X射线成像术(上)

该文着重从衬度的形成讨论了X射线成像。介绍衬度生成的三种机制:吸收、位相变动和衍射。还介绍了成像设备的主要构成部件:X射线源(X射线发生器、直线加速器和同步辐射),各类探测器、像增强器与显示器,机械、控制与数据处理系统等;应用各种衬度形成的一些成像方法也作了简述,如利用吸收衬度的造影成像、数字减影和双色减影成像、计算机断层成像;利用相位衬度的干涉仪法、类同轴全息法和衍射增强法;利用衍射衬度的Lang透射法和Berg-Barrett反射法等,并用少量例子说明。     

X射线显微镜

主要介绍X射线显微镜的显微成像原理和几种类型X射线显微镜的基本构造、特点和应用实例。成像衬度可以是吸收衬度,也可以是相位衬度;显微镜可以是透射式的,也可以是扫描式的;还有一类将一些X射线光谱技术与显微镜结合的光谱显微镜,介绍了X射线吸收近边光谱、X射线磁圆二色谱和光电子发射谱与X射线显微镜的结合;另外,简要叙述X射线全息显微术。     

利用原子力显微镜低频声学模式观察氧化锌压敏电阻

介绍在商用原子力显微镜上建立的低频声学成像模式,并利用其对氧化锌压敏电阻陶瓷晶界处进行了弹性性能成像.声学像中晶界处微晶的衬度反映了添加物的分布.而晶界处的衬度增强现象可能说明样品经热处理后发生富铋相的相变.结果显示低频声成像的分辨率达到了纳米量级,在功能材料的微区力学性能表征方面具有良好的应用前景.     

X射线束点尺寸对X射线相位衬度成像的影响

X射线相位衬度成像利用X射线穿过样品后的相位变化,通过衍射信息来获得样品的结构特征。X射线相位衬度成像在生物影像、显微成像以及材料科学研究中有重要的应用。如果X射线成像样品物质密度比较低,它对X射线的吸收很小,所以常规的吸收衬度成像质量较差,不易分辨样品的结构细节。理论分析和实验研究都表明当X射线束点尺寸减小到一定尺度后,X射线源的空间相干性增强,采用相位衬度成像可以提高低密度样品的成像质量。X射线相位衬度成像质量与X射线束点尺寸,样品到影像记录平面之间距离直接相关。本文研究了X射线束点尺寸与低密度样品影像边沿轮廓宽度和对比度之间的影响关系。研究结果表明,根据低密度样品的介电常数、X射线源到样品距离,以及样品到影像记录平面距离,存在最优化的X射线束点尺寸。在该最优化配置条件下,低密度样品的X射线成像可以获得最好的图像质量。     

扫描透射电子显微镜(STEM)在新一代高K栅介质材料的应用

扫描透射电子显微镜(STEM)原子序数衬度像(Z-衬度像)具有分辨率高(可直接“观察”到晶体中原子的真实位置)、对化学组成敏感以及图像直观易解释等优点, 成为原子尺度研究材料微结构的强有力工具。本文介绍了STEM Z-衬度像成像原理、方法及技术特点, 并结合具体的高K栅介质材料 (如铪基金属氧化物、稀土金属氧化物和钙钛矿结构外延氧化物薄膜)对STEM在新一代高K栅介质材料研究中的应用进行了评述。 目前球差校正STEM Z-衬度的像空间分辨率已达亚埃级, 该技术在高K柵介质与半导体之间的界面微结构表征方面具有十分重要的应用。对此, 本文亦进行了介绍。     

包含光源面积的整体相位衬度调制传递函数

在部分相干光学理论的基础上,建立了一个整体相位衬度调制传递函数理论模型,模型中包含了光源焦点面积大小对X线相衬成像系统相位调制的影响,并通过数值模拟和数据计算,提出了X线相衬成像系统对光源焦点面积的选择原则,和焦点面积确定条件下的成像参数优化方法,结果表明,这种包含X线光源面积因素的相位衬度调制传递函数模型,更能反映整个系统的光学成像性能,更能有利于成像参数的优化设计。     

用于相位衬度CT成像的大型精密转台轴系设计与分析

针对X射线相位衬度CT（computed tomography,计算机断层扫描）成像的高分辨率、高稳定性要求,设计了大型精密转台。转台采用焊接结构和密珠轴系支撑,具有质量轻、阻力小、回转精度高的特点。介绍了转台轴系的结构设计和工艺路线,根据成像视野区允许的运动误差对轴系精度指标进行了分解。通过静态分析、惯性释放分析和模态分析研究了转台的静、动态性能并验证了其结构刚度的合理性,结合精度分析对轴系关键部件的几何误差进行了分配,误差综合结果满足指标要求。最后,对转台样机的轴系精度进行了检测,结果表明各项指标满足相位衬度成像要求。焊接结构的轻量化设计和轴系精度分析方法对大型转台轴系的研发具有一定的借鉴意义。     

同步辐射的基本知识 第五讲同步辐射中的成像术及其应用（二）

4．3衍衬成像术的应用 4．3．1缺陷应变矢量的测定 缺陷周围的应变场总是各向异性的,e^-i2π·R是因缺陷引人的附加相位因子。当衍射矢量与缺陷应变场的最大应变矢量平行时,衍射衬度最大,垂直时无衬度或消象。因此,可以通过改变衍射矢量的方法拍摄一系列衍射面的貌相图,     

原子级分散负载催化剂的扫描透射电子显微学研究

球差校正扫描透射电子显微镜(STEM)因其原子级的空间分辨率和元素解析能力,在纳米功能材料的结构和成分分析中得到广泛使用.扫描透射电子显微镜高角环形暗场像技术(STEM-HAADF)凭借独特的原子序数衬度(Z衬度)和电子通道效应,在负载型纳米催化剂的结构研究中有着显著优势.通过STEM-HAADF成像,研究人员不仅可以...     

同步辐射的基本知识——第五讲 同步辐射中的成像术及其应用（一）

1概述 自1895年Ronetgen发现X射线并获得第一张X射线照片之后,基于吸收衬度的成像术就逐渐成为医院临床检查诊断的重要手段,直至现代的人     

Direct tomography with chemical-bond contrast

Three-dimensional (3D) X-ray imaging methods have advanced tremendously during recent years. Traditional tomography uses absorption as the contrast mechanism, but for many purposes its sensitivity is limited. The introduction of diffraction, small-angle scattering, refraction, and phase contrasts has increased the sensitivity, especially in materials composed of light elements (for example, carbon and oxygen). X-ray spectroscopy, in principle, offers information on element composition and chemical environment. However, its application in 3D imaging over macroscopic length scales has not been possible for light elements. Here we introduce a new hard-X-ray spectroscopic tomography with a unique sensitivity to light elements. In this method, dark-field section images are obtained directly without any reconstruction algorithms. We apply the method to acquire the 3D structure and map the chemical bonding in selected samples relevant to materials science. The novel aspects make this technique a powerful new imaging tool, with an inherent access to the molecular-level chemical environment.     

On coherence in neutron imaging

The variety of imaging signals in neutron radiography and tomography became quite large compared to the pure absorption and scattering contrast in neutron radiographies and topographies in the early sixties or seventies of the last century. The diversity of absorption based techniques for neutron radiography and tomography is comparable to coherence based imaging techniques such as phase contrast, differential phase contrast, dark field imaging, diffraction enhanced contrast, refraction contrast, ultra small angle scattering contrast, grating interferometry and crystal interferometry, also the spin of the neutron was successfully used for imaging [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11] and [12]. We show which effects (total reflection, diffraction, refraction) contribute to e.g. a step boundary or a phase boundary. Taking this simple object, one can learn to understand the imaging procedure and what is displayed in a radiograph.     

New opportunities for 3D materials science of polycrystalline materials at the micrometre lengthscale by combined use of X-ray diffraction and X-ray imaging

Non-destructive, three-dimensional (3D) characterization of the grain structure in mono-phase polycrystalline materials is an open challenge in material science. Recent advances in synchrotron based X-ray imaging and diffraction techniques offer interesting possibilities for mapping 3D grain shapes and crystallographic orientations for certain categories of polycrystalline materials. Direct visualisation of the three-dimensional grain boundary network or of two-phase (duplex) grain structures by means of absorption and/or phase contrast techniques may be possible, but is restricted to specific material systems. A recent extension of this methodology, termed X-ray diffraction contrast tomography (DCT), combines the principles of X-ray diffraction imaging, three-dimensional X-ray diffraction microscopy (3DXRD) and image reconstruction from projections. DCT provides simultaneous access to 3D grain shape, crystallographic orientation and local attenuation coefficient distribution. The technique applies to the larger range of plastically undeformed, polycrystalline mono-phase materials, provided some conditions on grain size and texture are fulfilled. The straightforward combination with high-resolution microtomography opens interesting new possibilities for the observation of microstructure related damage and deformation mechanisms in these materials.     

Hydride formation under cathodic charging of titanium and TiAl-based alloys in alkaline solutions

The electrochemical methods and the data of X-ray diffraction analysis are used to determine the parameters of cathodic polarization for the hydrogenation of α-Ti and alloys based on the TiAl intermetallic phase without formation of the hydride phase or with formation of hydrides. In α-Ti, the increasing cathodic polarization in a 0.1 M NaOH solution leads to the dissolution of hydrogen in the metal lattice and its modification and to the increase in the amount of hydrides. The hydride phase is not recorded TiAl-based alloys even for much higher levels of absorption of hydrogen as compared with pure titanium. However, hydrogen affects the phase composition of alloys and the lattice parameters of the phases. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 103–106, May–June, 2008.     

Coherent diffractive imaging using short wavelength light sources

Techniques that recover images from diffraction data obtained using coherent short-wavelength light sources are currently under active development for applications in nanotechnology and structural biology. In this review, an outline of paraxial optics is provided in a form that is sufficiently general to incorporate the coherence properties and frequency structure of illumination sources used in diffractive imaging applications. The Fourier phase problem is formulated in the context of imaging algorithms that are designed to obtain uniquely-determined phase distributions from measurements of diffraction data. The properties of several iterative phase retrieval algorithms for both coherent and partially-coherent diffractive imaging applications are presented in a unified formalism, together with a brief discussion of a non-iterative technique. Approaches to diffractive imaging based on Fraunhofer and Fresnel diffraction configurations are compared. Applications are described utilising quasi-monochromatic third-generation synchrotron X-ray sources and polychromatic high-harmonic generation table-top soft X-ray sources. The review concludes with a consideration of proposed applications of diffractive imaging approaches to the determination of biomolecular structures from isolated molecules using fourth-generation X-ray free-electron laser sources.     

醇-水热法制备钇铝石榴石(YAG)纳米粉体

首先采用共沉淀法制备钇铝石榴石前驱体,然后以乙醇-水混合溶剂作为反应介质,在较低的温度(300℃)和压力(10MPa)下,制备分散性好的钇铝石榴石纳米粉体.并借助XRD,TEM,BET与IR等测试手段,对所制备样品的性能进行了表征.实验结果表明,在适当的醇-水比条件下可在较低的温度和压力下制备纯相的YAG纳米粉体,其粒度大约为20nm,分散性良好.并对YAG的醇-水热形成机理进行了初步探讨.     

A new approach to understanding the mechanisms of diffraction imaging of dislocations in X-ray topography

Regularities in the formation of diffraction imaging of dislocations are studied by numerical modeling and experimental section X-ray topography. The study of X-ray scattering by irregularities of the crystal lattice is of interest for several reasons. First, the contrast of defects is connected with the fundamental problem of development of a dynamic theory of X-ray scattering in real crystals. Second, knowledge of the special features of diffraction makes possible a qualitative and, in some cases, quantitative analysis of the X-ray diffraction contrast of defects in a crystal lattice (measurements of the deformation, determination of the sign and parameters of the Burgers vector, etc.).     

Acoustic signatures of submicron contrast agents

Previous studies have revealed that hard-shelled submicron contrast agents exhibit large relative expansions and strong acoustical echoes that can be observed experimentally, and predicted by theoretical simulations. In this paper, we study harmonic imaging and pulse-pair imaging techniques designed to assist in the differentiation of these contrast agents from tissue. For harmonic imaging, we apply a high-sensitivity, narrowband strategy that differentiates the microbubble from tissue based on the generation of strong harmonic echoes. For pulse-pair imaging, we apply high spatial resolution, wideband strategies using phase inversion, which relies on the frequency differences observed in response to phase-inverted pulses, and signal subtraction, which takes advantage of the amplitude differences in response to identical pulses. The bubble-to-phantom signal amplitude ratio in the absence of motion approaches 20 dB using phase inversion and 30 dB using signal subtraction; both techniques are robust for up to 50 microm of simulated motion. With the experience gained in these studies, we hope to advance the development of multi-pulse or shaped-pulse techniques that are optimized for specific clinical applications.     

The raman spectra and X-ray powder diffraction data of stabilized hafnia phases

Raman spectra and X-ray powder diffraction data were measured for various compositions of Y₂O₃-doped hafnia, and interpreted on the basis of the growth of a stabilized hafnia phase apparently possessing tetragonal distortion with increasing dopant concentration. In contrast to the results for pure zirconia, there was no evidence in the Raman spectra or powder X-ray diffraction patterns to indicate the formation of a small particle size-stabilized tetragonal hafnia phase when X-ray amorphous hafnium hydroxide was heated at 425–600°C.