In-situ study of precipitates in Al–Zn–Mg–Cu alloys using anomalous small-angle x-ray scattering

In the present work,the precipitate compositions and precipitate amounts of these elements（including the size distribution,volume fraction,and inter-precipitate distance） on the Cu-containing 7000 series aluminum alloys（7150 and 7085 Al alloys）,are investigated by anomalous small-angle x-ray scattering（ASAXS） at various energies.The scattering intensity of 7150 alloy with T6 aging treatment decreases as the incident x-ray energy approaches the Zn absorption edge from the lower energy side,while scattering intensity does not show a noticeable energy dependence near the Cu absorption edge.Similar results are observed in the 7085 alloy in an aging process（120℃） by employing in-situ ASAXS measurements,indicating that the precipitate compositions should include Zn element and should not be strongly related to Cu element at the early stage after 10 min.In the aging process,the precipitate particles with an initial average size of ~ 8 ？A increase with aging time at an energy of 9.60 ke V,while the increase with a slower rate is observed at an energy of 9.65 ke V as near the Zn absorption edge.

The Significance of Solutions Obtained from Ill-Posed Systems of Linear Equations Constituted by Synchrotron Radiation Based Anomalous Small-Angle X-Ray Scattering

Synchrotron radiation based experimental techniques known as Anomalous Small-Angle X-ray Scattering (ASAXS) provide deep insight into the nanostructure of uncountable material systems in condensed matter research i.e. solid state physics, chemistry, engineering and life sciences thereby rendering the origin of the macroscopic functionalization of the various materials via correlation to its structural architecture on a nanometer length scale. The techniques constitute a system of linear equations, which can be treated by matrix theory. The study aims to analyze the significance of the solutions of the stated matrix equations by use of the so-called condition numbers first introduced by A. Turing, J. von Neumann and H. Goldstine. Special attention was given for the comparison with direct methods i.e. the Gaussian elimination method. The mathematical roots of ill-posed ASAXS equations preventing matrix inversion have been identified. In the framework of the theory of von Neumann and Goldstine the inversion of certain matrices constituted by ASAXS gradually becomes impossible caused by non-definiteness. In Turing’s theory which starts from more general prerequisites, the principal minors of the same matrices approach singularity thereby imposing large errors on inversion. In conclusion both theories recommend for extremely ill-posed ASAXS problems avoiding inversion and the use of direct methods for instance Gaussian elimination.

Real-time pore structure evolution difference between deep and shallow coal during gas adsorption:A study based on synchrotron radiation small-angle X-ray scattering

Coal seam CO_(2) sequestration is an important option to address global warming.A better knowledge on coal pore structure evolution during gas adsorption can provide guidance for coal seams CO_(2) seques-tration.However,few investigations on the pore structure evolution differences between the deep and shallow coal were conducted during gas adsorption.In this study,based on the real-time synchrotron radiation small-angle X-ray scattering(SAXS)observation,the average pore diameter and pore surface fractal dimension evolution differences between deep and shallow coal were investigated from the as-pects of coal compositions and stress history.Two types of coal deformation(inner-swelling and outer-swelling)coexist during gas adsorption.Coal compositions have significant impact on the dominance of deformation type.The dominance of inner-swelling in deep coal is induced by the higher ash contents,and there is the decrease of average pore diameter during gas adsorption.The impact of stress-history(burial depth)on adsorption-induced deformation is more prominent than that of gas adsorption ca-pacity.In deep coal,the surface fractal dimension evolution presents a negative correlation with the evolution of pore diameters.In shallow coal,the surface fractal dimension evolution presents a Langmuir-type correlation with the adsorption time.

DETERMINATION OF THE SPECIFIC INNER SURFACE OF CRYSTALLINE-AMORPHOUS TWO-PHASE SYSTEM BY SMALL-ANGLE X-RAY SCATTERING

The specific inner surface, S_p, of the crystalline-amorphous 2-phase system inCu_(73)Sn_6Ni_6P_(15) metallic glass, aged at 473 K, was determined by small-angle X-ray scatteringand wide-angle X-ray diffraction. The experimental results show that the specific innersurface decreases from 144 m^2/cm^3 to 96 m^2/cm^3 as aging period increases from 5 min to 4 h.The error of S_p values is about 7%.

光学表面的X射线异常散射现象

研究了用掠入射散射法测量光学表面散射分布实验中存在的异常散射现象。首先,介绍了实验装置,并用原子力显微镜(AFM)测量了样品的表面粗糙度,给出了工作波长为0.154nm时不同样品在不同掠入射角下的表面散射分布。然后,分析了异常散射角与临界角的关系。最后,对影响散射强度的因素进行了分析。实验结果表明:当掠入射角大于临界角时能观测到光学表面的异常散射现象。在波长一定的情况下,异常散射角与样品材料有关,与掠入射角和表面粗糙度无关;异常散射角略小于临界角,误差变化为-8.6%～-0.9%。另外,镜像反射强度随着入射角和表面粗糙度的增大而迅速减弱,但异常散射强度与镜像反射强度的比值(峰值比)反而随着掠入射角或表面粗糙度的增大而增大,其比值在0.012～2.667变化。结果证明样品的材料和表面形貌是影响异常散射分布的两个重要因素。

Determination of specific surfaces of silica xerogels by SAXS

Small angle X-ray scattering (SAXS) with synchrotron radiation as X-ray source has been used to study the structure of silica xerogels prepared by sol-gel process. Both the agreement of SAXS profiles with and the deviation from Porod’s law and Debye’s theory have been found, showing that there are differences between the structures of these xerogels. The specific surfaces of the samples whose SAXS profiles agreed with Porod’s law and Debye’s theory have been determined by analyzing SAXS data according to the methods of Porod and Debye, respectively, and the results of both methods used were found to be similar. We have proposed the corresponding Porod and Debye analysis methods to determine the specific surfaces of samples whose SAXS profiles do not agree with Porod’s law and Debye’s theory, i.e. the negative or positive deviation. The results of both methods used here were also found to be close to each other. The specific surfaces fell between approximately 80-150 m2/cm3 for the samples prepared

BN(110)弛豫表面电子结构的理论研究

本文利用形式散射理论的格林函数方法 ,采用考虑最紧邻的sp3s 模型描述体带 ,计算了BN(110 )面的电子结构 .分别给出了理想表面和驰豫表面的投影带结构和波矢分辨的层态密度 ,并进行了较详细的讨论 .结果表明 :BN(110 )面的电子结构与大多数Ⅲ Ⅴ族和Ⅱ Ⅵ族半导体的 (110 )面的电子结构定性上是类似的 .但在各表面态的能级位置、色散特性和轨道特性等方面均有较大的差别 .

Tunable perpendicular anisotropic magnetoresistance in CoO/Co/Pt heterostructures

Transport properties of magnetron-sputtered CoO/Co/Pt heterostructures were investigated by physical property measurement system.Different types of magnetoresistance are observed in the heterostructures,including isotropic anisotropic magnetoresistance(AMR),AMR with geometric size effect,and interfacial effect.A reversal in sign of perpendicular AMR is found in the film CoO(3 nm)/Co(3 nm)/Pt(3 nm)compared to the film CoO(3 nm)/Co(3 nm)/CoO(3 nm),which is associated with Pt.Moreover,perpendicular AMR is tunable in the films CoO(3 nm)/Co(3 nm)/CoO(t)/Pt(3 nm)and CoO(3 nm)/Co(3 nm)/Pt(t)/CoO(3 nm)at will,with either positive or negative value,by varying the inserting layer thickness.The electronic structure information of the samples was measured by X-ray photoelectron spectroscopy(XPS).The spin-related transport and XPS results manifest that magnetic proximity effect,surface scattering,together with oxygen migration contribute to the tunable function of Pt.

Lamellar thickness transition of melt-crystallized polybuten-1 tetragonal phase: configurational change in chain folding directions

Lamellar crystal thickness lc of isotactic polybutene-1(it-PB1)have been investigated for crystal-lization in the melt over a wide range of crystallization temperature T from 40°C to 90°C by small angle X-ray scattering experiments and density measurements.The crystal thickness lc demonstrates two linear dependences on inverse supercooling and a transition from one dependence to the other has been observed around T=65°C.Each of the two dependences obeys the nucleation theory in the high and low supercooling ranges,respec-tively.Chain folding free energy q determined from the low supercooling range is larger than that determined from the high supercooling range.Possible mechanisms for the transition are discussed taking account of entropy of chain folding directions.

金属微结构圆柱中损耗无关的异常散射

考虑一种工作在太赫兹波段且被广泛研究的表面带有周期性亚波长金属槽人工微结构的金属圆柱,通过在部分凹槽中引入损耗,研究材料损耗对金属微结构圆柱散射特性的影响和规律。研究发现:在某一频率处,无论损耗如何改变,整体金属微结构圆柱的吸收截面始终几乎为零。散射场分布和本征模式分析表明,这一损耗无关的异常散射是由于微结构存在一个由对称性破缺导致的无损耗束缚态,该束缚态的电场主要分布在没有损耗的凹槽中,而有损耗的凹槽内基本没有电场。本研究为基于带损耗金属微结构圆柱的高性能光子器件提供了一种新的方法。