Novel Mechanical Behavior Of Zno Nanorods

A novel stress-strain relation with two stages of linear elastic deformation is observed in [0 0 0 1]-oriented ZnO nanorods under uniaxial tensile loading. This phenomenon results from a phase transformation from wurtzite (WZ, P6(3)mc space group) to a body-centered tetragonal structure with four-atom rings (denoted as BCT-4) belonging to the P4(2)/mnm space group. The analysis here focuses on the effects of nanorod size and temperature on the phase transformation and the associated mechanical behavior. It is found that as size is increased from 19.5 to 45.5 angstrom, the critical stress for nucleation of the transformation decreases by 25% from 21.90 to 16.50 GPa and the elastic moduli of the WZ- and BCT-4-structured nanorods decrease by 24% (from 299.49 to 227.51 GPa) and 38% (from 269.29 to 166.86 GPa), respectively. A significant temperature effect is also observed, with the critical stress for transformation initiation decreasing 87.8% from 17.89 to 2.19 GPa as temperature increases from 300 to 1500 K. (c) 2007 Elsevier B.V. All rights reserved.

带有相变的三维温度场数值模拟

以激光熔凝表面强韧化处理为背景，应用空间的弹塑性有限单元和高精度的数值算法、同时考虑材料组织性能的变化来模拟材料的温度场。主要研究激光熔凝加工中瞬时温度场数值模拟，同时考虑相变潜热的影响，为第二步热应力场及残余应力的数值模拟做准备。最后用算例验证了模型的正确性，并给出了不同时刻温度场的分布。

Microstructure Evolution of Laser Pulse processed Ductile Iron Surface

Pulsed laser beam was used to modify surface processing for ductile iron. The microstructures of processed specimen were observed using optical microscope (OM). Nanoindentation and micro-hardness of microstructures were measured from surface to inner of sample. The experimental results show that, modification zone is consisted of light melted zone, phase transformation hardening area and transient area. The light melt area is made up of coarse dendrite crystalline with a thickness less than 20um, phase transformation hardening area mainly of laminal or acicular martensite, retained austenite and graphite, i.e. M+A prime+ G. The cow-eye microstructure around graphite sphere always is formed in phase transformation hardening area zone, which consisting of a variety structure with the distance from the surface. So, it maybe as a obvious sign distinguishing modification zone border. Finally, the microstructures evolution of laser pulse processed ductile iron was analyzed coupling with beam energy distribution in space and laser pulse heating procession characteristics. The analysis shows that energy distribution of laser pulse has an important effect on microstructure during laser pulse modified ductile iron. Multi-scale and interlace arrangement are the important features for laser pulse modified ductile iron. Of microstructure.

冲击压缩下玻璃等脆性材料中失效波的实验和理论研究

本文首先回顾了失效波的研究进展和存在的问题，然后在现有实验手段改进的基础上对目前失效波研究中尚存的问题进行了较系统的实验研究，并建立了理论模型，进行了失效波传播的数值模拟。本文实验工作给出了K9玻璃中失效波速度和冲击载荷之间的定量关系和产生失效波的最小载荷阈值；通过：（1）玻璃样品和飞片表面状况对萌生失效波的载荷阈值的影响；（2）高速摄影观测冲击压缩下玻璃样品表面和内置界面处失效波的萌生和冲击波后压缩区内损伤演化情况；（3）回收样品的显微分析和Ｘ光衍射分析等实验，证实失效波的萌生基本与冲击相变无关，主要与玻璃样品表面状况有关，失效波的本质是玻璃样品表面固有微裂纹和冲击瞬间在此处萌生的微裂纹系统向玻璃样品中扩展的宏观统计表现。高速摄影观测到冲击波后有破碎界面在移动，其速度明显高于同等加载条件下VISAR测试的失效波速度，据此推测失效波是由大量裂纹扩展的宏观表现一破碎界面和其后方声阻抗明显降低的移动界面组成。实验同时研究了微晶玻璃、高纯度石英玻璃以及碱石灰玻璃在冲击压缩下的动力学响应特性。本文关于失效波方面的研究工作结果大部分未见相关文献报道。实验工作对于深入了解玻璃中失效波的萌生机制和失效波的力学性质等是非常重要的，并有助于建立与失效波萌生、传播有关的理论模型。改进有关实验技术，是完成本文实验研究的必要条件，也是本文工作的重要组成部分。本文设计了一种高接收效率、景深可调的新型VISAR探头，其技术指标接近国外同类产品，成本不到国外同类产品的二十分之一，且结构是国内外同类产品中最简单的。本文设计高速摄影的阴影和纹影光路，用于观察冲击压缩下玻璃样品中冲击损伤和失效波的演化及发展规律，其技术优于国外同类实验。本文设计了两种冲击压力低于玻璃样品HEL值的爆轰加载装置，用于配合高速摄影诊断实验。爆轰驱动厚飞片装置的设计，在飞片的炸药透镜之间增加了一个空腔，既降低了飞片的速度，又有效避免了以往同类装置驱动厚飞片时经常遇到的层裂问题，并且成功地进行了与爆轰驱动有关的数值模拟及设计工作。本文在理想微裂系统演化理论的基础上，建立了描述失效波的理论模型，分别讨论了表面损伤、微裂纹扩展和微裂纹形核、长大对失效波萌生、传播的影响，给出了描述失效波扩展的损伤演化方程，结合冲击压缩下材料的Resende压缩损伤本构方程，进行了各种加载条件下玻璃样品后自由表面速度和玻璃体内应力分存的数值模拟，计算结果与实验结果相符，表明本文建立的理论模型是可靠的，能够反映冲击压缩下失效波的传播特性的基本力学特性。用飞片碰玻璃样品时，实验测量的表面速度时程曲线出现“过冲现象”。本文通过高速摄影和VISAR等测试手段从实验上对其进行了较系统的研究，发现这种现象与玻璃样品后自由表面的破碎有关，并且其萌生所需的载荷阈值与萌生失效波的载荷阈值接近。本文建立了描述这一破坏现象的损伤演化方程，对其进行了数值模拟。计算结果和实验结果吻合，表明本文对这一现象的解释是合理的。

双菱体λ/4消色差相位延迟器的设计

根据菲涅尔全内反射相变理论,给出了双菱体λ/4消色差器的结构设计、性能分析和测量方法.由有效通光孔径和光线追迹设计出BK7玻璃在波长532 nm时相位延迟λ/4的双菱体的结构,用作532 nm至1 064 nm波长范围的标准λ/4相位延迟器.理论分析了入射角变化和波长变化对双菱体相位延迟的影响,当入射角变化限制在±4.3°以内时,其影响得到补偿；波长从532 nm到1 064 nm产生的误差为－0.65°.采用椭偏法中的消光技术,分别实测了双菱体在532 nm和1 064 nm波长下的相位延迟为：90.08±0.14°和88.99±0.1°,可知两不同波长产生的相位延迟误差为－1.09°.

热致NiOx薄膜的结构和光学性质变化

利用直流磁控反应溅射技术制备了氧气和氩气的分压比为5:100的NiOx薄膜。利用X射线衍射仪(XRD)、扫描电镜(SEM)、原子力显微镜(AFM)和光谱仪研究了热处理对薄膜的微观结构和光学性质的影响, 并对沉积态薄膜的粉末进行了热分析。沉积态的NiOx薄膜在262 ℃时开始分解, 导致NiOx薄膜的透过率增加和反射率降低。X射线衍射和示差扫描量热曲线(DSC)分析表明, 在热处理过程中并无物相的变化, 光学性质的变化是由于NiOx薄膜热分解引起薄膜表面形貌发生变化而引起的。通过Kissinger公式计算出

Structure and properties of amorphous thin film for optical data storage

In this paper the magnetic and magneto-optical properties of amorphous rare earth-transition metal (RE-TM) alloys as well as the magnetic coupling in the multi-layer thin films for high density optical data storage are presented. Using magnetic effect in scanning tunneling microscopy the clusters structure of amorphous RE-TM thin films has been observed and the perpendicular magnetic anisotropy in amorphous RE-TM thin films has been interpreted. Experimental results of quick phase transformation under short pulse laser irradiation of amorphous semiconductor and metallic alloy thin films for phase change optical recording are reported. A step-by-step phase transformation process through metastable states has been observed. The waveform of crystallization propagation in micro-size spot during laser recording in amorphous semiconductor thin films is characterized and quick recording and erasing mechanism for optical data storage with high performance are discussed. The nonlinear optical effects in amorphous alloy thin films have been studied. By photo-thermal effect or third order optical nonlinearity, the optical self-focusing is observed in amorphous mask thin films. The application of amorphous thin films with super-resolution near field structure for high-density optical data storage is performed. (c) 2007 Elsevier B.V. All rights reserved.

薄膜材料对TiO2基薄膜激光损伤阈值的影响

abstract {The optical property, structure, surface properties (roughness and defect density) and laser-induced damage threshold (LIDT) of TiO₂ films deposited by electronic beam (EB) evaporation of TiO₂ (rutile), TiO₂ (anatase) and TiO₂ + Ta₂O₅ composite materials are comparatively studied. All films show the polycrystalline anatase TiO₂ structure. The loose sintering state and phase transformation during evaporating TiO₂ anatase slice lead to the high surface defect density, roughness and extinction coefficient, and low LIDT of films. The TiO₂ + Ta₂O₅ composite films have the lowest extinction coefficient and the highest LIDT among all samples investigated. Guidance of selecting materials for high LIDT laser mirrors is given.}

Effect of Si doping on cubic GaN films grown on GaAs(100)

Epitaxial layers of cubic GaN have been grown by metalorganic vapor-phase epitaxy (MOVPE) with Si-doping carrier concentration ranging from 3 x 10(18) to 2.4 x 10(20)/cm(3). Si-doping decreased the yellow emission of GaN. However, the heavily doped n-type material has been found to induce phase transformation. As the Si-doping concentration increases, the hexagonal GaN nanoparticles increase. Judged from the linewidth of X-ray rocking curve, Si-doping increases the density of dislocations and stacking faults. Based on these observations, a model is proposed to interpret the phase transformation induced by the generated microdefects, such as dislocations and precipitates, and induced stacking faults under heavy Si-doping. (C) 1999 Elsevier Science B.V. All rights reserved.

PHYSICAL VAPOR TRANSPORT AND CRYSTAL-GROWTH OF GESEXTE1-X SOLID-SOLUTIONS

Physical vapor transport studies of GeSe(x)Te1 - x (x = 0.1, 0.2, 0.3, and 0.4) solid solutions demonstrated, that individual, large single crystals of these materials can be grown in closed ampoules. A compositional analysis of the grown crystals revealed, that the mass transport (crystal growth) process under steady-state conditions is pseudo-congruent and controlled by diffusion processes in the source material. From these experiments, the degree of non-stoichiometry (Ge-vacancy concentrations) of GeSe(x)Te1 - x single crystals could be estimated. The effects of the cubic to rhombohedral phase transformation during cooling on the microstructure and morphology of the grown mixed crystals are observed. This work provides the basis for subsequent defect studies and electrical measurements on these crystals.