Wide-angle Diffraction Research Articles

Action of α-cyclodextrin on phospholipid assemblies

Interactions of α-cyclodextrin (α-CD) with dimyristoylphosphatidylcholine (DMPC) and Egg phosphatidylcholine (Egg-PC) were studied (i) by analyzing surface pressure-area isotherms and surface tension of phospholipid monolayers formed at the interface between air and α-CD aqueous solutions and (ii) by X-ray diffraction performed on fully hydrated α-CD/phospholipid binary mixtures. The cyclodextrin molecules strongly interact with the two-dimension phospholipid assembly. Their addition into the aqueous sub-phase leads to the removal of part of the phospholipids from the air-water interface: the higher the α-CD concentration, the higher the phospholipid depletion. This should preferentially involve interactions between cyclodextrin and the phosphatidylcholine head group as α-CD is water-soluble and not surface-active. At the three-dimension level, the bilayer packing of the phospholipid lamellar phase appears not affected by the presence of cyclodextrin as shown by X-ray scattering at small angles whereas wide-angle diffraction patterns reveal the formation of a crystalline phase organized in a pseudo-hexagonal lattice usually characteristic of α-CD dimers. These results point out that α-CD should interact with bilayer-forming phospholipid molecules but likely according to a process that would preserve intact at least a part of the multilamellar assembly.

On the heterogeneous character of water's amorphous polymorphism

In this paper we report in situ small-angle neutron scattering results on the high-density amorphous (HDA) and low-density amorphous (LDA) ice structures and on intermediate structures as found during the temperature-induced transformation of HDA into LDA. We show that the small-angle signal is characterized by two Q regimes featuring different properties [Q is the modulus of the scattering vector defined as Q = (4\pi/\lambda_{\rm i})\sin(\theta) with \theta being half the scattering angle and \lambda_{\rm i} the incident neutron wavelength]. The very low Q regime (\lt\, \sim \!5\times 10^{-2} Å−1) is dominated by a Porod-limit scattering. Its intensity reduces during the course of the HDA-to-LDA transformation following kinetics reminiscent of those observed in wide-angle diffraction experiments. The small-angle neutron scattering form factor in the intermediate regime of 5 \times 10^{-2} \,\lt\, Q \,\lt\, 0.5 Å−1 for HDA and LDA features a rather flat plateau. However, the HDA signal shows an ascending intensity towards smaller Q marking this amorphous structure as heterogeneous. When following the HDA-to-LDA transition, the form factor shows a pronounced transient excess in intensity marking all intermediate structures as strongly heterogeneous on a length scale of some nanometres.

Communication modes in scalar diffraction

The communication modes are a useful concept in studies of optical resolution, wave propagation, and image synthesis. We present an overview of earlier results on the communication modes in scalar diffraction theory. Besides the general theory, the modes are reviewed for the far-field and Fresnel regimes, and new eigenequations are derived for wide-angle diffraction. We prove a conjugate relationship between the transmitting and receiving modes in a general symmetric system. We also suggest an approximate method for far-field and Fresnel domain propagation, in which propagation amounts to a rotation of each mode in the complex plane. The main focus is on the near-field communication modes, where we present numerical examples of the modes and coupling strengths for a near-field geometry with a sub-wavelength size receiving domain. These results provide insights, for example, into the understanding of near-field scanning probe techniques.

In situ diffraction measurements of lattice response due to shock loading, including direct observation of the α– ε phase transition in iron

In situ diffraction is a technique to probe directly the lattice response of materials during the shock loading process. It is used to record diffraction patterns from multiple lattice planes simultaneously. The application of this technique is described for laser-based shock experiments. The approach to analyze in situ wide-angle diffraction data is discussed. This is presented in the context of single crystal [001] iron shock experiments where uniaxial compression of the bcc lattice by up to 6% was observed. Above the α– ε transition pressure, the lattice showed a collapse along the [001] direction by 15–18%. Additional diffraction lines appear that confirm the transformation of the iron crystal from the initial bcc phase to the hcp phase.

Link between the diversity, heterogeneity and kinetic properties of amorphous ice structures

Based on neutron wide-angle diffraction and small-angle neutron scattering experiments, we show that there is a correlation between the preparational conditions of amorphous ice structures, their microscopic structural properties, the extent of heterogeneities on a mesoscopic spatial scale and the transformation kinetics. There are only two modifications that can be identified as homogeneous disordered structures, namely the very high-density vHDA and the low-density amorphous LDA ice. Structures showing an intermediate static structure factor with respect to vHDA and LDA are heterogeneous phases. This holds independently from their preparation procedure, i.e. either obtained by pressure amorphization of ice Ih or by heating of vHDA. The degree of heterogeneity can be progressively suppressed when higher pressures and temperatures are applied for the sample preparation. In accordance with the suppressed heterogeneity the maximum of the static structure factor displays a pronounced narrowing of the first strong peak, shifting towards higher Q-numbers. Moreover, the less heterogeneous the obtained structures are the slower is the transformation kinetics from the high-density modifications into LDA. The well known high-density amorphous structure HDA does not constitute any particular state of the amorphous water network. It is formed due to the preparational procedure working in liquid nitrogen as thermal bath, i.e. at about 77K.

Nonparaxial scalar treatment of sinusoidal phase gratings

Scalar diffraction theory is frequently considered inadequate for predicting diffraction efficiencies for grating applications where lambda/d>0.1. It has also been stated that scalar theory imposes energy upon the evanescent diffracted orders. These notions, as well as several other common misconceptions, are driven more by an unnecessary paraxial approximation in the traditional Fourier treatment of scalar diffraction theory than by the scalar limitation. By scaling the spatial variables by the wavelength, we have previously shown that diffracted radiance is shift invariant in direction cosine space. Thus simple Fourier techniques can now be used to predict a variety of wide-angle (nonparaxial) diffraction grating effects. These include (1) the redistribution of energy from the evanescent orders to the propagating ones, (2) the angular broadening (and apparent shifting) of wide-angle diffracted orders, and (3) nonparaxial diffraction efficiencies predicted with an accuracy usually thought to require rigorous electromagnetic theory.

Versatile wide angle diffraction setup for simultaneous wide and small angle x-ray scattering measurements with synchrotron radiation

Here we present a novel, simple, and versatile experimental setup aimed to perform wide angle x-ray scattering (WAXS) measurements alone or in simultaneous combination with small angle x-ray scattering measurements. The design of the WAXS goniometer allows one to obtain high resolution diffraction patterns in a broad angular range. The setup can incorporate a hot stage in order to evaluate temperature resolved experiments. The performance of the equipment has been verified in the BM16 beam line of the European Synchrotron Radiation Facility with different well known samples such as alumina, isotropic film of high density polyethylene (HDPE), and oriented HPDE fiber.

Morphological Development of Oriented Isotactic Polypropylene in the Presence of a Nucleating Agent

The morphological development of sheared isotactic polypropylene (iPP) containing different amounts of sodium benzoate (SB) has been investigated using wide- and small-angle X-ray scattering techniques. The microbeam of synchrotron radiation allows us to gain, precisely and efficiently, the local morphology at a given position with a good spatial resolution. The morphological distributions such as crystallinity, fractions of α-form and β-form crystals, crystal size, and orientation functions can therefore be well constructed through the shear field or temperature gradient. The distribution of crystallinity is changed from a U-shape without SB to an almost flat with SB, in company with a minimum fraction of α-form crystal and a maximum fraction of β-form crystal. The epitaxial growth of branched lamellae in the presence of SB is confirmed from the orientation functions of two axes using wide-angle diffraction. The effect of SB on the molecular orientation is understood from the orientation function of c-axis and the azimuthal patterns of small-angle scattering. It is found that both the molecular orientation and the lamellar orientation of the α-form crystal are increased with increasing SB. The thickness of crystalline lamellae with respect to flow direction is found to increase with increasing SB in the whole range from shear zone to core center. A slight declination of crystalline lamellae has been observed in the presence of SB.

Structural investigation of water–acetonitrile mixtures: Small-angle and wide-angle neutron diffraction study compared to molecular dynamics simulation

In present work we report small-angle and wide-angle neutron diffraction study compared to molecular dynamics simulation on water–acetonitrile system. From small-angle scattering measurements resulted that the correlation length, as well as the density and concentration fluctuation have maximum around x an = 0.38; these findings are in agreement with previous results found, namely, that a strong microheterogeneity exists in acetonitrile–water system in the range of x an = 0.2–0.6 acetonitrile mole fraction. The total g( r) functions of mixtures obtained from wide-angle scattering are compared with molecular dynamics simulation results and they show an overall good agreement.

Optimizing synthesis of Na2Ti2SiO7 · 2H2O (Na-CST) and ion exchange pathways for Cs0.4H1.6Ti2SiO7 · H2O (Cs-CST) determined from in situ synchrotron X-ray powder diffraction

Observation of wide angle diffraction data collected in situ during synthesis of Na-CST (Na2Ti2O3SiO4·2H2O) showed initial crystallization of a precursor phase (SNT) at 30°C followed by conversion to CST after 1h at 220°C. In situ studies of Cs+ ion exchange into the H+ form of CST showed a site-by-site ion exchange pathway accompanied by a simultaneous structural transition from P42/mbc (cell parameters a=11.0690(6)Å, c=11.8842(6)Å) to P42/mcm (cell parameters a=7.847(2)Å, c=11.9100(6)Å). After approximately 18% Cs+ exchange into site designated Cs2 in space group P42/mcm, a site designated Cs1 in space group P42/mcm began to fill at the center of the 8MR windows until a maximum of approximately 22% exchange was achieved for Cs1. Bond valence sums of site Cs1 to framework O2− are 1.00 v.u., while bond valence sums of site Cs2 to framework O2− are 0.712 v.u. suggesting Cs1 to have a more stable bonding environment.

Wide-angle diffraction of the laser beam by a sharp edge

Using a rigorous theory of diffraction, we explain the origin and analyze the structure of a wide-angle illuminated area observed when a limited beam is diffracted by the sharp edge of an opaque screen. It is shown that the formed plume has the structure of a cylindrical wave traveling from the screen edge and its amplitude is proportional to the beam amplitude at this edge. The observed structure is Young’s boundary wave produced by diffraction of the limited beam.

Extraction of Hydrogen-Atom Positions in Polyethylene Crystal Lattice from Wide-Angle Neutron Diffraction Data Collected by a Two-Dimensional Imaging Plate System: Comparison with the X-ray and Electron Diffraction Results

Two-dimensional wide-angle neutron diffraction patterns have been measured successfully for uniaxially oriented fully deuterated and fully hydrogeneous polyethylene samples by using an imaging plate system (BIX-3) installed at the Japan Atomic Energy Research Institute. The detailed data analysis allowed us to extract the positions of hydrogen atoms in the crystal lattice accurately. The results were compared quantitatively with those obtained from the X-ray and electron diffraction experiments as well as the computer simulation result.

Starch transformation and structure development in production and reconstitution of potato flakes

Changes of parenchymous tissue structure and transformations of starch in the production and reconstitution of drum-dried potato flakes as instant mashed potatoes were investigated by light microscopy, iodine binding capacity, thermal analysis, wide-angle X-ray powder diffraction and rheology. Instant mashed potatoes are suspensions which are formed by separating whole potato tissue into individual cells. Mechanical stress during mashing and the subsequent steps also lead to undesirable cell disruption and extracellular starch. The stabilizing effect on starch by gelatinization and retrogradation in the preheating and cooling step was found to be far less important than mentioned in literature. While amylopectin does not retrograde, amylose crystallizes de novo during preheating, probably further aggregates during the cooling step and the ageing of mashed potatoes and melts fully during drum drying. The total amount of cells and the proportion of single cells to cell clusters as dispersed phase determine product flow properties as much as the amount of extracellular starch in the continuous fluid phase. Therefore, the iodine binding value of extracellular starch cannot serve as only measure to judge texture of mashed potato products.

Extraction of Hydrogen-Atom Positions of Synthetic Polymers from the2-Dimensional Neutron Diffraction Pattern Taken by an Imaging Plate System

2-Dimensional wide-angle neutron diffraction patterns have been measured successfullyfor the uniaxially-oriented samples of fully-deuterated and fully-hydrogeneouspolyethylene by using BIX-3 imaging plate system installed at the Japan Atomic Energy Research Institute.These data were analyzed in detail and the calculation of Fouriermaps allowed us to extract the positions of hydrogen atoms in the crystal latticeaccurately.The structural parameters obtained after refinement were compared withthose derived from the X-ray and electron diffraction experiments as well as thecomputer simulation result. The accurate determination of hydrogen atomic position byneutron technique makes it possible to perform the exact prediction of physicalproperties of polymer crystals in a quantitative manner.

Aberrations of diffracted wave fields: distortion.

Near-field diffraction patterns are merely aberrated Fraunhofer diffraction patterns. These aberrations, inherent to the diffraction process, provide insight and understanding into wide-angle diffraction phenomena. Nonparaxial patterns of diffracted orders produced by a laser beam passing through a grating and projected upon a plane screen exhibit severe distortion (W311). This distortion is an artifact of the configuration chosen to observe diffraction patterns. Grating behavior expressed in terms of the direction cosines of the propagation vectors of the incident and diffracted orders exhibits no distortion. Use of a simple direction cosine diagram provides an elegant way to deal with nonparaxial diffraction patterns, particularly when large obliquely incident beams produce conical diffraction.

Hydroxyapatite nanostructure material derived using cationic surfactant as a template

This article reports the successful synthesis of mesoporous hydroxyapatite, Ca10(PO4)6(OH)2 (denoted HA) using cationic surfactant as the template. The wide-angle (2θ > 10°) diffraction data revealed characteristic peaks of HA, where a hexagonal lattice structure can be deduced. The lattice structure is found in space group P63/m, the parameters of which are in excellent agreement with reference data; i.e.a = b = 0.9418 nm, c = 0.6884 nm. For small angle diffraction (2θ < 10°), the characteristic peaks occur at 2θ values of 3.30, 5.75, 7.25 and 8.30°, indicating the presence of atomic planes with a periodical spacing of 2.677 nm. Nitrogen adsorption indicated a pore size distribution of approximately 3 nm, and a corresponding pore volume of 0.0113 cm3 g−1, hence the volume ratio of the mesopores was found to be ∼0.036. SEM micrographs reveal a rod-like structure of HA, possessing a thickness of about 50–100 nm and length ranging from 500 to 1000 nm, while TEM micrographs revealed that nano-channels are formed within the rod-like structure. These nano-channels align in a lengthwise direction within the rods, consistent with the cavities being generated by the removal of “organic” CTAB templating structure during calcination. The channels have dimensions of around 3.5 nm and the spaces between the nano-channels are filled with an ordered crystalline HA structure. Comparing the pore size and the spacing between neighboring channels, the pore volume ratio of each rod was calculated to be ∼0.029, which is in agreement with the result from gas adsorption. A probable mechanism is that CTAB–PO43− mixtures form rod-like micelles, which contain many PO43− groups on the surface, and in the presence of Ca2+, Ca9(PO4)6 clusters are preferentially condensed on the rod-shaped micellar surface due to the conformation compatibility between the identical hexagonal shapes of the micelles and Ca9(PO4)6 clusters. The micelles act as nucleating points for the growth of HA crystals. During the thermal incubation stage, CTAB–HA complexes are produced and they coalesce to form a stable three-dimensional rod-like structure. The morphology of the final product shows about 10 layers of HA crystal grows on one micelle during the reaction in water.

Interlayer magnetic coupling for Fe/Si multilayers

The antiferromagnetic (AFM) interlayer exchange coupling for sputtered Fe/Si multilayers have been studied by magnetometry, wide-angle neutron diffraction, and spin-polarized neutron reflectometry. Ferromagnetic resonance and Raman scattering measurements have been applied for the characterization of the multilayers. To look for a possible modification of exchange coupling when Si is replaced by Ge, similar Fe/Ge multilayers have been prepared by the same technique. No AFM coupling has been found for Fe/Ge system. Present results differ in part from the literature data and suggest an influence of the sample preparation on the details of its magnetic properties.

Short-period GaMnAs/GaAs superlattices: Optical and magnetic characterization

Superlattices with magnetic layers containing from 8 to 16 GaMnAs monolayers corresponding to the mixed crystal composition between 5 and 6% of Mn and from 4 to 10 GaAs monolayers were grown by the low temperature MBE technique and characterized by Raman scattering. Folded acoustic phonons were observed for all superlattices in the Raman scattering spectra. The interlayer exchange coupling, found previously by the wide-angle neutron diffraction in selected superlattices was investigated by the spin-polarized neutron reflectometry. It was always of ferromagnetic type, no trace of antiferromagnetic coupling was found.

Microscopic structure studies on the diamond films fabricated by chemical vapor deposition method

The microscopic structures of the diamond films generated on Si (100) substrates by chemical vapor deposition have been studied by x-ray wide angle diffraction spectroscopy, grazing incidence x-ray scattering spectra, positrons annihilation lifetime spectroscopy, and qualitative software and Positronfit program. The di ffraction x-ray spectra show a structure difference between the near substrate p art (NSP) and near free-surface part (NFP) of the diamond film specimens, which reflect the weak ［111］texture in NSP and the strong［220］ texture in NFP. The positron annihilation lifetime spectroscopy of the specirnens and the analyzing data indicate that the majority of positrons annihilate around 200 ps and 400 p s. The vacancies, vacancy clusters, and voids were found in the film specimens, depending on the processes in which the chemical vapor deposition is generated.

デコンボリューションによる粉末Ｘ線回折データからの装置収差の除去

A novel method for eliminating instrumental aberrations from powder X-ray diffraction data has been developed. The method is based on fast Fourier transformation (FFT) combined with abscissa-scale transformation appropriately modeled for each instrumental aberration. All the main aberrations of laboratory powder diffractometer with Bragg-Brentano geometry, (1) Kα2 subpeak, (2) axial-divergence aberration, (3) flat-specimen aberration, and (4) sample transparency effect, can be automatically removed from the whole powder diffraction data ranging wide diffraction angles in quite a simple procedure. Propagation of the statistical errors attached to the source data through the Fourier transformation is also discussed.