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。     

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射线成像术(下)

该文的前半部分(本刊上一期)已扼要介绍了X射线成像的三种衬度机制及成像设备各主要组件的构造,下半部分将继续介绍应用各种衬度的不同的成像方法和一些实例。     

材料分析中合理使用各种试验研究方法（续）

6．2．2基于吸收衬度的成像术的主要应用领域 6．2．2．1人体的X射线透视检查 人体的X射线透视检查使用钨靶发出的连续X射线，因此吸收系数涉及到不同元素和不同波长的X射线，吸收系数的严格计算相当复杂。然而，不管人体器官的组成如何复杂，只要存在吸收差异，     

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     

同步辐射与分析测试

本文介绍一种大科学装置——同步辐射装置。这是一种数百人可同时在其上进行不同的科学技术实验的设备，其可达到的水平比实验室的极限水平高许多，从某些角度代表了国家的科学和技术水平。本文扼要介绍了同步辐射的特性，同步辐射装置的构造及一些主要的分析测试技术，如：X射线吸收精细结构光谱，X射线散射，高分辨X射线衍射，能量色散与时间分辨技术，聚集与微分析，成像与显微放大，综合测试原位测试及作铯对标定等。     

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（三）

5基于相位衬度的成像术及其应用 5．1相位衬度原理 当X射线通过一个样品时,它的振幅因为X射线被吸收而减弱,它的位相由于样品不同部分的相速差异而发生偏移,见图13。波前因为位相偏移而产生畸变,这意味着光波传播方向的改变,见图14,箭头表示位相的梯度方向。下面将证明这种畸变的波面能以可观察的强度变化显示出来。     

纳米二氧化钛表面组成及其微结构分析技术进展

介绍了纳米TiO2表面组成，微结构分析技术近年来的进展，光电子能谱技术包抱X光电子能谱（XPS）和俄歇光电子能谱（AES），光谱分析技术包括红外光谱（IR）和Raman光谱，显微分析技术中有扫描隧道显微镜（STM），原子动力显微镜（AFM）及扫描和透射电子显微镜（SEM，TEM），X射线分析技术主要是X射线衍射（XRD）。     

18.2nm正入射显微成像系统滤光片的研究

18．2nm正人射显微成像系统用多层膜可极大地提高18．2nm的反射率，但它对紫外、可见和红外光也产生很高的反射。显微成像系统用的激光等离子体光源会在红外到敦X射线产生大量的辐射，18．2nm正入射显微系统用的胶片对所有光谱都十分敏感。因此，182nm正人射显微成像系统需要用滤光片滤除不需要的光辐射并对18．2nm的软X射线有较大的透射比，这样才能获得18．2nm的软X射线像。本文讨论了18．2nm正入射显微成像系统用滤光片的设计、制作及其特性。为了去除滤光片膜中的应力，用交替蒸镀Al和C多层膜的方法来制备法光片，铝和碳膜是用磁控溅射法制备的。针孔透过率和成像实验表明，所制备的滤光片满足了18．2nm正入射显微成像系统对滤光片的要求，并且为进一步制备其他薄膜滤光片打下了基础。     

基于毛细管的X射线显微成像系统可行性

本文设计并实现了一套X射线毛细管特性研究实验平台,用于研究准直毛细管光学器件加入前后成像系统在射线调制及成像方面表现出的不同特性,涉及光强放大比、平行度、空间分辨力、对比度等方面,分析了毛细管在调制X射线及其成像特性方面的优势和劣势,实现对显微CT领域应用可行性的研究.在光强增益方面,准直毛细管可以对入射射线增益至50倍以上;其出射射线发散角在2.2 mrad左右,与理论值相契合;因毛细管结构及原理问题,其空间分辨力相比锥束射线有所降低;图像对比度在加入毛细管之后有了显著提高.     

Bimetallic iron and cobalt incorporated MFI/MCM-41 composite and its catalytic properties

The MFI/MCM-41 composite material with bimetallic Fe and Co incorporation was prepared using templating method via a two-step hydrothermal crystallization procedure. The obtained products were characterized by a series of techniques including powder X-ray diffraction, N₂ sorption, transmission electron microscopy, scanning electron microscope, H₂ temperature programmed reduction, thermal analyses, and X-ray absorption fine structure spectroscopy of the Fe and Co K-edge. The catalytic properties of the products were investigated by residual oil hydrocracking reactions. Characterization results showed that the FeCo-MFI/MCM-41 composite simultaneously possessed two kinds of stable meso- and micro-porous structures. Iron and cobalt ions were incorporated into the silicon framework, which was confirmed by H₂ temperature programmed reduction and X-ray absorption fine structure spectroscopy. This composite presented excellent activities in hydrocracking of residual oil, which was superior to the pure materials of silicate-1/MCM-41.     

水相中CdSe与核/壳CdSe/CdS量子点的制备与发光特性研究

以巯基乙酸为稳定剂在水相中制备了CdSe与核/壳型CdSe/CdS量子点水溶胶, 用紫外-可见吸收光谱和发射光谱研究了它们的发光特性, 并且用X射线粉末衍射(XRD)、透射电镜(TEM)和X射线光电子能谱(XPS)表征了它们的结构、形貌和化学组成, 结果表明使用该方法制备的量子点分散性良好, 而且用CdS对CdSe进行表面修饰以后的发光强度明显提高, 发射光谱和吸收光谱都有红移现象, 不同粒径颗粒的吸收峰的位置也有所不同.     

氧化铟纳米立方块的合成及其自组装膜

以乙酰丙酮铟为前驱体,在不同的有机溶剂中进行溶剂热反应,得到棱角规则清晰、尺寸可控的立方相氧化铟纳米立方块,通过X射线粉末衍射（XRD）、透射电子显微镜（TEM）等对产品进行详细表征,采用层层自组装技术,将氧化铟纳米立方块自组装戍厚度可控的薄膜,UV-vis吸收光谱强度的线性增长为多层膜组装提供了证据,且对氧化铟纳米立方块及其自组装薄膜的光致发光光谱进行了测试。     

铜掺杂纳米二氧化钛颗粒的相变研究

采用溶胶-凝胶法制备铜掺杂的纳米二氧化钛颗粒。应用X射线衍射(XRD)、透射电子显微镜(TEM)、扫描透射电子显微镜(STEM)、X射线光电子能谱(XPS)和紫外-可见分光光度计(UV-Vis)技术对纳米二氧化钛颗粒的物相组成、平均晶粒尺寸、微观结构、化学态及光吸收性能进行表征。结果表明:Cu掺杂抑制TiO_2的相变,在650℃时Cu的氧化物CuO在TiO_2颗粒表面出现,掺杂的Cu离子以Cu^+的形式存在。掺杂Cu的TiO_2光吸收带边显著红移,随着Cu掺杂量的提高,样品光吸收度提高,随着温度的升高,样品紫外-可见光光谱吸收带边红移。     

Size dependent ferromagnetism in dodecyl amine capped ZnO nanoparticles

We investigated the size dependent ferromagnetism in dodecyl amine capped zinc oxide nanoparticle. X-ray diffraction and X-ray photoelectron spectroscopy analysis demonstrated that density of oxygen vacancies was enhanced due to an increase in compressive strain concomitant with the decrease in particle size. Magnetic measurements showed increased ferromagnetic ordering in ZnO nanoparticles with reduced particle size. It was also found that the increase in coercive field, saturation magnetization and magnetic hysteresis loop area were invariably associated with increased oxygen defect population. The observed ferromagnetism in organic capped zinc oxide nanocrystals has therefore been assigned to defect induced phenomena. Results of sample characterization using optical absorption spectroscopy, photo luminescence spectroscopy and high resolution transmission electron microscope have also been presented.     

Synthesis and characterization of SnS/ZnO nanocomposite by chemical method

SnS nanorods and SnS/ZnO nanocomposite have been synthesized by chemical method. Structure and phase purity of the samples were confirmed by powder X-ray diffraction. Transmission electron microscope image of SnS nanorods showed the average diameter of nanorods was about 85 nm and length was several micrometers. Transmission electron microscope image of SnS/ZnO nanocomposite showed the average particle size of ZnO nanoparticle was about 12 nm. The formation of SnS/ZnO nanocomposite was confirmed by elemental analysis using energy dispersive X-ray spectroscopy. From the microRaman spectrum of SnS/ZnO nanocomposite, it was observed that the intensity of B_2g mode of SnS nanorods decreased dramatically compared to that of pure SnS nanorods, since the surface of the SnS nanorods were coated with ZnO nanoparticles. Both direct and indirect band gap transitions were observed for SnS nanorods from the optical absorption spectrum and the optical absorption spectrum of SnS/ZnO nanocomposite showed absorption in the visible region.     

Synthesis and characterisation of organic-modified inorganic nanorods

Gold and cadmium sulphide nanorods with aspect ratios ≈5 were synthesised in quantities of several hundred milligrams via surfactant-driven seed-mediated processes. Such nanorods then underwent surface-modification processes in which the surfactant coating was at least partially replaced with both commercially available alkanethiols and synthesised organic molecules with the intention of forming hybrid organic–inorganic nanorods capable of exhibiting liquid crystalline-like ordering. An increase in the localised alignment of functionalised nanorods was observed in transmission electron microscope images. Additional characterisation of these novel hybrid molecules has been performed using polarised optical microscopy, differential scanning calorimetry, energy dispersive X-ray spectroscopy, nuclear magnetic resonance and UV-Visible absorption spectroscopy.     

Preparation of PbSe nanoparticles by electron beam irradiation method

A novel method has been developed by electron beam irradiation to prepare PbSe nanoparticles. 2 MeV 10mA GJ-2-II electronic accelerator was used as radiation source. Nanocrystalline PbSe was prepared rapidly at room temperature under atmospheric pressure without any kind of toxic reagents. The structure and morphology of prepared PbSe nanoparticles were analysed by X-ray diffraction, transmission electron microscope and atomic force microscope. The results indicated that the obtained materials were cubic nanocrystalline PbSe with an average grain size of 30 nm. The optical properties of prepared PbSe nanocrystalline were characterized by using photoluminescence spectroscopy. The possible mechanism of the PbSe grain growth by electron beam irradiation method is proposed.     

Preparation, characterization and photocatalytic properties of Cu-loaded BiVO(4)

A series of Cu-loaded BiVO(4) (Cu-BiVO(4)) catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS) and special surface area. The photocatalytic activities of Cu-BiVO(4) catalysts for the degradation of methylene blue (MB) were found to depend largely on the Cu content and the calcination temperature. The optimum Cu loading and calcination temperature were found to be 5 at.% and 300 degrees C, respectively. The results of XPS and SEM analysis indicated that Cu, CuO in this case, was dispersed on the surface of BiVO(4). The results of DRS analysis showed that the Cu-BiVO(4) series catalysts had significant optical absorption in the visible region between 550 and 800 nm and found that the absorption intensity increased with the enhancement of Cu content. An efficient N-demethylation of MB using Cu-BiVO(4) catalyst (5 at.% Cu content) calcined at 300 degrees C was also observed.     

Efficient strategy to Cu/Si catalyst into vertically aligned carbon nanotubes with bamboo shape by CVD technique

Bamboo-shaped vertically aligned carbon nanotubes (bs-VACNTs) were fabricated on Cu/Si catalyst by chemical vapour deposition (CVD) technique under the atmospheric pressure. The catalytic material (Cu/Si) played a vital role in attaining bs-VACNTs, which is synthesized by drop cast method in a cost-effective manner. Using this catalytic support, we have achieved the tip growth bs-VACNTs at low temperature with well graphitization. The as-grown carbon material was then characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) analyzer, high-resolution transmission electron microscope (HRTEM) and Raman spectroscopy. XRD technique confirms the formation of hexagonal graphitic carbon planes of carbon nanotubes (CNTs). The surface morphology of the material was characterized by SEM, which clearly infer vertically aligned CNTs. The nature, diameter and crystallinity were noticed by HRTEM and Raman spectroscopy, respectively. Further, we have also studied the electrochemical properties of the bs-VACNTs and it seems to be proved as highly electroconductive when compared to multi-walled carbon nanotubes (MWCNTs).