软 X射线共振非弹性光散射及其应用

软 X射线共振非弹性光散射是近年来随着高亮度第三代同步辐射出现而发展起来的光散射光谱技术 ,可以用于对多原子构成的分子、凝聚态物质进行位置选择的价电子态结构的研究。与 X射线光电子能谱 ( XPS)或紫外光电子能谱 ( UPS)相比 ,这一光谱方法由于测量样品激发后产生的散射 X射线 ,因而不仅可以获得表面的原子分子信息 ,而且可以用于研究样品体内或掩埋薄层的原子分子。同时这一方法的共振特性使得其可以进行灵敏的元素选择测量。本文将介绍这一光散射光谱技术及其在原子分子物理、表面物理及凝聚态物理中的应用     

Reflective Optics for Hard X-ray Nanofocusing Applications at the ESRF

The advent of high-brightness X-ray light sources has provided the impetus for the development of focusing systems capable of yielding spatially resolved information from samples at length scales below 10 nm. Beams of such dimensions are fundamental elements in a range of instruments providing powerful analytical tools for a broad range of scientific domains including life, materials, chemical, environmental, and physical sciences. At the ESRF, particular efforts have been made towards the design and implementation of reflective optical systems capable of routine nanoprobe formation at hard X-ray wavelengths (0.1 nm and below) with resolutions in the sub-50 nm range. Often, one of the principal driving forces for the use of such systems is the capacity of reflective optics to deliver very high photon fluxes to the sample. For imaging applications at the ESRF, monochromatic photon fluxes in excess of 10⁸ph/s/nm² are achievable at energies above 15keV—typically 1–2 orders of magnitude greater than accessible with current alternative technologies. Of course, such performance is not straightforward to achieve and requires considerable care both in the manufacture and implementation of the mirror systems. In this article, we describe some of the technological characteristics and limits of these optics and report on the performance of some of the systems currently in service at ESRF beamlines.     

Resonant Inelastic X-ray Scattering: From band mapping to inter-orbital excitations

Resonant inelastic X-ray scattering (also known as resonant X-ray Raman spectroscopy when only valence and conduction states are involved in the final state excitation) has developed into a major tool for understanding the electronic properties of complex materials. Presently it provides access to electron excitations in the few hundred meV range with element and bulk selectivity. Recent progress in X-ray optics and synchrotron radiation engineering have opened up new perspectives for this powerful technique to improve resolving power and efficiency. We briefly present the basics of the method and illustrate its potential with examples chosen from the literature. To cite this article: J. Lüning, C.F. Hague, C. R. Physique 9 (2008).     

X-ray Optics at the ESRF

For nearly 20 years, the X-ray Optics Group of the ESRF has been playing a major role in the development of new X-ray optical systems, many of which are widely used at synchrotrons around the globe.     

Lattice Dynamics and Inelastic Nuclear Resonant X-Ray Scattering

Measurement of thermal and elastic properties of materials, like phonon density of states, specific heat or speed of sound, by a new X-ray scattering technique is presented. Inelastic nuclear resonant scattering of X-rays produced from new electron storage rings, coupled with advances in high-energy-resolution crystal optics and fast detectors has enabled the development of a new method of analyzing the energy loss in a scattering process with a resolution of 10⁷ or better in the X-ray region of 6–30 keV. Some unique aspects like element (isotope) selectivity, the amount of material needed for analysis (nanograms) and physical size that X-rays can be focused (5 micrometer or better) favors this approach over more established techniques of neutron scattering, Mössbauer, and Raman spectroscopy. Applications to several unique cases (e.g., multilayers and high pressure) are discussed.     

Looking Deeper: Angle-Resolved Photoemission with Soft and Hard X-rays

Traditional angle-resolved photoemission (ARPES) with excitation in the ca. 20 to 150 eV range has clearly evolved to be the technique of choice for studying the electronic structure of surfaces and complex new strongly correlated and magnetic materials. However, it is clear that ARPES with excitation only up to 150 eV or so remains a very surface-sensitive probe, thus necessitating careful in-situ sample treatment, cleaving, or even synthesis to avoid the measurement of surface-associated artifacts. A key measure of this surface sensitivity is the electron inelastic mean free path (IMFP orΛ_e), which measures the mean depth of electron emission without inelastic scattering, and both experimental [1 Offi, F., Iacobucci, S., Vilmercati, P., Rizzo, A., Goldoni, A., Sacchi, M. and Panaccione, G. 2008. Physical Review B, 77: 201101R[Crossref] , [Google Scholar], 2 Offi, F., Iacobucci, S., Petaccia, L., Gorovikov, S., Vilmercati, P., Rizzo, A., Ruocco, A., Goldoni, A., Stefani, G. and Panaccione, G. 2010. Journal of Physics: Condensed Matter, 22: 305002[Crossref] , [Google Scholar]] and theoretical [3 Tanuma, S., Powell, C. J. and Penn, D. R. 2011. Surface and Interface Analysis, 43: 689[Crossref], [Web of Science ®] , [Google Scholar]] IMFP studies showing that the only reliable way to increase bulk or buried layer/interface sensitivity for all material types is to go to higher photon energies in the soft X-ray (ca. 0.5–2 keV) or hard X-ray (ca. 2–10 keV) regime.     

Determination of Phonon Dispersion Curves at Gigapascal Pressures by Inelastic X-ray Scattering

The study of phonon dispersion curves of materials under hydrostatic pressure provides important information such as the evolution of sound velocities, elastic constants, interatomic potentials, phase transition mechanisms, etc. Until very recently, coherent inelastic neutron scattering was the only spectroscopic technique, which allowed performing these types of studies up to typically 10 GPa. Today, inelastic X-ray scattering with meV energy resolution provides a complementary spectroscopic technique, where, using diamond anvil cell techniques, pressures beyond 100 GPa can be reached.     

Nuclear Resonant Inelastic and Forward Scattering of Synchrotron Radiation by 40K

We achieved excitation of the first excited state of ⁴⁰K and confirmed both energy and lifetime. Furthermore, we observed nuclear resonant inelastic scattering by ⁴⁰K in a powdered KCl sample at room temperature using a high-resolution monochromator. The time spectrum of the nuclear resonant forward scattering was measured at 50 K. Our observations of nuclear resonant inelastic and forward scattering by ⁴⁰K make electronic and dynamic studies for potassium practical. The measurements of nuclear resonant scattering for the radioactive ⁴⁰K nuclide will enable and lead to further studies of other radioactive nuclides. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Coherent-Path Model for Nuclear Resonant Gamma-Ray Scattering: An Overview

Hyperfine Interactions - A “coherent-path” model for nuclear-resonant scattering of gamma radiation from resonant matter has been developed and is summarized here. The solution provides...     

表面特征与软X射线掠入射光学散射

介绍了短波段掠入射表面散射线性模型,并且根据这个理论,分析计算了不同的表面特征对软X射线掠入射光学散射特性的影响。实验发现:随着粗糙度的增加、自相关长度的减小,软X射线掠入射光学散射越来越严重。     

Resonant Raman Scattering of synchrotron X-rays by xenon: Test of angular and polarization dependence of RRS

Using monochromatized synchrotron radiation with variable photon energyE _i=33.94keV...34.54keV, Resonant Raman Scattering (RRS) by free Xenon atoms (B _1s=34.566keV) was investigated. The measured double-differential RRS cross sections are in excellent agreement with those calculated in the non-relativistic dipole approximation, modified by some relativistic corrections, and including the interference corrections predicted by Tulkki and Åberg. Within the experimental error of 5 % the RRS cross section is found to be independent of the scattering angle and of the polarization of the incident photons.     

User Training at SSRL: Crystallography,X-ray Absorption Spectroscopy,Small-Angle X-ray Scattering,and X-ray Scattering Techniques

The Stanford Synchrotron Radiation Lightsource (SSRL) is a national scientific user facility at the SLAC National Accelerator Laboratory that provides high-brightness X-ray beams, innovative experimental facilities, and expert scientific support as a resource to study our world at the atomic and molecular level. Operating within this context and being closely associated with a major research university (Stanford), SSRL is strongly committed to providing unique educational experiences, and serves as a vital training ground for future generations of scientists and engineers. As part of this program, SSRL oversees a series of schools and workshops each year which deliver theoretical, experimental, and hands-on training by leading experts in their respective fields. Several of the courses held this year, attended by graduate students, postdoctoral fellows, educators and junior/senior investigators, are described in this report.     

Resonant Raman Scattering of synchrotron X-rays by neodymium: Observation of fine structure in K-L-RRS and of K-N-RRS

Using monochromatized synchrotron radiation with variable photon energyE _i =43.01...43.35 keV, Resonant Raman Scattering (RRS) by Neodymium atoms (K-shell binding energyB _1s=43.57 keV) was investigated. For the first time the fine structure splitting in a K-L-RRS spectrum due to the energy difference of the L₂ and L₃ subshells was observed. In addition, the first observation of K-N-RRS in the spectrum of scattered photons is reported. The measured double-differential RRS cross sections are, on an absolute scale, in very good agreement with those calculated in the non-relativistic dipole approximation, modified by relativistic corrections.