Chemically assisted ion beam etching of silicon and silicon dioxide using SF6

A chemical flux of sulfur hexafluoride (SF₆) in conjunction with low-energy Ar-ion bombardment has been used for chemically assisted ion beam etching (CAIBE) of silicon and silicon dioxide. The study has shown a large degree of independent control over the selectivity and anisotropy in dry etching. The total etch rate could be controlled by varying either the Ar-ion milling parameters or the chemical flux of SF₆. Etch rate enhancement of 7–8 for silicon and 3–4 for silicon dioxide have been obtained over pure physical etching.     

直流放电制备CN自由基及其LIF探测

CN自由基是研究化学反应动力学的典型自由基，CN的动力学行为，如CN＋O2的反应已成为研究自由基－自由基反应的模型体系[1]，同时也在许多实际过程如燃烧过程，星际气体的形成过程中起着重要的作用[2，3]．利用含有CN的化合物进行光解、放电、与亚稳态原子分子进行传能反应是目     

Structural and Chemical Analysis of Materials with High Spatial Resolution

 An understanding of the correlation between microstructures and properties of materials require the characterization of the material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen and on the scattering power of the atoms (ions) present in the analyzed column. The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the electron charge density distribution of the bulk (defect-free) material. The different techniques are described and applied to different problems in materials science. It will be shown that nearly atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments in electron microscopy instrumentation will result in atomic resolution in the foreseeable future.     

Mass spectrometric diagnosis of the surface nitriding mechanism in a d.c. glow discharge

Reactive constituents have been investigated in a molecular beam generated in the cathode surface glow area and surface boundary layer. Mixtures of nitrogen and hydrogen form NH_x(x=0–4) compounds, which are of relevance in heterogeneous, plasma vs. metal nitriding reactions. Ammonia decomposition leads to NH_x(x=2–4). Strong cataphoretic enrichment of hydrogen has been observed in the cathode glow area. Heterogeneous reactions of NH_x with iron lead to the formation of iron nitrides via intermediates such as FeNH_2–3. In a pulsed d.c. glow discharge, increased sputtering and decreased hydrogen enrichment have been observed.     

Effects of Cone Angles on Nonlinear Vibration Responses of Functionally Graded Shells北大核心CSCD

The nonlinear vibration responses of functionally graded materials (FGMs) shells with different cone angles under external loads were studied. Firstly, the Voigt model was employed to describe the physical properties along the thickness direction of FGMs conical shells. Then, the motion equations were derived based on the 1st-order shear deformation theory, the von Kármán geometric nonlinearity and Hamilton’s principle. Next, the Galerkin method was applied to discretize the motion equations and the governing equations were simplified into a 1DOF nonlinear vibration differential equation under Volmir’s assumption. Finally, the nonlinear motion equations were solved with the harmonic balance method and the Runge-Kutta method, and the amplitude frequency response characteristic curves of the FGMs conical shells were obtained. The effects of different material distribution functions and different ceramic volume fraction exponents on the amplitude frequency response curves of conical shells were discussed. The bifurcation diagrams of conical shells with different cone angles, as well as time process diagrams and phase diagrams for different excitation amplitudes, were described. The motion characteristics were characterized by Poincaré maps. The results show that, the FGMs conical shells present the nonlinear characteristics of hardening springs. The chaotic motions of the FGMs conical shells are restrained and not prone to motion instability with the increase of the cone angle. The FGMs conical shell present a process from the periodic motion to the multi-periodic motion and then to chaos with the increase of the excitation amplitude. © 2022 Editorial Office of Applied Mathematics and Mechanics. All rights reserved.     

Elastic Analysis of Anisotropic Functionally Graded Rotating Disks With Non-Uniform Thicknesses北大核心CSCD

研究了任意梯度变化的变厚度各向异性转动圆盘的弹性问题.假设圆盘绕刚性轴匀速转动,其材料性能和厚度沿径向任意梯度变化.考虑圆盘在中心转轴处受位移约束,外侧自由,根据各向异性转动圆盘的平衡微分方程,得到关于径向应力的Fredholm积分方程,继而通过对Fredholm积分方程进行数值求解,得到结构的位移场和应力场.对具体梯度变化情况仅需代入相应梯度变化进行求解即可.数值算例部分,通过假设厚度、弹性模量等参数为特殊的幂函数形式,将由Fredholm积分方程求出的数值解与对应的精确解进行对比,以及针对常见的Voigt模型,将由该方法算得的数值解和ANSYS有限元计算结果进行对比,验证了该方法的准确性和精度.其次,针对Voigt模型,重点分析了厚度变化、材料性能梯度参数、各向异性度等对应力场和位移场的影响.提出了针对材料性能和厚度沿径向呈任意梯度变化的圆盘结构弹性分析方法,将为优化功能梯度圆盘的结构和材料参数、有效调整构件应力分布、提高结构安全性,提供强有力的工具;算例分析结果对功能梯度圆盘在复杂条件下的结构安全设计有重要的理论指导意义.     

Analysis and simulation on the performance of a gyro-penitron amplifier

A cylindrical waveguide gyro-peniotron amplifier is analysed theoretically in this paper. By a ballistic method and directly using the energy conservation in the beam-wave system, a set of interaction equations for the cylindrical waveguide gyro-peniotron amplifier is derived. Computer simulation shows that under defined conditions an interaction efficiency of 47%, an output power of 240kW at a gain of 22. 5 dB and a 3 dB-instantaneous bandwidth of 1. 9% for a central frequency of 35GHz, TE₀₃ mode gyro-peniotron amplifier could be achieved. The influence of the operation parameters on the amplifier performance is also presented.     

Polymeric flocculants processing by accelerated electron beams and microwave heating

Results obtained by accelerated electron beam, microwave and simultaneous microwave and electron beam application in the chemistry of acrylamide and acrylic acid copolymers (polymeric flocculants used for wastewater treatment) are presented. Comparative results concerning the molecular weight and Huggins’ constant for the acrylamide and acrylic acid copolymers obtained by classical heating, microwave heating, electron beam irradiation and simultaneous microwave and electron beam treatment are reported. Microwave heating produces high water solubility of the polymeric flocculants but median molecular weight values. Electron beam irradiation gives high molecular weight values but associated with a cross-linked structure (poor water solubility) while microwave energy addition to electron beam energy gives simultaneously high molecular weight values and high water solubility.     

Electron beam crosslinking of non-lead PVC formulations

PVC samples with lead-free and lead-base stabilizer, containing TMPTMA (trimethylolpropane trimethacrylate) as a crosslinker and DOP (2-ethylhexyl phthalate) as a plasticizer, were electron beam treated at different doses (2–200 kGy) and characterized to evaluate crosslinking and other several properties, as a continuation of our previously reported paper, where these PVC formulations, typical for wire and cable applications, underwent gamma irradiation. The PVC was formulated with two different stabilizing systems: Ca/Zn and dibasic lead phthalate for comparison, to use them as jackets for a 22 wire gage (AWG). Small samples of the jacketed wires were irradiated in an industrial Dynamitron electron accelerator for the corresponding doses, along with two dosimetric systems: radiochromic thin film and alanine pellets dosimeters. The maximum dose applied was decided as the crosslinking increased, until the gel content was stable. The dose of 200 kGy was the condition for the highest crosslinking, so most of the wire was irradiated at such dose. Chemical and mechanical evaluations were carried out to the irradiated wire. The results show that 200 kGy was too high dose for the materials, since an important degradation is observed for the Ca/Zn systems. Unfortunately, such dose affects basically to CaZn formulations, which showed much poorer performance than classical lead-containing compositions. The results also indicate that gel content is not the best way of deciding the optimum condition for irradiation.     

Reactions of Laser Ablation-magnesium Plasma with Methanol Clusters

IntroductionReactions of metal ions with neutral molecules orclusters produce a variety of metal complex ions andother new series of cluster ions including cations andanions.The laser ablation-molecular beam(LA-MB)method has marked its relevance in the st…