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.     

La掺杂BaTiO3陶瓷的介电性与缺陷

La掺杂BaTiO₃陶瓷的介电常数在0.40at％La含量内随掺La量呈现倒U型变化,在1kHz内随频率增加急剧减小,之后随频率变化缓慢,介电性的这些变化起因于掺La引起的如下缺陷变化:独立的Ba空位( V″_Ba→(La_Ba·V″_Ba)型复合缺陷→(La_Ba·V″_Ba·La_Ba型复合缺陷型复合缺陷。     

正电子湮没谱和光致发光谱研究掺锌GaSb质子辐照缺陷

用正电子湮没谱和光致发光谱研究了质子辐照后掺锌GaSb中的缺陷.通过分析正电子的缺陷寿命τ₂及强度I₂的变化发现,在高能质子的辐照下产生了双空位缺陷V_GaV_Sb,可能同时产生了小的空位团.正电子平均寿命τ_av和S参数随着质子辐照剂量的变化也证明了这一结论.通过分析不同质子辐照剂量下掺锌GaS     

质子辐照硼硅酸盐玻璃盖片的物理效应分析

作为航天器电源系统的重要组成部分,太阳电池需要更高的转换效率和可靠性以及更长的使用寿命。通过在太阳电池表面覆盖抗辐照玻璃盖片,可以增强太阳电池对粒子辐射的防护,延长太阳电池的服役寿命,使航天器获得可靠的能源供应。硼硅酸盐玻璃就是一种理想的太阳电池玻璃盖片材料。采用蒙特卡罗方法,结合SRIM软件模拟研究质子辐照硼硅酸盐玻璃的损伤物理机理。基于粒子与物质相互作用的理论以及基本公式,通过分析不同入射能量的质子在硼硅酸盐玻璃中的阻止本领、电离能损、位移能损、空位的产生情况,对辐照损伤的物理机制进行研究。结果表明:能量为30~120 keV的质子辐照损伤主要发生在硼硅酸盐玻璃表面;质子沉积、空位分布等均为Bragg峰型分布;电离能损是能量损失的主要部分,随入射能量的增加而增大,导致电子的电离和激发;位移能损在玻璃内部随能量降低而增大,导致硼、氧和硅等空位缺陷的产生;电离效应和缺陷的产生是硼硅酸盐玻璃色心形成的重要原因。     

3 MeV质子辐照对AlGaN/GaN高电子迁移率晶体管的影响

研究了AlGaN/GaN 高电子迁移率晶体管(HEMT)的质子辐照效应. 在3 MeV质子辐照下, 当辐照剂量达到1× 10¹⁵ protons/cm²时, 漏极饱和电流下降了20%, 最大跨导降低了5%. 随着剂量增加, 阈值电压向正向漂移, 栅泄露电流增加. 在相同辐照剂量下, 1.8 MeV质子辐照要比3 MeV质子辐照退化严重. 从SRIM软件仿真中得到不同能量质子在AlGaN/GaN异质结中的辐射损伤区, 以及在一定深度形成的空位密度. 结合变频C-V测试结果进行分析, 表明了质子辐照引入空位缺陷可能是AlGaN/GaN HEMT器件电学特性退化的主要原因.     

α-Al2O3(0001)表面原子缺陷对ZnO吸附影响

采用基于密度泛函理论的分子动力学方法，对α-Al₂O₃(0001)表面 Al，O原子空位缺陷及其对ZnO吸附进行了理论计算.电子局域函数显示了表面空位处的电子密度变化，表面Al原子空缺处有非常明显的缺电子区域，悬挂键临近O的电子密度增大，有利于对Zn的吸附；O原子空缺处的Al原子处存在孤立电子，其ELF值为005—03，将有利于同电负性较大的O或O^2-结合.通过吸附动力学模拟与体系能量的计算发现，表面缺陷显著增强了表面 的化学吸附，空缺原子处都被吸附原子填补，吸附结合能远大于单晶表面的情况.在Al空缺的表面，由于ZnO的O与表面O形成双键，破坏了α-Al₂O₃(0001)表面O六 角对称结构，减小了 O的表面扩散，从而不利于规则的ZnO薄膜生长.相反，O的空缺表面，弥补了α-Al_{2O3(0001)表面O空位缺陷，不影响基片表面O六角对称结构.}     

聚变α粒子对第一壁辐照损伤的蒙特-卡罗研究(Ⅱ)——溅射

本文应用蒙特-卡罗方法研究聚变α粒子对不锈钢第一壁的溅射损伤。首先,计算单种元素Fe,Cr,Ni的溅射产额随入射能量的变化,并与实验结果比较,以确定计算中所用到的一些重要参数,如原子位移能等。在此基础上计算聚变α粒子对不锈钢(Fe_0.73Cr_0.18Ni_0.09)的部分(和总)溅射产额,溅射粒子的能谱、角分布和源深度分布,以及上述各量与α粒子入射角的关系。结果表明,在考虑入射α粒子随能量及入射角的分布后,其平均总溅射产额为0.375。由于1     

氧离子辐照二氧化钛单晶后的结构与磁性

氧离子辐照二氧化钛单晶可以诱发其铁磁性．辐照后在室温下也能观察到二氧化钛的铁磁性,且对温度依赖性较小．结合X射线衍射实验、卢瑟福背散射/沟道实验、拉曼散射实验谱、电子自旋共振实验谱、超导量子干涉仪实验、单位原子随沟道位移实验,测定了晶格的损伤随辐照流强的增加而增加．发现在氧离子辐照二氧化钛时出现了Ti³⁺替代氧空位(O_V)的缺陷复合体,即形成Ti³⁺-OV复合体．这种缺陷复合体导致了局部(TiO_6-x)的拉曼模式的伸展．说明了Ti³⁺结合一个未成对的3d电子是二氧化钛局部铁磁性的起源.     

氮气退火对二氧化钛薄膜光学性能的影响

 提出了一种利用离子注入和后续退火制备氮掺杂TiO₂薄膜的方法。首先在室温下向石英玻璃中注入Ti离子，随后在氮气中退火到900 ℃，从而制备了氮掺杂的玻璃基TiO₂薄膜。SRIM2006程序模拟和卢瑟福背散射谱（RBS）研究表明注入离子从样品表面开始呈高斯分布，实验结果和模拟结果吻合很好。X射线光电子能谱（XPS）研究结果表明注入态样品中形成了金属Ti和TiO₂，900 ℃退火后金属Ti转变成TiO₂，同时N原子替代少量的晶格O原子形成了O－Ti－N化合物。紫外-可见吸收光谱（UV-Vis）结果显示，当退火温度至500 ℃时，在吸收光谱中开始出现TiO₂的吸收边，随退火温度升高到900 ℃，由于O－Ti－N化合物形成，TiO₂的吸收边从3.98 eV红移到3.30 eV，TiO₂吸收边末端延伸到可见光区，在可见光区的吸收强度明显增加。     

用第一性原理研究K空位对KDP晶体激光损伤的影响

 用基于密度泛函理论及超软赝势的第一性原理研究了KH­­­₂PO₄(KDP)晶体中K空位的电子结构、形成能及驰豫构型。讨论了K空位形成后电荷密度的重新分布、相应的电子态密度和能带结构等性质。计算得到中性K空位的形成能为6.5 eV, 远小于间隙K原子点缺陷形成能13.07 eV。K空位的存在使晶胞体积增大, 分别沿结晶学轴a方向增大近0.8%, b方向增大近0.87%, c方向增大近1.2%，同时使与之配位的8个氧原子发生较大位移，使这8个氧形成的空腔体积增大近3.2%。空腔体积的增大不仅促进了各种点缺陷的扩散迁移，而且有利于其它杂质原子的填隙。K原子迁移率的增大会引起离子电导率的增大，因而会降低KDP的激光损伤阈值，因此从这个方面讲，K空位的存在是不利的。但是如果能从实验上（如热退火）利用K空位所造成的扩散通道排出或改善缺陷结构，则可提高KDP晶体的光学质量。     

Proton radiation damage in SrTiO3 thin film by computer simulation

Perovskite ferroelectrics (FEs) have high endurance to radiation. Strontium titanate (STO) (SrTiO₃) is a kind of perovskite FE with a large dielectric constant, which has attracted a good deal of attention due to its excellent dielectric, photoelectric and optical properties. The proton radiation damage in STO thin films is investigated by computer simulations in this work. The threshold displacement energy is an important input parameter for Monte Carlo simulation based on a binary collision approximation model, so we first use molecular dynamics to calculate the averaged threshold displacement energy of Sr, O and Ti atom. The calculated values are 67, 50 and 136 eV, which are obviously larger than default value (25 eV) in the Stopping and Range of Ions in Matter (SRIM) code. The results of the SRIM simulation demonstrate the dependency of vacancy number and position distribution on the proton's energy and the angle of incidence.     

Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3

We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.     

Atomistics of helium diffusion in copper and tungsten

Using previously determined interatomic potentials, the activation energy for migration of a single substitutional helium atom in copper and tungsten has been determined. The mechanism of migration involves the jump of the helium atom out of the vacancy concurrent with the jump of a host atom into that vacancy. The helium then occupies the vacant site created by the jumping host atom, resulting in a substitutional helium at a distance of √2 r ₀ (√3r ₀) from its original site in copper (tungsten). The rate-limiting step in the process is found to be the jump of the helium out of the vacancy, the activation energy for which is 2.15 eV in copper and 4.69 eV in tungsten.     

Electronic,optical, vibrational and EFG properties of tetragonal BaTiO3 under pressure: By first-principles study

The First principles study on structural, electronic, Electron Field Gradient (EFG), optical and vibrational properties of tetragonal BaTiO₃ have been done in the framework of Density Functional Theory (DFT). Obtained structural properties are in agreement with others, and also the electronic study shows that the tetragonal BaTiO₃ has an indirect energy gap (E_g) about 1.864 eV by GGA and 2.6 eV by GGA-mbj at equilibrium state which E_g shifts toward small values by decreasing pressure. By increasing pressure to 31.479 GPa, the EFG decrease for O atom, and increase for Ba and Ti atoms that is a sign to piezoelectric property for tetragonal BaTiO₃. The optical parameters were studied under pressure, such as the real and imaginary parts of the dielectric function, Loss function, reflection index, absorption coefficient, conductivity and reflection. Moreover, by applying hydrostatic pressure, the roots of the real part of the dielectric function shift toward higher energies, and the energy loss and absorption peak intensity were reduced. Finally, lattice vibration survey indicates the stability of tetragonal BaTiO₃ under pressure.     

质子辐照对国产“一”字型保偏光纤损伤效应研究

航天器在空间环境中运行时,会受到质子的辐照,光纤环作为航天器上光纤陀螺的重要组成部件受辐照影响 最为严重.为了研究国产“一”字型保偏光纤因质子辐照导致辐照诱导损耗的变化规律及其辐照损伤机理, 选择质子能量为5 MeV和10 MeV,光源波长为1310 nm,原位测量了光纤传输功率变化情况,计算出辐照诱导损耗. 利用SRIM软件,模拟能量分别为5 MeV和10 MeV质子辐照在光纤中的电离和位移损伤分布.借助X 射线光电子能谱仪分析辐照前后O 1s和Si 2p解析谱,借助傅里叶变换红外光谱仪观察光纤辐照前后光谱变化情况研究发现,在波长为1310 nm处, 光纤的辐照诱导损耗随着质子注量的增加而增长,主要原因是由于光纤纤芯中Si-OH的浓度增加所导致. 而且能量为5 MeV质子辐照造成光纤的辐照诱导损耗比10 MeV严重,这是因为5 MeV质子在光纤纤芯处造成的 位移和电离损伤均比10 MeV严重,即产生的Si-OH数量多.     

Molecular dynamics simulation of defects production in the vicinity of voids

We report on the results of computer simulation of point defect production near voids in crystalline Cu at primary knock-on atom (PKA) kinetic energies ranging from 5 to 1000?eV. The PKA energy dependence of numbers of created defects are revealed. The threshold energy for a stable vacancy formation is found to be much smaller than that for an interstitial atom, which results in a biased formation of vacancies in the void proximity in the whole investigated range of PKA energies. Dissolution of small voids by subthreshold irradiation is simulated. The impact of considered radiation effects on kinetics of radiation damage is discussed.     

Ferroelectricity associated with the metastable phase “III” of AgNO3

The dielectric constant, dc resistance, D-E ferroelectric hysteresis loop and dilatometric analysis of the three phases I, II, and III of AgNO₃ single crystals has been studied over the temperature range 100–200° C. A ferroelectric behaviour of the metastable phase III was detected here for the first time similar to what happened in KNO₃. The ferroelectric is attributed here to Ag⁺-ion vacancy formation in the unit cell of AgNO₃. The energy activating the process of vacancy formation was found to beE _v=2.6 eV. It was found that an ionic shift from one lattice point to another requires an amount of energy to overcome a potential barrierE _m=0.1 eV. A model is suggested to explain such behaviour. Dilatometric analysis indicated that this metastable phase transition III is accompanied by an expansion of the unit cell.     

Structure, ferroelectric and dielectric properties of Bi2WO6 with different bismuth content

This paper reports that the Bi 2 WO 6 ferroelectric ceramics with excess Bi 2 O 3 of 0.0, 2.0, 3.5 and 5.0 wt.% of the stoichiometric composition are prepared by the conventional solid-state reaction method. Their microstructure, ferroelectric properties, the concentration and mobility of the defects have been analysed systematically. With increasing Bi content, the remnant polarization decreases, and the broken-down voltage increases. The optimum Bi excess, 3.5, lowers the oxygen vacancy concentration, while further Bi-addition brings about more defects. The activation energies fitted from cole-cole plots are 0.97 eV, 1.07 eV, 1.18 eV, and 1.33 eV, respectively. This suggests that the mobility of the defects is weakened by Bi-addition, which may be due to the increase of the ratio of the number of Bi 2 O 2 layers to that of the perovskite blocks.     

Valence band offset of ZnO/BaTiO3 heterojunction measured by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset of the ZnO/BaTiO₃ heterojunction grown by metal-organic chemical vapor deposition. The valence band offset (VBO) is determined to be 0.48±0.09 eV, and the conduction band offset (CBO) is deduced to be about 0.75 eV using the band gap of 3.1 eV for bulk BaTiO₃. It indicates that a type-II band alignment forms at the interface, in which the valence and conduction bands of ZnO are concomitantly higher than those of BaTiO₃. The accurate determination of VBO and CBO is important for use of semiconductor/ferroelectric heterojunction multifunctional devices.