纳米材料的同步辐射研究

近年来,科学家们在纳米材料的生长及应用研究等诸多方面取得了巨大的进展.然而,由于受到表征手段的限制,纳米科技领域的许多关键科学问题至今仍未得到清楚的解答.同步辐射具有多种独特优点,随着国内第三代同步辐射光源的逐步发展,基于同步辐射的各种实验技术将为实时、原位、动态地表征纳米结构提供功能强大的研究平台.文章简单介绍了基于同步辐射的一些新型纳米结构表征技术,并根据作者的研究举例说明了同步辐射技术在纳米材料研究方面的一些优势.     

纳米材料的同步辐射研究

近年来,科学家们在纳米材料的生长及应用研究等诸多方面取得了巨大的进展.然而,由于受到表征手段的限制,纳米科技领域的许多关键科学问题至今仍未得到清楚的解答.同步辐射具有多种独特优点,随着国内第三代同步辐射光源的逐步发展,基于同步辐射的各种实验技术将为实时、原位、动态地表征纳米结构提供功能强大的研究平台.文章简单介绍了基于同步辐射的一些新型纳米结构表征技术,并根据作者的研究举例说明了同步辐射技术在纳米材料研究方面的一些优势.     

同步辐射技术在无序合金结构与性能研究中的应用

同步辐射装置作为大科学装置和多学科的实验平台,已成为物质结构,特别是无序物质结构研究最有效、最先进的手段之一.文章简单介绍了同步辐射技术在研究无序合金结构、液态合金结构、非晶多形态相变以及块体金属玻璃力学行为等方面的应用.随着第三代的上海同步辐射光源（SSRF）的建立,国内用户利用先进的同步辐射技术开展研究又多一个选择, 相信上海光源对中国科研的发展将起到积极的推动作用.     

同步辐射技术在无序合金结构与性能研究中的应用

同步辐射装置作为大科学装置和多学科的实验平台,已成为物质结构,特别是无序物质结构研究最有效、最先进的手段之一.文章简单介绍了同步辐射技术在研究无序合金结构、液态合金结构、非晶多形态相变以及块体金属玻璃力学行为等方面的应用.随着第三代的上海同步辐射光源(SSRF)的建立,国内用户利用先进的同步辐射技术开展研究又多一个选择,相信上海光源对中国科研的发展将起剑积极的推动作用.     

X-ray magnetic scattering

The magnetic scattering of synchrotron X-rays has been developed to the point where it is now a standard technique for the study of magnetism and magnetic materials, often complementing neutron investigations of magnetic structures. In this article, after a brief historical introduction, examples of experiments on lanthanide and actinide antiferromagnets are presented. X-ray diffraction and Compton scattering studies of ferromagnets are then considered. Finally future prospects and possibilities are discussed.     

小角X射线散射表征非晶合金纳米尺度结构非均匀

表征纳米尺度结构非均匀对于理解非晶合金的变形、弛豫等动力学行为至关重要.受时空尺度限制,非晶合金纳米尺度结构非均匀的实验表征具有很大的挑战性.本文针对一种典型的锆基非晶合金,开展了同步辐射小角X射线散射原位拉伸实验.通过对散射曲线的定量分析,揭示了非晶合金在纳米尺度的非均匀结构图像.首先,Porod散射曲线呈现正偏离行为,表明非晶合金属于非理想两相散射体系,两相界面弥散且任一相内都存在电子密度涨落.基于散射曲线的Guinier定律分析,进一步揭示非晶合金中散射体形状远偏离球形,其特征尺度主要分布在0.8—1.6 nm之间,且在弹性变形阶段几乎不变.最后,通过Debye相关函数分析,发现这些纳米尺度散射体仅在1 nm之内存在强关联,符合非晶合金短程有序、长程无序的结构特征.研究结果表明非晶合金中存在具有复杂空间分布的纳米尺度非均匀结构.     

Dynamics of water intercalation fronts in a nano-layered synthetic silicate: A synchrotron X-ray scattering study

We performed synchrotron X-ray scattering studies of the dynamics of the water intercalation front in a Na–Fluorohectorite clay. Like other smectite clays, fluorohectorite particles can swell due to intercalation of successive water layers. Monitoring the intensities of Bragg peaks of the known 1- and 2-water-layer hydration states at different positions in the sample enabled spatial and temporal measurement of the proportions of the different hydration states. From experiments with controlled temperature and an imposed humidity gradient on a quasi one-dimensional powder sample, we were able to localize the intercalation front and demonstrate that the width of this front was smaller than 2 mm after penetrating 9 mm into the sample. The speed at which the intercalation front advanced through the sample during the diffusion process was shown to decrease with time. The diffraction signature of random water intercalation in the vicinity of the intercalation front also provided information on the changes in the water content of the mesopores around clay particles.     

Degree of structural perfection of icosahedral quasicrystalline grains investigated by synchrotron X-ray diffractometry and imaging techniques

A study of the structural perfection of icosahedral quasicrystalline grains of various alloys (Al-Pd-Mn, Zn-Mg-RE (RE L rare earth) and Al-Cu-Fe), grown by different slow solidification techniques (Czochralski, Bridgman, flux and annealing) was performed using high-resolution diffraction, including recording rocking curves combined with X-ray topography and phase contrast radiography, at a third-generation synchrotron radiation source (European Synchrotron Radiation Facility, Grenoble, France). For Al-Pd-Mn, additional coherent diffraction and diffuse scattering measurements were also carried out. After evaluating the potentialities of the techniques used, in the light of the criteria defined for crystals, it is shown that the structural perfection of icosahedral quasicrystals is quite comparable with that of metallic crystals but is considerably influenced by either uniform phason strains which can destroy the quasiperiodic long-range order, or by long-wavelength phason fluctuations leading to diffuse scattering. The structural perfection was also found to be extremely variable across the as-grown quasicrystalline grains and to be dependent on the presence and characteristics of inhomogeneities (pores and precipitates) often included in the quasicrystalline matrix. Regarding the grains that we used, it has been impossible to distinguish a clear influence of either the type of alloy or the growth method. It has, however, been noticed that Al-Pd-Mn and Al-Cu-Fe grains appeared less defective than Zn-Mg-RE grains and that the microstructure of these latter grains looks like that of crystals grown by the same technique. Annealing and mechanical polishing effects have also been analysed in the case of Al-Pd-Mn grains. It appeared that annealing improves the quasicrystalline lattice perfection by lowering phason strains insofar as no precipitates are nucleated. Mechanical polishing can introduce defects, located at the external surfaces, having the shape of bands.     

Coherent soft X-ray magnetic scattering

X-ray sources are exceptional tools for studying the structure of matter down to atomic-length scales, but across a wide range of fields there are samples that have remained notoriously difficult to study, such as airborne particles, particles in solution, membrane proteins, and macromolecular complexes. The advancement of imaging techniques to address these elusive samples has been a big motivation for constructing new X-ray light sources. Fourth-generation light sources, commonly called X-ray free-electron lasers (XFELs) [1 Madey, J. 1971. Journal of Applied Physics, 42: 1906–1913. [Crossref], [Web of Science ®] , [Google Scholar]], represent a huge step forward, with upwards of nine orders of magnitude increase in peak brightness for hard X-rays. As of 2012, four such XFELs are already productively operational (in Germany [2 Ackermann, W. 2007. Nature Photonics, 1: 336–342. [Crossref], [Web of Science ®] , [Google Scholar]], the U.S. [3 Emma, P. 2010. Nature Photonics, 4: 641–647. [Crossref], [Web of Science ®] , [Google Scholar]], Japan [4 Ishikawa, T. 2012. Nature Photonics, 6: 540–544. [Crossref], [Web of Science ®] , [Google Scholar]], and Italy [5 Allaria, E. 2012. Nature Photonics, 6: 699–704. [Crossref], [Web of Science ®] , [Google Scholar]]), with at least five more planned for the next 10 years. These lasers produce femtosecond pulses of extremely intense coherent radiation through the positive feedback between a co-moving electron bunch and the radiation it emits when they traverse an extended undulator. This process creates remarkably strong, tunable probes that will undoubtedly change the way we examine nanoscale structure and dynamics.     

Element specific magnetism with resonant X-ray magnetic scattering

Beam line X29 of the National Synchrotron Light Source (NSLS) has been operating for a year for macromolecular crystallography (PX) research, employing a mini-gap, in-vacuum undulator as its X-ray source. Development of this facility involved a close collaboration among the groups of Mark Chance (Case Proteomics Center, Case Western Reserve Univ. [CWR]), Erik Johnson [NSLS], and Robert Sweet (Macromolecular Crystallography Research Resource [PXRR] of BNL's Biology Dept.).

There were several joint objectives and complexities to this project. Firstly, we hoped to provide an undulator-based beam line with the attractive features of high collimation and high flux for macromolecular crystallography at the NSLS.     

Soft X-ray resonant magnetic scattering of magnetic nanostructures

Soft X-ray resonant magnetic scattering offers a unique element-, site- and valence-specific probe to study magnetic structures on the nanoscopic length scale. This new technique, which combines X-ray scattering with X-ray magnetic circular and linear dichroism, is ideally suited to investigate magnetic superlattices and magnetic domain structures. The theoretical analysis of the polarization dependence to determine the vector magnetization profile is presented. This is illustrated with examples studying the closure domains in self-organising magnetic domain structures, the magnetic order in patterned samples, and the local configuration of magnetic nano-objects using coherent X-rays. To cite this article: G. van der Laan, C. R. Physique 9 (2008).     

Investigation of craze development using small-angle X-ray scattering of synchrotron radiation

The development of crazes in polycarbonate was investigated with the method of ultra-small-angle X-ray scattering (USAXS) of synchrotron radiation. Measurements at different temperatures and with different draw rates were carried out. The two-dimensional scattering patterns were analyzed by means of a fibrillar model of the craze. The geometrical parameters of the craze as a function of the macroscopic draw ratio were determined by using a curve-fitting procedure. From the measured values of the diameter and the mean distance of the fibrils, it is possible to calculate the volume fraction v_f of the fibrils directly. Additional scattering caused by submicrocracks is discussed.     

Soft X-ray resonant magnetic scattering study of magnetization reversal in low dimensional magnetic heterostructures

Soft X-ray resonant magnetic scattering (SXRMS) has been used to investigate the microscopic magnetization reversal behavior of complex magnetic systems. SXRMS is a unique technique, providing chemical, spatial and magnetic sensitivity, which is not affected by external magnetic fields. The study of two selected thin magnetic heterostructures is presented, amorphous rare-earth transition metal alloys and perpendicular exchange coupled antiferromagnetic/ferromagnetic films. In the first system, the internal structure of magnetic stripe domains on nanometer length scales is obtained by measuring bi-dimensional (2D) scattering images. In the second system, the element specificity is exploited to identify the role of the uncompensated spins in the antiferromagnetic layer on the exchange coupling phenomena. Future trends are also discussed.     

Complementary application of neutron and synchrotron X-ray scattering to the determination of the magnetic microstructure of exchange-coupled layered nanoheterostructures

Complementary neutron and synchrotron X-ray scattering techniques have been considered as applied to the investigation of an inhomogeneous magnetic microstructure typical of exchange-coupled nanoheterostructures consisting of alternating ferromagnetic and antiferromagnetic metal layers. It has been demonstrated that changes in magnetic moments in both the magnitude and the direction within ferromagnetic layers can be determined by combining polarized neutron and resonant X-ray magnetic reflectometry, and those within antiferromagnetic layers, by combining X-ray and neutron diffractometry.     

X-ray lithography with synchrotron radiation

Manufactures of silicon integrated circuits increasingly rely on high resolution, high throughput, and litography techniques based on parallel mask projection. The once simple technique of projecting an image of a mask on a wafer, however, is now being replaced by more elaborate systems at an ever faster rate. Of the possible successors to photolithography in the production of structures smaller than 0.7 m, the most promising appears to be X-ray litography with synchrotron radiation. The development problems of this new technique are related to the mask technology, alignment systems, resist materials, and compact, low-cost storage rings.     

The beauty of non-resonant X-ray magnetic scattering

The Canadian Light Source's 11^th Annual Users' Meeting (AUM), held June 9 and 10 in Saskatoon, marked several firsts for the regular gathering of the Canadian synchrotron community. It was the first time the meeting was held in conjunction with an international meeting hosted by the CLS, sharing joint workshops with the Fifth International MEDSI workshop and 15^th Pan-American SRI conference. In addition, for the first time all of the papers presented at the AUM described results obtained with data from the CLS.     

Resonant X-ray magnetic scattering has gone soft

The Linac Coherent Light Source [1] (LCLS) at SLAC National Accelerator Laboratory is preparing for the arrival of its first scientific users in the fall of 2009. LCLS is the world's first free-electron in the spectral range 800?8,000?eV, producing intense, sub-picosecond pulses of Xrays with very high spatial coherence. The accelerator facility has been commissioned in stages, beginning in April 2007 [2] with the injector linac and culminating in December 2008 [3] with the first transport of electrons through the complete beam path. On April 10, 2009, the LCLS Project team was rewarded for years of planning, design, construction, and checkout with a dream-come-true: as undulators were placed on the beam path one-by-one, the laser simply turned on without drama in the course of one hour [4]. First visible evidence of light amplification at 8,000?eV was observed on a fluorescent screen with ten undulators in place, at which point a highly collimated spot of X-rays could be discerned in the center of the spontaneous radiation pattern. After just four days of further checkout, the intensity of this spot increased smoothly and exponentially to the threshold of “saturation” at full power with just 20 of 33 undulators in place. The commissioning team was faced with a mixture of shock and euphoria. The Project team has spent years focused on everything that could possibly go wrong, and what to do about each concern. Speaking for myself, I found I was mentally unprepared for the special case of NOTHING going wrong! In fact, a critical aspect of the FEL performance was significantly better than design goals—the gain length (the distance the electron beam must travel in undulators to increase X-ray power by a factor e) proved to be just 3.5 meters. With this gain length, and room for 33 undulators in the tunnel, we find we have ten more spares! The shutter was closed at about midnight, temporarily preventing the electron beam entering the undulator. At 8:00 A.M. the next morning, the shutter was retracted to reveal the FEL producing an 8,000?eV laser beam without need for operator intervention.     

A simulation study of Tsinghua Thomson scattering X-ray source

Thomson scattering X-ray sources are compact and a?ordable facilities that produce short duration, high brightness X-ray pulses enabling new experimental capacities in ultra-fast science studies, and also medical and industrial applications. Such a facility has been built at the Accelerator Laboratory of Tsinghua University, and upgrade is in progress. In this paper, we present a proposed layout of the upgrade with design parameters by simulation, aiming at high X-ray pulses flux and brightness, and also enabling advanced dynamics studies and applications of the electron beam. Design and construction status of main subsystems are also presented.