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1.
    
The crystal structure of the title compound, C8H24N2Mo6O19 was determined by single crystal X‐ray diffraction technique. The crystals are trigonals, space group P‐3c1, with a = b = 10.0176(11) Å, c = 14.089(2) Å, γ = 120°, V = 1224.4(3) Å3, Z = 2. The structure was solved by direct methods and refined by least‐squares methods to a Final R = 0.0316 for 1114 observed reflections with I > 2σ(I). In hexamolybdate anion, six MoO6 distorted octahedra are fused together so that they all share a common vertex. O atoms are of three types: central, terminal and bridging, bonded to six, one and two Mo atoms, respectively. The crystallographic data of the structure was deposited with the Cambridge Data Center as No. CCDC 199679. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
    
A novel bis (dmit) complex of copper (II), [(C3H7)4N]2[Cu(dmit)2] ( 1 ), where dmit is 2‐thioxo‐1,3‐dithiole‐4,5‐dithiolate, was prepared and structurally characterized by X‐ray single crystal diffraction. The copper (II) atom is tetracoordinated by four dmit S atoms, forming a nearly square planar arrangement. The [Cu(dmit)2]2‐ anions and the [(C3H7)4N]+ counter‐cations form a three‐dimensional solid‐state structure by C–H…S hydrogen bonds. The third‐order nonlinear optical properties of the complex were determined by picosecond Z‐scan technique at a wavelength of 1064 nm. The results indicate the compound exhibits reverse saturation absorption and self‐defocusing performance. The molecular second‐order hyperpolarizability γ is calculated to be as high as (1.8±0.2)×10‐30 esu. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
    
X‐ray absorption fine structure measurements are a prime tool at synchrotrons around the world, accounting for over 30% of all synchrotron research. They are incisive tools for elucidating local structure, ionization state and coordination geometry. However, in general, it has not been possible to apply them to perfect or near‐perfect crystals, and their dominant application is to micro‐samples, powders, metals and solutions. The reasons for this are given, and an experimental technique to yield high‐precision data for good crystals is developed. This widens the applicability of the technique dramatically, and permits standards and calibration samples to be used and transferred for new types of measurement. It is shown that this is particularly appropriate for discrete measurements of absorption, X‐ray absorption fine structure and X‐ray absorption near‐edge spectroscopy, and in cases of strong oscillations.  相似文献   

4.
    
The application of V‐shaped channel‐cut GeSi(220) and Ge(220) monochromators for one‐dimensional extreme X‐ray beam compression was tested on a table‐top setup for grazing‐incidence small‐angle X‐ray scattering (GISAXS) with a microfocus source. A lattice constant gradient and different asymmetry angles of the diffractors were employed to enhance the compression factor to 21 and 15, respectively. It was demonstrated that the output beam parameters in terms of the size, divergence, photon flux and spectral bandwidth surpass those of the slit collimators used traditionally in GISAXS. A beam size far below 100 µm allows a high‐resolution spatial GISAXS mapping, while the reciprocal space resolution of ∼500 nm approaches the level of synchrotron measurements and allows a fast one‐shot detection of high‐resolution GISAXS patterns. An oversampling shifts the detection limit up to ∼1 µm. The very short design of the compact high‐resolution table‐top GISAXS setup is another advantage of the extreme beam compression. Benefits of V‐shaped monochromators for medium‐resolution X‐ray diffraction experiments as a bonus application are demonstrated by a comparison with parallel channel‐cut monochromators combined with a slit.  相似文献   

5.
    
This study reports on the characterization of a carbon nanotube fibre using synchrotron radiation microbeam small‐ and wide‐angle X‐ray scattering in combination with microfluorescence. The fibre, spun directly from a chemical vapour deposition reaction zone, is imaged in terms of microstructural heterogeneities. The results reveal a fibre consisting of highly oriented nanotube bundles and unoriented carbonaceous material. Within the oriented component there is a variable orientation distribution and evidence of differences in nanotube packing. Single catalyst crystallites can be located within the fibre from their wide‐angle X‐ray scattering signal, and the particulate distribution imaged using X‐ray microfluorescence. Whilst this study only constitutes a preliminary analysis, it demonstrates the application of existing fibre characterization methods to new materials. It also highlights the potential of synchrotron radiation micro‐ and nanobeam small‐ and wide‐angle X‐ray scattering and microfluorescence for the study of fibres of a few µm diameter.  相似文献   

6.
    
A series of ionic complexes of 1,8–bis(dimethylamino)naphthalene with selected inorganic acids such as HCl, HBr, HI, HSCN and HBF4 were synthesised and thoroughly investigated by means of powder diffractometry and analytical methods. The crystallographic data for these compounds as well as the results of the structure solution by powder diffraction methods of the 1,8–bis(dimethylamino)naphthalene.HI complex, which crystallizes in the monoclinic system, S.G. P21/c (14), a=7.999(2)Å, b=23.053(3)Å, c=7.948(1)Å, β=99.63°, RF=17.1%, Rwp=15.5%, are discussed and presented in this work. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
    
A novel computational method based on atomic form factors and the fast Fourier transform (FFT) is developed to compute small‐ and near‐wide‐angle X‐ray scattering profiles of biomacromolecules from explicit solvent modeling. The method is validated by comparing the results with those from non‐FFT approaches and experiments, and good agreement with experimental data is observed for both small and near‐wide angles. In terms of computational efficiency, the FFT‐based method is advantageous for protein solution systems of more than 3000 atoms. Furthermore, the computational cost remains nearly constant for a wide range of system sizes. The FFT‐based approach can potentially handle much larger molecular systems compared with popular existing methods.  相似文献   

8.
    
Reverse Monte Carlo (RMC) refinements of local structure using a simultaneous fit of X‐ray/neutron total scattering and extended X‐ray absorption fine structure (EXAFS) data were developed to incorporate an explicit treatment of both single‐ and multiple‐scattering contributions to EXAFS. The refinement algorithm, implemented as an extension to the public domain computer software RMCProfile, enables accurate modeling of EXAFS over distances encompassing several coordination shells around the absorbing species. The approach was first tested on Ni, which exhibits extensive multiple scattering in EXAFS, and then applied to perovskite‐like SrAl1/2Nb1/2O3. This compound crystallizes with a cubic double‐perovskite structure but presents a challenge for local‐structure determination using a total pair‐distribution function (PDF) alone because of overlapping peaks of the constituent partial PDFs (e.g. Al—O and Nb—O or Sr—O and O—O). The results obtained here suggest that the combined use of the total scattering and EXAFS data provides sufficient constraints for RMC refinements to recover fine details of local structure in complex perovskites. Among other results, it was found that the probability density distribution for Sr in SrAl1/2Nb1/2O3 adopts Td point‐group symmetry for the Sr sites, determined by the ordered arrangement of Al and Nb, as opposed to a spherical distribution commonly assumed in traditional Rietveld refinements.  相似文献   

9.
    
The design and operation of a versatile ultra‐small‐angle X‐ray scattering (USAXS) instrument at the Advanced Photon Source (APS) at Argonne National Laboratory are presented. The instrument is optimized for the high brilliance and low emittance of an APS undulator source. It has angular and energy resolutions of the order of 10−4, accurate and repeatable X‐ray energy tunability over its operational energy range from 8 to 18 keV, and a dynamic intensity range of 108 to 109, depending on the configuration. It further offers quantitative primary calibration of X‐ray scattering cross sections, a scattering vector range from 0.0001 to 1 Å−1, and stability and reliability over extended running periods. Its operational configurations include one‐dimensional collimated (slit‐smeared) USAXS, two‐dimensional collimated USAXS and USAXS imaging. A robust data reduction and data analysis package, which was developed in parallel with the instrument, is available and supported at the APS.  相似文献   

10.
    
At the National Synchrotron Radiation Research Center, a small/wide‐angle X‐ray scattering (SAXS/WAXS) instrument has been installed at the BL23A beamline with a superconducting wiggler insertion device. This beamline is equipped with double Si(111) crystal and double Mo/B4C multilayer monochromators, and an Si‐based plane mirror that can selectively deflect the beam downwards for grazing‐incidence SAXS (GISAXS) studies of air–liquid or liquid–liquid interfaces. The SAXS/WAXS instrument, situated in an experimental hutch, comprises collimation, sample and post‐sample stages. Pinholes and slits have been incorporated into the beam collimation system spanning a distance of ∼5 m. The sample stage can accommodate various sample geometries for air–liquid interfaces, thin films, and solution and solid samples. The post‐sample section consists of a 1 m WAXS section with two linear gas detectors, a vacuum bellows (1–4 m), a two‐beamstop system and the SAXS detector system, all situated on a motorized optical bench for motion in six degrees of freedom. In particular, the vacuum bellows of a large inner diameter (260 mm) provides continuous changes of the sample‐to‐detector distance under vacuum. Synchronized SAXS and WAXS measurements are realized via a data‐acquisition protocol that can integrate the two linear gas detectors for WAXS and the area detector for SAXS (gas type or Mar165 CCD); the protocol also incorporates sample changing and temperature control for programmable data collection. The performance of the instrument is illustrated via several different measurements, including (1) simultaneous SAXS/WAXS and differential scanning calorimetry for polymer crystallization, (2) structural evolution with a large ordering spacing of ∼250 nm in a supramolecular complex, (3) SAXS for polymer blends under in situ drawing, (4) SAXS and anomalous SAXS for unilamellar lipid vesicles and metalloprotein solutions, (5) anomalous GISAXS for oriented membranes of Br‐labeled lipids embedded with peptides, and (6) GISAXS for silicate films formed in situ at the air–water interface.  相似文献   

11.
    
This paper describes a computational approach to estimating wide‐angle X‐ray solution scattering (WAXS) from proteins, which has been implemented in a computer program called SoftWAXS. The accuracy and efficiency of SoftWAXS are analyzed for analytically solvable model problems as well as for proteins. Key features of the approach include a numerical procedure for performing the required spherical averaging and explicit representation of the solute–solvent boundary and the surface of the hydration layer. These features allow the Fourier transform of the excluded volume and hydration layer to be computed directly and with high accuracy. This approach will allow future investigation of different treatments of the electron density in the hydration shell. Numerical results illustrate the differences between this approach to modeling the excluded volume and a widely used model that treats the excluded‐volume function as a sum of Gaussians representing the individual atomic excluded volumes. Comparison of the results obtained here with those from explicit‐solvent molecular dynamics clarifies shortcomings inherent to the representation of solvent as a time‐averaged electron‐density profile. In addition, an assessment is made of how the calculated scattering patterns depend on input parameters such as the solute‐atom radii, the width of the hydration shell and the hydration‐layer contrast. These results suggest that obtaining predictive calculations of high‐resolution WAXS patterns may require sophisticated treatments of solvent.  相似文献   

12.
    
A method for collimation correction and combination of anisotropic scattering patterns recorded in tandem experiments is proposed. It includes both an advanced two‐dimensional extrapolation procedure for the center of the pattern and (compared with the `blind deconvolution' method) a more justified procedure for desmearing from an unknown broad primary beam profile. This semi‐blind deconvolution rests on the availability of unsmeared data in a region of the smeared image. Materials exhibiting both ultra‐small‐angle X‐ray scattering (USAXS) and small‐angle X‐ray scattering (SAXS) must be studied in both angular bands (tandem experiment), in order to collect the complete range of discrete scattering for nanostructure analysis. Merging of the patterns requires desmearing of at least the SAXS pattern from its point‐spread function, i.e. the primary beam profile. The distorting effect of single‐band experiments on the reconstructed nanostructure of polymer materials is demonstrated.  相似文献   

13.
    
A method of using X‐ray absorption spectroscopy together with resolved grazing‐incidence geometry for depth profiling of atomic, electronic or chemical local structures in thin films is presented. The quantitative deconvolution of thickness‐dependent spectral features is performed by fully considering both scattering and absorption formalisms. Surface oxidation and local structural depth profiles in nanometric FePt films are determined, exemplifying the application of the method.  相似文献   

14.
    
The crystal structure and the local atomic order of a series of nanocrystalline ZrO2–CaO solid solutions with varying CaO content were studied by synchrotron radiation X‐ray powder diffraction and extended X‐ray absorption fine structure (EXAFS) spectroscopy. These samples were synthesized by a pH‐controlled nitrate–glycine gel‐combustion process. For CaO contents up to 8 mol%, the t′ form of the tetragonal phase (c/a > 1) was identified, whereas for 10 and 12 mol% CaO, the t′′ form (c/a = 1; oxygen anions displaced from their ideal positions in the cubic phase) was detected. Finally, the cubic phase was observed for solid solutions with CaO content of 14 mol% CaO or higher. The t′/t′′ and t′′/cubic compositional boundaries were determined to be at 9 (1) and 13 (1) mol% CaO, respectively. The EXAFS study demonstrated that this transition is related to a tetragonal‐to‐cubic symmetry change of the first oxygen coordination shell around the Zr atoms.  相似文献   

15.
    
The structure of the Zr atomic environment in a CaO–ZrO2–SiO2 glass ceramic as a function of thermal treatments has been studied, combining X‐ray absorption spectroscopy (XAS), X‐ray diffraction (XRD) and anomalous XRD (a‐XRD) techniques. The analysis of XRD patterns demonstrates that the devitrification process proceeds through the partial segregation of Zr‐depleted phases (wollastonite‐like) and Zr‐rich phases (Zr oxides). The XAS and a‐XRD measurements at the Zr K‐edge have been exploited in order to obtain a closer insight into the atomic structure around the Zr atoms. In the as‐quenched glass the Zr atom is sixfold coordinated to O atoms in an amorphous environment rich in Ca and Si. Thermal treatment firstly (T = 1273–1323 K) causes partial segregation of Zr in the form of an oxide with a tetragonal zirconia (t‐ZrO2) crystalline structure. Raising the temperature (T = 1373 K) causes the formation of ZrO2 crystallites in the monoclinic crystallographic phase (baddeleyite, m‐ZrO2). Analysis of the XAS data shows that a considerable amount of Zr remains in an amorphous calcium silicate phase.  相似文献   

16.
    
Bis{2,6‐bis (hydroxymethyl) pyridine‐O,O,N} {μ‐bis(2‐hydroxymethylpyridyl) methanolate‐O,N} dicopper(II) di(propionate) (CCDC 143763) has been prepared and studied by single‐crystal X‐ray diffraction methods at 293(2) K. The crystal structure consists of dimeric complex cation, [Cu2(μ‐bhmp)2(bhmpH)2]+2 and propionate anions (bhmp ‐ 2,6‐bis(hydroxymethyl) pyridine; bhmpH ‐ 2‐(6‐hydroxymethylpyridyl) methanolate ) and propionate anions. The complex cation contains two neutral and two monodeprotonated bhmp molecules, each coordinate to one Cu(II) atom in a tridentate chelating manner, via two O atoms and N atom. The monodeprotonated bmph molecules are also tridentate coordinate via N atom and only one O atom, which serve as bridge between two CuO4N2 moieties. The propionate anions are “ fixed” to the complex by the hydrogen bonds.  相似文献   

17.
    
The atomic pair distribution function (PDF) as obtained from X‐ray or neutron total scattering experiments has proved to be powerful in obtaining valuable structural information for many complex functional materials, be they amorphous or crystalline. In the case of measurements made with X‐rays and for samples containing more than one kind of atom, the usefulness of the PDF is, however, somewhat hampered because of the lack of an exact and simple expression relating it to the structure of the materials. Only an approximate relationship exits, which is still in use today. This is particularly detrimental given the wide availability of X‐ray sources and the increasing quality of PDFs obtained with laboratory sources. In this paper, the exact and explicit expression of the PDF as obtained from X‐ray scattering is derived with respect to partial functions. This expression allows exact and efficient calculation of the PDF from any structure model without using approximate formulae.  相似文献   

18.
    
A laboratory in situ grazing‐incidence small‐angle X‐ray scattering (GISAXS) tracking of the self‐assembled growth of a regular 3D Ge quantum dot (QD) structure in an amorphous Al2O3 matrix during the ion beam sputter deposition of a periodic Ge/Al2O3 multilayer on silicon is reported. A 573 K substrate temperature proved to be necessary to achieve the self‐assembly effect. Relying on a fast repeated acquisition of GISAXS patterns, the temporal evolution of the growing 3D Ge QD structure was analyzed bilayer by bilayer to determine its type, lateral and vertical correlation lengths, and inter‐QD distance. The QD structure was found to have body‐centered tetragonal lattice type with ABA stacking, with the lattice parameters refined by fitting the final GISAXS pattern relying on a paracrystal model. A single set of paracrystal parameters enables one to simulate the temporal evolution of the in situ GISAXS patterns throughout the deposition process, suggesting that the Ge QD self‐assembly is driven from the very beginning solely by the growing surface morphology. Ex situ GISAXS and X‐ray reflectivity measurements along with a cross‐section high‐resolution transmission electron microscopy analysis complete the study.  相似文献   

19.
    
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20.
    
This paper reports recent tests performed on the Bonse–Hart‐type ultra‐small‐angle X‐ray scattering (USAXS) instrument at the Advanced Photon Source with higher‐order reflection optics – Si(440) instead of Si(220) – and with X‐ray energies greater than 20 keV. The results obtained demonstrate the feasibility of high‐energy operation with narrower crystal reflectivity curves, which provides access to a scattering q range from ∼2 × 10−5 to 1.8 Å−1 and up to 12 decades in the associated sample‐dependent scattering intensity range. The corresponding size range of the scattering features spans about five decades – from less than 10 Å to ∼15 µm. These tests have indicated that mechanical upgrades are required to ensure the alignment capability and operational stability of this instrument for general user operations because of the tighter angular‐resolution constraints of the higher‐order crystal optics.  相似文献   

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