金属有机化学气相淀积技术制备GaMnN薄膜材料光学性质研究

研究由MOCVD 技术制备的 GaMnN 外延薄膜光吸收谱.实验发现Mn掺杂后较未掺杂GaN吸收系数在近紫外区增加,在吸收谱低能区144 eV附近观察到吸收峰,吸收系数随Mn浓度的增加而增大.实验结果与基于密度泛函理论的第一性原理计算结果一致,结合理论计算分析认为144 eV附近的吸收峰源于Mn³⁺离子e态与t₂态间的带内跃迁⁵T₂→⁵E. 关键词： GaMnN MOCVD 密度泛函理论 光学性质     

基于电子回旋共振-等离子体增强金属有机物化学气相沉积技术生长GaMnN稀磁半导体的研究

利用电子回旋共振-等离子体增强金属有机物化学气相沉积 (ECR-PEMOCVD)方法，采用二茂锰(Cp₂Mn)作为Mn源，高纯氮气作为氮源，三乙基镓(TEGa)作为Ga源，在蓝宝石(α-Al₂O₃)(0001)衬底上外延生长GaMnN稀磁半导体薄膜.反射高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)表征了GaMnN薄膜的晶体结构和表面形貌.GaMnN薄膜均表现出良好的(0002)择优取向，表明制备的薄膜倾向于     

基于电子回旋共振-等离子体增强金属有机物化学气相沉积技术生长GaMnN稀磁半导体的研究

利用电子回旋共振-等离子体增强金属有机物化学气相沉积 (ECR-PEMOCVD)方法,采用二茂锰(Cp₂Mn)作为Mn源,高纯氮气作为氮源,三乙基镓(TEGa)作为Ga源,在蓝宝石(α-Al₂O₃)(0001)衬底上外延生长GaMnN稀磁半导体薄膜.反射高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)表征了GaMnN薄膜的晶体结构和表面形貌.GaMnN薄膜均表现出良好的(0002)择优取向,表明制备的薄膜倾向于 关键词： GaMnN薄膜 稀磁半导体 铁磁性 居里温度     

氧空位对钴掺杂氧化锌半导体磁性能的影响

从实验和理论上阐述了氧空位对Co掺杂ZnO半导体磁性能的影响.采用磁控溅射法在不同的氧分压下制备了Zn_095Co_005O薄膜,研究了氧分压对薄膜磁性能的影响.实验结果表明,高真空条件下制备的Zn_095Co_005O薄膜具有室温铁磁性,提高氧分压后制备的薄膜铁磁性逐渐消失.第一性原理计算表明,在Co掺杂ZnO体系中引入氧空位有利于降低铁磁态的能量,铁磁态的稳定性与氧空位和Co之间的距离密切相关. 关键词： Co掺杂ZnO 稀磁半导体 第一性原理计算 氧空位缺陷     

Influence of defects on magnetism of Co-doped ZnO

Two kinds of Zn_0.97Co_0.03O powders were prepared by precursor thermal decomposition under different conditions. One grown at low temperature has a positive Curie-Weiss temperature Θ, while the other grown at high temperature has a negative Θ. Both of them contain oxygen vacancies. There are more shallow donors in the former than those in the latter. It is proposed that coexistence of oxygen vacancies and shallow donors is necessary to induce ferromagnetic coupling between Co ions.     

LiAl中空位形成能的第一原理计算

LiAl是一种非常典型和有重要用途的金属间化合物.采用平面波展开和第一原理赝势法，计算了LiAl化合物中Li空位和Al空位的形成能和空位周围的原子弛豫，讨论了空位形成时电荷密度的重新分布、相应的电子态密度以及能带结构等性质. 关键词： LiAl 空位形成能 第一原理计算     

氮掺杂的金刚石磁性研究

采用第一性原理计算方法研究金刚石中由空位或者N掺杂引起的磁特性. 发现-1价和-2 价的碳空位能分别产生3 μ_B和2μ_B的磁矩; -2价的碳空位能够引发长程有序的铁磁耦合状态, 而-1价的碳空位更倾向于反铁磁耦合.掺杂N元素能有效地控制空位的荷电状态及相应的磁相互作用, 这一结果为在金刚石中实现非过渡族金属掺杂的铁磁性提供了一条新的路径. 关键词： 第一性原理计算 氮掺杂 金刚石 磁性     

N空位对Cu掺杂AlN电磁性质的影响的第一性原理研究

利用基于密度泛函理论的平面波超软赝势法研究了N空位对Cu掺杂AlN的电子结构和磁学性质的影响。结果表明,与Cu最近邻的N原子更易失去形成N空位。N空位的引入减小了Cu掺杂AlN体系的半金属能隙;减弱了Cu及其近邻N原子的自旋极化的强度以及Cu3d与N2p轨道间的杂化,因而减小了体系的半金属铁磁性。因此,制备Cu掺杂AlN稀磁半导体时应尽可能地避免产生N空位。     

Towards understanding the carbon trapping mechanism in copper by investigating the carbon-vacancy interaction

We propose a vacancy trapping mechanism for carbon-vacancy (C-V) complex formation in copper (Cu) according to the first-principles calculations of the energetics and kinetics of C-V interaction. Vacancy reduces charge density in its vicinity to induce C nucleation. A monovacancy is capable of trapping as many as four C atoms to form CnV (n=1,2,3,4) complexes. A single C atom prefers to interact with neighboring Cu at a vacancy with a trapping energy of 0.21 eV. With multiple C atoms added, they are preferred to bind with each other to form covalent-like bonds despite of the metallic Cu environment. For the CnV complexes, C2V is the major one due to its lowest average trapping energy (1.31 eV). Kinetically, the formation of the CnV complexes can be ascribed to the vacancy mechanism due to the lower activation energy barrier and the larger diffusion coefficient of vacancy than those of the interstitial C.     

纳米铜薄膜塑性变形中空位型缺陷形核与演化的分子动力学研究

本文采用分子动力学方法模拟了纳米单晶铜薄膜在单向拉伸载荷作用下的塑性变形过程, 重点分析了空位型缺陷的形核过程和演化机理. 在模拟过程中, 采用镶嵌原子势描述原子间的相互作用. 模拟结果表明纳米铜薄膜中塑性变形起源于位错的表面形核, 而空位型缺陷的形核及演化都与晶体内部的位错运动密切相关. 空位型缺陷通常从位错割阶及层错交截处开始形核, 以单空位、层错四面体和不规则空位团等形式存在. 关键词： 纳米薄膜 塑性变形 空位 层错四面体     

GaMnN铁磁共振隧穿二极管自旋电流输运以及极化效应的影响

通过理论计算研究GaMnN铁磁共振隧穿二极管自旋电流输运特性.理论结果表明在电流特性曲线上出现两个明显的自旋分裂峰.该电流自旋分裂峰和相应的自旋极化随温度的升高而逐渐减小消失.当进一步考虑到GaN异质结界面极化电荷影响时,自旋向下的电流共振峰得到明显增强,同时电流的自旋极化也得到相应的提高.在一定的极化电荷条件下,可以获得较高的自旋极化电流. 关键词： GaMnN 共振隧穿 自旋电流 极化电荷     

GaMnN材料红外光谱中洛伦兹振子模型的遗传算法研究

利用红外反射光谱研究了蓝宝石衬底上用金属有机物化学气相淀积方法生长的稀磁半导体GaMnN材料的晶格振动特性. 并成功地将改进的遗传算法应用于其红外反射光谱洛伦兹振子模型参数的提取. 通过与GaN薄膜的洛伦兹振子模型参数的对比研究发现,GaN掺入Mn后,ω_TO向高频方向移动,γ,ε_∞和ε_s均增加,而ω_LO基本保持不变. 文中同时分析和讨论了Mn对晶格振动特性的影响及 关键词： 稀磁半导体GaMnN材料 遗传算法 洛伦兹振子模型 参数提取     

Influencing range of vacancy defects in zigzag single-walled carbon nanotubes

The influencing range of a vacancy defect in a zigzag single-walled nanotube is characterized with both structural deformation and variation in bandstructure. This paper proposes a microscopic explanation to relate the structural deformation to the bandstructure variation. With an increasing defect density, the nanotubes become oblate and the energy gap between the deep localized gap state and the conducting band minimum state decreases. Theoretical results shed some light on the local energy gap engineering via vacancy density for future potential applications.     

基于XPS与XAS的稀磁半导体GaMnN电子结构研究

采用基于同步辐射技术的X射线光电子能谱(XPS)与X射线吸收谱(XAS)测试由金属有机化学气相沉积(MOCVD)技术制备的不同Mn掺杂浓度的稀磁半导体GaMnN薄膜的电子结构,探究Mn掺杂浓度对磁性原子Mn周围的局域环境和电子态等方面的影响,并阐述材料铁磁性变化的机理. XPS和XAS图谱分析表明：Mn²⁺和Mn³⁺共存于薄膜样品内,样品D中Mn²⁺占比高达70%-80%,N空位随Mn掺杂浓度增加而增多且N空位能够使空穴浓度降低,导致Mn 3d和N 2p轨道间的相互交换作用减小,从而减弱体系铁磁性.此外,Mn不同的掺杂浓度会影响GaMnN薄膜p-d耦合杂化能力的强弱,当掺Mn 1.8%时具有较强的p-d耦合杂化能力.     

Role of intrinsic defects and impurities in forming the optical characteristics of ZnWO4 and CdWO4 crystals

We analyze the optical characteristics of crystals within the framework of a model representation that presupposes the entry of the background impurity of iron ions in two valence states, Fe³⁺ and Fe²⁺, into regular lattice nodes. The spectral manifestation of intrinsic defects of vacancy-type structure depending on the conditions of crystal growth and heat treatment is comprehensively investigated. With allowance for the specific features of the technology applied, we have tested the technique suggested in scientific periodicals for bleaching ZnWO₄ and CdWO₄ crystals by doping with nonisovalent ions, in particular, with Sb and Ag impurities. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 211–216, March–April, 2000. The work was carried out with support from INTAS-UKRAINE within the framework of the project INTAS-UA-95-0166.     

本征空位缺陷对ZnO:Mn体系电子特性及磁性的影响

本文采用基于密度泛函理论的第一性原理赝势法,分析了ZnO:Mn掺杂体系中本征空位缺陷V_(Zn)和V_O分别出现在相对Mn为近邻、次近邻、远次近邻位置时体系的晶体结构、能带分布、态密度和磁性.结果表明:ZnO:Mn体系中V_(Zn)比V_O更容易产生,且两种缺陷均更容易在Mn的近邻位置形成.其中V_(Zn)的出现没有明显改变ZnO:Mn体系的带隙,然而会使体系的导电性增加,且V_(Zn)与Mn的距离越远,导电性越强.同时,V_(Zn)减弱了体系的磁性,但与V_(Zn)的位置无关. V_O的出现会使体系带隙变宽,且电导率显著低于无缺陷ZnO:Mn体系,但是其导电性会随着V_O与Mn的距离变远而增强.同时,V_O的出现不会影响体系原来的磁性.     

Mn掺杂LiZnN新型稀磁半导体磁电性质的第一性原理计算

采用基于密度泛函理论的第一性原理平面波超软赝势方法,对纯LiZnN、Mn掺杂LiZnN及Li不足和过量时Mn掺杂LiZnN体系进行几何结构优化,分析体系的电子结构、半金属性和磁电性质.结果表明,Mn的掺入使体系产生自旋极化杂质带,自旋极化率为100%,表现出半金属铁磁性,且形成较强的Mn-N共价键.当Li不足时,Mn-N键的共价性最强,键长变短,体系半金属性明显增强,形成能最低,结构最稳定.Li过量时,体系半金属性消失,表现为金属性,杂质带宽度增大,体系导电能力增强.表明Mn掺杂LiZnN新型稀磁半导体可以通过Mn的掺入和改变Li的含量来实现磁性和电性的分离调控.掺杂体系的基态均为铁磁性,其净磁矩主要由Mn原子贡献,通过海森堡模型计算发现,Li空位可以有效提高体系的居里温度.     

Strain-induced magnetism in ReS_2 monolayer with defects

We investigate the effects of strain on the electronic and magnetic properties of ReS_2 monolayer with sulfur vacancies using density functional theory.Unstrained ReS_2 monolayer with monosulfur vacancy(V_s) and disulfur vacancy(V_(2S))both are nonmagnetic.However,as strain increases to 8%,V_S-doped ReS_2 monolayer appears a magnetic half-metal behavior with zero total magnetic moment.In particular,for V_(2S)-doped ReS_2 monolayer,the system becomes a magnetic semiconductor under 6%strain,in which Re atoms at vicinity of vacancy couple anti-ferromagnetically with each other,and continues to show a ferromagnetic metal characteristic with total magnetic moment of 1.60μb under 7%strain.Our results imply that the strain-manipulated ReS_2 monolayer with V_S and V_(2S) can be a possible candidate for new spintronic applications.     

First-principles study of diffusion behaviour of point defects in the O-terminated (0001) surface in wurtzite ZnO

A detailed first-principles study of the diffusion behaviour of point defects in the O-terminated (0001) surface in wurtzite ZnO was performed. The O vacancy and interstitial are found to diffuse much more easily in surface than in bulk. The Zn vacancy has a similar migration barrier for both bulk and surface, but has much smaller barrier for the diffuse-in process. The Zn interstitial is difficult to diffuse in the surface directly, but it can diffuse into the bulk relatively easily. Specific values of corresponding migration barriers are obtained.