第一原理计算Al_2Mg中间相的电子结构

对镁合金材料研发应用现状与发展趋势进行了论述,展望了镁合金研发应用的未来发展趋势。采用基于密度泛函理论的第一性原理平面波赝势法,通过选用广义梯度近似(GGA)和局域密度近似(LDA)分别计算了Al2Mg晶体的几何与电子结构,分析了其电子态密度以及电荷密度分布,研究了Al2Mg晶体的电子结构和成键特性。     

SrTiO3材料中氧空位的密度泛函理论

计算了SrTiO3-δ（δ=0，δ=0．125）体系电子结构，分析了氧空位对SrTiO3晶体的价键结构、能带、态密度、分波态密度、差分电荷密度的影响。所有计算都是基于密度泛函理论（DFT）框架下的第一性原理平面波超软赝势方法。计算结果表明：当氧空位浓度δ=0．125时，空位在母体化合物SrTiO3中引入了大量的传导电子，费米能级进入导带，体系显示金属型导电性。由于空位掺杂，导带底附近的态密度发生了畸变，刚性能带模型不再适合描述SrTiO2.875体系。同时，在导带底附近距离费米能级0．3eV处引入了空位能级，这和实验测得的SrTiO3材料内中性氧空位的电离能约为0．4eV相符。此外，Mulliken布局分析、分波态密度和差分电荷密度分析表明，该空位能级主要由与其最近邻的两个Ti原子的3d电子态贡献，并且由该空位引入的导电电子大部分都局域在空位最近邻的两个Ti原子周围。最后，计算了三种典型平衡条件下SrTiO3晶体内中性氧空位的形成能。     

立方氮化硼电子结构和光学性质的第一性原理计算

通过第一性原理计算可以预测材料的组分、结构与性能，设计具有特定性能的新材料，甚至可以模拟实验无法实现的工作。密度泛函理论巧妙地将电子之间的交换相关势表示为密度泛函，使得薛定谔方程在考虑了电子之间的复杂作用后，依然可以利用自洽的方法求解。利用CASTEP软件在不同机制下计算了立方氮化硼的能带结构、电荷密度分布、状态密度、...     

Ce:KNSBN晶体两波耦合特性研究

研究了Ｃｅ：ＫＮＳＢＮ晶体两波耦合增效益系Г与２θ的关系,并对Ｃｅ：ＫＮＳＢＮ单晶样品进行了两波耦合测量,用光折变理论拟合实验结果,求出了该晶体有效光折变电荷密度有效电光泵数和电子－空穴对抗率数据,实验与理论符合完好。     

多晶材质电子结构及热电性能的模拟

发展了一种研究多晶体系电子态以及热电性质的计算机模拟方法。首先采用相场动力学方法模拟多晶材质图案，再利用其模型序参量构造晶界的势函数，用近自由电子近似构造体系的哈密顿量。求解薛定谔方程得到体系的本征态。通过电荷密度的分布研究电子的限域特征,分析模拟结果发现对于晶界为势垒的情况，电子的基态出现在最大晶粒中；而对于晶界为势阱的情况，电子更容易限域在多个晶粒交叉的晶界附近，由得到的本征能级和波函数可以计算出温差导致的电位差，即得到赛贝克系数随温度的变化。结果表明具有导电晶界的多晶体的赛贝克系数要高于具有导电晶粒的多晶体。     

晶体化学中的键电荷模型及其应用前景

键电荷模型将晶体中原子的有效电荷与键长有机地联系起来，从而提供了一种揭示分子晶体结构和电子结构相关关系的方法。键电荷模型的建立被看作是当今无机固体化学的一个重大进展，它具有简洁性、可靠性和实用性的特点。对于晶体中原子的电荷分布，结构畸变的研究和键长的确定有独特之处。值得研究和发展。本文简述了这一模型的基本原理及其应用前景。同时做出了简单的评价。     

双掺杂碳纳米管电子场发射性能的密度泛函研究

采用第一性原理的密度泛函理论(DFT)研究了(5,5)碳纳米管(CNT)顶端硼(B)、氮(N)、硅(Si)等元素双掺杂体系的电子场发射性能.结果表明,在外电场下,各种双掺杂CNT帽端态密度(DOS)向价带移动.电子轨道分布变化显著,电荷分布明显局城化.根据电子态密度、差分电荷密度、最高分子占据轨道(HOMO)/最低分子非占据轨道(LUMO)分布等计算结果可预期Si双掺杂后更有利于场致电子发射.     

LaNi4.5Mn0.5储氢合金及氢化物的电子结构

基于密度泛函理论,采用总能量计算方法与结合超软赝势平面波函数方法,对LaNi4.5Mn0.5储氢合金及其氢化物的晶体几何结构进行了优化,计算了其相应的总体能量、晶体结构、能带结构、及态密度分布等,从理论上给出了其结构参数及性质.结果表明,锰取代3g位后合金晶胞略有膨胀,并伴随着晶体稳定性变差.LaNi4.5Mn0.5合金中EF附近的态密度贡献最主要来自La的p电子,以及Ni和Mn原子的d电子.     

第二十讲 真空离子镀膜

<正>(接2019年第5期第80页)13.2.3电弧放电等离子体参数电弧放电等离子体的参数主要有电子温度Te、电离强度αe、电场强度E、带电粒子密度ni(≈ne)及等离子体电位Ui及阳极电流Ia。A等离子体电位Ui首先做如下假设:(1)除电荷层外,等离子体中ni=ne=n;(2)带电粒子的速度分布符合麦克斯韦分布;(3)电荷层厚度小于电子平均自由程,即电荷     

第一性原理研究PDP放电单元MgO保护层各种空缺对二次电子发射系数的影响

基于密度泛函理论的第一原理赝势法,研究了PDP放电单元中MgO保护层在形成氧空缺后的电子结构的变化.通过对能带结构和态密度分布的计算,可以看到MgO形成氧空缺后在禁带中引入了能级.本文计算了完整MgO以及含F、F~+、F~(2+)空缺的MgO晶体,得到不同能带结构和态密度分布,同时计算了相应的二次电子发射系数.结果表明空缺的形成,可有效提高二次电子发射系数,其中形成F空缺的MgO晶体的二次电子发射系数最大.     

TEM-based dislocation tomography: Challenges and opportunities

Dislocation tomography based on transmission electron microscopy (TEM) exhibits excellent capabilities in three dimensional (3D) visualization of various dislocation structures but still suffers from poor quantification and coupling between the geometry and crystallography of dislocations. In the present paper, we review the research on 3D quantitative characterization of dislocation structures using TEM-based dislocation tomography and stereo pair methods, and briefly introduce a novel TEM-based tomographic crystallography method which can simultaneously and quantitatively characterize the geometric and crystallographic features of dislocations. We summarize some technical problems and challenges in the workflow of TEM-based dislocation tomography, including image contrast optimization, irradiation damage, image processing, reconstruction algorithms as well as dislocation segmentation and identification. We further discuss the potential applications of TEM-based dislocation tomography and envisage several promising approaches for developing an advanced four-dimensional (4D) dislocation characterization technique.     

Texture in solid-state reactions

The crystallography and texture of solid-state reactions have been studied using electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM). The crystallography of both the reaction interfaces and the grain boundaries plays an important role in the kinetics of the formation of the reaction products. The growth of the reaction products is dependent upon the transport of ions through the material, which is, in turn, affected by both the orientation of the reactants and by grain boundaries in the reactants and in the reaction products. In order to predict or control the behavior of the reactions, the crystallography of all the interfaces present in the reaction must be more fully understood. In the present study, MgIn₂O₄ was formed by the reaction between a single-crystal MgO substrate and a thin film of In₂O₃ with and without an applied electric field.     

EBSD and reconstruction of pre-transformation microstructures,examples and complexities in steels

Electron backscattered diffraction has provided a quantitative tool to study micro/nano-structures in large scales. A recent application of electron backscattered diffraction is the reconstruction of pre-transformed phases in polymorphic systems, especially when there is no retained pre-transformed phase at room temperature. This capability has been demonstrated by various researchers utilizing different approaches towards grain structure and orientation recovery. However, parameters affecting reconstruction have not been investigated systematically. Factors such as post-transformed microstructures (morphology and crystallography), lattice strain (deformation), pattern and sample quality are among the affecting factors. Two-dimensional datasets of different steels have been reconstructed along with a limited 3-dimensional dataset in the current paper. Preliminary results intended for large-scale automatic reconstructions have been presented. They indicate that the successfulness of reconstruction is strongly dependent on the post-transformed microstructure. Factors such as morphology, grain size, variant selection, and deformation play roles. Few examples of reconstruction complexity at prior austenite boundaries leading to uncertain results are presented. Lastly, reconstructions are discussed in terms of meaningfulness and if they correctly represent pre-transformed grains and orientations.     

From structure to mechanism: electron crystallographic studies of bacteriorhodopsin

Bacteriorhodopsin is a protein found in cell membranes of the organism H. salinarum, where it functions as an efficient light-driven proton pump. Because bacteriorhodopsin is one of the simplest ion pumps known in biology, it has been the subject of intensive investigations over the last three decades, using methods spanning the range from femtosecond spectroscopy and crystallography to biochemistry and molecular biology. Here, we focus on the structural basis for the function of this protein, with primary emphasis on the contributions of electron microscopy and crystallography towards unravelling the mechanism of vectorial proton pumping.     

Electron backscattering diffraction study of coalesced bainite in high strength steel weld metals

Abstract

Coalesced bainite is a coarse constituent recently found to develop along with the classical martensite, lower and upper bainite in steel weld metals. Its crystallography has been characterised using electron backscattering diffraction in combination with field emission gun scanning electron microscopy. It is confirmed that coalesced bainite grains are crystallographically homogeneous but do contain orientation gradients. The misorientations across different grains of coalesced bainite and relative to conventional bainite have also been studied. The observations are discussed in the context of the mechanism by which coalesced bainite evolves.     

Sub‐Micron Polymeric Stomatocytes as Promising Templates for Confined Crystallization and Diffraction Experiments

The possibility of using sub‐micrometer polymeric stomatocytes is investigated to effectuate confined crystallization of inorganic compounds. These bowl‐shaped polymeric compartments facilitate confined crystallization while their glassy surfaces provide their crystalline cargos with convenient shielding from the electron beam's harsh effects during transmission electron microscopy experiments. Stomatocytes host the growth of a single nanocrystal per nanocavity, and the electron diffraction experiments reveal that their glassy membranes do not interfere with the diffraction patterns obtained from their crystalline cargos. Therefore, it is expected that the encapsulation and crystallization within these compartments can be considered as a promising template (nanovials) that hold and protect nanocrystals and protein clusters from the direct radiation damage before data acquisition, while they are examined by modern crystallography methodologies such as serial femtosecond crystallography.     

Twin quintuplet surfaces in CVD diamond

Chemical vapor deposition (CVD) of diamond films and wafers is a well established and flexible technology in which deposition parameters control the deposition rate as well as diamond properties, quality and shape. This article deals with surface morphology and crystallography of wafers, with emphasis on twin blocks and twin quintuples. In the study described here we have determined surface facet crystallography of two diamond wafers groups, one that contains Σ3 twin blocks and the other that has a large population of twin quintuplets. The tool used for the study is a scanning electron microscope (SEM) and the technique to identify surface crystallography involves only accurate tilting and surface observation. A basic knowledge of the twin structure enables accurate determination of surface crystallography.     

The nature of inclusions in heavily tellurium-doped gallium arsenide

Large elongated inclusions in heavily Te-doped 〈001〉 Czochralski pulled, GaAs crystals have been studied by a combination of scanning and transmission electron microscopy, electron microprobe analysis and X-ray topography. They have been shown to lie along the 〈110〉 directions in the {001} growth plane and to consist of two parts, an outer single crystal region of varying composition based on Ga₂Te₃ and an inner polycrystalline core rich in Te and As. Their crystallography has been interpreted in terms of impurity segregation and facet formation during crystal growth while their composition is discussed with reference to the Ga-As-Te phase diagram.     

离子束增强反应磁控溅射AIN膜的组织结构及光学特性

对离子束增强反应磁控溅射低温沉积 AIN 膜层组织形貌、晶体结构、电子结构及其光学特性进行了研究。结果表明膜层组织均匀,晶粒细小,薄膜 AIN 是呈(002)择优取向的密排六方结构。由于Al-N 键的形成,使 Al 的2p 轨道电子结合能发生2.6eV 的化学位移。薄膜在可见光区域有很高的透射率,在紫外区域300nm 处有很强的吸收峰,在红外600—800cm~(-1)处有个吸收带,通过计算得到了 AIN膜的折射率,禁带宽度和晶格振动力学常数。     

The effects of crystallography on grain-boundary migration in alumina

The sintering process of ceramics involves mass transport across grain boundaries resulting in the migration of these boundaries. When there is a liquid at the interface—as in liquid-phase sintering—the mass transport can be enhanced. In this study, electron backscatter diffraction has been used to examine grain-boundary migration of controlled interfaces in alumina. The interfaces were prepared by hot pressing single-crystal and polycrystalline alumina to single-crystal alumina substrates of known orientation. EBSD patterns, taken near the sintered interfaces, have been used to study the effects of crystallography on migration direction and rate.