Search results for "scatter"
showing 10 items of 8475 documents
Towards automated diffraction tomography: Part I—Data acquisition
2007
Abstract The ultimate aim of electron diffraction data collection for structure analysis is to sample the reciprocal space as accurately as possible to obtain a high-quality data set for crystal structure determination. Besides a more precise lattice parameter determination, fine sampling is expected to deliver superior data on reflection intensities, which is crucial for subsequent structure analysis. Traditionally, three-dimensional (3D) diffraction data are collected by manually tilting a crystal around a selected crystallographic axis and recording a set of diffraction patterns (a tilt series) at various crystallographic zones. In a second step, diffraction data from these zones are com…
Ab Initio Structure Determination of Vaterite by Automated Electron Diffraction
2012
tion that is fundamental for understanding material properties. Still, a number of compounds have eluded such kinds of analysis because they are nanocrystalline, highly disordered, with strong pseudosymmetries or available only in small amounts in polyphasic or polymorphic systems. These materials are crystallographically intractable with conventional Xray or synchrotron radiation diffraction techniques. Single nanoparticles can be visualized by high-resolution transmission electron microscopy (HR-TEM) up to sub�ngstrom resolution, [2] but obtaining 3D information is still a difficult task, especially for highly beam-sensitive materials and crystal structures with long cell parameters. Elec…
Liquid Structure of Trihexyltetradecylphosphonium Chloride at Ambient Temperature: An X-ray Scattering and Simulation Study
2009
We report on an experimental and simulation study done on a representative room temperature ionic liquid, namely tetradecyltrihexylphosphonium chloride, at ambient conditions. The study was conducted using small and wide angle X-ray scattering and molecular dynamics simulations. Both approaches converge in indicating that this material is characterized by the existence of strong P-Cl interactions (with characteristic distances between 3.5 and 5.0 Å) and by the occurrence of nanoscale segregation, despite the symmetric nature of the cation and similarly to other room temperature ionic liquids. A good agreement is found between the structure factor and pair correlation functions obtained from…
Fourier optical approach to the extraction of morphological parameters from the diffraction pattern of biological cells.
1978
A new procedure for fast quantitative extraction of cell parameters from diffraction patterns was deduced from model calculations and applied to cervical gynecological material. Based on radial scans of the diffraction pattern, the technique permits simultaneous determination of the nuclear and cytoplasmic diameters by Fourier analysis of the radial scanning signals after compensation for the intensity falloff by an amplification proportional to the third power of the radial position in the diffraction plane. Illustrative examples of measurements on exfoliated cells of different types are presented.
Linker depletion for missing cluster defects in non-UiO Metal-Organic Frameworks
2021
Defect engineering is a valuable tool to tune the properties of metal–organic frameworks. However, defect chemistry remains still predominantly limited to UiO-type MOFs. We describe the preferential formation of missing cluster defects in heterometallic titanium–organic frameworks of the MUV-10 family when synthesised in sub-stoichiometric linker conditions. Our results show the value of integrating experimental work, computational modelling and thorough characterization in rationalizing the impact of defects over the porosity and structure of this family of materials. Correlation of experiment with computational models reveals the dominance of missing cluster vacancies in the pore size dis…
An X-ray scattering study of lipid monolayers at the air-water interface and on solid supports
1988
Abstract Monolayers of the lipid arachidic acid (C20) and of the phospholid dimyristolyphosphatidic acid (PMDA) have been studied by X-ray reflection and diffraction technique, using a purpose-built Langmuir trough installed at the sample stage of our high-resolution X-ray diffractometer at the DORIS synchroton X-ray source in Hamburg. For comparison we also report data for monolayers of C20 on a solid support using a 10 kW rotating anode X-ray source. By the X-ray reflection method, the density profile across the interface is probe, while in-plane diffraction measurements gauge the two-dimensional crystalline properties of the monolayers. Flourescence microscopy experiments of DMPA monolay…
Treatment of grazing-incidence small-angle X-ray scattering data taken above the critical angle
2001
The equations taking into account refraction at the sample surface in grazing-incidence small-angle X-ray scattering (GISAXS) when the angle between the incoming beam and the sample surface is slightly larger than the critical angle are derived and discussed. It is demonstrated that the refraction of both the incoming and the scattered beam at the sample surface affects the GISAXS pattern and that, when a planar bidimensional detector perpendicular to the incoming beam is used, the effect depends on the azimuthal detector angle. The smearing of the pattern depending on the size of the illuminated sample area in grazing incidence is estimated by simulations with Cauchy functions of different…
Cation Distribution in a Titanium Ferrite Fe2.75Ti0.25O4Measured byin-SituAnomalous Powder Diffraction Using Rietveld Refinement
1998
Many ferrites contain different cations with various valence states and location in the spinel structure. In compounds such as these, only a combination of different techniques such as Mussbauer spectroscopy, IR analysis, and thermogravimetry allows the distribution of cations to be obtained. For very complicated distributions, the mathematical decomposition of derivative thermogravimetric curves (DTG) leading to quantitative distribution is uncertain. In this paper, we present an alternative technique based on resonant diffraction. The anomalous scattering of each cation in the crystalline material is used to determine its amount and position by Rietveld refinement. Since the energy for su…
Structure solution of zeolites by automated electron diffraction tomography - Impact and treatment of preferential orientation
2014
Abstract In this paper the reliability of structure solution of nano-crystalline porous compounds with preferred orientation based on automated electron diffraction tomography (ADT) is discussed. It will be shown that the limitations of the data acquisition geometry can be overcome by completing the missing diffraction data with additional diffraction information. Apart from different ways of sample preparation, data merging with either additional ADT data sets or intensities derived from X-ray powder diffraction comprise an effective way to improve the accuracy of the structure solution.
Applications of automated diffraction tomography (ADT) on nanocrystalline porous materials
2013
Abstract Many porous materials, both inorganic and hybrid organic–inorganic, can only be synthesized as nanocrystals. X-ray powder diffraction delivers one-dimensional data from the overall sample and is therefore often limited by peak overlap at low or medium resolution and by peak broadening. Thus, structure solution of materials with large unit cells and low symmetry, disorder or pseudosymmetry, or available only in polyphasic systems, turns out to be problematic or even impossible. Electron diffraction allows collecting three-dimensional structure information from nanocrystalline materials, but is traditionally biased by low completeness of the diffraction data, dynamical scattering and…