Changes in the near-edge X-ray absorption fine structure spectra of long-chain diacetylene derivatives through photopolymerization in Langmuir–Blodgett films

Photopolymerization of cadmium 10,12-pentacosadiynoate (CdDA) in Langmuir–Blodgett (LB) films, with the molecular packing well arranged by moderate preannealing, was investigated with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Greenish films of polydiacetylene with an absorption wavelength of 705 nm were obtained through the photopolymerization of preannealed monomer LB films, and this resulted in an extended π-conjugate system based on the well-ordered monomer in a two-dimensional arrangement. The electronic structures of the polydiacetylenes were found to be correlated to the variation of the molecular arrangements in the films from the changes in the NEXAFS spectra through photopolymerization in the LB films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2329–2336, 2004     

Structural and Chemical Analysis of Materials with High Spatial Resolution

 An understanding of the correlation between microstructures and properties of materials require the characterization of the material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen and on the scattering power of the atoms (ions) present in the analyzed column. The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the electron charge density distribution of the bulk (defect-free) material. The different techniques are described and applied to different problems in materials science. It will be shown that nearly atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments in electron microscopy instrumentation will result in atomic resolution in the foreseeable future.     

NaAlH4 表面Ti催化空间构型和X射线吸收光谱: Car-Parrinello分子动力学和密度泛函理论研究

通过采用Car-Parrinello分子动力学方法对掺杂Ti前后的NaAlH₄(001)2×2×1超晶胞表面晶体在333 K(60 ℃)温度条件催化脱氢的空间构型做了理论研究,发现掺杂Ti的合金中AlH₄团的其中两个Al—H键长分别从约1.64 (1 =0.1 nm)增大至1.74和1.93 ,而未掺杂合金表面中AlH₄团的4个Al—H键长基本不变,这意味着掺杂Ti相对未掺杂的合金更易于放氢.但在模拟温度条件下并未发现Ti-Al成键趋     

Sulfur speciation in two typical soil samples using X-ray absorption near-edge structure spectroscopy and chemical fractionation

Sulfur K-edge X-ray absorption near-edge structure spectroscopy and chemical sequential extraction was respectively used to study the speciation of sulfur in two sulfur-rich soils samples. Sulfur K-edge X-ray absorption near-edge structure spectroscopy analysis obtained a variety of spectra. Spectral fitting of the X-ray absorption near-edge structure spectra utilizing a large set of model compounds showed great differences between these two sulfur-rich soil samples. It was found that both of the soil samples had high sulfur content (8.40 and 11.57?g?kg^?1, respectively). Chemical extraction results suggested that sulfur mainly existed as organic in the ancient paddy soil (7.37?g?kg^?1) and more reduced sulfur was identified in it. X-ray absorption near-edge structure spectroscopy also got similar results. These organic forms of sulfur existed in organic matter across a range of oxidation states. There was high proportion of oxidized sulfur in the sulfuric acid plant that mainly existed as sulfate.     

A theoretical study of the oxygen K-edge near-edge X-ray absorption ne structure of N2O/Ir(110)

A multiple-scattering cluster method is employed to calculate the oxygen K-edge near-edge X-ray absorption fine structure of N₂O/Ir(110) and its monolayer. Two peaks and one weak resonance appear in both cases. The selfconsistent field DV-X calculations of the peaks and resonance show that the physical origin of the pre-edge peak x is different from those of the main peak 1 and the other weak resonance σ₁. This setup is intrinsic to the N₂O monolayer, owing to the interaction between the neighbouring molecular chains in the monolayer and partly to the adsorbed atomic oxygen, according to both the theoretical and experimental data.     

A review on speciation of iodine-129 in the environmental and biological samples

As a long-lived beta-emitting radioisotope of iodine, ¹²⁹I is produced both naturally and as a result of human nuclear activities. At present time, the main part of ¹²⁹I in the environment originates from the human nuclear activity, especially the releases from the spent nuclear fuel reprocessing plants, the ¹²⁹I/¹²⁷I ratios have being reached to values of 10⁻¹⁰ to 10⁻⁴ in the environment from 10⁻¹² in the pre-nuclear era. In this article, we review the occurrence, sources, inventory, and concentration level of ¹²⁹I in environment and the method for speciation analysis of ¹²⁹I in the environment. Measurement techniques for the determination of ¹²⁹I are presented and compared. An overview of applications of ¹²⁹I speciation in various scientific disciplines such as radiation protection, waste depository, and environmental sciences is given. In addition, the bioavailability and radiation toxicity (dose to thyroid) of ¹²⁹I are discussed.     

Synthesis,structure, and X-ray absorption spectra of LixNbO2 and NaxNbO2 (x ≤ 1)

The two series of compounds, Li_xNbO₂ and Na_xNbO₂, were synthesized from LiNbO₂ and NaNbO₂ with oxidizing agents. From neutron diffraction, it is concluded that the Li position is fully occupied for x = 1. Even though the long-range crystal symmetry does not seem to change for x < 1, as monitored by Guinier X-ray powder patterns, the Nb? L_III XANES spectra exhibit significant spectral variations with x which reflect changes in the unoccupied d-density of states.     

X射线吸收谱研究碳纳米管内Rh-Mn纳米粒子结构的变化

利用X射线吸收谱技术研究了负载于多壁碳纳米管内的Rh-Mn纳米粒子在不同气氛和温度下的结构. 结果表明,Rh-Mn粒子在空气中是由氧化铑团簇和混合锰氧化物组成. 经过氢气在300 ℃下还原后,混合锰氧化物种转化成MnO. 而氧化铑团簇在He气氛下当温度达到250 ℃时就会发生分解而形成金属铑团簇. 对形成的铑团簇用H₂或CO进行热处理,发现其分散性随温度升高而提高; 同时,X射线吸收谱实验没有观察到Mn和Rh之间存在显著的相互作用,助剂Mn的主要作用是提高了Rh的分散性.