Synchrotron Technique Research Articles

High spatial resolution grain orientation and strain mapping in thin films using polychromatic submicron x-ray diffraction

The availability of high brilliance synchrotron sources, coupled with recent progress in achromatic focusing optics and large area two-dimensional detector technology, has allowed us to develop an x-ray synchrotron technique that is capable of mapping orientation and strain/stress in polycrystalline thin films with submicron spatial resolution. To demonstrate the capabilities of this instrument, we have employed it to study the microstructure of aluminum thin film structures at the granular and subgranular levels. Due to the relatively low absorption of x-rays in materials, this technique can be used to study passivated samples, an important advantage over most electron probes given the very different mechanical behavior of buried and unpassivated materials.

Synchrotron X-ray residual strain scanning of a friction stir weld

Synchrotron X-ray strain scanning has been used to determine the residual stress distribution over the cross-sectional area of a friction stir weld across an I-section made of extruded aluminium alloy type AA 7108 in the T79 condition. Measurements were made using the 311 reflection and a wavelength of about 0.35 A. The dominant longitudinal residual stress field is tensile within and to just outside the friction band where the field drops steeply. Further out there are regions of balancing compression falling to near zero at the outer edges of the sample. The longitudinal residual stresses vary within the range from -60 to 140 MPa. The transverse residual stresses are generally weaker but show a more marked through-thickness variation below the friction band. The residual stress maps show detailed features which are related to the heat flow from crown to root faces and differences between the advancing and retreating sides. The results demonstrate that synchrotron strain scanning is a practicable technique for determining non-destructively internal and through-surface residual strains in light element components. The synchrotron technique complements and extends the range at present covered by neutron and X-ray diffraction methods and is capable of substantial development.

The "In Situ" Research of the Synthesis of NiMoO4

The formation of the crystal structure of the NiMoO4 high temperature phase the solid phase reaction NiO+α-MoO3→β-NiMoO4 at 600 C has been in situ studied with the high temperature synchrotron technique. We have performed the measurements of the Extended X-ray Absorption Fine Structure (EXAFS) and the X-ray Absorption Near Edge Structure (XANES) at the K-edge of Ni atom during the -niMoO4synthesis. The analysis of the XANES data and the Fourier transformants of the EXAFS data has led us to the conclusion that at the initial stage of synthesis the nearest oxygen surrounding of Ni atoms the final production reaction has got an unique geometry that differs from the octahedral oxygen surrounding of Ni atoms the both structures of NiO and β-NiMoO4. At the initial stage of the β-NiMoO4 synthesis there is not the final product of the synthesis, but the formation of the β-NiMoO4 crystal structure takes place essentially later, contrary to how it has been considered so far. We have concluded that at the original stage of the β-NiMoO4 synthesis the some intermediate phase is formed that is characterized with the low concentration of nickel and the low symmetrical geometry for the nearest oxygen surrounding of Ni atoms.

Temperature dependence of nuclear forward scattering of synchrotron radiation in alpha -57Fe.

The resonant forward scattering of synchrotron radiation by $^{57}\mathrm{Fe}$ nuclei was investigated over the temperature range from 9.7 to 1048 K. The temperature dependence of the Lamb-M\"ossbauer factor and the internal magnetic field were determined from the observed time spectra. The data presented here demonstrate the suitability of the synchrotron technique for precise measurements of these quantities. In addition these results demonstrate in a straightforward way the difference between the x-ray Debye-Waller factor and the Lamb-M\"ossbauer factor.

The application of synchrotron radiation to X-ray multiple-diffraction studies

Multiple diffraction using parallel-beam synchrotron X-radiation is described. Data recorded on the Daresbury Synchrotron Radiation Source from a single-crystal of InSb are presented and compared with data recorded with the pseudo-Kossel technique. The wide-beam synchrotron technique has demonstrated for the first time the feasibility of the synchrotron radiation multiple-diffraction topographic technique. Potential applications for this technique in the characterization of low-dimensional structures are outlined.

Powder diffraction with synchrotron radiation. I. Absolute measurements

Accurate measurements of the integrated intensities of several reflections from a standard powder sample of Ni have been made using monochromatic synchrotron X-ray radiation of wavelength 1.5413 A from a perfect double-crystal Si(111) monochromator. A perfect Ge(111) analyzer crystal was mounted on the detector arm of the diffractometer to serve as a narrow 'angular' receiving slit. The intensities were placed on an absolute scale by application of the appropriate powder diffraction expressions, which require the incident photon counts, the axial and equatorial openings of the receiving 'slit', and the polarization factor to be known. The procedure for evaluating these instrumental parameters is described in some detail. The quantitative agreement between these and previous absolute measurements on a standard Ni sample with Cu Kα radiation demonstrates that the synchrotron technique can be used for absolute measurements of high accuracy.