用红外光和X射线组合研究光与物质相互作用

美国科学家首次用红外光与X射线激光的组合,在原子尺度上研究光与物质的相互作用.这种技术是使用红外光和X射线照射同一个钻石样品.部分红外光被钻石的价电子吸收,其能量又转移给一些从样品散射出的X射线.由此,研究人员能够将与价电子相互作用的X射线和从样品原子的壳层内的电子散射的X射线区分开.X射线衍射技术是利用从物质原子周围的电子云散射的X射线,可以给出大量关于物质结构和成分的     

圆形阵列法在能谱测量中的应用

在高能闪光照相技术中,高能X射线的能谱测量一直是一个难点。在以往研究方法的基础上,指出控制散射的影响程度是提高能谱测量精度的关键。提出采用圆形阵列法对X射线能谱进行测量,并针对一特定能谱的X射线设计了测量装置,蒙特卡罗模拟结果表明,可以将散射的影响控制在4%以内,这对提高能谱测量精度具有十分重要的意义。     

用双探测器系统实现实验室EXAFS测量

扩晨X射线吸收谱(FXAFS)是用于研究凝聚态物质原子近邻结构的一种有效方法.它既可用于研究晶态物质,又可以用于研究非晶态物质及液体.由于不同元素的吸收边能量不同,所以可通过改变人射X射线能量,对不同种类原子分别进行测量。取得不同仲类原子各自周围的结构信息,因而这种方法     

中性红共振光散射法测定脱氧核糖核酸

本文基于脱氧核糖核酸 (DNA)对有机染料中性红的共振光散射的增强效应 ,拟订了一种测定DNA的共振光散射法。在pH 5 0～ 7 0范围内 ,有机染料中性红在DNA分子表面进行长距组装导致共振光散射增强。在 335 0nm处的共振光谱散射增强程度与DNA浓度呈线性关系 ,其线性范围为 0～ 6 0 0ng·mL-1,检出限可达 12 8ng·mL-1。该方法简便、快速 ,具有较高的灵敏度和准确度。将该方法用于混合样品中DNA的测定 ,结果令人满意。     

紫外光下毛竹的自由基与光电子能谱分析

分析了紫外光照射下毛竹自由基的变化规律和表面化学组成及结构的变化.利用电子自旋共振波谱和X射线光电子能谱技术,分别测量紫外光辐照后毛竹颗粒的自由基波谱和X射线光电子能谱.结果表明:毛竹自由基的光谱分裂因子g=2.003 3,自由基的强度随着辐照时间按Y=1-e-b,Pt规律增加;紫外光照60 min后毛竹表面O/C原子比稍有增加,C-C和C-H含量增加,C-O和C=O含量减少,-O-C=O含量增加为原来的3倍左右,说明毛竹表面生成了一些含氧官能团或碳的氧化态增高.     

表面电子能量损失谱

表而电子能量损失谱是表面分析实验技术中较新的一种.这一方法是用具有高度单色性的低能电子束作为入射粒子束,来测量经晶体样品表面散射后的电子的能谱.在入射电子(设其能量为E0)被样品背向散射到真空中去的过程中,有可能激发起若干量子能量分别为 等的振动模,因而在散射谱中会出现能量分别为E1=E0- …等的一系列损失峰.这些振动模或者仅与衬底原子有关(如声子激发),或者同时与吸附在表面上的原子或分子有关.因此,通过对谱的分析可以得到关于表面结构、吸附物种类和吸附位置等许多重要信息. 在表面电子能量损失谱中所用的入射电子的动能…     

紫外光下毛竹的自由基与光电子能谱分析

分析了紫外光照射下毛竹自由基的变化规律和表面化学组成及结构的变化.利用电子自旋共振波谱和X射线光电子能谱技术,分别测量紫外光辐照后毛竹颗粒的自由基波谱和X射线光电子能谱.结果表明:毛竹自由基的光谱分裂因子g=2.003 3,自由基的强度随着辐照时间按Y=1-e^-b_iPt规律增加;紫外光照60 min后毛竹表面O/C原子比稍有增加,C-C和C-H含量增加,C-O和C=O含量减少,-O-C=O含量增加为原来的3倍左右,说明毛竹表面生成了一些含氧官能团或碳的氧化态增高.     

实现冷原子或冷分子囚禁的双层光阱列阵

提出了一种新颖的实现冷原子或冷分子囚禁的双层光阱方案,它由二元π相位板列阵和会聚透镜列阵所组成,用平面光波通过此光学系统时将在透镜焦平面两侧形成双层光阱.介绍了产生双层光阱的基本原理,分析了光阱光强分布、强度梯度等与光学系统参数间的关系,研究了双层光阱囚禁原子(或分子)的光学偶极势和自发散射速率(包括瑞利散射和拉曼散射)等.该方案不仅可用于多样品原子(或分子)的光学囚禁及全光型玻色一爱因斯坦凝聚(BEC),而且可用于制备新颖的双层2D光学晶格.     

拉曼光谱检测生物大分子损伤的研究进展

拉曼光谱是基于拉曼散射效应而发展起来的一种光谱分析技术,体现的是分子的振动或转动信息。由于拉曼光谱技术与常规化学分析技术相比,具有对样品无损、样品制备简单和所需样品量少等特点,广泛用于生物大分子结构变化的研究。拉曼光谱不仅可以用于蛋白质、核酸和脂类等生物大分子损伤的快速检测,而且可以用于癌症的诊断与手术治疗。通过对比正常组织与癌变组织的拉曼光谱,可以找到两种组织特征吸收峰的差异,从而为癌症的最终确诊和确定肿瘤切除范围提供重要信息。文章综述了拉曼光谱检测生物大分子损伤的研究进展,介绍了利用表面增强拉曼光谱、傅里叶变换拉曼光谱和紫外共振拉曼光谱等技术在检测蛋白质二级结构、膜脂及DNA损伤中的应用,并展望了未来拉曼光谱技术的发展前景。     

光电子能谱中的一些物理问题

近十几年来,现代能谱学领域又出现了光电子能谱学.由于它在表面组成和状态分析方面有巨大的潜力,引起了物埋学和化学工作者的广泛兴趣. 光电子能谱学的基本原理是光电效应:光照射样品,样品表面会光致电离放出光电子.五十年代以来,随着超高真空技术的发展以及电子能量分析器的灵敏度和分辨率的改进到六十年代末,七十年代初期光电子能谱仪开始商品化。开拓了有关电子能谱学的广泛研究和应用. 许多光谱的产生,如X光谱、俄歇谱等都要涉及到两个或三个束缚态电子的能级,而光电子的产生,只涉及一个束缚态电子的能级,即原子或分子中电于的某一能级…     

More power to X‐rays: New developments in X‐ray spectroscopy

Recent developments in X‐ray spectroscopy in the last decade are reviewed. A specific emphasis is placed on displaying the strong natural connection between X‐ray spectroscopy and materials science. Brief explanations of several X‐ray spectroscopic methods are given. X‐ray spectroscopic instruments such as table‐top X‐ray sources are discussed in detail, whereas those employing synchrotron and other sources are briefly addressed. The spectroscopic methods and results from materials investigations are reviewed according to their positions in a 3D parameter space of time, length, and energy. New experimental measurements on atoms, molecules, nanomaterials, and bulk materials that include insulators, semiconductors, metals and magnetic materials using both static and time‐resolved methods are reviewed.     

Quantitative speciation of manganese oxide mixtures by RIXS/RRS spectroscopy

Resonant inelastic X‐ray scattering, also named X‐ray resonant Raman scattering, was recently used to discriminate local chemical environments. By means of this novel technique, the speciation of samples could be attained in a variety of samples and experimental conditions. Until now, this discrimination methodology had been applied only to pure compounds, being the speciation possible by two different mathematical treatments. Nevertheless, the effectiveness/sensitivity of this technique has not been tested yet in samples containing mixtures of oxides of the same element. In this work, the first results of quantitative speciation of mixtures of manganese compounds, using resonant inelastic X‐ray scattering/X‐ray resonant Raman scattering spectroscopy, are presented. The results show that it is possible to discriminate and quantify oxide mixtures of the same element in slightly different proportions, allowing a quantitative speciation of compound mixtures in a variety of experimental conditions, presenting also several advantages over conventional spectroscopic techniques. Copyright © 2017 John Wiley & Sons, Ltd.     

An attempt at kidney stone analysis with the application of synchrotron radiation

X‐ray absorption near‐edge spectroscopy (XANES) is a spectroscopic technique using synchrotron light to determine the valence state of excited atoms as well as the electronegativity of their neighbouring atoms. XANES spectra can provide information about the chemical bond in the second coordination shell of the excited atom. In this study, XANES spectra of unknown compounds from human kidney stones were recorded around the K‐edges of sulfur, phosphorus and calcium. The XANES results agree well with the diffractogram data of the same stones obtained through an X‐ray powder diffraction (XRPD) technique. By comparing the measurement techniques presented here, it is shown that XANES requires a smaller amount of each sample than XRPD for analysis.     

A new method to study complex materials in solid state chemistry: application to chalcogenide materials

We show that a combined application of Mössbauer spectroscopy and other experimental tools such as X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy and nuclear magnetic resonance provides a coherent picture of the local electronic structure in chalcogenide materials. In order to develop this idea we propose an analysis of the Sn, Sb and Te local electronic structures for three different systems of materials. The first example concerns the In–Sn–S system. We show that Li insertion in In₁₆Sn₄S₃₂ leads to changes of the Sn oxidation states from Sn(IV) to Sn(II). The second example concerns materials of the Tl–Sb–S system. We show that variations of the ¹²¹Sb Mössbauer isomer shift and surface of the first peak of the X‐ray absorption spectra at the Sb L_III edge can be linearly correlated because of the main influence of the Sb 5s electrons. This is explained by changes in the local environment of the Sb atoms. The last example concerns the crystalline phases of the Tl–Sn–Te system. The formal oxidation numbers of the Te atoms are determined from ¹²⁵Te Mössbauer spectroscopy and X‐ray photoelectron spectroscopy. They are related to the different types of bonds involving the Te atoms in the Tl–Sn–Te compounds.     

Application of kinoform lens for X‐ray reflectivity analysis

In this paper the first practical application of kinoform lenses for the X‐ray reflectivity characterization of thin layered materials is demonstrated. The focused X‐ray beam generated from a kinoform lens, a line of nominal size ～50 µm × 2 µm, provides a unique possibility to measure the X‐ray reflectivities of thin layered materials in sample scanning mode. Moreover, the small footprint of the X‐ray beam, generated on the sample surface at grazing incidence angles, enables one to measure the absolute X‐ray reflectivities. This approach has been tested by analyzing a few thin multilayer structures. The advantages achieved over the conventional X‐ray reflectivity technique are discussed and demonstrated by measurements.     

Resonant laser ablation of copper and its application in microanalysis

Resonant laser ablation (RLA) is a two-step process, occurring within a pulse of a tunable laser, in which the leading edge of the laser pulse ablates a solid surface to produce neutral atoms or molecules that are then resonantly ionized by the trailing edge of the same laser pulse. The sensitivity and selectivity of RLA allow detection and quantitation at very low concentrations. In our preliminary RLA research, a sub-ppm detection level has been reached for copper in a standard aluminium sample. In addition, the threshold and saturation effects of RLA have been observed.     

Laser nitriding investigated with Mössbauer spectroscopy

The effect of the nitrogen take‐up upon irradiation of iron or steel with excimer laser pulses in air or in nitrogen atmosphere is well established. The resulting phase compositions and nitrogen depth profiles were measured by a combination of simultaneous Conversion Electron Mössbauer Spectroscopy (CEMS), Conversion X‐ray Mössbauer Spectroscopy (CXMS), and Resonant Nuclear Reaction Analysis (RNRA) as a function of the nitrogen gas pressure during irradiation. A maximum nitrogen content and a maximum fraction of the ?-nitride was found at 0.1 MPa. This result is in accordance with hardness measurements performed by the nanoindentation technique.     

A new ultra‐high‐vacuum variable temperature and high‐magnetic‐field X‐ray magnetic circular dichroism facility at LNLS

X‐ray magnetic circular dichroism (XMCD) is one of the most powerful tools for investigating the magnetic properties of different types of materials that display ferromagnetic behavior. Compared with other magnetic‐sensitive techniques, XMCD has the advantage of being element specific and is capable of separating the spin and magnetic moment contributions associated with each element in the sample. In samples involving, for example, buried atoms, clusters on surfaces or at interfaces, ultrathin films, nanoparticles and nanostructures, three experimental conditions must be present to perform state‐of‐the‐art XMCD measurements: high magnetic fields, low temperatures and an ultra‐high‐vacuum environment. This paper describes a new apparatus that can be easily installed at different X‐ray and UV beamlines at the Brazilian Synchrotron Light Laboratory (LNLS). The apparatus combines the three characteristics described above and different methods to measure the absorption signal. It also permits in situ sample preparation and transfer to another chamber for measurement by conventional surface science techniques such as low‐energy electron diffraction (LEED), reflection high‐energy electron diffraction (RHEED), X‐ray photoelectron spectroscopy (XPS) and X‐ray photoelectron diffraction (XPD). Examples are given of XMCD measurements performed with this set‐up on different materials.     

Hybrid materials with an increased resistance to hard X‐rays using fullerenes as radical sponges

The protection of organic and hybrid organic–inorganic materials from X‐ray damage is a fundamental technological issue for broadening the range of applications of these materials. In the present article it is shown that doping hybrid films with fullerenes C₆₀ gives a significant reduction of damage upon exposure to hard X‐rays generated by a synchrotron source. At low X‐ray dose the fullerene molecules act as `radical scavengers', considerably reducing the degradation of organic species triggered by radical formation. At higher doses the gradual hydroxylation of the fullerenes converts C₆₀ into fullerol and a bleaching of the radical sinking properties is observed.