bulk, single-crystal ZnO produced highly anisotropic profiles although some trenches were observed near the sidewalls.     

60MHz电容耦合等离子体中电子能量分布函数特性研究

甚高频(频率大于30 MHz)耦合放电源由于能产生大面积高密度的等离子体而受到了人们的广泛关注. 采用电流、电压探针以及朗缪尔探针诊断技术对60MHz射频激发产生的容性耦合等离子体的放电特性及电子行为进行了研究. 实验结果表明,等离子体的等效电阻/电容随着射频输入功率的增加而减小/增加;等离子体中电子行为不仅依赖于射频输入功率,还与放电气压密切相关;放电气压的增加导致电子能量概率分布函数(EEPF)从双温Maxwellian分布向Druyvesteyn分布转变,而且转变气压远低于文献所报道的数值,这主要是由于在60MHz容性耦合等离子体中电子反弹共振加热效率大为降低. 关键词： 甚高频容性耦合等离子体 朗缪尔探针诊断 电子加热模式     

Collisional effects on the current-filamentation instability in a dense plasma

The collisional current-filamentation instability (CFI) is studied for a nonrelativistic electron beam penetrating an infinite uniform plasma. It is analytically shown that the CFI is driven by the drift-anisotropy rather than the classical anisotropy of the beam and the background plasma. Therefore, collisional effects can either attenuate or enhance the CFI depending on the drift-anisotropy of the beam-plasma system. Numerical results are given for some typical parameters, which show that collisional effects cannot stabilize but enhance the CFI in a dense plasma. Thus, the CFI may play a dominant role in the fast electron transport and deposition relevant to the fast ignition scenario (FIS).     

The thermal state of a small spherical body in an air plasma

Heat exchange between an air plasma and a low-heat-capacity spherical body made from a refractory (tungsten) or fusible (aluminum) material is studied under conditions when the body exhibits the properties typical of either a thermally thin or thermally thick body. The problem is solved for an unperturbed plasma temperature of 5000–20000 K, a pressure of up to 1 atm, and a body (particle) size of 10 μm to 1 cm. The model developed accounts for the possible phase transitions at melting and boiling. It is shown that, under proper physical conditions, a refractory particle can relax to a steady thermal state (in various aggregate states). This property can be used in plasma sputtering of refractory coatings, which requires the preparation of a spatially homogeneous thermal state of the sputtered macroparticles that underwent a metal-liquid phase transition.     

Magnetorotational instability in nonmagnetized plasma

It is shown that the magnetorotational instability (MRI) can be driven in nonmagnetized plasma. In this case, in contrast to the case of strongly magnetized plasma, radial derivative of plasma rotation frequency should be positive for such a driving. The characteristic wave lengths of MRI in nonmagnetized plasma are of the same order of magnitude as those for the Weibel instability.