X-ray Measurements (x-ray + measurement)

Distribution by Scientific Domains


Selected Abstracts


Irradiated polymethylmethacrylate studied by positron annihilation spectroscopy

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007
Hamdy F. M. Mohamed
Abstract The effect of gamma irradiation dose on microscopic structure of polymethylmethacrylate (PMMA) has been studied using positron annihilation lifetime (PAL) and Doppler broadening of annihilation radiation (DBAR) techniques. The measurements were performed at room temperature as a function of the ,-irradiation doses from 60-1200 kGy. The observed lifetime spectra were resolved into three components. The size and the fraction of the o-Ps hole volume were estimated from the positron annihilation parameters. The effect of ,-irradiation was identified at lower doses to be cross-linking while at higher doses the chemical degradation of the polymer was observed. Moreover, the distribution of the free volume shifts from a large to small size as the irradiation increases and has very similar Gaussian-like distribution. The PAL results were confirmed with X-ray measurement. A correlation between the macroscopic mechanical properties Hv and positron annihilation parameters has been demonstrated. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


A simple hermetic sample holder for X-ray diffraction analysis of uranium hydride

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2007
Bingyun Ao
In order to help resolve unknowns regarding aging effects of uranium during long-term storage of tritium, a number of experiments have been carried out by several researchers. However, almost no literature is available on the structural change of uranium tritide, mainly because its high toxicity and air-sensitivity render appropriate experiments very difficult. In this paper, a simple hermetic sample holder that fits the Philips X'Pert Pro X-ray diffractometer is described. It may be used to study the aging effects of uranium tritide during storage. The sample holder mainly consists of an aluminium container for sample storage and a Mylar window for X-ray measurements. This sample holder can also be used with other air-sensitive, radioactive and toxic materials. In this paper, the first results obtained from X-ray diffraction analysis of uranium hydride are presented. [source]


X-ray diffraction analysis of GaInNAs double-quantum-well structures

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004
Kiichi Nakashima
The structures of GaInNAs/GaAs double-quantum-well (DQW) samples with various well-layer thicknesses were analysed by X-ray diffraction measurements. Two types of rocking-curve analysis were applied with different scanning configurations: a conventional configuration without a receiving slit and one with an analyser crystal placed in front of the receiving detector (the latter is the same as that usually used in reciprocal-space mapping measurements). It was found that systematic combination of both types of analysis is essential for the characterization of the sample structures. The two types of X-ray profiles obtained using the different scanning configurations exhibit a considerable difference in intensity as the thickness of the well layers increases. The increasing difference clearly indicates deterioration of the DQW structures. The two profiles exhibit little difference in terms of shape, merely showing that the DQW layers are coherently strained relative to the substrate. This implies that measurement in only one of the configurations is insensitive to the deterioration and leads to the wrong conclusion that a sample has a perfect structure without dislocations and defects. Photoluminescence and transmission electron microscope analyses both reveal that defects really do exist in the DQW structures, which is consistent with the difference in intensity observed in the X-ray measurements. From these results, a clear picture that consistently explains the sensitivity of X-ray diffraction analysis to the deterioration of samples is presented. In addition, based on this picture, it is proposed that the procedure of comparing the two types of profiles represents a new type of analysis method for the precise characterization of samples. [source]


Developing 100,ps-resolved X-ray structural analysis capabilities on beamline NW14A at the Photon Factory Advanced Ring

JOURNAL OF SYNCHROTRON RADIATION, Issue 4 2007
Shunsuke Nozawa
NW14A is a newly constructed undulator beamline for 100,ps time-resolved X-ray experiments at the Photon Factory Advanced Ring. This beamline was designed to conduct a wide variety of time-resolved X-ray measurements, such as time-resolved diffraction, scattering and X-ray absorption fine structure. Its versatility is allowed by various instruments, including two undulators, three diffractometers, two pulse laser systems and an X-ray chopper. The potential for the detection of structural changes on the 100,ps time scale at NW14A is demonstrated by two examples of photo-induced structural changes in an organic crystal and photodissociation in solution. [source]


Low-Temperature Aging Behavior of Alumina-Toughened Zirconia

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008
Jens Schneider
The corrosion of alumina-toughened zirconia (ATZ) as a consequence of hydrothermal treatment was investigated, especially the transformation kinetics from tetragonal zirconia to the monoclinic phase. For this purpose, polished ATZ specimens (Ra<5 nm) were aged in water vapor at different temperatures ranging from 70 to 134C. The fraction of the monoclinic phase was determined using X-ray diffraction and Rietveld refinement. The isothermal transformation curves obtained were fitted to the Mehl,Johnson,Avrami equation by least squares. An Arrhenius plot of the fitted transformation rates was used to determine the activation energy and the pre-exponential factor. Following this procedure, the kinetic parameters of the phase transformation were extrapolated down to body temperature and the formation of the monoclinic phase was simulated. In addition, optical interferometry on well-polished specimens (Ra<2 nm) was alternatively used to calculate the monoclinic fraction from the histogram dataset. The results agree very well with those of the X-ray measurements. Additionally, the development of surface roughness with increasing aging time is discussed. [source]


Addition of a Sr, K, Nb (SKN) Combination to PZT(53/47) for High Strain Applications

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007
Niall J. Donnelly
A lead zirconate titanate composition incorporating the dopants Sr, K, and Nb (SKN) in the specific ratio 4:1:3 has been studied. In principle, the SKN should act as a donor dopant but since its addition reduced the grain size from 11.4 ,m (for 1% SKN) to 1.5 ,m (for 5% SKN), the overall effect was found to be more complicated. It was observed that the addition of SKN reduced the Curie temperature, by 16C/mol (%) and broadened the dielectric peak. X-ray measurements further suggested that the ceramic was a mixture of rhombohedral and tetragonal phases and that the room temperature c/a ratio of the tetragonal phase decreased with SKN addition. The piezoelectric coefficient d33, determined from high field unipolar drives, gave an optimum value of 779 pm/V for the 0.02 SKN compositions, which also exhibited a relatively high Curie temperature of 356C. Competing effects of enhanced domain wall mobility from donor doping and reduced mobility due to smaller grain size may explain the observed compositional variation in the measured material properties. Materials based on this composition are attractive for high performance piezoelectric actuator applications such as fuel injection. [source]


X-ray diffraction and Raman study of nanogranular BaTiO3,CoFe2O4 thin films deposited by laser ablation on Si/Pt substrates

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007
J. Barbosa
Abstract Nanocomposite thin films composed by (BaTiO3)1,x,(CoFe2O4)x with different cobalt ferrite concentrations (x) have been deposited by pulsed laser ablation on platinum covered Si(001) substrates. The films structure was studied by X-ray diffraction and Raman spectroscopy. It was found that the CoFe2O4 phase unit cell was compressed along the growth direction of the films, and it relaxed with increasing x. The opposite behavior was observed in the BaTiO3 phase where the lattice parameters obtained from the X-ray measurements presented a progressive distortion of its unit cell with increasing x. The presence of the strain in the films induced a blueshift of the Raman peaks of CoFe2O4 that decreased with increasing CoFe2O4 concentration. Cation disorder in the cobalt ferrite was observed for lower x, where the nanograins are more isolated and subjected to more strain, which was progressively decreased for higher CoFe2O4 content in the films. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Observation of nanocrystals in porous stain-etched germanium

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
V. A. Karavanskii
Abstract Porous nanocrystalline films were prepared by stain etching and subsequent annealing in hydrogen at 600 C. The structural properties of the as-etched and annealed films were investigated using Raman scattering and various X-ray techniques. It was shown that the as-etched film had a thickness of ,2 ,m and consisted of two sublayers of different porosity and amorphous-like microstructure The annealing did not change essentially the porosity and thickness but resulted in notable crystallinity transformation. The results of Raman spectroscopy and X-ray measurements and modelling revealed the presence of germanium nanocrystals with mean sizes of about 8,10 nm in the annealed films. [source]


EuI2, a low-temperature europium(II) iodide phase

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009
Michael Krings
Light-yellow europium(II) diiodide, prepared by the low-temperature reaction of europium and ammonium iodide in liquid ammonia at 200,K and characterized by high-resolution X-ray powder diffraction, represents a new phase for EuI2 that adopts an orthorhombic Pnma structure with all three atoms lying on 4c positions (.m.). It is isotypic with SrI2(IV). Temperature-dependent X-ray measurements performed to investigate the thermal stability of the new phase show that it decomposes irreversibly to amorphous material around 673,K. Total-energy density-functional calculations using the generalized gradient approximation suggest this to be the ground-state structure of EuI2. [source]


`Broken symmetries' in macromolecular crystallography: phasing from unmerged data

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2010
Marc Schiltz
The space-group symmetry of a crystal structure imposes a point-group symmetry on its diffraction pattern, giving rise to so-called symmetry-equivalent reflections. Instances in macromolecular crystallography are discussed in which the symmetry in reciprocal space is broken, i.e. where symmetry-related reflections are no longer equivalent. Such a situation occurs when the sample suffers from site-specific radiation damage during the X-ray measurements. Another example of broken symmetry arises from the polarization anisotropy of anomalous scattering. In these cases, the genuine intensity differences between symmetry-related reflections can be exploited to yield phase information in the structure-solution process. In this approach, the usual separation of the data merging and phasing steps is abandoned. The data are kept unmerged down to the Harker construction, where the symmetry-breaking effects are explicitly modelled and refined and become a source of supplementary phase information. [source]


Instrumentation for synchrotron-radiation macromolecular crystallography

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2006
Eric Girard
X-ray diffraction is an extremely important tool for structure determination of biological macromolecules, to the extent that currently around 85% of Protein Data Bank entries result from X-ray measurements. Many of these structure determinations use synchrotron radiation for data collection. This article aims to give synchrotron users an overview of the functioning of a synchrotron beamline and how the performance of various instruments combines to allow the collection of diffraction data. [source]