Amorphization of embedded Cu nanocrystals by ion irradiation

While bulk crystalline elemental metals cannot be amorphized by ion irradiation in the absence of chemical impurities, the authors demonstrate that finite-size effects enable the amorphization of embedded Cu nanocrystals. The authors form and compare the atomic-scale structure of the polycrystalline, nanocrystalline, and amorphous phases, present an explanation for the extreme sensitivity to irradiation exhibited by nanocrystals, and show that low-temperature annealing is sufficient to return amorphized material to the crystalline form

Focusing monochromator and imaging-plate camera for grazing-incidence diffraction studies of thin films

A multiple-imaging-plate detector system and focusing monochromator have been developed and successfully applied to the time-resolved study of phase transitions in Langmuir-Blodgett films by grazing-incidence X-ray diffraction (GIXD). The monochromator described here combines fixed-exit-beam height with sagittal focusing of the second crystal. The design is similar to that of Matsushita et nl. [Matsushita, Ishikawa & Oyanagi (1986). Nucl. Instrum. Methods, A246, 377-379], with the exception that the motion of the first crystal is achieved via a computer-controlled X-Y translation table rather than a set of cams. The second crystal is a ribbed Si(111) wafer mounted in a four-point bending mechanism. The first reported application of imaging plates to a GIXD study was carried out by our group and proved to be very successful in the determination of thin-film structure [Foran, Peng, Steitz, Barnes & Gentle (1996). Langmuir, 12, 774-777]. To extend the capabilities of this system, an imaging-plate camera was designed and built which can accommodate up to 13 imaging plates (40 x 20 cm) inside the vacuum chamber of the main diffractometer at the Australian Beamline at the Photon Factory

Observation of hexagonal crystalline diffraction from growing silicate films

Clear evidence for hexagonal crystallinity in surfactant-templated silicate films growing at the air-water interface is presented for the first time. Grazing incidence synchrotron radiation diffraction shows the development of diffraction spots just as the `induction phase', identified previously, is completed. The observed hexagonal diffraction represents the in-plane ordering of the first two-three layers of film formed at the interface

Multiple Scattering Effects on the EXAFS of Ge Nanocrystals

We present a detailed extended x-ray absorption fine structure (EXAFS) spectroscopy study on the influence of multiple scattering effects on the analysis of bulk polycrystalline Ge (c-Ge) and of four Ge nanocrystal (NC) distributions with mean sizes fro

The effects of temperature and pressure on the oxidation state of chromium in silicate melts

The oxidation state of Cr, Cr /ΣCr (where ΣCr = Cr + Cr = 0.35 wt%), in Fe-free silicate glasses quenched from melts equilibrated as a function of pressure to 3.5 GPa at 1500 °C, and as a function of temperature to 1500 °C at atmospheric pressure, and at oxygen fugacities (fO , in log units relative to the quartz-fayalite-magnetite (QFM) buffer) between ∆QFM = − 1 and − 2, was determined by XANES spectroscopy. Increasing temperature stabilises Cr and increasing pressure stabilises Cr . A general expression for Cr /Cr in silicate melts was derived: log(Cr /Cr ) = 1/4(∆QFM + 8.58 − 25,050/T + 940P/T − 0.02P) + 9770/T − 7.69 + 6.22Λ + (900P − 172P )/T, where P is pressure in GPa, T is temperature in K, and Λ is the optical basicity of the composition. This equation reproduces 213 Cr /ΣCr values reported here and in the literature with an average ΔCr /ΣCr of 0.02. A MORB melt at 1400 °C and QFM is predicted to have Cr /ΣCr ~ 0.35 at the surface but Cr /ΣCr ~ 0 at a depth of ~ 60 km. Although Cr is an important oxidation state in silicate melts it is not preserved at low temperatures due to an electron exchange reaction with Fe3+.Part of this work was performed at the Australian National Beamline Facility with support from the Australian Synchrotron Research Program, which was funded by the Commonwealth of Australia under the Major National Research Facilities Progra

Fingerprinting the water site in mantle olivine

Nominally anhydrous minerals such as olivine contain trace amounts of water and may accommodate the entire water budget of the upper mantle. Here we report for the first time synthetic olivines, crystallized experimentally under upper mantle conditions, that reproduce the most common and intense infrared hydroxyl stretching bands (at 3572 and 3525 cm-1) observed in spinel peridotite mantle olivines. These bands arise from water accommodated at point defects associated with the trace element Ti, and we suggest that this is the most important defect site in the shallow upper mantle. Additional hydrated defects may occur at higher pressures. We also identify bands related to water associated with Fe3+; these are unlikely to reflect equilibrium with the mantle, and indicate water incorporation during exhumation or retrogression. Water must be present at the defect site appropriate for the mantle, at the conditions of interest, for partitioning, seismic wave speed, and deformation experiments on hydrous olivine to be relevant