Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

International audienceA prototype X-ray pixel area detector (XPAD3.1) has been used for X-ray diffraction experiments with synchrotron radiation. The characteristics of this detector are very attractive in terms of fast readout time, high dynamic range and high signal-to-noise ratio. The prototype XPAD3.1 enabled various diffraction experiments to be performed at different energies, sample-to-detector distances and detector angles with respect to the direct beam, yet it was necessary to perform corrections on the diffraction images according to the type of experiment. This paper is focused on calibration and correction procedures to obtain high-quality scientific results specifically developed in the context of three different experiments, namely mechanical characterization of nanostructured multilayers, elastic-plastic deformation of duplex steel and growth of carbon nanotubes

Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector

A prototype X-ray pixel area detector (XPAD3.1) has been used for X-ray diffraction experiments with synchrotron radiation. The characteristics of this detector are very attractive in terms of fast readout time, high dynamic range and high signal-to-noise ratio. The prototype XPAD3.1 enabled various diffraction experiments to be performed at different energies, sample-to-detector distances and detector angles with respect to the direct beam, yet it was necessary to perform corrections on the diffraction images according to the type of experiment. This paper is focused on calibration and correction procedures to obtain high-quality scientific results specifically developed in the context of three different experiments, namely mechanical characterization of nanostructured multilayers, elastic-plastic deformation of duplex steel and growth of carbon nanotubes

The phase of iron catalyst nanoparticles during carbon nanotube growth

We study the Fe-catalyzed chemical vapor deposition of carbon nanotubes by complementary in situ grazing-incidence X-ray diffraction, in situ X-ray reflectivity, and environmental transmission electron microscopy. We find that typical oxide supported Fe catalyst films form widely varying mixtures of bcc and fcc phased Fe nanoparticles upon reduction, which we ascribe to variations in minor commonly present carbon contamination levels. Depending on the as-formed phase composition, different growth modes occur upon hydrocarbon exposure: For γ-rich Fe nanoparticle distributions, metallic Fe is the active catalyst phase, implying that carbide formation is not a prerequisite for nanotube growth. For α-rich catalyst mixtures, Fe3C formation more readily occurs and constitutes part of the nanotube growth process. We propose that this behavior can be rationalized in terms of kinetically accessible pathways, which we discuss in the context of the bulk iron–carbon phase diagram with the inclusion of phase equilibrium lines for metastable Fe3C. Our results indicate that kinetic effects dominate the complex catalyst phase evolution during realistic CNT growth recipes.S.H. acknowledges funding from ERC grant InsituNANO (No. 279342). We acknowledge the European Synchrotron Radiation Facility (ESRF) for provision of synchrotron radiation facilities. We acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University. C.T.W. and C.S.E. acknowledge funding from the EC project Technotubes. A.D.G. acknowledges funding from the Marshall Aid Commemoration Commission and the National Science Foundation. R.S.W. acknowledges funding from EPSRC (Doctoral training award) and B.C.B. acknowledges a Research Fellowship at Hughes Hall, Cambridge.This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/cm301402g

Growth of aligned multi-walled carbon nanotubes: First in situ and time-resolved X-ray diffraction analysis

International audienceCatalytic chemical vapour deposition has become a method of choice to produce carbon nanotubes (CNT), particularly for the synthesis of aligned nanotube forests. But a thorough understanding of the mechanisms for CNT nucleation, growth and alignment is still missing. In situ and time resolved experiments allowing to study these processes in real conditions are required. We have developed a specific reactor and furnace to perform such experiments using X-ray diffraction (XRD). Experiments were performed at synchrotron SOLEIL. XRD patterns were recorded as a function of time, during nucleation and growth. We present here our first results, discussing the interest of the XRD method with respect to other existing in situ methods

Text-book of human physiology, including histology and microscopical anatomy, with especial reference to the practice of medicine,

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Anomalous thermal expansion of γ -iron nanocrystals inside multiwalled carbon nanotubes

International audienceThe thermal expansion of α-Fe (ferrite) and γ -Fe (austenite) nanocrystals confined inside multiwalled carbon nanotubes (MWCNTs) is studied in situ, using synchrotron x-ray diffraction, as a function of temperature. While the thermal expansion of ferrite is similar to that of bulk material, a peculiar behavior is evidenced for austenite: The thermal expansion becomes abnormally high above 500 ◦C. A scenario involving progressive carbon uptake in γ -Fe nanocrystals gives a satisfactory understanding of the phenomenon, and allows one to propose a value of the carbon solubilization rate in γ -Fe particles confined inside MWCNTs