GaN中质子辐照损伤的分子动力学模拟研究

本文利用分子动力学方法研究了GaN在质子辐照下的损伤。对不同能量(1～10 keV)初级离位原子(PKA)引起的级联碰撞进行了研究,分析了点缺陷与PKA能量的关系、点缺陷随时间的演化规律、点缺陷的空间分布及点缺陷团簇的尺寸特征。研究结果表明,点缺陷的产生与PKA能量呈线性关系,不同类型的点缺陷随时间演化规律相似,点缺陷多产生在PKA径迹旁,点缺陷团簇多为孤立的点缺陷和小团簇。     

3C-SiC辐照诱发缺陷演化及温度效应分子动力学模拟

运用分子动力学方法,采用LAMMPS程序模拟了3C-SiC中的级联碰撞过程。研究了不同初始运动方向、不同能量下的PKA级联碰撞产生点缺陷的演化,结果表明,级联碰撞产生的空位数与PKA初始运动方向无关而与PKA能量之间呈线性关系。通过对级联碰撞过程中热峰、损伤区域瞬态温度分布分析可看出,级联碰撞过程中会产生高温区域,且此区域大小随时间的变化与PKA能量无关。     

不同温度下α-Fe中级联碰撞分子动力学模拟研究

采用分子动力学方法模拟了500~700 K温度下α-Fe中由1~50 keV的初级离位原子（PKA）引发的级联碰撞，研究了缺陷演化过程，并分析了不同阶段的PKA能量（E_PKA）与缺陷存活数量（N_FP）、成团率的关系以及温度对级联碰撞过程的影响，讨论了级联碰撞后产生的缺陷的取向结构，并得到以下结论：级联碰撞后产生的缺陷的原子取向与尺寸相关，可指导构建团簇、位错环等多种缺陷结构；E_PKA较高时，大尺寸团簇的保留会明显提高缺陷存活数量，从而导致不同PKA能量阶段的N_FP-E_PKA拟合曲线指数有较大差别，温度的升高会使拟合曲线指数的变化量减小。     

质子在砷化镓材料中产生位移损伤的Geant4模拟

本文使用Geant4模拟了1、5、10、20、50、100、500、1000 MeV能量的质子入射GaAs的位移损伤情况。随入射质子能量的增大，产生的初级离位原子（PKA）数目增加、种类增多；PKA能谱分布总体上呈递减趋势，PKA在低能量区间所占份额降低，在高能量区间所占份额升高。研究结果表明，辐射缺陷浓度在质子入射方向上遵循布拉格规律。     

3 超短脉冲激光与原子团簇相互作用实验研究

实验研究了超短脉冲激光与原子团簇相互作用过程中各种实验条件对团簇吸收激光能量的影响。实验发现高Z稀有气体（Xe）以及较高的气体压力都更易形成大团簇，对激光能量的吸收较高。还研究了激光波长（744与248nm）、激光强度以及偏振态等对吸收效率的影响。结果表明，短波长激光更易被团簇吸收；在一定强度范围内（10^15～10^16W／cm^2），随激光强度的增强，团簇对激光的吸收效率也增高；P极化光比S极化光更易被团簇吸收。     

5 激光团簇相互作用实验系统的建立

为了研究激光团簇相互作用对激光吸收机制的影响，建立了团簇产生系统、激光团簇同步系统以及一套飞行时间谱仪。团簇产生系统主要由螺线管脉冲阀和电源控制器以及产生团簇的气系统组成，为了尽可能地产生大的团簇，选用Xe作为实验气体；激光团簇同步系统由2台数字脉冲延迟器（DG535）构成，第1台用于激光器系统各部分的协调运行，第2台输入端连接到第1台的延迟输出端上，通过一定的时间延迟再控制脉冲阀的信号输出，使得激光与团簇达到同步产生；飞行时间谱仪采用MCP作为探测器，能够对弱信号进行测量，主要用来测量激光团簇相互作用产生的高能离子能谱。     

用串列静电加速器获取MeV高能团簇离子束

利用复旦大学现有的串列静电加速器（ＮＥＣ ９ＳＤＨ－２）获得了能量为１－４ＭｅＶ的硼、碳、硅及金等小型高能团簇离子束：Ｂｎ＾＋（ｎ＝２）、Ｃｎ＾＋（ｎ〈１０）、Ｓｉｎ＾＋（ｎ＝２，３，４）以及Ａｕｎ＾＋（ｎ＝２）；束流强度与团簇的种类和所含的原子数有关，为０．１－１００ｎＡ量级。注入加速器的低能团簇负离子由铯溅射离子源（ＳＮＩＣＳ Ⅱ）产生，高能团簇正离子的质量鉴别用磁分析器完成，高能碳团簇负离子     

非均匀形核对辐照诱导钨内微结构演化行为影响的团簇动力学模拟

金属钨(W)及其合金作为未来聚变堆最具应用前景的面向等离子体结构材料(PFMs),其服役性能直接影响聚变堆长期服役的安全性,辐照诱导W及其合金内微结构演化导致的辐照脆化现象始终是限制其工程应用的关键因素。本文基于分子动力学计算结果,进一步完善了辐照诱导材料微结构演化行为的团簇动力学模型,采用更加完备的物理模型描述材料内辐照缺陷的产生行为,并进一步探讨了W基体内辐照缺陷产生过程对微结构演化行为的影响。模拟结果表明,高能初始离位原子(PKA)诱发级联碰撞直接产生的缺陷团簇是W内位错环、空洞演化中最重要的形核机制;非均匀形核所产生的间隙团簇的扩散行为对位错环的长大行为有重要影响,会导致位错环尺寸分布中出现亚尖峰与台阶状形貌。     

超短脉冲激光与原子团簇相互作用实验研究

实验研究了超短脉冲激光与原子团簇相互作用过程中各种实验条件对团簇吸收激光能量的影响。实验发现高Z稀有气体(Xe)以及较高的气体压力都更易形成大团簇,对激光能量的吸收较高。还研究了激光波长(744与248nm)、激光强度以及偏振态等对吸收效率的影响。结果表明,短波长激光更易被团簇吸收;在一定强度范围内(1015~1016W/cm2),随激光强度的增强,团簇对激光的吸收效率也增高;P极化光比S极化光更易被团簇吸收。利用能量计测量了不同实验条件下激光的吸收效率,室温下,2MPa Xe气体形成团簇对激光的吸收效率达50%,并利用飞行时间谱仪测量了离子…     

碳团簇Cn^＋（n=1—5）注入NaCl晶体的研究

能量为0.6MeV/C荷能碳团簇离子Cn^ (n=2-5)注入到NaCl单晶，利用TRIM程序对碳团簇在NaCl单晶中的射程进行模拟，碳团簇NaCl单晶内存在一定长度的“团簇区域”。光学吸收谱表明：由于团簇区域的存在，不同碳离子团簇辐照产生的缺陷种类浓度都有很大不同，较大团簇会产生V2和V3色心，色心浓度也较大。     

Simulation of radiation damages in molybdenum by combining molecular dynamics and OKMC

In this paper,radiation defects in bcc molybdenum with the primary knock-on atom(PKA) energies of2-40 keV are simulated by the molecular dynamics.The binding energy of single point defect-to-defect clusters increases with the cluster size.The stabiUty and mobility of point defects and defect clusters are analyzed.The interstitial-type clusters are found to be easily migrating along the 111 direction with low barriers(0.01-0.10 eV).Then,the object kinetic Monte Carlo is used to gain insight into the long-term defect evolution in the cascade.The simulation results indicate that Stage I almost occurs at annealing temperature of 100K,which corresponds to the correlated recombination resulting from the motion of small interstitial clusters(n ≤2).The formation of substage partly as result of the small vacancy clusters motion.At about 460 K,the Stage II starts because of uncorrected recombination due to an emitting mechanism of larger clusters.Size distribution of the clusters at the cascade quenching stage is positively correlated with the PKA energies,affecting notably the subsequent annealing process.     

MD and OKMC simulations of the displacement cascades in nickel

The molecular dynamics(MD) method was used to investigate the displacement cascades with primary knock-on atom(PKA) energies of 2-40 keV at 100 and600 K.The migration energy of defects and their clusters was calculated by nudged elastic band(NEB) method.Object kinetic Monte Carlo(OKMC) was used to simulate the evolution of defects in Ni under annealing.In each annealing stage,the recombination mechanism was discussed and evolution of the defects under different cascade conditions was compared.It was found that the defects generated in high-temperature cascades are more stable than those in the low-temperature cascades.In addition,almost all the defects are annihilated during annealing process at low PKA energy.At PKA energy of 20-40 keV,however,a large number of defects would remain after annealing.     

MD simulations to evaluate effects of applied tensile strain on irradiation-induced defect production at various PKA energies

Molecular Dynamics (MD) simulations were conducted to investigate the influence of applied tensile strain on defect production during cascade damages at various Primary Knock-on Atom (PKA) energies of 1–30 keV. When 1% strain was applied, the number of surviving defects increased at PKA energies higher than 5 keV, although they did not increase at 1 keV. The rate of increase by strain application was higher with higher PKA energy, and attained the maximum at 20 keV PKA energy with a subsequent gradual decrease at 30 keV PKA energy The cluster size, mostly affected by strain, was larger with higher PKA energy, although clusters with fewer than seven interstitials did not increase in number at any PKA energy.     

Effects of Fe-He potential on primary damage formation in Fe-1%He

The effects of different Fe-He interatomic potentials on primary damage formation in Fe-1%He are investigated using molecular dynamics (MD) methods. Simulations of cascades produced by primary knock-on atoms (PKA) of energy E_p = 0.5-10 keV were performed at an irradiation temperature of 100 K. It is found that the Fe-He potentials have significant effects on the point defect creation and the formation of Fe-He interstitial clusters, whereas small effects on the formation of He-vacancy clusters.     

Damage production in GaAs during MeV ion implantation

The influence of the nuclear and electronic energy loss on the damage production in GaAs has been studied by Se⁺ ion implantation at T_I = 293 K with energies ranging from 2 MeV up to 20 MeV. The ion dose was varied between 5 × 10¹² /cm² and 1 × 10¹⁵ /cm². The damage production was investigated using RBS in channeling regime. Temperature and energy dependent backscattering measurements and TEM investigations were performed to study the kind of defects in more detail. The resulting defect profiles are compared with the depth distribution of the nuclear and electronic energy loss which were simulated by TRIM 87. The results show that the remaining defect concentration strongly decreases with increasing implantation energy even if the same energy density is deposited into nuclear processes. We suppose, that the electronic energy loss increases the defect transformation and annealing during implantation at T_I = 293 K. The defects in the samples implanted with energies greater than 5 MeV are characterized as point defects, point defect clusters and small dislocation loops; the kind of defects are the same over the whole implantation depth and the existence of amorphous zones can be widely excluded.     

Defect cluster formation in displacement cascades in copper

Extensive study of primary damage in displacement cascades in metals by computer simulation has shown that the total number of defects produced is significantly lower than predicted by the Norgett, Robinson and Torrens (NRT) model and that a significant fraction of the self-interstitials forms glissile clusters. However, there is a lack of variety of defect types observed in cascade simulation, which, in many cases, makes it difficult to explain experimental data. For example, experiments on copper show efficient production of stacking fault tetrahedra (SFTs) but they were not observed systematically in computer simulation. To consider this further, extensive simulation of displacement cascades in copper has been performed using two different interatomic potentials, a short-range many-body potential (MBP) and a long-range pair potential (PP). Primary knock-on-atom (PKA) energy in the range 2–20 keV and temperatures of 100 and 600 K were considered. Special attention was paid to cascade statistics and the accuracy of simulation in the collision stage. The former required many simulations for each energy whereas the latter involved a modification of the simulation method to treat a hot region with high accuracy by applying a smaller time step. Results showing the variety of clusters observed, e.g. SFTs, glissile and sessile interstitial clusters, and faulted and perfect interstitial dislocation loops, are presented.     

On the stochastic theory of point defect diffusion during irradiation: Cascade size and shape effects

Collison cascade size and shape effects on point defect diffusion during irradiation are studied in this paper. In contrast to the point cascade model of the cascade-diffusion theory of Mansur et al., where cascades are mathematically modeled as δ-functions, we represent cascades as spheres and spherical shells. The dimensions of the vacancy cascade sphere, or the interstitial cascade shell correspond to the energy of the PKA. Subcascades are also studied at high PKA energies. It is shown that the δ-function representation of collision cascades overestimates the RMS value of the magnitude of point defect fluctuation by a factor of 2–5, for large size cascades typical of fusion reactor conditions.