Crystal optics for hard-X-ray spectroscopy of highly charged ions

A twin crystal-spectrometer assembly, operated in the focusing compensated asymmetric Laue geometry has been developed for accurate spectroscopy of fast highly charged heavy ions in the hard-X-ray region. Coupled to the focusing crystal optics is a specially developed two-dimensional position-sensitive X-ray detector which is necessary for retaining spectral resolution also for fast moving sources. We summarize the crystal optics and demonstrate the usefulness of the instrument for spectroscopy of both stationary and fast moving X-ray sources. Results are reported from several tests employing a ¹⁶⁹Yb gamma-ray source and the Lyman radiation of one-electron Pb⁸¹⁺ ions traveling at a velocity corresponding to β ≡ v/c ≈ 0.59. The features of the instrument presented may be useful in many applications where it appears difficult to make the leap from conventional X-ray energy measurements to wavelength-dispersive spectroscopy based on crystal optics.     

A Probe of Valence and Conduction Band Electronic Structure of Lead Oxide Films for Photodetectors

We investigate how the electronic structure of amorphous lead oxide (a-PbO) films deposited on ITO substrate is changed after annealing at various temperatures. Both experimental soft X-ray spectroscopic and density functional theory (DFT) based computational techniques are used to explore the electronic structure of this material. X-ray emission, resonant X-ray inelastic scattering, and X-ray absorption spectroscopic techniques are employed to directly probe the valence and conduction bands. We discover that the films are very stable and remain amorphous when exposed to temperatures below 300 °C. An amorphous-to-polycrystalline (α-PbO phase) transformation occurs during annealing at 400 °C. At 500 °C, an alpha to beta phase change is observed. These structural modifications are accompanied by the band gap value changing from 1.4±0.2 eV to 2.0±0.2 eV upon annealing at 400 °C and to 2.6±0.2 eV upon annealing at 500 °C. A difference between surface and bulk structural properties is found for all samples annealed at 500 °C and above; these samples also exhibit an unexpected suppression of O : 2p density of states (DOS) near the bottom of the conduction band, whereas additional electronic states appear well within the valence band. This study provides a significant step forward to understanding the electronic properties of two polymorphic forms of PbO needed for optimization of this material for use in X-ray sensors.     

X-Ray Absorption Spectroscopy on Free Molecules

The most recent spectroscopic method that can be applied to chemical problems is X-ray absorption spectroscopy, in which the excitation of individual core electrons of an atom is studied. The analysis of the spectra with the aid of simple theoretical models yields information both about the core orbitals of the atom and about the unoccupied molecular orbitals, from which various molecular properties can be deduced. These not only include charge distribution, electronic configuration, geometry, and spatial and energy characteristics of orbitals of the molecule under investigation; one can also obtain parameters of radicals (such as stability, bond length, ionization potential, and electronic excitation energy) that differ from the molecule under investigation in that the nuclear charge of one atom is one unit higher.     

Characterization of Calcium Oxalate Hydrates and the Transformation Process

Calcium oxalate can be found in humans as kidney stones and in cultural heritage as films in two crystallographic species, dihydrate (COD/weddellite) and/or monohydrate (COM/whewellite). Due to its instability, COD is transformed into COM. Studying this crystalline conversion provides information about the origin of the monohydrated species, which will help in the assessment of prevention measurements to avoid their formation. In the present study, the synthesis of calcium oxalate hydrate microcrystals has been carefully performed to avoid mixture of phases in the final products; the long and short range order structure of both species have been studied by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS), respectively. This structural information was considered in the density functional theory (DFT) computational study performed to assign the characteristic vibrational IR and Raman frequencies found. This detailed characterization allows an unambiguous assignment of the vibrations, thus providing the appropriate parameters required to monitor and characterize the transformation process.     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 5. Novel complexes of asymmetric polydentate macrocyclic Schiff bases. Step-by-step synthesis

Reactions of 2,6-bis(3-aminopropylaminocarbonyl)pyridine (1) with 4-tert-butyl-2,6-diformylphenol and 2,5-diformylpyrrole in the presence of Ba(ClO₄)₂ in EtOH afford barium complexes with asymmetric macrocyclic Schiff bases as soft and hard ligands. The reaction of compound 1 with Cu(OCOCMe₃)₂ involves closure of a tetrahydropyrimidine ring to give a mononuclear complex, which was structurally characterized by X-ray diffraction analysis.     

Influence of coordination on N-H X hydrogen bonds. Part II. Zn(NH3)2Br2 and Ni(NH3)2X2 (X is Cl and Br)

Microcrystalline samples of Zn(NH₃)₂Br₂ and Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻) have been investigated from 100 to 293 K using X-ray diffraction and IR spectroscopy measurements (range 400–4000 cm⁻) performed with isotopically dilute (5% deuterated) samples. Values of Δν(ND)/ΔT for all compounds hint at the existence of hydrogen bonds. Zn(NH₃)₂Br₂ shows The dynamics of ammonia molecules even at 100 K, and no indications are apparent that dynamic disorder of ammonia molecules takes place in Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻). A comparison between octahedrally coordinated ammoniates [Ni(NH₃)₆]Br₂, Ni(NH₃)₂Br₂ and [Zn(NH₃)₆]Br₂ with tetrahedrally coordinated ones [Zn(NH₃)₂Br₂] leads to the conclusion that the lower coordination number increases the strength of the hydrogen bonds. Because this effect is small, it is not possible to separate the influence of the type of coordinating ions for one coordination number from the influence of the coordination number itself.     

Raman spectroscopy and structural properties of InxBi40−xSe60 system

In_xBi_40−xSe₆₀ (x = 1.6, 4.4, 7, 10 and 13.2) alloys were synthesized by melt-quenching technique. The X-ray diffraction and Raman spectroscopy investigations confirm that the materials are in single phase. Archimedes method and Energy Dispersive Spectroscopy (EDS) have been used for density and chemical characterization of the obtained materials. Indium content dependences of different parameters such as the density (D), the compactness (δ), and the average coordination number (Z) have been investigated and discussed in light of chemical order network and topological models.     

Mercury L3 and sulfur K-edge studies of Hg-bound thiacrowns and back-extracting agents used in mercury remediation

Effective methods for the removal of mercury from water are in demand due to the high levels of mercury released from industrial and natural processes. Polymer pendant thiacrown compounds used for the sequestration of Hg(II) from aqueous solutions passed through columns have shown great promise as effective tools for remediation. The mercury can potentially be removed from the columns by extraction with diethyldithiocarbamate (dtc) and diphenylthiocarbazone, aka dithizone (dtz). In this study, Hg L3 and sulfur K-edge X-ray absorption spectroscopy are used to contrast the structure of the mercury thiacrown complex Hg[17]aneS5 with the structure of mercury bound to two potential back-extracting agents, Hg(dtc)₂ and Hg(dtz)₂. In Hg(dtc)₂, it was found that Hg(II) was bound to four sulfur atoms, with two Hg-S bond lengths of 2.66 Å and two Hg-S at 2.49 Å. In Hg(dtz)₂, Hg(II) was bound to two sulfur atoms with Hg-S bond distances of 2.38 Å and two nitrogen atoms with Hg-N at 2.54 Å. This contrasts with Hg[17]aneS5 with three Hg-S bonds at 2.40 Å. Mercury L3 and S K-edge results show that electron density shifts from sulfur in dtc and dtz, to mercury in Hg(dtc)₂ and Hg(dtz)₂.The increase in the number of bonds, and the more stable geometry and electron distribution in the back-extraction complexes confirms that these compounds are more stable than the mercury thiacrown complex, and thus suitable for regeneration of the pendant-arm [17]aneS₅ for further remediation processes.     

二价钇配位化合物的ESCA的表征

本文用钇的3P_(1/2)和3P(3/2)的间距及3P能级的半高宽(FWHM)的变化以及￥4s能级的多重分裂确定了新合成的有机金属化合物的价态。在铝靶上,利用轫致辐射诱导的俄歇谱,对高动能的YL_3M_(45)M_(45)峰(大约1737eV)进行了研究,进一步验证了钇的价态。这与X射线衍射的结果相互补充。     

In-Situ/Operando X-ray Characterization of Metal Hydrides

In this article, the capabilities of soft and hard X-ray techniques, including X-ray absorption (XAS), soft X-ray emission spectroscopy (XES), resonant inelastic soft X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), and their application to solid-state hydrogen storage materials are presented. These characterization tools are indispensable for interrogating hydrogen storage materials at the relevant length scales of fundamental interest, which range from the micron scale to nanometer dimensions. Since nanostructuring is now well established as an avenue to improve the thermodynamics and kinetics of hydrogen release and uptake, due to properties such as reduced mean free paths of transport and increased surface-to-volume ratio, it becomes of critical importance to explicitly identify structure-property relationships on the nanometer scale. X-ray diffraction and spectroscopy are effective tools for probing size-, shape-, and structure-dependent material properties at the nanoscale. This article also discusses the recent development of in-situ soft X-ray spectroscopy cells, which enable investigation of critical solid/liquid or solid/gas interfaces under more practical conditions. These unique tools are providing a window into the thermodynamics and kinetics of hydrogenation and dehydrogenation reactions and informing a quantitative understanding of the fundamental energetics of hydrogen storage processes at the microscopic level. In particular, in-situ soft X-ray spectroscopies can be utilized to probe the formation of intermediate species, byproducts, as well as the changes in morphology and effect of additives, which all can greatly affect the hydrogen storage capacity, kinetics, thermodynamics, and reversibility. A few examples using soft X-ray spectroscopies to study these materials are discussed to demonstrate how these powerful characterization tools could be helpful to further understand the hydrogen storage systems.     

DSC and TSDC Study of Unsaturated Polyester Resin. Influence of the promoter content

This work reports on the curing kinetics of unsaturated polymer resins (UPRs) cured with styrene, studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. The data lead to determination of the experimental conditions with which to obtain a fully cured material and open the way for study of the relaxation phenomena by means of thermally stimulated depolarization current analysis (TSDC). In relaxation studies on fully cured resins, the TSDC spectra revealed important overlapping of the main relaxation peak with an extra upper peak. The importance of this extra peak a priori prevents further analysis of the main relaxation. To identify the origins of this peak (space charge or other), the purity of the resin was checked by X-ray fluorescence spectroscopy. The use of UPR specimens with different compositions (in terms of the resin/activator/initiator ratio) demonstrated that the bulk of the impurities Cl, K, Ca, Sr, Zr and Ba are due to the promoter. Decoupling of the mixed peaks (α-relaxation and extra) revealed that the a peak is independent of the proportion of the promoter in the resin and that the extra peak is principally due to the presence of these impurities. This revised version was published online in July 2006 with corrections to the Cover Date.     

唐代彩绘陶俑中无机颜料的化学组成

采用X射线粉末衍射（XRD）、X射线荧光光谱（XRF）和扫描电子显微镜-能谱（SEM-EDS）等测试技术对西安西曹M16唐墓出土的2尊唐代彩绘陶俑颜料进行了化学组成分析。结果表明,陶俑中含有丰富的无机颜料,其中红色颜料的显色成分为铅丹（Pb₃O₄）;白色颜料的显色成分为铅白（PbCO₃）和石灰石（CaCO₃）;粉色颜料的主要显色成分为铅丹和铅白的混合物;青色颜料为铜绿（Cu₂（OH）₂CO₃）和青石（Cu₃（OH）₂（CO₃）₂）混合物。     

X-ray photoelectron spectroscopy of boron compounds

The results of X-ray photoelectron (XPS) studies of boron compounds (predominantly boron hydrides and their derivatives — 49 compounds) are presented. The results are analyzed to form a representative set of XPS data for the boron element.     

X-ray photoelectron spectroscopic studies of the charged state of 3d metal ions in CuCr1?xVxS2 (x = 0–0.4)

The charged state of the 3d metal ions in layered cation-substituted disulfides CuCr_1−x V _x S₂ was studied by X-ray photoelectron spectroscopy. An analysis of the energy positions and structure of the Cu2p _3/2 and Cr2p _3/2 X-ray photoelectron lines showed that the corresponding polycrystalline samples of CuCr_1−x V _x S₂ contained mixed-valence chromium and copper ions. It was shown that the charged states of chromium and copper ions depended on the concentration of vanadium cations (x). The presence of mixed-valence Cu¹⁺ and Cu²⁺ ions in CuCr_1−x V _x S₂ may be correlated with the crystal structure of the corresponding layered disulfides. Original Russian Text Copyright ? 2009 by L. N. Mazalov, V. V. Sokolov, N. A. Kryuchkova, E. I. Vovk, I. Yu. Filatova, and G. M. Abramova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 461–467, May–June, 2009.     

砷化镓半导体表面自然氧化层的X射线光电子能谱分析

用X射线光电子能谱(XPS)，测量了Ga3d和As3d光电子峰的结合能值，指认了砷化镓(GaAs)晶片表面的氧化物组成，计算了表面氧化层的厚度，定量分析了表面的化学组成；比较了几种不同的砷化镓晶片表面的差异。结果表明：砷化镓表面的自然氧化层主要由Ga2O3、As2O5、As2O3和单质As组成，表面镓砷比明显偏离理想的化学计量比，而且，氧化层的厚度随镓砷比的增大而增加；溶液处理后，砷化镓表面得到了改善。讨论了可能的机理。