Angular distribution of N-doped carbon nanotubes in alumina membrane channels : A high-energy X-ray diffraction study

An alignment study of multi-wall N-doped carbon nanotubes prepared by a template pyrolytic carbon deposition method inside channels of an alumina membrane has been performed using high-energy X-ray diffraction on the ID15B beamline at the European Synchrotron Radiation Facility (ESRF, Grenoble). The two-dimensional diffraction pattern of the deposited carbon nanotubes, recorded directly, within the alumina membrane, using an image plate detector, exhibits two non-continuous arcs corresponding to the 002 graphitic reflection. The following values of the angle between the axis of the carbon nanotubes lying along the membrane channels and the incident beam were taken for five positions: 0±, 30±, 45±, 60± and 90±. The anisotropic scattering distribution of the two-dimensional patterns indicates an orientational alignment of the nanotubes. The one-dimensional intensity patterns obtained by scanning around the circumference of the (0 0 2) ring have allowed an estimation of the angular distribution of the nanotubes axes

A multiple length scale description of the mechanism of elastomer stretching

Conventionally, the stretching of rubber is modeled exclusively by rotations of segments of the embedded polymer chains; i.e. changes in entropy.</p

Hard X-ray polarimetry with Caliste, a high performance CdTe based imaging spectrometer

Since the initial exploration of soft gamma-ray sky in the 60's, high-energy celestial sources have been mainly characterized through imaging, spectroscopy and timing analysis. Despite tremendous progress in the field, the radiation mechanisms at work in sources such as neutrons stars and black holes are still unclear. The polarization state of the radiation is an observational parameter which brings key additional information about the physical process. This is why most of the projects for the next generation of space missions covering the tens of keV to the MeV region require a polarization measurement capability. A key element enabling this capability is a detector system allowing the identification and characterization of Compton interactions as they are the main process at play. The hard X-ray imaging spectrometer module, developed in CEA with the generic name of Caliste module, is such a detector. In this paper, we present experimental results for two types of Caliste-256 modules, one based on a CdTe crystal, the other one on a CdZnTe crystal, which have been exposed to linearly polarized beams at the European Synchrotron Radiation Facility. These results, obtained at 200-300 keV, demonstrate their capability to give an accurate determination of the polarization parameters (polarization angle and fraction) of the incoming beam. Applying a selection to our data set, equivalent to select 90 degrees Compton scattered interactions in the detector plane, we find a modulation factor Q of 0.78. The polarization angle and fraction are derived with accuracies of approximately 1 degree and 5%. The modulation factor remains larger than 0.4 when essentially no selection is made at all on the data. These results prove that the Caliste-256 modules have performances allowing them to be excellent candidates as detectors with polarimetric capabilities, in particular for future space missions.Comment: 17 pages, 14 figures, 2 tables in Experimental Astronomy, 201

Achieving homogeneity in a high-Fe β-Ti alloy laser-printed from blended elemental powders

Blended Elemental powders are an emerging alternative to pre-alloyed powders in metal additive manufacturing due to the wider range of alloys producible with them and the cost savings from not developing novel feedstock. In this study, in situ alloying and concurrent microstructure evolution during SLM are investigated by performing SLM on a BE Ti-185 powder while tracking the surface temperatures via Infra-red imaging and phase transformation via synchrotron X-ray Diffraction. We then performed post-mortem electron microscopy (Backscatter Electron imaging, Energy Dispersive X-ray Spectroscopy and Electron Backscatter Diffraction) to further gain insight into microstructure development. We show that although exothermic mixing aids the melting process, laser melting results only in a mixture of alloyed and unmixed regions. Full alloying and thus a consistent microstructure is only achieved through further thermal cycling in the heat-affected zone

Local structure of saccharose- and anthracene-based carbons studied by wide-angle high-energy X-ray scattering

A series of porous carbon materials, produced by pyrolysis of saccharose and anthracene and heat treated at 1000, 1900 and 2300 degreesC have been studied by wide-angle X-ray scattering. The X-ray data were collected at European Synchrotron Radiation Facility (ESRF) in Grenoble on the ID15Angstrom beam line (high-energy X-ray diffraction) using a wavelength of E = 116.2 keV, lambda = 0.1067 Angstrom. The data were recorded in the scattering vector range from 0.5 to 24 Angstrom(-1) which enabled them be converted to a real-space representation via the Fourier transform. The structure of these carbons has been described in terms of a model based on disordered, graphite-like layers with very weak interlayer correlations. At higher temperatures the anthracene-based carbon transforms into graphite while the carbon produced from saccharose remains disordered. The graphitization process has been studied in detail by careful analysis of the diffraction data in real and reciprocal space. (C) 2003 Elsevier B.V. All rights reserved

Structural studies of oriented carbon nanotubes in alumina channels using high energy X-ray diffraction

Structural studies of multi-wall carbon nanotubes prepared by template pyrolytic carbon deposition from thermal decomposition of propylene at 800 degrees C inside channels of an alumina membrane have been performed using X-ray diffraction. The two-dimensional diffraction pattern of the deposited carbon nanotubes, recorded directly within the alumina template using an image plate detector, exhibits two dark arcs corresponding to the (002) graphitic reflection. The anisotropic scattering distribution indicates alignment of the nanotubes. The diffracted intensity was measured for the powdered samples after removing the alumina membrane using a point detector. A maximum scattering vector of K-max = 20 angstrom(-1) yielded the radial distribution function, providing evidence that the investigated nanotubes form a distorted hexagonal network that implies the presence of five-membered rings. (C) 2005 Elsevier Ltd. All rights reserved

Structural studies of saccharose- and anthracene-based carbons by high energy X-ray scattering

A series of porous carbon materials, produced by pyrolysis of saccharose and anthracene and heat-treated at 1000 °C, 1900 °C and 2300 °C have been studied by wide-angle X-ray scattering. The X-ray data were collected at European Synchrotron Radiation Facility (ESRF) in Grenoble on the ID 15 beam line (high-energy X-ray diffraction) using the wavelength λ = 0,1067 Å (E = 116,2 keV). The data were recorded in the scattering-vector range from 0.5 to 24 Å- 1 which allowed to conversion to real space via the Fourier transform yielding the radial distribution function of a good quality. Analysis of the experimental radial distribution function shows that carbons produced from anthracene transforms into graphite at 1900 °C and this process is almost complete at 2300 °C. The saccharose-based carbons remain disordered even at high temperature

A sample chamber for in situ high-energy X-ray studies of crystal growth at deeply buried interfaces in harsh environments

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