Sectioning of multilayers to make a multilayer Laue lens

We report a process to fabricate multilayer Laue lenses (MLL's) by sectioning and thinning multilayer films. This method can produce a linear zone plate structure with a very large ratio of zone depth to width (e.g., >1000), orders of magnitude larger than can be attained with photolithography. Consequently, MLL's are advantageous for efficient nanofocusing of hard x rays. MLL structures prepared by the technique reported here have been tested at an x-ray energy of 19.5 keV, and a diffraction-limited performance was observed. The present article reports the fabrication techniques that were used to make the MLL's.     

多层膜Laue透镜对10 keV硬X射线聚焦性能的理论计算

采用NbC/Si材料组合设计多层膜Laue透镜,总膜厚为40μm,利用衍射动力学理论分析多层膜Laue透镜对硬X射线的衍射效率及聚焦分辨率。通过两种方法提高多层膜Laue透镜的分辨率。第一种方式是减小膜层的最外层宽度,该方法要求结构必须是楔型结构,制备极其困难。第二种方法是使用多层膜Laue透镜的高级次,该方法在不增加制备难题的前提下能有效提高分辨率。通过使用多层膜Laue透镜的-3级次,对10keV硬X射线获得了分辨率为6.72nm,衍射效率为49.31%的聚焦光斑。     

堆叠型太赫兹通信透镜天线设计

为了提高太赫兹通信天线的增益和定向性,提出了"井"字堆叠型透镜天线。该透镜天线工作在太赫兹第一大气传播窗口内,由初级馈源天线和透镜两部分构成。设计了角锥喇叭天线作为透镜天线的初级馈源;根据菲涅耳-基尔霍夫衍射理论和傍轴近似条件设计了"井"字堆叠型透镜用于聚焦太赫兹波,并分析了透镜结构在平面波入射时的聚焦场分布。利用控制变量法分析了透镜天线的全波周期和焦径比等结构参数对其远场辐射性能的影响。对所设计的透镜天线进行了实物加工和测试。实验结果表明:"井"字堆叠型透镜天线的加工和组装工艺简便,具有对称的辐射模式,在320~380GHz的工作频段内的增益高于26.4dB,3dB主瓣宽度低于4.8°,基本满足太赫兹通信系统对天线的高增益和强定向性等要求。     

楔块连接的壳体力学特性分析

楔块连接是飞行器结构中广泛应用地一种连接方式。本文建立了楔块连接壳体的三维有限元模型,通过自行研制的非线性分析软件(GCAASA),分析了楔块连接在不同过盈量和外载荷下应力场的变化和该连接方式的传力路径。计算结果表明过盈量的大小对楔块连接的应力场有明显的影响,应力场的非线性变化符合理论分析规律,进而验证了分析软件的正确性和可信度。     

Non-zeroth-order Laue zone effects and alchemi

The depth-dependence of fast electron probability density is calculated for the 〈111〉 zone axis orientation of GaAs, and the effects of slight tilt from this orientation. Although Ga and As project onto equivalent sites for beams in the zeroth-order Laue zone, differences in mean probability density on Ga and As occur, due to higher-order Laue zone effects. Whether preferential peaking takes place on Ga or As depends upon which atom is assumed to be in the top surface layer. 64×64 beam multislice calculations are compared with 49-beam Bloch wave computations, in which the fast oscillatory depth-dependence of probability density is not accounted for. These results have implications for the interpretation of dynamical X-ray fluorescence effects, and particularly for site determination under zone axis diffraction conditions.     

Accurate d-spacings from zero-order Laue zone patterns.

Experimental d-spacing values are criteria towards the identification of crystallites by electron diffraction. Conclusive identifications often rely on accurate d-spacings. It is shown here that accurate orthogonal components (in mm) for the primitive unit vectors of a zero-level diffraction pattern can be obtained through least-squares processing of (x,y) coordinates for all spots on the film. Valid vectors from the origin spot to any spot in the plane of the film are integer linear combinations of the two selected unit vectors. Accurate lengths and standard deviations for such vectors therefore can be calculated from the least-squares results. Corresponding d-spacings can then be calculated from the vector lengths on the film and the camera constant. In order to obtain d-spacing values that are not only precise, but also accurate, an accurate value of the camera constant should be used. This requires calibration of the experimental setup with reference materials in the same experimental conditions, with careful control of the sample height. For the same quality of measurements, the improvement in the accuracy of the d-spacings obtained with the proposed method is approximately proportional to the square root of the number of measurements taken. Practically, typical improvement in accuracy is about threefold, and accuracies of a fraction of a percent in d-spacings are achievable in this way. The above approach has been programmed as an option in the NRCBED program.     

A dynamical Bragg equation for high-order Laue zone reflections

A dynamically corrected Bragg equation for high-order Laue zone (HOLZ) reflections is derived directly from the Bloch wave formalism instead of the geometric argument used to deduce the kinematical Bragg condition. It differs from the kinematical Bragg equation by replacing the plane wave vector in the kinematical equation with the Bloch wave vectors. This dynamical equation reduces to the kinematical equation when the crystal potential is zero. It also demonstrates the occurrence of dynamical shifts for the HOLZ reflections but their absence for the zero-order Laue zone (ZOLZ) reflections in the symmetrical Laue case.     

Improvement of Lubrication Performance in External Gear Machines through Micro-surface Wedged Gears

This article demonstrates how a properly designed micro-surface linear wedge added to the lateral surfaces of the gear teeth can improve the lubricating ability of external gear machines (EGMs), resulting in lower power losses and chance of wear during their operation. The approach of study is based on the use of a fluid structure interaction (FSI) model for the analysis of the lateral lubricating gaps developed in the authors' research team. Such a model is used to determine the best design of the wedged gear by considering the overall axial balance problem of pressure compensated EGMs for high-pressure applications. The article shows the numerical predictions along with the experimental verifications of the advantages offered by the proposed solution in terms of torque loss reduction for a particular reference pump.     

楔式单闸板阀门阀体锥度气动测头的设计

根据单闸板阀门阀体内腔的结构特点,采用气动测量方法对精加工阀体的重要配对工艺尺寸进行非接触测量。通过分析气动测头的测量原理,设计了高精度锥度气动测头及其校对规。     

Higher-order Laue zone line contrast in large-angle convergent-beam electron diffraction around a dislocation

The physical picture of higher-order Laue zone (HOLZ) line contrast in a large-angle convergent-beam electron diffraction pattern around a dislocation, which is used for determining the Burgers vector, was examined. To evaluate the analytical expression of diffracted wave amplitude, we introduced an approximate form of the atomic displacement field of a dislocation. We showed that the four features of the HOLZ line contrast, that is, splitting, fading, bending and periodical contrast can be explained by analysis of the atomic displacement field. The localized lattice plane bending around a dislocation core made a HOLZ line split, fade and bend. However, we found that the periodical contrast of a HOLZ line was produced by the change of phase difference of the atomic displacement field between the crystals above and below the slip plane across the dislocation line.     

Lead-free multilayer piezoelectric transformer

In this article, a multilayer piezoelectric transformer based on lead-free Mn-doped 0.94(Bi(12)Na(12))TiO(3)-0.06BaTiO(3) ceramics is presented. This piezoelectric transformer, with a multilayered construction in the thickness direction, is 8.3 mm long, 8.3 mm wide, and 2.3 mm thick. It operates in the second thickness extensional vibration mode. For a temperature rise of 20 degrees C, the transformer has an output power of >0.3 W. With a matching load resistance of 10 Omega, its maximum efficiency approaches 81.5%, and the maximum voltage gain is 0.14. It has potential to be used in low voltage power supply units such as low power adapter and other electronic circuits.     

楔横轧楔入段端面移动量规律

楔横轧多楔轧制是内楔和外楔同时对轧件进行径向压下、轴向延伸的塑性成形.随着交通运输业的飞速发展,火车轴、汽车半轴等长轴类零件的需求量与日俱增,采用楔横轧多楔工艺成形长轴类零件,具有显著节省辊面、减小设备体积、生产效率高、节材、降低成本等优点.为了充分发挥多楔显著节省辊面的优点,保持内外楔同时起楔,就必须要准确弄清楔入段移动量的变化规律.采用弹塑性有限形变有限元数值方法,根据实际工况模拟楔横轧轧制过程,分析楔入段移动量的变化规律,详细阐述各工艺参数对移动量的影响规律,并与试验测试结果进行比较,得到楔入段端面移动量的变化和影响规律.研究结果为楔横轧多楔同步轧制模具设计提供了重要的理论依据,进一步完善了楔横轧多楔轧制理论.     

基于混合镜组模型的变焦镜头设计

为了优化变焦镜头的设计过程,本文提出了基于混合镜组模型的变焦镜头设计方法,包括近轴设计,镜组模型确定以及基于混合镜组模型的像差设计。近轴设计阶段采用了高斯括号和矩阵光学,可以很方便地构建镜组间隔和镜组焦距之间的关系。镜组模型确定阶段是根据现有镜头专利训练了一个镜组分类模型,它可以根据镜组近轴数据将镜组分为薄透镜模型或者厚透镜模型。像差设计阶段综合了薄镜组模型像差设计和厚镜组模型像差设计。镜组分类模型成功地将80%以上的镜组进行了分类。最后采用基于混合镜组模型设计方法设计了一个物方远心的变焦镜头。结果表明,该镜头具有良好的设计初值,基于混合镜组模型的变焦镜头设计方法能减少像差变量数量,准确、方便地完成像差设计。     

Tribological properties of composite multilayer coating

Abstract

The use of surface coatings is emerging as one of the most important approaches in reducing friction and wear in various tribological applications. Even though single layer coatings have a wide range of applications, the performance of the single layer alone may not always be adequate to meet the desired tribological property requirements. Hence, coatings consisting of multilayers to meet different property requirements in demanding applications are required. In this study, the tribological properties of a graded composite multilayer coating, with a specific layer sequence of MoS₂/Ti–MoS₂/TiBN–TiBN–TiB₂–Ti deposited on tool steel substrate, have been investigated at temperatures of 40 and 400°C respectively. The experimental results from the tests at 40°C have shown that the friction coefficient value ranges between 0·02 and 0·034. It was found that the deposition parameters influenced the friction and durability of the coatings. Higher substrate bias was found to result in higher friction, and the coating deposited at high substrate bias and low N₂ flow showed the lowest durability. The friction coefficient and durability of the coatings were found to be highly dependent on temperature. At high temperature, the friction coefficient increases almost threefold, and the durability decreases significantly.     

High resolution short focal distance Bent Crystal Laue Analyzer for copper K edge x-ray absorption spectroscopy

We have developed a compact short focal distance Bent Crystal Laue Analyzer (BCLA) for Cu speciation studies of biological systems with specific applications to cancer biology. The system provides high energy resolution and high background rejection. The system is composed of an aluminum block serving as a log spiral bender for a 15 micron thick Silicon 111 crystal and a set of soller slits. The energy resolution of the BCLA-about 14 eV at the Cu Kα line- allows resolution of the Cu Kα(1) and CuKα(2) lines. The system is easily aligned by using a set of motorized XYZ linear stages. Two operation modes are available: incident energy scans (IES) and emission energy scans (EES). IES allows scanning of the incident energy while the BCLA system is maintained at a preselected fixed position--typically CuKα(1) line. EES is used when the incident energy is fixed and the analyzer is scanned to provide the peak profile of the emission lines of Cu.     

On the inclusion of upper Laue layers in computational methods in high resolution transmission electron microscopy

Three different methods for computing scattering amplitudes in High Resolution Transmission Electron Microscopy (HRTEM) have been investigated as to their ability to include upper Laue layer (ULL) interaction. The conventional first-order multislice method using fast Fourier transform (FFT) and the second-order multislice method (SOM method) are shown to yield calculated intensities of first-order Laue reflections with the use of slice thicknesses smaller than the crystal periodicity along the incident electron beam direction. It is argued that the calculated intensities of ULL reflections approach the correct values in the limiting case of vanishing slice thickness and electron wavelength. The third method, the improved phasegrating method (IPG), does also in principle include ULL effects, but is severely limited as to choice of slice thickness and sampling interval. A practical way to use slice thicknesses less than the crystal periodicity along the incident beam direction is shown for both the conventional FFT method and the second-order multislice method and tested on a spinel structure. It is also shown that the IPG method does not easily allow for aslice thickness different from the crystal periodicity in the beam direction.     

全角度反射的多层介质膜系

在总结金属反射镜及多层介质反射镜的优缺点的基础上 ,按照一维光子晶体的设计思想 ,提出用λ/4膜系设计特定波长范围内的全偏振全角度反射镜的方法 ,给出了反射带中心波长、边缘波长及带宽的表达式 ,并对如何避免 Brewster窗作了定量分析。