合成金刚石晶体缺陷的同步辐射形貌研究

采用同步辐射白光貌相术研究合成金刚石单晶体中的晶体缺陷,观察到晶体中存在籽晶,籽晶周围存在着大量的位错线.位错线起源于籽晶表面,终止于晶体表面.计算了位错束的空间走向和位错密度.分析了晶体的生长阶段和影响晶体缺陷的主要因素,指出通过减少籽晶表面的缺陷,保持生长条件的稳定,能够有效地降低合成金刚石晶体中缺陷的密度,提高合成金刚石晶体的完整性.     

CVD金刚石厚膜晶格缺陷分析

应用X射线衍射仪的薄膜附件对热丝化学气相沉积金刚石厚膜的成核面和生长面进行分析,结果表明,金刚石厚膜的晶格常数从生长面到形核面沿深度方向是逐渐变小的.化学气相沉积金刚石初期生长的晶体存在大量的空位等缺陷,晶格松弛,在金刚石膜持续生长过程中,形核面和膜内部在高温下发生长时间的自退火,缺陷浓度下降,晶格松弛现象消除,晶格常数变小并趋于理论值.试验表明,经长时间高温自退火的金刚石厚膜比薄膜具有更高的耐磨性.     

化学汽相沉积金刚石薄膜的生长

利用热丝化学汽相沉积法生长出优异的金刚石薄膜，研究表明，金刚石的成核依赖于沉积点的尖锐度，薄膜的生长包括晶粒长大和薄膜上的二次成核及其生长，可用分层生长来描述，金刚石晶粒的生长由外延生长和二次成核及其生长组成。也是分层进行的，结果导致了金刚石晶体和薄膜的层状结构。     

氢氧等离子体预处理对单晶金刚石刻蚀坑的研究

采用自制的微波等离子体化学气相沉积装置,在高温高压法合成的金刚石的衬底上外延生长单晶金刚石。实验分为两步,首先用氢氧等离子体在生长之前进行预处理刻蚀,然后外延生长30 h。利用金相显微镜和激光拉曼光谱来表征单晶金刚石刻蚀坑以及外延生长的单晶金刚石质量。研究结果表明,氧会优先刻蚀籽晶表面的缺陷和位错,可以通过刻蚀坑密度来判断衬底质量,且经过预处理刻蚀能消除单晶金刚石表面的缺陷。籽晶表面经刻蚀后会出现平底型和尖锥型两种倒金字塔型刻蚀坑,且晶体表面的原本缺陷或由抛光造成起的缺陷会随刻蚀时间延长、刻蚀强度增大而消失。经过氢氧等离子体预处理外延生长的单晶中非金刚石相杂质含量较少,结晶性高。     

优质克拉级Ib型金刚石单晶的高温高压合成及应用研究

利用温度梯度法,在国产六面顶压机上进行优质克拉级Ib型金刚石单晶的高温高压合成及应用研究.通过合理设计实验组装,优化生长工艺,严格控制生长速度等成功合成出了多颗优质克拉级金刚石单晶.借助扫描电子显微镜(SEM)对克拉级金刚石单晶的表面缺陷进行了测试分析.考察了生长速度对晶体品质的影响.同时,对优质克拉级大单晶在饰品钻石...     

温度梯度法合成金刚石大单晶的研究进展

介绍了金刚石大单晶的温度梯度法合成技术,详细综述了影响金刚石晶体形貌、晶体品质以及生长速度等相关因素的最新进展,简要叙述了掺杂对金刚石晶体晶形、性能的影响,最后指出了温度梯度法合成金刚石大单晶的发展方向。     

金刚石表面生长石墨烯的纳观尺度机理研究进展

近年来，将石墨烯转移至金刚石表面形成的石墨烯/金刚石异质结构在精密制造、电子制造等领域展现出显著优势，但石墨烯本征特性会因转移至介电基材后缺陷和界面处的声子散射而明显减弱。因此，以金刚石作为衬底直接生长石墨烯成为获得高质量石墨烯/金刚石异质结构的一种全新尝试。虽然以金刚石作为衬底相比于其他介电材料拥有众多优势，但是现阶段在金刚石表面生长的石墨烯通常存在晶格缺陷多、畴区尺寸小等缺点，也缺乏纳观尺度下金刚石结构表面石墨烯生长的机理解析和理论指导。本文评述了在金属催化、非金属诱导和高温热解三种催化方式下金刚石表面生长石墨烯的纳观尺度机理研究进展，对不同催化方式下金刚石表面生长石墨烯的原子机理进行了总结，并对不同催化条件下生长石墨烯的典型结果进行对比分析，最后归纳了金刚石结构表面生长石墨烯研究所面临的关键问题与挑战，展望了基于金刚石表面石墨烯生长研究的发展方向，可为高质量石墨烯/金刚石异质结构的研究与应用提供有益借鉴。     

生长温度对CVD金刚石薄膜的影响

系统研究了ＣＶＤ金刚石薄膜成膜过程中生长温度对薄膜质量、生长率和力学性能的影响。研究结果表明：在典型沉积条件下，生长温度愈高、薄膜的晶体质量愈好；但薄膜的应力状况和附着性能变坏；在８００℃时，金刚石薄膜的生长速率最大。讨论了ＣＶＤ金刚石薄膜作为机械工具涂层的最佳生长温度。     

Ia型天然金刚石结构缺陷的同步辐射形貌研究

红外吸收光谱表明样品含片状和分散状分布的杂质氮 ,属Ia型金刚石。利用同步辐射对晶体进行了形貌学研究 ,在近完整晶体内近中心的 ( 0 0 1)和 ( 0 10 )结晶学平面内观察到生长带 ,生长方向平行于 ( 10 0 )和 ( 0 10 )。在欠完整晶体内小角度晶界发育 ,取向角达 2 .5°以上。晶体完整性与氮含量无明显相关关系     

Ce∶YAG晶体色心和缺陷的伽马射线辐照研究

利用伽玛射线研究了Ce3+∶Y3Al5O12晶体的辐照色心缺陷,比较了采用提拉法和温梯法生长的Ce3+∶Y3Al5O12晶体中产生的不同色心缺陷,并利用吸收光谱、激发发射光谱和退火等方法分析了晶体中235nm和370nm色心吸收带的形成原因,指出晶体中的235nm吸收带由F+色心引起。进一步分析了YAG晶体的辐照,证实了370nm色心的来源,表明370nm吸收带与F-类色心相关。     

Characterization of a-Si:H thin films prepared by dc glow discharge of silane

A dc glow discharge apparatus for preparing amorphous silicon films from silane gas is described. The films are characterized by electron microscopy, infrared spectroscopy, electrical conductivity and photoconductivity. The deposition parameters which give good photoconducting films are established. The Staebler-Wronski effect is studied and is found to be smaller in vacuum than in air. A photovoltage is observed in structures with gold as the Schottkybarrier metal. The conversion efficiency of the device is about 1%. The results are compared with those in the literature, and the improvements which might result in a better conversion efficiency are pointed out.     

标准化是人类进化和社会进步的要素

本文对标准化的存在与感觉进行对比,提示了常被忽略的标准化重要性,讨论了人类进化的标准化因素,论证了语言、文字等作用对标准化的依赖及对人脑的进化作用,得出多维因素标准化推进了人脑进化的结论,讨论了社会进步的标准化因素,论证了畜牧业、农业、手工业、商业劳动的社会化对标准化的依赖,论证了第一次、第二次、第三次工业革命对标准化的依赖,得出劳动方式和生产方式标准化推进了社会进步的结论,深入讨论了标准化不存在的影响和标准化存在的意义。本文发掘出人类进化的两个重要关系,即"离现"交流和"离现离人"交流因素。     

Two models for a repairable two-system with phase-type sojourn time distributions

This paper investigates a general repairable two-system. The operational and repair times are general, but for applicability, are approached by phase-time distributions, given that this class is dense in the set of distribution functions on the positive real line. Two models are studied, depending on the remembering of the failure phase when the unit is repaired. The versatility of this class of functions is shown. For these models, the availability and the rate of occurrence of failures are calculated. These performance measures are presented in a well-structured form, and are computationally implemented. The method and results are illustrated by a numerical example. The present work generalizes others in the specialized literature, and completes the study of two-systems under the Markov system.     

广义标准概念的构建

本文对典型的标准概念的定义进行了讨论,分析了这些标准概念定义的历史局限性、目的局限性、形式局限性、用途局限性、确认局限性、内容来源局限性等问题,研究构建了具有普遍适用性的广义标准概念,建立了狭义标准的概念,使典型标准(狭义标准)的概念得以完善。本文还讨论了标准和标准化间的因果关系。本文研究的内容是标准化理论建设的重要基础。     

A Meshless Approach Towards Solution of Macrosegregation Phenomena

The simulation of macrosegregation as a consequence of solidification of a binary Al-4.5%Cu alloy in a 2-dimensional rectangular enclosure is tackled in the present paper. Coupled volume-averaged governing equations for mass, energy, momentum and species transfer are considered. The phase properties are resolved from the Lever solidification rule, the mushy zone is modeled by the Darcy law and the liquid phase is assumed to behave like an incompressible Newtonian fluid. Double diffusive effects in the melt are modeled by the thermal and solutal Boussinesq hypothesis. The physical model is solved by the novel Local Radial Basis Function Collocation Method (LRBFCM). The involved physical relevant fields are represented on overlapping 5-noded sub-domains through collocation by using multiquadrics Radial Basis Functions (RBF). The involved first and second derivatives of the fields are calculated from the respective derivatives of the RBFs. The fields are solved through explicit time stepping. The pressure-velocity coupling is calculated through a local pressure correction scheme. The evolution of the solidification process is presented through temperature, velocity, liquid fraction and species concentration histories in four sampling points. The fully solidified state is analyzed through final macrosegregation map in three vertical and three horizontal cross-sections. The results are compared with the classical Finite Volume Method (FVM). A surprisingly good agreement of the numerical solution of both methods is shown and therefore the results can be used as a reference for future verification studies. The advantages of the represented meshless approach are its simplicity, accuracy, similar coding in 2D and 3D, and straightforward applicability in non-uniform node arrangements. The paper probably for the first time shows an application of a meshless method in such a highly non-linear and multi-physics problem.     

Analysis of nets with hexagonal mesh using triangular elements

The calculation of net shapes is achieved using the finite element method. A triangular element is developed for the modelling of the net. The main hypotheses are that the strain in each triangular element is constant, that the hexagonal meshes have three directions of twine, and that the twines are elastic. The forces due to the tension in twines are described and calculated by a direct method. The results of the model based on such triangular elements are provided. The comparison with a model where each twine is described as an elastic bar, is quite good. Copyright © 2003 John Wiley & Sons, Ltd.     

消费者偏好下基于辐条模型的寡头定价研究

从消费者的购买行为着手,研究考虑消费者偏好下的寡头价格博弈。基于Hotelling模型建立寡头竞争的辐条模型,通过数理推导得出企业在消费者不同购买意愿下的最优定价,并得出如下结论：当消费者购买意愿较小时,市场处于区域垄断;当消费者购买意愿较大时,市场处于非区域垄断。应用算例验证理论分析的结果,同时还发现,不管是在区域垄断竞争还是非区域垄断竞争,消费者购买意愿与企业的期望收益都呈正相关关系。     

概率局部应力应变法

实际工程中的结构件往往具有多个不确定因素,包括材料、几何、载荷等。这些不确定因素导致构件的局部应力应变响应和疲劳寿命响应具有随机性。因此对低周疲劳分析中的局部应力应变法进行了概率分析。通过基本随机变量将诺伯法中的循环应力应变曲线(迟滞回线)和诺伯公式表示为概率曲线,基本随机变量反映了构件的不确定因素。通过建立近似拟合多项式的方法,求得局部应力应变的随机响应。将应变寿命曲线视为概率曲线,采用随机累积损伤理论,通过同样方法得到疲劳寿命的随机响应。算例表明结果与蒙特卡罗模拟的结果十分接近。该方法是一个简单有效的疲劳寿命概率分析方法。     

Static and dynamic analysis of an FGM doubly curved panel resting on the Pasternak-type elastic foundation

The static, dynamic, and free vibration analysis of a functionally graded material (FGM) doubly curved panel are investigated analytically in the present paper. The FGM Panel is originated from a rectangular planform and its principle curvatures are considered to be constant. All mechanical properties of the FGM panel are assumed to vary continuously through the thickness according to a power law formulation except Poisson’s ratio, which is kept constant. A Pasternak-type elastic foundation containing damping effects is considered to be in contact with the panel during deformation. The elastic foundation reacts in both compression and tension. Equations of motion are established based on the first order shear deformation and the modified Sanders shell theories. Following the Navier type solution, the established equations are reduced to time-dependent ordinary differential equations. Using the Laplace transform, the time-dependency of the problem is eliminated. The solutions are obtained analytically in the Laplace domain and then are inverted to the time domain following an analytical procedure. Finally, the analytical results are verified with those reported in the literature.     

竖向地震动场的空间相干函数模型

根据台湾SMART 1台阵采集的六次重大地震的加速度数据记录,利用数字信号处理技术,对竖向地震动场的空间相干函数进行分析。按照各测点对在波传播方向上的投影距离进行分组,研究了竖向地震动场空间相干函数与它们的空间距离(投影距离)、频率的关系,发现它们随两点的距离增大而减小,且与这两点在地震波的传播方向上的投影距离有较大的关系,不具有“各向同性”的性质;它们均随频率的增大而减小。在总结前人研究成果的基础上,采用Hao提出的相干函数模型来描述竖向地震动场空间相干函数。根据实测地震数据,分别对相干函数理论表达式中的一些参数进行了拟合。结果表明,该模型具有较强的合理性和实用性。