Cr掺杂AlN半导体电磁性质的第一性原理研究

基于密度泛函理论(DFT)的第一性原理方法,在广义梯度近似(GGA)下分别计算了无掺杂和掺杂过渡金属Cr原子的AlN半导体的电磁性质,结果表明,掺杂后AlN由半导体转变为半金属,并具有较宽的半金属能隙.当掺杂浓度为25%、12.5%、5.6%时,半金属能隙分别为0.8eV、1.1eV、1.2eV.以掺杂浓度为12.5%的Cr-AlN(2×2×1)为例,详细分析了其能带结构、态密度分布和电子布居数以及磁矩等.     

MgB2（001）面超导结构的电子浓度第一原理分析

采用密度范函理论计算了金属化合物MgB2（001）薄膜结构的电子能带结构和状态密度,计算的交换相关能分别采用LDA和GGA。规范保守赝势的计算结果表明,晶格常数与实验值误差在很小的范围内,分析了引起MgB2（001）面结构超导转变时电子浓度和偏态密度的变化情况,发现构成该超导体结构的成健有3种,着重从结构的电子浓度变化分析了其超导特性,六角蜂窝状结构中硼原子间相互作用为sp^2杂化的共价健,镁原子和硼原子之间是离子健结合,镁原子层是金属健结合,镁原子的价电子部分转移到硼原子的pz轨道,部分电子为镁原子层共用。MgB2的超导机制为强烈的电子-声子耦合,为B原子间强烈的共价作用形成,是传统S波超导体。对Mg元素同一主族的其它硼化物进行布居分析,发现M出,中Mg原子电子转移明显强于BeB2和CaB2,说明电子浓度是引起超导转变的一个重要因素。     

基于第一性原理的新型铁基超导材料AFeAs电子结构和磁结构的研究

基于密度泛函理论(DFT),采用线性增强平面波展式结合改进的局域轨道(APW+lo)方法,计算分析了新型铁基超导材料LiFeAs和NaFeAs的电子结构、能量和磁结构.通过系统磁性质的计算表明,系统磁矩和原子磁矩与晶体的晶格结构有着直接关系,这与实验中发现的超导温度压制效应直接相关.计算得到了与材料物性直接相关的电子能带和电子态密度.     

物理气相输运法生长AlN六方微晶柱（英文）

采用物理气相输运法(Physical Vapor Transport,PVT),在1700~1850℃生长温度下制备出AlN六方微晶柱;晶柱长度在1 cm左右,宽度在200~400μm,光学显微镜下观察为六棱柱形状并呈透明浅黄色光泽;扫描电子显微镜和原子力显微镜测试表明:AlN晶柱表面为整齐台阶状形貌,台阶宽度为2~4μm,高度在几个纳米;拉曼光谱测试AlN晶柱具有良好结晶质量。PVT法生长AlN六方微晶柱主要是在偏低温度下AlN晶体生长速率较慢,Al原子和N原子有足够时间迁移到能量较低位置结晶生长,进而沿着0001方向形成柱状结构。AlN六方微晶柱是对一维半导体材料领域的补充,通过对晶柱尺寸及杂质控制的进一步研究,有望在微型光电器件领域表现出应用价值。     

脉冲激光沉积制备立方AlN薄膜的研究

采用脉冲激光沉积(PLD)方法,在SrTiO3(100)衬底上在650℃、10Pa N2条件下成功制备了立方结构的AlN薄膜.高能电子衍射(RHEED)及X射线衍射(XRD)分析表明立方AlN和SrTiO3的外延关系为AlN[100]∥SrTiO3[100]和AlN(200)∥SrTiO3(100).其AlN(200)衍射峰的摇摆曲线半高宽(FWHM)为0.44°,说明薄膜结晶性能良好.原子力显微镜(AFM)表明外延的立方AlN薄膜表面具有原子级平整度,其表面均方根粗糙度(RMS)为0.674nm.通过X光电子能谱(XPS)分析AlN薄膜表面成分,结果表明AlN薄膜表面没有被氧化.     

物理气相输运法生长AlN六方微晶柱

采用物理气相输运法(Physical Vapor Transport, PVT), 在1700 ~ 1850℃生长温度下制备出AlN六方微晶柱; 晶柱长度在1 cm左右, 宽度在200 ~ 400 μm, 光学显微镜下观察为六棱柱形状并呈透明浅黄色光泽; 扫描电子显微镜和原子力显微镜测试表明: AlN晶柱表面为整齐台阶状形貌, 台阶宽度为2 ~ 4 μm, 高度在几个纳米; 拉曼光谱测试AlN晶柱具有良好结晶质量。PVT 法生长AlN六方微晶柱主要是在偏低温度下AlN晶体生长速率较慢, Al原子和N原子有足够时间迁移到能量较低位置结晶生长, 进而沿着<0001>方向形成柱状结构。AlN六方微晶柱是对一维半导体材料领域的补充, 通过对晶柱尺寸及杂质控制的进一步研究, 有望在微型光电器件领域表现出应用价值。     

AlN在α-Al2O3(0001)表面吸附过程的理论研究

采用基于密度泛函理论的平面波超软赝势法,对α-Al2O3(0001)表面吸附AlN进行了动力学模拟计算,研究了AlN分子在a-Al2O3(0001)表面吸附成键过程、吸附能量与成键方位.计算表明吸附过程经历了物理吸附、化学吸附与稳定态形成的过程,其化学结合能达到4.844eV.吸附后AlN化学键(0.189±0.010nm)与最近邻的表面Al-O键有30°的偏转角度,Al在表面较稳定的化学吸附位置正好偏离表面O六角对称约30°,使得AlN与蓝宝石之间的晶格失配度降低.     

以第一性原理研究CaCO_3的表面能与电子结构

采用第一性原理方法和slab模型研究了方解石型CaCO3(10~10)和(0001)晶面的表面能、表面驰豫与电子结构。结果表明(0001)面因较高的表面能而更不稳定,易与其它物质反应且具有较快的生长速度。(10-10)晶面因表面能低而生长缓慢,容易暴露。弛豫后(10-10)表面的Ca、C原子向内收缩而O原子却略微向外扩张,CO2-3集团发生转动使结构更稳定。(0001)表面的Ca原子以及第二层的C、O原子均向内收缩并且原子弛豫程度比(10-10)面大。计算的DOS表明:与CaCO3体相约5.0eV的带隙相比,表面结构的带隙略微减少,而(0001)表面减少更多。虽然表面C原子与O原子由于强烈的DOS交叠形成典型的共价键,而Ca-O键则相对较弱,(0001)表面结构的C-O和Ca-O键相对更弱,且表面稳定性主要与O-p电子有关。电荷密度表明(0001)面内的C原子与周围3个O原子之间存在强烈的C-O共价键而组成三角形状的CO2-3集团,其键能远大于Ca-O键。(10-10)表面模型的CO和Ca-O键均比(0001)面强,并且表面的电荷密度也高于(0001)面,因而更稳定。     

α-A12O3基片（0001）表面及其对ZnO吸附位置研究

建立了一种2×2α-Al2O3 (0001)基片表面吸附ZnO模型,在周期边界条件下的k空间中,采用基于密度泛函理论的局域密度近似平面波超软赝势法,对α-Al2O3 (0001)基片表面结构及其ZnO分子在表面最初吸附生长位置进行了计算研究.由于较大的表面弛豫,使得氧原子全部暴露于基片最外表面,明显地表现出O原子电子表面态;驰豫后的表面能对ZnO分子产生较强的化学吸附,表面电子结构将发生明显的变化,其表面最优吸附生长点的方位正好偏离α-Al2O3 (0001)表面氧六角对称30°;并计算了这些吸附生长点处Zn与表面O的结合能.     

Mg掺杂AlN的磁性

采用基于密度泛函理论(Density function theory,DFT)的第一性原理方法,计算研究了AlN中掺杂Mg后的电子结构和磁性。我们从理论上给出了AlN∶Mg的晶体结构参数和电子结构,计算了铁磁相和反铁磁相的总能,发现AlN∶Mg具有半金属特性,并且其铁磁相更稳定。我们通过分析比较AlN和AlN∶Mg的电子结构,解释了非磁性杂质Mg掺杂在AlN中产生磁性的原因是Mg取代Al后,会在自旋向下的价带顶部引入空穴,导致费米能级移入价带中,从而使自旋向上和自旋向下的态密度产生不对称的分布,从而导致材料中有净磁矩。另外,通过比较AlN∶Mg的多种构型的形成能,发现在纤锌矿结构AlN中掺入Mg比较容易实现,在闪锌矿结构中次之,但对于其它几何构型,由于形成能太高,Mg很难掺入到材料中。这种材料可作为制备非磁性掺杂的半导体自旋电子器件的备选材料。     

Petri Net modelling approach for analysing the behaviour of Wnt/ β ‐catenin and Wnt/ Ca2+ signalling pathways in arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited heart muscle disease that may result in arrhythmia, heart failure and sudden death. The hallmark pathological findings are progressive myocyte loss and fibro fatty replacement, with a predilection for the right ventricle. This study focuses on the adipose tissue formation in cardiomyocyte by considering the signal transduction pathways including Wnt/ β ‐catenin and Wnt/Ca²⁺ regulation system. These pathways are modelled and analysed using stochastic petri nets (SPN) in order to increase our comprehension of ARVC and in turn its treatment regimen. The Wnt/ β ‐catenin model predicts that the dysregulation or absence of Wnt signalling, inhibition of dishevelled and elevation of glycogen synthase kinase 3 along with casein kinase I are key cytotoxic events resulting in apoptosis. Moreover, the Wnt/Ca²⁺ SPN model demonstrates that the Bcl2 gene inhibited by c‐Jun N‐terminal kinase protein in the event of endoplasmic reticulum stress due to action potential and increased amount of intracellular Ca²⁺ which recovers the Ca²⁺ homeostasis by phospholipase C, this event positively regulates the Bcl2 to suppress the mitochondrial apoptosis which causes ARVC.Inspec keywords: molecular biophysics, enzymes, cancer, muscle, Petri nets, cellular biophysics, bioelectric potentials, biomembranes, tumours, cardiology, genetics, biochemistry, calciumOther keywords: heart failure, sudden death, hallmark pathological findings, progressive myocyte loss, fibro fatty replacement, adipose tissue formation, signal transduction pathways, Ca²⁺ regulation system, stochastic petri nets, ARVC, $β‐catenin model, Wnt signalling, glycogen synthase kinase 3, Bcl2 gene, c‐Jun N‐terminal kinase protein, petri Net modelling approach, Ca²⁺ signalling pathways, arrhythmogenic right ventricular cardiomyopathy, inherited heart muscle disease, Ca²⁺ SPN model, Ca     

The 10 KM/S, 10 KG railgun

The system design for a railgun powered by capacitor-based energy stores distributed along its length is presented. It is assumed that it is required to accelerate a mass of 10 kg to a velocity of 10 km/s. Parameters for the railgun and its energy stores are derived, and the performance of the system is computed with particular attention being paid to the efficiency with which store energy is converted to launch-package kinetic energy. It is shown that efficiencies of 90% can be expected from a properly designed system     

Ni—20Cr—10Mo—10Co高温合金的相分析

Ni-20Cr-10Mo-10Co高温合金是以碳化物为主要强化相的一种铸造高温合金,用X射线衍射与扫描电镜的背散射象及能谱分析确定了该合金的相组成,即基体为Ni-Mo-Cr-Co的固溶体,及（Cr,Mo,Co,Ni)(23C6和（Mo,Cr,Co,Ni)6C两种碳化物。     

10-kY 10-mA DC Supply with 0.1-ppm Stability

A 10-kV stabilized supply with a dc capacity of 10 mA has been constructed. Its drift rate measured over time intervals greater than about 1 minute and extending to times of more than 10 hours is about 1 part in 107 per hour. For shorter times from 1 second to 1 minute the peak-to-peak deviation from the mean is about 2 mV at 9.2 kV or ±1 part in 107. This performance has been achieved by the use of an initially well regulated commercial 10-kV supply in a closed-loop control system. High dc loop gain has been achieved by the use of a chopper-stabilized amplifier, and a guarded resistive divider of special design. The reference voltage is made up of a bank of unsaturated standard cells enclosed in a temperature-controlled air bath whose short term temperature stability is ±0.001°C. The control resistive divider, together with a measuring divider and a guard divider, are enclosed in an oil bath whose temperature is controlled near ambient to within ±0.01°C.     

Effect of cooling on fatigue strength of metastable austenitic 30Kh10G10 [30Cr10Mn10] steel in relation to specimen length

This investigation was concerned with the kinetics of phase transformations in metastable austenitic 30Kh10G10 steel specimens fatigued in rotating bending and with the effect of specimen temperature on the fatigue strength of this steel in relation to the specimen length. It was shown that spray cooling produces substantial changes in the kinetics of phase transformations, increases the fatigue strength of the steel in question and substantially inhibits the manifestation of the size factor.