SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: X-ray scattering techniques

139

We have produced a superconducting binary-elements intercalated graphite, CaxSr1-xCy, with the intercalation of Sr and Ca in highly-oriented pyrolytic graphite; the superconducting transition temperature, T c, was ~3 K. The superconducting CaxSr1-xCy sample was fabricated with the nominal x value of 0.8, i.e., Ca0.8Sr0.2Cy. Energy dispersive X-ray (EDX) spectroscopy provided the stoichiometry of Ca0.5(2)Sr0.5(2)Cy for this sample, and the X-ray powder diffraction (XRD) pattern showed that Ca0.5(2)Sr0.5(2)Cy took the SrC6-type hexagonal-structure rather than CaC6-type rhombohedral-structure. Consequently, the chemical formula of CaxSr1-xCy sample could be expressed as ‘Ca0.5(2)Sr0.5(2)C6’. The XRD pattern of Ca0.5(2)Sr0.5(2)C6 was measured at 0-31 GPa, showing that the lattice shrank monotonically with increasing pressure up to 8.6 GPa, with the structural phase transition occurring above 8.6 GPa. The pressure dependence of T c was determined from the DC magnetic susceptibility and resistance up to 15 GPa, which exhibited a positive pressure dependence of T c up to 8.3 GPa, as in YbC6, SrC6, KC8, CaC6 and Ca0.6K0.4C8. The further application of pressure caused the rapid decrease of T c. In this study, the fabrication and superconducting properties of new binary-elements intercalated graphite, CaxSr1-xCy, are fully investigated, and suitable combinations of elements are suggested for binary-elements intercalated graphite.

Concepts: Diffraction, Crystallography, Fundamental physics concepts, Graphite, X-ray crystallography, Phase transition, Superconductivity, X-ray scattering techniques

28

Among double perovskites, the interpretation of the magnetic, thermal and transport properties of Sr(2)YRuO(6) remains a challenge. Characterization using different techniques reveals a variety of features that are not understood, described as anomalous, and yields contradictory values for several relevant parameters. We solved this situation through detailed susceptibility, specific heat, thermal expansion and x-ray diffraction measurements, including a quantitative correlation of the parameters characterizing the so-called anomalies. The emergence of short-range magnetic correlations, surviving well above the long-range transition, naturally accounts for the observed unconventional behavior of this compound. High resolution x-ray powder diffraction and thermal expansion results conclusively show that the magnetic and thermal responses are driven by lattice changes, providing a comprehensive scenario in which the interplay between the spin and structural degrees of freedom plays a relevant role.

Concepts: Diffraction, Crystallography, Temperature, X-ray crystallography, Bragg diffraction, Powder diffraction, Neutron diffraction, X-ray scattering techniques

25

Ethylone, a synthetic cathinone with psychoactive properties, is a designer drug which has appeared on the recreational drug market in recent years. Since 2012, illicit shipments of ethylone hydrochloride have been intercepted with increasing frequency at the Canadian border. Analysis has revealed that ethylone hydrochloride exists as two distinct polymorphs. In addition, several minor impurities were detected in some seized exhibits. In this study, the two conformational polymorphs of ethylone hydrochloride have been synthesized and fully characterized by FTIR, FT-Raman, powder XRD, GC-MS, ESI-MS/MS and NMR ((13) C CPMAS, (1) H, (13) C). The two polymorphs can be distinguished by vibrational spectroscopy, solid-state nuclear magnetic resonance spectroscopy and X-ray diffraction. The FTIR data are applied to the identification of both polymorphs of ethylone hydrochloride (mixed with methylone hydrochloride) in a laboratory submission labelled as ‘Ocean Snow Ultra’. The data presented in this study will assist forensic scientists in the differentiation of the two ethylone hydrochloride polymorphs. This report, alongside our recent article on the single crystal X-ray structure of a second polymorph of this synthetic cathinone, is the first to confirm polymorphism in ethylone hydrochloride. © 2015 Canada Border Services Agency. Drug Testing and Analysis published by John Wiley & Sons, Ltd.

Concepts: Diffraction, X-ray, Nuclear magnetic resonance, Magnetic resonance imaging, X-ray crystallography, In vivo magnetic resonance spectroscopy, X-ray scattering techniques, Recreational drug use

25

The entrance and diffusion pathway of CO2 and dimethyl ether (DME) in MFI-type zeolite channels were investigated by a selective sealing method using large silicalite-1 crystals. The MFI-type zeolite has two kinds of orthogonal channels: straight channels and sinusoidal channels. The mouths of the straight channels are on (010) crystal faces, while those of the sinusoidal channels are on (100) faces. The channel mouths are directly sealed by silicone resin on the (100) and (010) faces so as to restrict the entrance and diffusion pathways to straight and sinusoidal channel pathways, respectively. The locations and loadings of the guest CO2 and DME molecules are determined by single-crystal X-ray diffraction structural analysis. The loadings show the difference of the adsorption rates between the pathways. The straight channel pathway is 4.2 times faster than the sinusoidal channel pathway for the CO2, and the sinusoidal channel pathway is 5.1 times faster than the straight channel pathway for the DME. It reveals their dominant pathways and the anisotropy of adsorption. The dominant pathway correlates to the stability of the channel as adsorption sites.

Concepts: Oxygen, Diffraction, X-ray, Adsorption, Silicon, X-ray crystallography, X-ray scattering techniques, Dimethyl ether

23

A procedure to quantitatively analyse the relationship between the wetting layer (WL) and the quantum dots (QDs) as a whole in a statistical way is proposed. As we will show in the manuscript, it allows determining, not only the proportion of deposited InAs held in the WL, but also the average In content inside the QDs. First, the amount of InAs deposited is measured for calibration in three different WL structures without QDs by two methodologies: strain mappings in high-resolution transmission electron microscopy (HRTEM) images and compositional mappings with ChemiSTEM X-ray energy spectrometry (EDS). The area under the average profiles obtained by both methodologies emerges as the best parameter to quantify the amount of InAs in the WL, in agreement with high-resolution X-ray diffraction (HR-XRD) results. Second, the effect of three different GaAs capping layer (CL) growth rates on the decomposition of the QDs is evaluated. The CL growth rate has a strong influence on the QD volume as well as the WL characteristics. Slower CL growth rates produce an In enrichment of the WL if compared to faster ones, together with a diminution of the QD height. In addition, assuming that the QD density does not change with the different CL growth rates, an estimation of the average In content inside the QDs is given. The high Ga/In intermixing during the decomposition of buried QDs does not only trigger a reduction of the QD height, but above all, a higher impoverishment of the In content inside the QDs, therefore modifying the two most important parameters that determine the optical properties of these structures.

Concepts: Scientific method, Electron, Diffraction, X-ray, X-ray crystallography, Transmission electron microscopy, Parameter, X-ray scattering techniques

22

Soil traces are useful as forensic evidences because they frequently adhere to individuals and objects associated with crimes and can place or discard a suspect at/from a crime scene. Soil is a mixture of organic and inorganic components and among them soil clay contains signatures that make it reliable as forensic evidence. In this study, we hypothesized that soils can be forensically distinguished through the analysis of their clay fraction alone, and that samples of the same soil type can be consistently distinguished according to the distance they were collected from each other. To test these hypotheses 16 Oxisol samples were collected at distances of between 2m and 1.000m, and 16 Inceptisol samples were collected at distances of between 2m and 300m from each other. Clay fractions were extracted from soil samples and analyzed for hyperspectral color reflectance (HSI), X-ray diffraction crystallographic (XRD), and for contents of iron oxides, kaolinite and gibbsite. The dataset was submitted to multivariate analysis and results were from 65% to 100% effective to distinguish between samples from the two soil types. Both soil types could be consistently distinguished for forensic purposes according to the distance that samples were collected from each other: 1000m for Oxisol and 10m for Inceptisol. Clay color and XRD analysis were the most effective techniques to distinguish clay samples, and Inceptisol samples were more easily distinguished than Oxisol samples. Soil forensics seems a promising field for soil scientists as soil clay can be useful as forensic evidence by using routine analytical techniques from soil science.

Concepts: Scientific method, Diffraction, X-ray, Law, Erosion, X-ray scattering techniques, Clay, Forensic evidence

4

Transmission X-ray diffraction imaging in both monochromatic and white beam section mode has been used to measure quantitatively the displacement and warpage stress in encapsulated silicon devices. The displacement dependence with position on the die was found to agree well with that predicted from a simple model of warpage stress. For uQFN microcontrollers, glued only at the corners, the measured misorientation contours are consistent with those predicted using finite element analysis. The absolute displacement, measured along a line through the die centre, was comparable to that reported independently by high-resolution X-ray diffraction and optical interferometry of similar samples. It is demonstrated that the precision is greater than the spread of values found in randomly selected batches of commercial devices, making the techniques viable for industrial inspection purposes.

Concepts: Diffraction, X-ray, Measurement, Finite element method, Hilbert space, Integrated circuit, X-ray scattering techniques, Microcontroller

1

It is shown that energy-dispersive X-ray diffraction (EDXRD) implemented in a back-reflection geometry is extremely insensitive to sample morphology and positioning even in a high-resolution configuration. This technique allows high-quality X-ray diffraction analysis of samples that have not been prepared and is therefore completely non-destructive. The experimental technique was implemented on beamline B18 at the Diamond Light Source synchrotron in Oxfordshire, UK. The majority of the experiments in this study were performed with pre-characterized geological materials in order to elucidate the characteristics of this novel technique and to develop the analysis methods. Results are presented that demonstrate phase identification, the derivation of precise unit-cell parameters and extraction of microstructural information on unprepared rock samples and other sample types. A particular highlight was the identification of a specific polytype of a muscovite in an unprepared mica schist sample, avoiding the time-consuming and difficult preparation steps normally required to make this type of identification. The technique was also demonstrated in application to a small number of fossil and archaeological samples. Back-reflection EDXRD implemented in a high-resolution configuration shows great potential in the crystallographic analysis of cultural heritage artefacts for the purposes of scientific research such as provenancing, as well as contributing to the formulation of conservation strategies. Possibilities for moving the technique from the synchrotron into museums are discussed. The avoidance of the need to extract samples from high-value and rare objects is a highly significant advantage, applicable also in other potential research areas such as palaeontology, and the study of meteorites and planetary materials brought to Earth by sample-return missions.

Concepts: Diffraction, X-ray, Crystallography, X-ray crystallography, Powder diffraction, X-ray scattering techniques, Synchrotron, Mica

1

Versatility in metal substitution is one of the key aspects of metal-organic framework (MOF) chemistry, allowing properties to be tuned in a rational way. As a result, it important to understand why MOF syntheses involving different metals arrive at or fail to produce the same topological outcome. Frequently, conditions are tuned by trial-and-error to make MOFs with different metal species. We ask: is it possible to adjust synthetic conditions in a systematic way in order to design routes to desired phases? We have used in situ X-ray powder diffraction to study the solvothermal formation of isostructural M2 (bdc)2 dabco (M=Zn, Co, Ni) pillared-paddlewheel MOFs in real time. The metal ion strongly influences both kinetics and intermediates observed, leading in some cases to multiphase reaction profiles of unprecedented complexity. The standard models used for MOF crystallization break down in these cases; we show that a simple kinetic model describes the data and provides important chemical insights on phase selection.

Concepts: Diffraction, Crystallography, Metal, X-ray crystallography, Bragg diffraction, Powder diffraction, Neutron diffraction, X-ray scattering techniques

1

Proteins must move between different conformations of their native ensemble to perform their functions. Crystal structures obtained from high-resolution X-ray diffraction data reflect this heterogeneity as a spatial and temporal conformational average. Although movement between natively populated alternative conformations can be critical for characterizing molecular mechanisms, it is challenging to identify these conformations within electron density maps. Alternative side chain conformations are generally well separated into distinct rotameric conformations, but alternative backbone conformations can overlap at several atomic positions. Our model building program qFit uses mixed integer quadratic programming (MIQP) to evaluate an extremely large number of combinations of sidechain conformers and backbone fragments to locally explain the electron density. Here, we describe two major modeling enhancements to qFit: peptide flips and alternative glycine conformations. We find that peptide flips fall into four stereotypical clusters and are enriched in glycine residues at the n+1 position. The potential for insights uncovered by new peptide flips and glycine conformations is exemplified by HIV protease, where different inhibitors are associated with peptide flips in the “flap” regions adjacent to the inhibitor binding site. Our results paint a picture of peptide flips as conformational switches, often enabled by glycine flexibility, that result in dramatic local rearrangements. Our results furthermore demonstrate the power of large-scale computational analysis to provide new insights into conformational heterogeneity. Overall, improved modeling of backbone heterogeneity with high-resolution X-ray data will connect dynamics to the structure-function relationship and help drive new design strategies for inhibitors of biomedically important systems.

Concepts: DNA, Protein structure, Electron, Diffraction, X-ray, Crystallography, X-ray crystallography, X-ray scattering techniques