高电荷态离子与Si(110)晶面碰撞的沟道效应研究

不同电荷态低速离子(Ar^q+,Pb^q+)轰击Si(110)晶面,测量不同入射角情况下的次级粒子的产额. 通过比较溅射产额与入射角的关系,证实沟道效应的存在. 高电荷态离子与Si相互作用产生的沟道效应说明溅射产额主要是由动能碰撞引起的. 在小角入射条件下,高电荷态离子能够增大溅射产额. 当高电荷态离子以40°—50°入射时,存在势能越高溅射产额越大的势能效应. 关键词： 高电荷态离子 溅射 沟道效应     

高电荷态离子207Pb36+与金属Nb表面作用产生的二次离子产额

本文报道了利用兰州重离子加速器国家实验室的ECR离子源引出的高电荷态离子207Pb36 入射到金属Nb表面产生的二次离子的实验测量结果.实验发现,二次离子产额Y随入射初动能Ek的增加有先增加后减小的关系,在初动能为576 keV时二次离子产额达到最大.通过对实验点做高斯拟合发现,曲线峰值对应的入射初动能为602 keV.分析表明,这是势能沉积作用与线性级联碰撞过程协同作用的结果.高电荷态离子本身携带的高势能沉积在靶表面引起势能溅射,促进了二次离子的发射;而主导二次离子溅射的过程是动能溅射,它与靶表面的动量沉积(核能损)过程密切相关.     

高电荷态离子40Arq+与Si表面作用中的电子发射产额

报道了在兰州重离子加速器国家实验室电子回旋共振离子源原子物理实验平台上，用高电荷态⁴⁰Ar^q+(1≤q≤12)离子作用于半导体Si固体表面时的电子发射产额实验测量.实验中，通过改变炮弹离子的电荷态和引出电压选取其不同的势能和动能，系统地研究了入射离子势能沉积和与其在固体中的电子能损对表面电子发射产额的贡献.结果表明，作为引起表面电子发射的两个主要因素，单离子的电子发射产额与炮弹离子在固体表面的势能沉积和电子能损都有近似的正比关系.     

多成分靶优先溅射的蒙特-卡罗计算

基于两体碰撞近似,本文用蒙特-卡罗方法研究离子轰击多成分靶引起的溅射。计算了1keV,10keV的氦离子和氖离子入射引起多成分、无定型靶表面总溅射产额和部分溅射产额;溅射粒子的能谱、角分布和深度来源分布。并计算了择优溅射引起材料表面组分相对浓度的变化。结果还表明,离子轰击多成分靶时,碰撞效应足以引起优先溅射,它是造成靶表面各种成分相对浓度变化的重要因素。 关键词：     

高电荷态离子207Pb36+与金属Nb表面作用产生的二次离子产额

本文报道了利用兰州重离子加速器国家实验室ECR源引出的高电荷态离子207Pb36+入射到金属Nb表面产生二次离子溅射的实验测量结果.实验发现,二次离子产额Y随入射初动能Ek的增加有先增加后减小的关系,二次离子产额有一个峰值.理论分析认为,这一过程是势能沉积作用与线性级联碰撞过程协同作用的结果.     

低速Xe~(q+)(4≤q≤20)离子与Ni表面碰撞中的光辐射

实验中测量了0.38V_(Bohr)(460 keV)高电荷态Xe~(q+)(4≤q≤20)离子轰击高纯Ni表面发射的400-510 nm光谱.实验结果包括NiⅠ原子谱线,NiⅡ离子谱线,以及入射离子中性化发射的XeⅠ,XeⅡ和XeⅢ谱线.研究了谱线XeⅡ410.419,XeⅢ430.444,XeⅡ434.200,XeⅡ486.254,NiⅠ498.245,NiⅠ501.697,NiⅠ503.502,NiⅠ505.061和NiⅠ508.293 nm的光子产额随着入射离子电荷态的变化.结果表明,入射离子中性化和溅射Ni原子发射谱线的光子产额随着入射离子电荷态的增加而增加,其趋势与入射离子势能一致.     

高电荷态离子207Pbq+(24≤q≤36)与Si(110)固体表面作用的电子发射研究

报道了利用兰州重离子加速器国家实验室ECR源引出的高电荷态离子²⁰⁷Pb^q+(24≤q≤36)入射到Si(110)表面产生的电子发射的实验测量结果.结果表明,高电荷态离子与固体表面相互作用产生的电子发射产额Y与入射离子的电荷态q、入射角度ψ和入射能量E都有很强的关联.首次发现,电子发射产额Y与入射角度ψ间有接近1/tanψ的关系.理论分析认为,这些过程与基于经典过垒模型的势能电子发射过程密切相关. 关键词： 高电荷态离子 经典过垒模型 电子发射产额     

260～520 keV Krq+ (8≤q≤17)离子轰击Al靶产生的可见光辐射

低速高电荷态离子与金属表面相互作用,原子从靶材表面溅射,其中一部分处于激发态的溅射原子通过辐射退激产生可见光。在这一相互作用过程中,低速高电荷态离子从靶材表面捕获一个或多个电子进入其激发态,这些处于激发态的入射离子也会通过辐射退激产生可见光。研究表明,离子在靶材中的核阻止本领与溅射原子产额密切相关。为了更好地理解溅射原子的激发过程,认识低速高电荷态离子与金属相互作用过程中,溅射原子的激发概率与入射离子动能和势能之间的关联,研究了260～520 keV Krq+ (8≤q≤17)离子与Al靶相互作用过程中的可见光发射。给出了520 keV Kr13+ 与Al表面相互作用过程中,发射300～550 nm波长范围的发射光谱。实验结果包括溅射的Al原子在309.0和395.9 nm处的共振跃迁,Al+和Al2+分别在358.3和451.6 nm处的共振跃迁,以及Kr+在430.0,434.1,465.8和486.0 nm处的共振跃迁。还给出了谱线强度比值Y(309.0)/Y(395.9),Y(358.5)/Y(395.9),Y(452.8)/Y(395.9)随入射离子动能和势能的变化。结果表明：谱线强度比值均随入射离子动能的增加而增大,而比值Y(309.0)/Y(395.9)随势能的增加而减小。分析表明,在低速高电荷态离子与Al靶相互作用过程中,动能（电子阻止本领）和势能共同作用导致Al原子的激发,与激发态Al(4s)相比,电子布居较高激发态Al(3d)的概率随着离子电子阻止本领的增加而增大,而随着离子势能增加而减小。在低速高电荷态离子与金属表面相互作用过程中,入射离子在靶材中的核阻止本领影响溅射原子产额,而电子阻止本领与激发概率相关。在这一作用过程中,动能和势能共同决定溅射原子的激发概率,当动能和势能在同一数量级时,动能作用比势能作用小两个量级。     

高电荷态离子^207Pb^36＋与金属Nb表面作用产生的二次离子产额

本文报道了利用兰州重离子加速器国家实验室ECR源引出的高电荷态离子^207Pb^36＋入射到金属Nb表面产生二次离子溅射的实验测量结果，实验发现。二次离子产额Y随入射初动能B的增加有先增加后减小的关系，二次离子产额有一个峰值。理论分析认为，这一过程是势能沉积作用与线性级联碰撞过程协同作用的结果。     

高电荷态离子207Pbq+(24≤q≤36)与Si(110)固体表面作用的电子发射研究

报道了利用兰州重离子加速器国家实验室ECR源引出的高电荷态离子207Pbq+(24≤q≤36)入射到Si(110)表面产生的电子发射的实验测量结果.结果表明,高电荷态离子与固体表面相互作用产生的电子发射产额Y与入射离子的电荷态q、入射角度ψ和入射能量E都有很强的关联.首次发现,电子发射产额Y与入射角度ψ间有接近1/tanψ的关系.理论分析认为,这些过程与基于经典过垒模型的势能电子发射过程密切相关.     

Ni原子倾斜轰击Pt(111)表面低能溅射现象的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,通过分子动力学模拟详细研究了以不同角度入射的低能Ni原子与Pt (111)基体表面相互作用过程中的低能溅射行为.结果表明:随着入射角度从0°增加到80°,溅射产额Y_s和入射原子钉扎系数S的变化均可以根据入射角θ近似地分为以下三个区域:当θ ≤ 20°时,Y_s和S几乎保持不变,其值与垂直入射时接近,溅射原子的发射角分布和能量分布也与垂直入射时的情 关键词： 分子动力学模拟 入射角 低能溅射     

Anisotropic energy distribution of sputtered atoms induced by low energy heavy ion bombardment

The theory of anisotropic sputtering published in Phys. Rev. B 71(2), 026101 (2005) and Radiat. Effects Defects Solids 159(5), 301 (2004) has been modified and used to calculate the sputtering yield energy distributions for copper, tungsten, and aluminum targets bombarded by low-energy argon ion. As usual, the electronic stopping is ignored in the analysis. The present theory (modified Sigmund’s theory) has been shown to fit the corresponding experimental results of sputtering yield energy distributions well, except for the cases where the larger ion incident angle and larger sputtering emission angles were considered. The larger discrepancy between the present theory and the experimental result in the latter cases is probably due to the influence of direct recoil atoms on the energy spectrum. Compared with Falcone’s analytical theory, the present theory can reproduce much better experimental results of sputtering phenomena. The fact clearly demonstrates the intrinsic relation between the ion–energy dependence of the total sputtering yield and the sputtering yield energy distribution and suggests the great importance of momentum deposited on the target surface in the physical sputtering     

连续碳纤维增强碳化硅的辐照效应

连续碳纤维增强碳化硅材料除了具有碳化硅材料固有的低中子活化性能,低衰变热性能和低氚渗透性能等优点以外,还具有密度低、线性膨胀系数小、高比强度、高比模量、耐高温、抗氧化、抗蠕变、抗热震、耐化学腐蚀、耐盐雾、优良的电磁波吸收特性等一系列优异性能,是各类核工程重要的潜在候选材料。在核聚变工程应用领域,连续碳纤维增强碳化硅材料作为第一壁材料不可避免地会受到各种辐射粒子的影响。研究清楚这些辐射粒子对它的辐照效应对其在核工程领域的安全使用至关重要。采用蒙特卡罗方法与分子动力学方法进行模拟计算,研究了氕、氘、氚和氦四种粒子对连续碳纤维增强碳化硅的辐照效应。SRIM和LAMMPS计算结果表明:当入射原子能量为100 eV,连续碳纤维增强碳化硅中碳的浓度在80%~85%时,氕、氘、氚和氦原子的溅射率存在最小值;入射粒子的种类对溅射率的影响显著,氦原子的溅射率大于氘原子和氚原子,而氘原子和氚原子的溅射率相差不大但均显著大于氕原子;溅射率随入射能量的增加先迅速增加后逐渐减小,氕、氘、氚和氦原子入射能量分别在200,400,600和800 eV时存在溅射率最大值;当氦原子入射能量为100 eV时,溅射率随入射角度的增加而逐渐减少。这些结果对连续碳纤维增强碳化硅材料在核工程上的应用具有一定的参考意义。Continuous carbon fiber reinforced silicon carbide material has the low neutron activation, low decay heat performance and tritium permeability, which are inherent performance of silicon carbide materials. It also has other advantages such as low density, small linear expansion coefficient, specific strength and specific modulus, high temperature resistance, oxidation resistance, creep resistance, thermal shock, resistance to chemical corrosion, salt fog resistance, excellent electromagnetic wave absorption properties, etc. It is an important potential candidate material in various field of nuclear engineering. In the field of nuclear fusion engineering applications, continuous carbon fiber reinforced silicon carbide as the first wall material will inevitably be bombarded by a variety of radiation particles. The radiation effect is critical to its safe use in nuclear engineering. The Monte Carlo method and the molecular dynamics method were used to study the radiation effect of protium, deuterium, tritium and helium on continuous carbon fiber reinforced silicon carbide. The SRIM and LAMMPS simulation results show that when the incident energy is 100 eV and the concentration of carbon in the continuous carbon fiber reinforced silicon carbide is about 80% ~ 85%, the sputtering yield of protium, deuterium, tritium and helium atoms have the minimum values. The kind of incident particle has a significant effect on the sputtering yield. The sputtering yield of helium atoms is larger than that of tritium atoms and deuterium atoms. There is not much difference between the sputtering yield of deuterium atoms and tritium atoms, and both the sputtering yield of deuterium atoms and tritium atoms are larger than that of protium atoms. The sputtering yield initially increases rapidly with the increase of the incident energy and then decreases gradually. The incident energy of the protium, deuterium, tritium and helium atoms has the maximum value of the sputtering yield at 200, 400, 600 and 800 eV, respectively. When the incident energy of helium atoms is 100 eV, the sputtering yield decreases while the increase of the incident angle. These results can provide a certain reference for the application of continuous carbon fiber reinforced silicon carbide materials in nuclear engineering.     

辐照导致钨表面的溅射现象的理论研究

采用基于量子力学的分子动力学方法,模拟了高能粒子辐照导致钨表面的溅射和结构损伤.结果显示,当PKA能量高于200 eV且入射角度大于65°时开始产生溅射原子,当入射角度在45°-65°之间时,钨表面因受辐照而导致的空位数目最少.因此,当PKA入射角度取在45°-65°之间时,可以有效地降低辐照导致的钨表面的结构损伤.还发现钨表面含有间隙原子时会加剧表面原子溅射,而包含空位原子且PKA取在空位附近时则会抑制表面原子的溅射.     

低能Pt原子与Pt(111)表面相互作用的分子动力学模拟

利用分子动力学模拟方法详细研究了低能Pt原子与Pt(111)表面的相互作用所导致的表面吸附原子、溅射原子、表面空位的产生及分布规律,给出了表面吸附原子产额、溅射原子产额和表面空位产额随入射Pt原子能量的变化关系.模拟结果显示:溅射产额、表面吸附原子产额和表面空位产额随入射原子的能量的增加而增加,溅射原子、表面吸附原子的分布花样呈3度旋转对称性质;当入射粒子能量高于溅射阈值时,表面吸附原子主要是基体最表面原子的贡献,入射粒子直接成为表面吸附原子的概率很小.其主要原因是:当入射粒子能量高于溅射能量阈值时,入射 关键词： 分子动力学 低能粒子 表面原子产额 空位缺陷 溅射     

Pt(111)表面低能溅射现象的分子动力学模拟

利用嵌入原子方法的原子间相互作用势，通过分子动力学模拟，详细研究了贵金属原子在Pt (111)表面的低能溅射现象.模拟结果显示：对于垂直入射情况，入射原子的质量对Pt (11 1)表面的溅射阈值影响不大.当入射原子的能量小于溅射阈值时，入射原子基本以沉积为主 ；当入射原子的能量大于溅射阈值时，溅射产额随入射原子能量的增加而线性增大；当入射 原子能量达到200 eV时，各种入射原子的溅射产额都达到或接近1，此时入射原子主要起溅 射作用.溅射原子发射的角分布概率和溅射花样与高能溅射相类似.研究表明：与基于二体碰 撞近似的线性级联溅射理论不同，当入射原子能量大于溅射阈值时，低能入射原子的溅射产 额正比于入射原子的约化能量和入射原子与基体原子的质量比.通过对低能入射原子的钉扎 能力分析，提出了支配低能溅射的入射原子反射物理机理. 关键词： 分子动力学模拟、低能溅射     

Sputtering studies with the Monte Carlo Program TRIM.SP

The Monte Carlo Program TRIM.SP (sputtering version of TRIM) was used to determine sputtering yields and energy and angular distributions of sputtered particles in physical (collisional) sputtering processes. The output is set up to distinguish between the contributions of primary and secondary knock-on atoms as caused by in- and outgoing incident ions, in order to get a better understanding of the sputtering mechanisms and to check on previous theoretical models. The influence of the interatomic potential and the inelastic energy loss model as well as the surface binding energy on the sputtering yield is investigated. Further results are sputtering yields versus incident energy and angle as well as total angular distributions of sputtered particles and energy distributions in specific solid angles for non-normal incidence. The calculated data are compared with experimental results as far as possible. From this comparison it turns out that the TRIM.SP is able to reproduce experimental results even in very special details of angular and energy distributions.     

The effect of incident angle on the C60 bombardment of molecular solids

The effect of incident angle on the quality of SIMS molecular depth profiling using C₆₀⁺ was investigated. Cholesterol films of ∼300 nm thickness on Si were employed as a model and were eroded using 40 keV C₆₀⁺ at an incident angle of 40° and 73° with respect to the surface normal. The erosion process was characterized by determining at each angle the relative amount of chemical damage, the total sputtering yield of cholesterol molecules, and the interface width between the film and the Si substrate. The results show that there is less molecule damage at an angle of incidence of 73° and that the total sputtering yield is largest at an angle of incidence of 40°. The measurements suggest reduced damage is not necessarily dependent upon enhanced yields and that depositing the incident energy nearer the surface by using glancing angles is most important. The interface width parameter supports this idea by indicating that at the 73° incident angle, C₆₀⁺ produces a smaller altered layer depth. Overall, the results show that 73° incidence is the better angle for molecular depth profiling using 40 keV C₆₀⁺.     

Dynamic evolution of impaction and sticking behaviors of fly ash particle in pulverized coal combustion

This paper aims to reveal the mechanisms governing the impaction and sticking dynamics of fly ash particles in pulverized coal combustion. The modeling work is of relevance to experiments in a 25?kW self-sustained down-fired furnace, which provides a sequence of real deposit shapes as varied boundary conditions for CFD simulations. Although the formed ash deposit has a comparable length scale with the probe, it has little effect on the global impaction efficiency of newly-coming particles. However, as the deposit builds up, incident particles impact the deposit and probe at generally larger impact angles and smaller normal velocities despite the almost invariant global impaction efficiency. It results in an enhanced local sticking probability in the center region of the probe, but a decreased one in the lateral regions. The incident kinetic energy of newly sticking particles to the deposit exhibits a converse correlation with their impact angle. The relationship of the averaged local sticking probability as a function of the azimuthal angle of probe is illustrated. Finally, the effect of Reynolds number on global particle impaction efficiency is examined. A universal formula is proposed, which is of importance to bridge lab-scale experiments and practical applications.