Fe-Cr合金辐照空洞微结构演化的相场法模拟

Fe-Cr合金作为包壳材料在高温高辐照强度等极端环境下服役,产生空位和间隙原子等辐照缺陷,辐照缺陷簇聚诱发空洞、位错环等缺陷团簇,引起辐照肿胀、晶格畸变,导致辐照硬化或软化致使材料失效.理解辐照缺陷簇聚和长大过程的组织演化,能更有效调控组织获得稳定服役性能.本文采用相场法研究Fe-Cr合金中空洞的演化,模型考虑了温度效应对点缺陷的影响以及空位和间隙的产生和复合.选择400—800 K温度区间、0—16 dpa辐照剂量范围的Fe-Cr体系为对象,研究在不同服役温度和辐照剂量下的空位扩散、复合和簇聚形成空洞的过程.在400—800 K温度区间,随着温度的升高,Fe-Cr合金空洞团簇形核率呈现出先升高后下降的趋势.考虑空位与间隙的重新组合受温度的影响可以很好地解释空洞率随温度变化时出现先升高后降低的现象.由于温度的变化将影响Fe-Cr合金中原子离位阀能,从而影响产生空位和间隙原子.同一温度下,空洞半径和空洞的体积分数随辐照剂量的增大而增大.辐照剂量的增大,级联碰撞反应加强,空位与间隙原子大量产生,高温下空位迅速的扩散聚集在Fe-Cr合金中将形成更多数量以及更大尺寸的空洞.     

硅中硼离子注入的带电缺陷动力学模拟

为准确描述硼离子注入硅后缺陷/杂质的动力学物理过程,获得硼浓度空间分布及其演化行为,构建一个跨尺度带电缺陷动力学模型,考虑离子注入缺陷的产生及其演化的多种微观过程,包括缺陷电荷态和带电缺陷间的反应、硼-自间隙团簇（BICs）演化以及缺陷与载流子相互作用等物理过程。模拟得到与实验一致的硼浓度深度分布。结果表明：BICs对硼浓度的深度分布起主要作用,而间隙硼（B_I）导致硼浓度分布向深处扩展;计及缺陷的不同电荷态修正自间隙（I）和硼间隙（B_I）的扩散系数,从而更准确地描述硼浓度分布。模型揭示了硼离子注入硅发生的物理过程和微观机理,证明BICs和缺陷真实的电荷态是描述硼浓度分布的重要因素,为半导体器件制造与研发提供理论指导。     

中子预辐照损伤对钨中氢滞留行为影响机制的多尺度模拟

高温等离子体作用下的中子辐照损伤和氢氦滞留行为一直是聚变堆钨基材料面临的两个关键问题,尤其是预辐照损伤对氢氦滞留的协同作用。鉴于制约因素的复杂性和实验上的困难,相关基础问题的理论研究至关重要。我们基于发展的顺序多尺度模拟方法研究了多晶钨的中子预辐照损伤及其对低能（20 eV）氢注入下缺陷动力学演化和氢滞留分布的影响。通过定量对比有无中子预辐照的多晶钨中氢的滞留行为,我们发现中子预辐照损伤产生的稳定空位团簇作为新的氢捕获点,加剧了氢在近表面处的滞留和表面损伤,限制了其向深度的扩散,从而导致了低能氢滞留量的急剧增加。相关结果将直接为实际等离子体环境下聚变堆钨基材料的辐照损伤和氢氦效应提供理论指导与预测。     

载能团簇离子的非线性辐照损伤

由于团簇离子在能量损失、二次离子发射和辐照损伤上的非线性效应,所以团簇离子与物质的相互作用倍受关注。对团簇作用的非线性效应研究不仅对于了解团簇离子与物质相互作用的机制具有十分重要的理论意义,而且载能团簇离子还有可能成为材料表面改性与分析、新功能材料的合成与研究的一种有效的新手段。因此,团簇离子与物质的相互作用成为当今国际上的研究热点之一。主要评述了载能团簇离子在物质中的非线性辐照损伤,介绍了典型的研究方法和实验结果。 Due to energetic cluster produces simultaneous impacts of several atoms and deposits extremely high energy density in a very small area, the cluster impingement on solids has produced non-linear radiation damages not presented in the collisions of individual atoms with those solids. The radiation damages are usually investigated by channeling Rutherford backscattering, Scanning Tunneling Microscope （STM）, Transmission Electronic c Microscope（TEM） and computer simulation. The typical methods and results on the non-linear radiation damages induced by clusters are reviewed in this paper.     

氦在铝表面辐照和积聚的团簇动力学模拟

我们利用团簇动力学模型(IRadMat)研究了keV-He离子辐照金属铝的缺陷动力学和氦的聚集行为.通过对不同俘获类型(团簇、晶界和位错)俘获He浓度的定量分析,我们发现大多数He原子被晶界吸收,这成为铝在低辐照通量下发生脆化的主要原因.随着辐照能量的增加,He滞留峰的位置会变得更深.然而,随着辐照通量的增加,He在体内的滞留量会变得更多,但滞留深度的峰值位置不变.我们的结果表明,晶界的影响在He的滞留分布以及铝的脆化行为中起着关键作用,这也有助于我们理解He在金属中的动力学行为和损伤的分布.     

氦在铝表面辐照和积聚的团簇动力学模拟

我们利用团簇动力学模型(IRadMat)研究了keV-He离子辐照金属铝的缺陷动力学和氦的聚集行为.通过对不同俘获类型(团簇、晶界和位错)俘获He浓度的定量分析，我们发现大多数He原子被晶界吸收，这成为铝在低辐照通量下发生脆化的主要原因.随着辐照能量的增加，He滞留峰的位置会变得更深.然而，随着辐照通量的增加，He在体内的滞留量会变得更多，但滞留深度的峰值位置不变.我们的结果表明，晶界的影响在He的滞留分布以及铝的脆化行为中起着关键作用，这也有助于我们理解He在金属中的动力学行为和损伤的分布.     

气相碳原子成笼的动力学模拟

分析了高温气相条件下纳米团簇形成的动力学过程.采用所谓的“速度遗忘”方法尝试建立了一个简化的动力学模型，并用此模型模拟了气相碳原子成笼的动力学过程.通过分析不同的模拟条件（对应于不同的实验条件）下碳原子在成笼过程中的运动轨迹，得到了与气相合成碳纳米团簇实验相符合的规律. 关键词： 分子动力学模型 纳米团簇     

强流脉冲电子束辐照诱发多晶纯铝中的空位缺陷簇结构

利用强流脉冲电子束（HCPEB）技术对多晶纯铝样品进行辐照,采用透射电子显微镜详细分析了辐照诱发的空位簇缺陷.HCPEP辐照后,在辐照表层内形成了大量的四方形空位胞,其间包含位错圈和堆垛层错四面体（SFT）等类型的空位簇缺陷.1次辐照后,空位胞内产生空位型位错圈,5次辐照则主要产生SFT;10次辐照后,空位胞内产生的空位簇缺陷主要是位错圈,局部区域也观察到了SFT缺陷,在产生SFT的附近区域具有很低的位错密度或者几乎无位错出现.HCPEB辐照产生的瞬间加热和冷却诱发了幅值极大且应变速率极高的应力,这一因素 关键词： 强流脉冲电子束 多晶纯铝 空位簇缺陷 堆垛层错四面体     

超短强激光脉冲激励甲烷团簇的内电离机理

采用三维粒子动力学模拟方法研究了甲烷团簇在超短强激光脉冲激励下的爆炸动力学行为,重点讨论了几种典型的内电离机理对团簇爆炸过程中离子的价态和动能的影响.研究表明,在激光脉冲强度比较小的情况下,团簇中的原子主要是在光场作用下通过隧道电离的方式发生电离.当激光场进一步增强时,势垒压低电离是电离的主要方式.在相同的较高激光强度下,团簇更容易通过势垒压低电离达到高的电离价态.团簇发生电离后,其内部库仑电场的点火电离效应和内部滞留自由电子的碰撞电离效应也将增强团簇的再次电离过程. 关键词： 超短强激光脉冲 甲烷团簇 内电离     

嵌埋于沸石分子筛中的Fen团簇的磁性能研究

运用RKKY理论,推导了金属球形团簇间交换作用,并利用蒙特卡罗（MC）方法模拟了嵌埋于沸石分子筛中的Fen团簇体系的磁性能与团簇尺寸的关联效应。结果表明：嵌埋式团簇体系的磁性能随团簇间距离呈震荡型,体系磁化强度随团簇分布密度及填充率的增大而增大,这对新型复合磁性材料的制备提供了参考。     

Influence of helium on the evolution of irradiation-induced defects in tungsten: An object kinetic Monte Carlo simulation

Understanding the evolution of irradiation-induced defects is of critical importance for the performance estimation of nuclear materials under irradiation. Hereby, we systematically investigate the influence of He on the evolution of Frenkel pairs and collision cascades in tungsten (W) via using the object kinetic Monte Carlo (OKMC) method. Our findings suggest that the presence of He has significant effect on the evolution of irradiation-induced defects. On the one hand, the presence of He can facilitate the recombination of vacancies and self-interstitial atoms (SIAs) in W. This can be attributed to the formation of immobile He-SIA complexes, which increases the annihilation probability of vacancies and SIAs. On the other hand, due to the high stability and low mobility of He-vacancy complexes, the growth of large vacancy clusters in W is kinetically suppressed by He addition. Specially, in comparison with the injection of collision cascades and He in sequential way at 1223 K, the average sizes of surviving vacancy clusters in W via simultaneous way are smaller, which is in good agreement with previous experimental observations. These results advocate that the impurity with low concentration has significant effect on the evolution of irradiation-induced defects in materials, and contributes to our understanding of W performance under irradiation.     

Statical critical properties of gadolinium models

Microscopic models of real ferromagnetic gadolinium are proposed, and their critical properties are studied by the Monte Carlo method. The critical exponents α (heat capacity), γ (susceptibility), and β (magnetization) are calculated. The α, β, and γ exponents are determined by the approximation of the data on the basis of traditional power functions and in the framework of the finite-size scaling theory. It is revealed that the critical behavior of gadolinium is affected by the dipole-dipole interactions. It is shown that the Monte Carlo method is a powerful tool for investigations into the critical properties of complex models in which two types of weak relativistic interactions are jointly taken into account against the background of each of these interactions.     

Monte Carlo simulations of TL and OSL in nanodosimetric materials and feldspars

The study of luminescent materials consisting of nanoclusters is an increasingly active research area. It has been shown that the physical properties of such nanodosimetric materials can be very different from those of similar conventional microcrystalline phosphors. In addition, it has been suggested that traditional energy band models may not be applicable for some of these nanodosimetric materials, because of the existence of strong spatial correlations between traps and recombination centers. The properties of such spatially correlated materials have been previously simulated by using Monte Carlo techniques and by considering the allowed transitions of charge carriers between the conduction band, electron traps and recombination centers. This previous research demonstrated successfully the effect of trap clustering on the kinetics of charge carriers in a solid, and showed that trap clustering can significantly change the observed luminescence properties. This paper presents a simplified method of carrying out Monte Carlo simulations for thermoluminescence (TL) and optically stimulated luminescence (OSL) phenomena, based on a recently published model for feldspar. This model is based on tunneling recombination processes involving localized near-neighbor transitions. The simulations show that the presence of small clusters consisting of a few traps can lead to multiple peaks in both the TL and linearly modulated OSL signals. The effects of donor charge density, initial trap filling and cluster size are simulated for such multi-peak luminescence signals, and insight is obtained into the mechanism producing these peaks.     

On the thermal stability of vacancy-carbon complexes in alpha iron

In this work we have summarized the available ab initio data addressing the interaction of carbon with vacancy defects in bcc Fe and performed additional calculations to extend the available dataset. Using an ab initio based parameterization, we apply object kinetic Monte?Carlo (OKMC) simulations to model the process of isochronal annealing in bcc Fe doped with carbon to compare with experimental data. As a result of this work, we clarify that a binding energy of ～0.65?eV for a vacancy-carbon (V-C) pair fits the available experimental data best. It is found that the V (2)-C complex is less stable than the V-C pair and its dissociation with activation energy of 0.55?+?0.49?eV also rationalizes a number of experimental data where the breakup of V-C complexes was assumed instead. From the summarized ab initio data, the subsequently obtained OKMC results and critical discussion, provided here, we suggest that the twofold interpretation of the V-C binding energy, which is believed to vary between 0.47 and 0.65?eV, depending on the ab initio approximation, should be removed. The stability and mobility of small and presumably immobile SIA clusters formed at stage II is also discussed in the view of experimental data.     

Modeling the Effect of Surface Modification of Gold Nanoparticles Irradiated with <Superscript>60</Superscript>Co on the Secondary Рarticles Emission Spectrum

The Monte Carlo method (computer simulation) is used to construct a physical model of secondary particles emission induced by the simulated irradiation of a gold nanoparticle with ⁶⁰Co. It is demonstrated that the modification of the nanoparticle surface with polyethylene glycol affects the spectrum of secondary electrons produced in a nanoparticle and leaving it and its shell. The model takes into account the size and the chemical composition of the shell and provides an opportunity to design antitumor radiosensitizers based on gold nanoparticles.     

C20离子团簇在氧化物中穿行时库仑爆炸过程的理论研究

研究了C20团簇在几种金属氧化物(Al2O3,SiO2)中穿行时发生的库仑爆炸过程.采用线性介电响应理论,并结合Mermin形式的介电函数,得到了团簇中各组成离子的空间感应势,其中组成团簇中各组成离子的电荷分布情况由Brandt-Kitagawa有效电荷理论模型来描述.通过求解运动方程得到离子团结构随时间的演化过程,并采用Monte Carlo方法模拟了爆炸过程中的多重散射现象.我们发现,尾流效应使团簇的空间结构和电荷分布呈现非对称性.     

Yield estimation of metallic layers in integrated circuits

In the existing models of estimating the yield and critical area, the defect outline is usually assumed to be circular, but the observed real defect outlines are irregular in shape. In this paper, estimation of the yield and critical area is made using the Monte Carlo technique and the relationship between the errors of yield estimated by circular defect and the rectangle degree of the defect is analysed. The rectangular model of a real defect is presented, and the yield model is provided correspondingly. The models take into account an outline similar to that of an original defect, the characteristics of two-dimensional distribution of defects, the feature of a layout routing, and the character of yield estimation. In order to make the models practicable, the critical area computations related to rectangular defect and regular (vertical or horizontal) routing are discussed. The critical areas associated with rectangular defect and non-regular routing are developed also, based on the mathematical morphology. The experimental results show that the new yield model may predict the yield caused by real defects more accurately than the circular model. It is significant that the yield is accurately estimated using the proposed model for IC metals.     

Benchmarking and validation of a Geant4–SHADOW Monte Carlo simulation for dose calculations in microbeam radiation therapy

Microbeam radiation therapy (MRT) is a synchrotron‐based radiotherapy modality that uses high‐intensity beams of spatially fractionated radiation to treat tumours. The rapid evolution of MRT towards clinical trials demands accurate treatment planning systems (TPS), as well as independent tools for the verification of TPS calculated dose distributions in order to ensure patient safety and treatment efficacy. Monte Carlo computer simulation represents the most accurate method of dose calculation in patient geometries and is best suited for the purpose of TPS verification. A Monte Carlo model of the ID17 biomedical beamline at the European Synchrotron Radiation Facility has been developed, including recent modifications, using the Geant4 Monte Carlo toolkit interfaced with the SHADOW X‐ray optics and ray‐tracing libraries. The code was benchmarked by simulating dose profiles in water‐equivalent phantoms subject to irradiation by broad‐beam (without spatial fractionation) and microbeam (with spatial fractionation) fields, and comparing against those calculated with a previous model of the beamline developed using the PENELOPE code. Validation against additional experimental dose profiles in water‐equivalent phantoms subject to broad‐beam irradiation was also performed. Good agreement between codes was observed, with the exception of out‐of‐field doses and toward the field edge for larger field sizes. Microbeam results showed good agreement between both codes and experimental results within uncertainties. Results of the experimental validation showed agreement for different beamline configurations. The asymmetry in the out‐of‐field dose profiles due to polarization effects was also investigated, yielding important information for the treatment planning process in MRT. This work represents an important step in the development of a Monte Carlo‐based independent verification tool for treatment planning in MRT.     

Critical properties of the models of small magnetic particles of the antiferromagnet MnF2

The static critical behavior of the models of small magnetic particles of the real two-sublattice antiferromagnet MnF₂ is investigated by the Monte Carlo method taking into account the interaction of the second nearest neighbors. Systems with open boundaries are considered to estimate the influence of the sizes of particles on the pattern of their critical behavior. The behavior of thermodynamic functions in the phase transition region is investigated. The data on the maxima of the temperature dependences of heat capacity and magnetic susceptibility are shown to be insufficient to unambiguously determine the effective temperature of the phase transition in the models of small magnetic particles. This requires an additional investigation of the spatial orientation of the sublattice (sublattices) magnetization vector for the models under study.     

Structural properties of the condensate in two-dimensional mesoscopic systems of strongly correlated excitons

A two-dimensional mesoscopic Bose system of dipoles in a 2D trap is considered using computer simulation by the quantum path-integral Monte Carlo method. The model describes a rarefied system of spatially indirect excitons in a confining potential. Bose condensation in the system and its superfluid and structural properties are studied over a wide range of interparticle spatial correlations, from an almost ideal Bose gas to the regime of a strongly correlated system. It is found that, at strong interparticle spatial correlations, particles in the condensate form a crystal-like structure. In this case, the spatial correlations of particles in the condensate are less pronounced than the correlations of noncondensed particles. The effect of recurrent crystallization is observed in the regime of strong interparticle correlations.