Formal conditions for unambiguous residual strain determination by CBED

The method of residual strain determination using convergent beam electron diffraction (CBED) is attractive because of its good spatial resolution. However, attempts to obtain all six independent strain components from a CBED pattern lead to ambiguous results. This paper contains analysis of the ambiguities based on the complete algorithm for matching experimental and strain-dependent simulated CBED patterns. The strain parameters which are not determinable by the CBED method are identified by examination of the most common goodness-of-fit functions. The indeterminable parameters are confirmed to be the ‘13’ and ‘23’ components and a combination of the diagonal components of the tensor given in the Cartesian systems having the ‘3’ axis parallel to the beam direction. The ambiguity can be eliminated based on multiple diffraction patterns. It is shown that two different patterns may be insufficient to get a unique strain tensor. The ambiguity can be removed only if certain characteristics of the two patterns are different, or if more than two patterns are used.     

Fast and reliable evaluation of lattice distortions from convergent-beam electron diffraction patterns

A manual method for higher order Laue zone (HOLZ) line detection with an improved effective high-voltage correction for fast and reliable evaluation of local lattice distortions from convergent-beam electron diffraction (CBED) is presented. It is compared with a high-precision Hough transform method with a dynamic correction for each individual HOLZ line used by Krämer and Mayer. Both methods are applied to unfiltered and filtered experimental CBED patterns. As an example, the local lattice distortions in the γ ? γ′ raft-like structure of a creep-deformed single-crystal nickel-based superalloy (CMSX-6) were measured. The lattice distortions obtained from both methods were analysed and showed good agreement. As a by-product, it was noted that specimen cooling enhanced the contrast of CBED patterns to the extent that the quality of CBED patterns taken at low temperatures without energy filtering was found to be qualitatively similar to that of CBED patterns taken at room temperature with energy filtering.     

大角度会聚束电子衍射的新方法

会聚束电子衍射是测定晶体点群、空间群的有效方法。要清楚地判断会聚束电子衍射图样的对称性,电子束的会聚角要大,但衍射盘不能重叠。本文提出了一种新方法来获得不重叠的大角度会聚束电子衍射。新方法是使电子束离焦,固定样品,从而保留了样品的同心倾动位置,作大角度倾动时不会失去原来感兴趣的区域。新方法在原理上和田中等人提出的方法相同,但优越性更大。同时也研究了大束斑(≥2μm)大角度会聚束电子衍射。 关键词：     

有简单取向关系的两晶体间电子衍射图相重的规律

有简单取向关系的两个晶体在倒易空间中有部分倒易点相重。仅由相重倒易点构成的倒易面所对应的电子衍射图必定被基体的衍射斑点所覆盖。给出判定第二相相重电子衍射图晶带轴指数的方法,用此方法考察了立方晶体与孪晶、六角密堆相和ω相等衍射图相重的情况。 关键词：     

Measuring the aspect ratios of ZnO nanobelts

Nanobelts are new materials that have a rectangular cross-section and are characterized by widths and width-to-thickness aspect ratios. In this paper, the thickness and aspect ratios of ZnO nanobelts are measured by a conjunction application of convergent beam electron diffraction (CBED) and electron energy-loss spectroscopy (EELS). The thicknesses of thicker nanobelts are first determined by CBED under two-beam diffracting condition, then they are used to determine the electron inelastic mean-free-path (MFP) length, which is 161±15 nm for ZnO at 200 kV. The thicknesses of the thinner nanobelts are then determined by EELS using the calibrated MFP. The results show that the aspect ratio depends on conditions under which the sample was synthesized.     

A tilting procedure to enhance compositional contrast and reduce residual diffraction contrast in energy-filtered TEM imaging of planar interfaces

This paper systematically demonstrates that energy-filtered transmission electron microscope (EFTEM) images of a planar interface between two single crystals have increased compositional contrast and decreased residual diffraction contrast when the sample is oriented so that the electron beam is parallel to the interface, but not directly on a zone axis. This off-axis orientation reduces diffraction contrast in the unfiltered (and zero-loss) image, which in turn, reduces residual diffraction contrast in single energy-filtered TEM (EFTEM) images, thickness maps, jump-ratio images, and elemental maps. Most importantly, this procedure produces EFTEM images that are more directly interpretable and, in most cases, possess superior spatial resolution compared to EFTEM images acquired directly on a zone axis.     

软X射线Bragg-Fresnel二维聚焦镜的设计理论和方法

Ｘ射线Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ元件是近十年发展起来的一种用于Ｘ射线波段的新型光学元件。本文介绍一种具有二维聚焦效能的Ｂｒａｇｇ－Ｆｒｅｓｎｅｌ元件的设计理论和方法。设计中采用衍射理论并用Ｃ语言编制计算机程序系统对衍射图形进行设计。对于使用波长１３．８ｎｍ，入射角５°，使用焦距２００ｍｍ的使用条件，设计结果为３５Ｍｏ／Ｓｉ双层多层膜，周期厚度７．１４ｎｍ，理论反射率约为６０％；衍射图形共４００个环带，最内环半宽度５２．５μｍ，最外环宽度１．３μｍ。     

光轴平行晶体表面时的锥光干涉图

针对光轴平行晶体表面时的锥光干涉图,提出了计算干涉场中振幅和相位分布的方法,据此绘制完整的干涉图,方便地显示出晶体参数改变时锥光干涉图的变化规律．用CCD摄像机拍摄了铌酸锂晶体的锥光干涉图,结果与理论完全一致。     

Charge density determination in icosahedral AlPdMn quasicrystal using quantitative convergent beam electron diffraction

Charge density distribution in icosahedral AlPdMn quasicrystal has been studied on a single-crystal specimen by using quantitative convergent beam electron diffraction (QCBED) technique. The QCBED systematic row method was used in the refinement of structure factors. To refine the low-order structure factors, the wave-mechanical formulation of electron diffraction dynamical theory was used in the calculation of electron diffraction intensities for the quasicrystal in fitting the experimental intensity line scan profiles. The shapes of atomic surfaces (occupation domains) were described with symmetry-adapted series of surface harmonics. An iterative procedure was used in determination of structure factors of the quasicrystal. The structure factors of nine strongest symmetry inequivalent reflections according to X-ray diffraction experiment were refined with QCBED technique. The average of refinement results for a given reflection performed on several CBED patterns, which were slightly different in orientation and sample thickness, and on different line scans, was taken as the value of structure factor for the reflection. The obtained structure factors for electrons were transformed into X-ray structure factors with Mott formula. The bonding charge density map for the quasicrystal was constructed with the obtained nine structure factors. Assuming that the atoms are spheres, the gain or loss of electrons for different atoms were calculated. It shows that identical atoms can have different valences at different kinds of positions. The bonding charge is localized along certain directions.     

Biaxial Orientation Mechanism of Drawn Natural Rubber. II. Quantitative Analysis of the Biaxial Orientation

Natural rubber film was prepared from triple centrifuged latex. The film was uniaxially drawn at room temperature and the induced crystalline orientation was quantitatively studied by wide angle X‐ray diffraction. The intensity distribution of 200 and 120 reflections confirmed that the induced crystals have a biaxial orientation with the c‐axis parallel to the draw direction. The orientation of the a‐axis was evaluated by using an orientation function of the (200) plane. The function (F ₂₀₀) indicated that the crystalline a‐axis is parallel to the film surface depending on the draw ratio and on positions in the film. The experimental results are possible to explain by shish‐kebab‐like crystallization developed from a highly oriented fibril. The secondary crystallization grows perpendicularly to the draw direction along the a‐axis. The population of the secondary crystals is controlled by an ellipsoidal free space. The shape of the ellipsoid is changed by the fibril distribution depending on width and thickness of the sample film. In this study, the quantitative biaxial orientation is consistently explained by the shish‐kebab‐like crystallization and the ellipsoidal free space.     

菲涅尔区修正圆柱面天线的辐射特性

在圆柱面上进行一维菲涅尔区相位修正结构设计，可以构成一类新型的点源馈电透镜天线。本文利用矢量场绕射理论研究菲涅尔区修正圆柱面天线的辐射特性，并进一步分析馈源阵列作用下的辐射性能。文中天线远场方向图的计算结果与有关文献中的结果吻合。     

Optimized FIB silicon samples suitable for lattice parameters measurements by convergent beam electron diffraction

The aim of this paper is to check the effect of artefacts introduced by focused ion beam (FIB) milling on the strain measurement by convergent beam electron diffraction (CBED). We show that on optimized silicon FIB samples, the strain measurement can be performed with a sensitivity of about 2.5 × 10⁻⁴ which is very close to the theoretical one and we conclude that FIB preparation can be suitable for such measurements in microelectronic devices.

To achieve this, we first used CBED and electron energy loss spectroscopy (EELS) which provide a procedure permitting an exact knowledge of the sample geometry, i.e. the thickness of both amorphous and crystalline layers. This procedure was used in order to measure the FIB-amorphized sidewall layer. It was found that if the FIB preparation is optimized one can reduce this amorphous layer down to around 7 nm on each side. Secondly different preparation techniques (cleavage, Tripod™ and FIB) permit to check if the surface damaged layer introduced by FIB influences the strain state of the sample. Finally, it was found that the damaged layer does not introduce measurable strain in pure silicon but reduces appreciably the quality of the CBED patterns.     

Mapping fibre orientation in complex-shaped biological systems with micrometre resolution by scanning X-ray microdiffraction

A fully automated procedure to extract and to image local fibre orientation in biological tissues from scanning X-ray diffraction is presented. The preferred chitin fibre orientation in the flow sensing system of crickets is determined with high spatial resolution by applying synchrotron radiation based X-ray microbeam diffraction in conjunction with advanced sample sectioning using a UV micro-laser. The data analysis is based on an automated detection of azimuthal diffraction maxima after 2D convolution filtering (smoothing) of the 2D diffraction patterns. Under the assumption of crystallographic fibre symmetry around the morphological fibre axis, the evaluation method allows mapping the three-dimensional orientation of the fibre axes in space. The resulting two-dimensional maps of the local fibre orientations - together with the complex shape of the flow sensing system - may be useful for a better understanding of the mechanical optimization of such tissues.     

Young's fringes analysis with a computer image-processing system

A two-dimensional Fourier transform analysis is presented for numerically processing the Young's fringes diffraction pattern from a double- exposure speckle photograph. The fringe spacing and orientation are determined using only one Young's fringes pattern without any other diffraction halo patterns. This algorithm is based on the 2-D FFT of the fringe pattern with 256 × 256 pixels. Therefore, it enables automatic analysis to be performed on specklegram with noisy and poor fringe patterns. The measurement of deformation by the laser speckle method can be carried out with high accuracy, reliability and speed.     

Magnetic Properties and Nanostructures of FePtCu：C Thin Films with FePt Underlayers

Magnetic properties and nanostructures of FePtCu：C thin films with FePt underlayers （ULs） are studied. The effect of FePt ULs on the orlentation and magnetic properties of the thin films are investigated by adjusting FePt UL thicknesses from 2nm to 14nm. X-ray diffraction （XRD） scans reveal that the orientation of the films is dependent on FePt UL thickness. For a 5-nm FePtCu：C nanocomposite thin film with a 2-nm FePt UL, the coercivity is 6.S KOe, the correlation length is 59 nm, the desired face-centred-tetragonal （fct） ordered structure [Llo phase] is formed and the c axis normal to the film plane [（001） texture] is obtained. These results indicate that the beffer orientation and magnetic properties of the films can be tuned by decreasing the thockness of the FePt UL.     

全谱拟合法研究聚丙烯腈基碳纤维形成过程中晶态结构演变

通过全谱拟合法对碳纤维制备过程中不同阶段纤维的XRD谱图进行处理,得到不同阶段纤维的微观结构参数,研究了聚丙烯腈(PAN)基碳纤维制备过程中晶态结构的演变.全谱拟合法基于晶体衍射的严格物理理论,拟合目标为整个衍射谱,并不是个别衍射峰,所得结果具有更高的可信度.研究结果表明:PAN原丝中的高分子链沿纤维轴高度取向,表观晶粒尺寸为6.5 nm左右;经过预氧化处理,纤维中的有序结构遭到破坏,表观晶粒尺寸锐减.纤维中逐渐形成梯形结构并沿纤维轴取向,从而形成新的有序结构;经过碳化处理后,环状梯形结构转变为碳的层状结 关键词： 碳纤维 晶体结构 XRD 全谱拟合法     

上海光源硬X射线相干衍射成像实验方法初探

相干X射线衍射成像方法是一种先进的成像技术,分辨率可达纳米量级.国际上大多数的同步辐射装置和自由电子激光装置都建立了该成像方法,并有将其作为主要成像技术的趋势.上海光源作为目前国内唯一的一台第三代同步辐射光源,尚未建立基于硬X射线的相干衍射成像实验平台.随着一批以波荡器为光源的光束线站投入使用,使得该方法的建立成为了可能.本文基于上海光源BL19U2生物小角散射线站,通过有效的光路设计,搭建了相干衍射实验平台,在12 keV和13.5 keV能量点均获得了硬X射线相干光束,并基于小孔衍射测量了入射光束的空间相干长度.该平台支持常规和扫描相干衍射实验模式,对小孔衍射图样及波带片扫描衍射图样实现了正确的相位重建,证明了该平台初步具备开展硬X射线相干衍射成像实验的能力.硬X射线相干衍射成像实验平台为国内首次建立,将为国内该实验方法的发展和应用提供有效的软硬件支持.     

熊猫光纤背向衍射图样的图像互相关定轴方法

针对基于背向衍射图像的熊猫光纤定轴法需要建立标准图样库的难题,进行了熊猫光纤在不同方位角所产生的背向衍射图样相关性分析的实验研究.实验显示：快轴方向的背向衍射图样与慢轴方向的背向衍射图样之间具有差异性;在快轴或慢轴方向附近的背向衍射图样之间具有相似性;快轴或慢轴方向的背向衍射图样自身具有对称性.根据差异性、相似性和对称性这三个特性,建立了一种基于熊猫光纤背向衍射图样的图像互相关定轴方法,用于确定熊猫光纤快轴或慢轴这些特殊方位角.此方法不用建立标准图库就可以实现熊猫光纤特殊方位角的定轴.     

结合会聚束电子衍射和高分辨电子显微术来测定十四铌酸锂的结构

我们在一台有0.4nm点分辨率的分析透射电子显微镜上,结合会聚束电子衍射(CBED)和高分辨电子显微术(HREM)研究了十四铌酸锂的结构。CBED结果证明十四铌酸锂的空间群是C2/m,HREM结构象表明十四铌酸锂是由4×4氧八面体方块组成,方块中3×3通道及八面体中心的金属原子可以清楚地看到,其距离是0.38nm。结合CBED和HREM来做结构分析是发展电子晶体学的重要的一步。 关键词：     

Optical properties of chiral photonic crystals with an anisotropic defect layer

Properties of defect modes in chiral photonic crystals with an anisotropic defect are considered. The influence of the defect layer thickness, its location in the crystal and orientation of its optical axis, as well as of the chiral photonic crystal thickness on the properties of defect modes is studied. It is shown that at certain values of the defect layer thickness the medium loses its main property, namely, the polarization dependence of the diffraction reflection. At certain thicknesses of the defect layer this system transforms from the source of the right circular polarization into the source of the left circular polarization, if the layer position in the chiral photonic crystal changes.