The molecular structure and conformation of cellulose II (Fortisan) using accurate X-ray diffraction intensities

The previous Polymer Diffraction Symposium saw the use of x-ray film data array calculations to obtain diffraction intensities with computed accuracies. Subsequently, methods for geometrical deconvolution of overlapped diffraction spots have been developed. The techniques have now been applied to data arrays from films of Fortisan. Severely overlapped reflection arcs were splined and transformed into polar coordinate space, yielding orthogonalized diffraction spot groups. Spots were then identified     

Temperature dependent structure of spider silk by X-ray diffraction

We have investigated the structure of spider dragline silk by X-ray diffraction over a broad temperature range from room temperature up to thermal denaturation conditions. The dominating signal from the β-sheet crystallites is analyzed. Pronounced changes of scattering intensity starting at temperatures around 150 °C are observed. These changes are discussed in view of the respective lattice constants, crystal size, size distribution, crystallite number density and amino acid composition. PACS 87.68.+z; 87.15.-v; 87.64.Bx     

Crystal orientation in poly(ethylene 2,6-naphthalate) ultrathin films revealed by reflection-absorption infrared spectroscopy and grazing incidence X-ray diffraction

Crystal orientation of poly(ethylene 2, 6-naphthalate) (PEN) ultrathin films was investigated by the combination of reflection-absorption infrared spectroscopy (RAIR) and grazing incidence X-ray diffraction (GIXD) techniques. It is concluded that the main-chain of PEN molecule in ultrathin film is prone to alignment parallel to the substrate when compared with thicker films. During the formation of α form crystalline, the naphthalene ring, the CO group in molecular chain of PEN as well as the b axis in crystalline tend to take orientation more parallel to the substrate due to the surface-induced effect. However, such an anisotropic structure could not be observed in the bulk PEN.     

The structure of Ni(II)−Fe(III) hydroxy-chloride green rusts by Mössbauer spectroscopy and X-ray diffraction

The crystallographic structure of Ni(II)?Fe(III) hydroxy-chloride green rusts obtained by oxidation of a Fe_xNi_1?x(OH)₂ precipitate is isomorphous with that of the ferrousferric green rust one and independent of the value of P=Fe/Ni. Mössbauer spectra exhibit two quadrupole doublets after further oxidation of the compounds which correspond to a formula (3-x)Ni(OH)₂ · xFeOOH · Fe(OH)₂Cl. The Fe³⁺ ions are found to occupy preferentially the sites close to the Cl^? ions and the Ni²⁺ those far from them. However the ordering of the Fe³⁺ ions is not perfect.     

3D structure of dendritic and hyper-branched macromolecules by X-ray diffraction

The atomic ordering in dendritic and hyper-branched macromolecules has been determined by X-ray diffraction. The approach of the atomic pair distribution function technique has been used due to the lack of 3D periodicity in these polymeric materials. Dendrimers are found to possess a semi-regular structure riddled with nanosize cavities. The cavities are joined into channels connecting dendrimer's surface and core. In contrast, hyper-branched polymers are rather irregular at the atomic scale and with less accessible interior.     

Effects of proton irradiation on structure of NdFeB permanent magnets studied by X-ray diffraction and X-ray absorption fine structure

The effects of proton irradiation on the structure of NdFeB permanent magnet were investigated by X-ray diffraction and X-ray absorption fine structure (XAFS). The results reveal that proton irradiation has no effect on the long-range structure, but significantly affects the atomic local structure of the NdFeB magnet. The alignment degree of the magnet decreases and the internal stress of the lattice increases after proton irradiation. XAFS results show that the coordination number of Fe-Nd in the first neighboring coordination shell of the Fe atoms decreases and the disorder degree increases.     

The structure of solvated halide ions in dimethyl sulfoxide studied by Raman spectroscopy and X-ray diffraction

The solvation structure of chloride, bromide, and iodide ions, X⁻, in dimethyl sulfoxide (DMSO) has been investigated by using Raman spectroscopy and large angle X-ray diffraction under ambient conditions. The positively charged sulfur atom in DMSO interacts with X⁻ and slightly positively charged methyl groups in the coordinating molecules also interact with X⁻. The X⁻---S, X⁻···C, and X⁻···O distances are determined as follows: Cl⁻---S: 416, Cl⁻···C: 363, Cl⁻···O: 543, Br⁻---S: 433, Br⁻···C: 372, Br⁻···O: 544, I⁻---S: 437, I⁻···C: 374 and I⁻···O: 520 pm. The coordination numbers of DMSO molecules around the anions are six, seven and eight for Cl⁻, Br⁻ and I⁻ ions, respectively, with the uncertainty of ±1. Rather large uncertainties in the measured solvation numbers suggest large fluctuations in the solvation structure of the anions.     

Correlation of ferromagnetism and structure in Fe observed by high resolution X-ray diffraction

In order to find evidence of the ferromagnetic interaction, the crystal structure and the magnetic property of pure Fe are investigated from room temperature to 950 °C by measuring X-ray diffraction patterns and magnetizations. The ferro–paramagnetic transition occurs near 770 °C with large stretch and contraction of lattice constants, which is an evidence of correlation of ferromagnetism and crystal structure. The structural phase transition between α-bcc and γ-fcc is observed above 850 °C. The d-spaces between (011) and (101) planes, observed with a high resolution triple-axis X-ray diffractometer, differ at RT; Δd≡d₁₀₁–d₀₁₁≈0.45%. The structure of Fe is pseudocubic, showing a body-centered tetragonal structure of c/a<1 generated by magnetostriction (exchange striction) induced by spontaneous magnetization.     

X射线衍射的发现

简单介绍了埃瓦尔德(Ewald P P)、劳厄(von Laue M)和布拉格父子(Bragg W H及Bragg W L)在1912年发现X射线衍射方面的贡献．1911年埃瓦尔德在索末菲的指导下在慕尼黑大学从事博士论文研究，劳厄在与他的讨论中了解到晶格的平移周期与X射线的波长属于同一量级，因此想到在二维光栅的两个衍射方程组中再加一个类似的方程，就可以描述X射线在三维晶体中的衍射．在此假设的指导下，Friedrieh W和Knipping P在1912年4月开始用CuSO4后来用闪锌矿(立方ZnS)进行实验，很快就得到X射线衍射的证据．这不但证明了X射线的波动性，还确定了晶体的三维周期性．老布拉格在1912年夏得知这个消息，与他儿子小布拉格一道尝试用X射线的粒子性解释它，并由小布拉格在剑桥大学重复这个实验．根据衍射斑点的椭圆形状和从Pope与Below那里学到的晶格理论(由此得知ZnS具有面心立方晶格)，小布拉格将X射线在晶体中的衍射看作是X射线从一些晶格平面的反射，从而推导出著名的布拉格方程．布拉格父子开拓了X射线晶体结构分析这门新兴学科，从简单的无机化合物和矿物，逐渐发展到有机化合物和生物大分子．劳厄和布拉格父子分别强调慕尼黑和剑桥的优良科学环境对发现X射线衍射的重要性．鉴于埃瓦尔德在发现X射线衍射的作用及他后来在倒易格子及动力学衍射理论方面的贡献，不少晶体学家认为他也应获得诺贝尔物理奖．     

Thermal trapped iron(II) high spin state investigated by X-ray diffraction

The possibilities to trap by flash cooling the high spin (HS) state of iron(II) in the [Fe(PM-BiA)₂(NCS)₂] complex have been investigated by X-ray diffraction. This study reveals that trapping the HS state is possible under some conditions depending on the final temperature. If the latter is lower than the T(LIESST) temperature, the HS→LS (low spin) relaxation is slow enough to determine the trapped HS crystal structure by X-ray diffraction. The crystal structure of this complex in the 30 K trapped HS state shows differences from either the room temperature (HS) or the 30 K (LS) crystal structures, as for example differences in the strength of the S?H-C hydrogen bond like intermolecular interaction or the π-π interactions, known to play a crucial role in this compound for the propagation of the change in spin at the spin crossover (SCO), i.e. the cooperativity. The differences in intermolecular interactions are directly linked to the differences between the crystallographic unit cell modifications induced by pure thermal effects and those induced by the SCO.     

X-ray diffraction pattern of quasiperiodic (Fibonacci) Nb-Cu superlattices

1-D quasiperiodic Nb-Cu metallic superlattices have been prepared by magnetron sputtering. The X-ray diffraction pattern may be indexed by the projection method from the high-dimensional periodic structure.     

Analysis of a ZnO surface structure by a combination of leed and X-ray diffraction

The hexagonal LEED pattern obtained from a clean, reconstructed (0001)Zn face of a ZnO crystal could indicate either a (2 × 2) or a (√3 × √3) structure. We prove that we observed a (√3 × √3) pattern by identifying the line of h, h, $\text{2}$h, λ reflections from an X-ray diffraction photograph of the sample.     

X-ray diffraction investigation of the structure of propolis films

The structure of films of a biological organic material (propolis) on inorganic substrates is investigated for the first time. It is established that, despite the complex chemical composition (involving more than 300 different components), the propolis films prepared from an alcohol solution on amorphous glass substrates and on semiconductor substrates with a small number of dangling bonds have a crystal structure.     

Polymorphism and chevron layer structure of an antiferroelectric liquid crystal studied by X-ray diffraction

We report X-ray diffraction experiments performed on an antiferroelectric compound exhibiting a very rich polymorphism (). The structural study of the unknown phases only allows us to exclude some phenomenological models. The use of oriented planar samples prepared between solid glass plates generate by cooling from the phase a chevron structure of tilted layers already well characterized for the phase. The extensive analysis of the evolution of the chevron structure through the numerous smectic-smectic phase transitions provides some original information in three distinct areas: fundamental data on the important physical parameters in the chevron structure formation, detection of the smectic-smectic phases transition by small change of the chevron structure, and information on the local molecular order induced by the alignment layer (interaction with a rubbed polymer). Received: 13 November 1996 / Received in final form: 19 January 1997 / Accepted: 30 January 1998     

Orientation of adsorbed ethylene oxide on Ni(110) by X-ray photoelectron diffraction

The adsorption of ethylene oxide on Ni(110) was studied at 95 K and monolayer coverage by angle-resolved X-ray photoelectron spectroscopy. A slow radiation-induced decomposition at hv = 1486.7 eV to most likely methoxy was noted. The orientation of the adsorbed ethylene oxide was determined by measuring forward scattering enhancements in the O 1s intensity distribution. Peaks in polar (θ) as well as azimuthal (φ) scans occurred at four angular positions in 2π above the surface: (θ = 54°, φ = 36°, 144°, 216°, 324°). These positions were evaluated to yield the tilt angle of the molecule at 48°_relative to normal, and the COC bond angle of adsorbed C₂H₄O of about 57°. The molecule is tilted towards the [001] and [001&#x0304;] directions (two domains), with a mirror plane in the [001] azimuth.     

Liquid water structure from X-ray absorption and emission,NMR shielding and X-ray diffraction

Here we investigate to what extent X-ray absorption(XAS) and emission(XES) spectroscopy, the oxygen-oxygen radial distribution function and σ(~1H) and σ(~(17)O) NMR shielding can be represented by a common set of model structures of liquid water. This is done by using a Monte Carlo-based fitting technique which fits the spectra based on a library of ～1400 precomputed spectra and assigns weights to contributions from different model structures. These are then used to reweight the contributions from the structures in the library to reveal classes of structures that are over-or under-represented in the library. The goal is to include different experimental data sets which are sensitive to different aspects of liquid water structure and thus narrow down which types of structures must exist in the real liquid.     

Correlation between density and structure. in boron nitride thin films by X-ray diffraction

* _ion=100 eV. Above E^* _ion the average density (deduced from X-ray reflectivity) shows a strong increase, indicating the sudden appearance of the cubic boron nitride phase consistent with the sp³ concentration deduced from IR absorption spectroscopy. The in-plane X-ray diffraction shows that this cubic phase consists of small nanocrystals of 70 Å linear size. Received: 26 November 1996/Accepted: 27 January 1997