Imogolite nanotubes: a 2D x-ray scattering study of films of oriented samples

International audienceInorganic nanotubes represent an emerging class of nanobuilding blocks. Among them, imogolites are alumino-silicate or alumino-germanate nanotubes with well controlled diameter and helicity. As such, they constitute a model platform for the study of molecular interactions and confinement at the nanoscale, complementing the one constituted by carbon nanotubes. We focus here on double-walled alumino-germanate nanotubes, discovered very recently [1]. They are formed of two concentric tubes (figure inset), with respective internal diameters of 1.6 and 3.1nm and up to 1 micron in length [2]. We report the first experimental study, using wide angle x-ray scattering, performed on films of oriented nanotubes (figure). Structural changes of the nanotubes and behavior of the confined water under heating are investigated in-situ. The study of oriented samples gives new information that is not available with powder diffraction. Above all, the contribution to the scattering signal of internal and external tubes can be separated as well as the translational/rotational correlations. The use of wide image plate detectors allows one to access large area of the reciprocal space in a single image. Simulations of the two-dimensionnal scattering diagrams will be presented. A key question, the correlation between internal and external tube, which is of great interest for understanding friction properties at the nanoscale, will be discussed

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

Temporally ordered collective creep and dynamic transition in the charge-density-wave conductor NbSe3

We have observed an unusual form of creep at low temperatures in the charge-density-wave (CDW) conductor NbSe$_3$. This creep develops when CDW motion becomes limited by thermally-activated phase advance past individual impurities, demonstrating the importance of local pinning and related short-length-scale dynamics. Unlike in vortex lattices, elastic collective dynamics on longer length scales results in temporally ordered motion and a finite threshold field. A first-order dynamic phase transition from creep to high-velocity sliding produces "switching" in the velocity-field characteristic.Comment: 4 pages, 4 eps figures; minor clarifications To be published in Phys. Rev. Let

Variable-range hopping in quasi-one-dimensional electron crystals

We study the effect of impurities on the ground state and the low-temperature dc transport in a 1D chain and quasi-1D systems of many parallel chains. We assume that strong interactions impose a short-range periodicicity of the electron positions. The long-range order of such an electron crystal (or equivalently, a $4 k_F$ charge-density wave) is destroyed by impurities. The 3D array of chains behaves differently at large and at small impurity concentrations $N$. At large $N$, impurities divide the chains into metallic rods. The low-temperature conductivity is due to the variable-range hopping of electrons between the rods. It obeys the Efros-Shklovskii (ES) law and increases exponentially as $N$ decreases. When $N$ is small, the metallic-rod picture of the ground state survives only in the form of rare clusters of atypically short rods. They are the source of low-energy charge excitations. In the bulk the charge excitations are gapped and the electron crystal is pinned collectively. A strongly anisotropic screening of the Coulomb potential produces an unconventional linear in energy Coulomb gap and a new law of the variable-range hopping $-\ln\sigma \sim (T_1 / T)^{2/5}$. $T_1$ remains constant over a finite range of impurity concentrations. At smaller $N$ the 2/5-law is replaced by the Mott law, where the conductivity gets suppressed as $N$ goes down. Thus, the overall dependence of $\sigma$ on $N$ is nonmonotonic. In 1D, the granular-rod picture and the ES apply at all $N$. The conductivity decreases exponentially with $N$. Our theory provides a qualitative explanation for the transport in organic charge-density wave compounds.Comment: 20 pages, 7 figures. (v1) The abstract is abridged to 24 lines. For the full abstract, see the manuscript (v2) several changes in presentation per referee's comments. No change in result

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

Friedel oscillations and charge density wave pinning in quasi-one dimensional conductors: Thermal effects

An original interference effect observed in one-dimensional (1D) disordered conductors between X-ray scattering due to the disorder and the charge density wave (CDW)- periodic lattice modulation (PLD) allows to study the pinning of the modulation at local scale. We apply this effect to determine the phase of the CDW at the pinning centres and to show that the response of the CDW to the impurity potential leads to the formation of Friedel oscillations (FO). We report experimental determination and quantitative interpretation of the thermal evolution of both features. The thermal dependence of the interference effect allows one to determine the pinning energy of the 2k$_{\rm F}$-CDW in the V-and W-doped blue bronzes. We show in particular that in these compounds the regular CDW is pinned to the dopant dressed by its FO. In the organic charge transfer salts irradiation leads to an enhancement of the 2k$_{\rm F}$ and 4k$_{\rm F}$ X-ray scattering that we show, by its thermal dependence, to be due to the formation of FO

Friedel oscillation and charge density wave pinning in vanadium-doped blue bronze

An analysis of x-ray data from vanadium-doped blue bronze K$_{0.3}$(Mo$_{\rm 1-x}$V$_{\rm x}$)O$_3$ is presented for x=2.8% and 1.44%. 2k$_{\rm F}$ satellite reflections are broadened in all the directions and exhibit a peculiar profile asymmetry in the chain direction We interpret this profile asymmetry by the presence of Friedel oscillations around the charged vanadium impurities

Presence and role of trace elements in urinary calculi

International audienceAim. - To assess the possible nature and role of trace elements in the pathogenesis of urinary stones. Material and method. - A series of 76 calculi from the East-Algerian region has been investigated through Fourier transform infrared spectroscopy for chemical analysis and X-ray fluorescence for detecting trace elements. Results. - Among the detected trace elements, Zn, Sr, Pb, Cu, Rb and Se, only the first three had significant values. Overall, the calcium components, namely calcium oxalate and calcium phosphate, were the most loaded by these elements contrary to organic components such as uric acid and cystine, which had low contents. Conclusion. - The correlation of contents of Zn and Sr with the stone components (carbapatite, weddellite and whewellite) suggests an adsorption of these trace elements in the case of calcium stones rather than a catalytic process. (C) 2014 Elsevier Masson SAS. All rights reserved

Fullerene-cubane: X-ray Scattering Experiments and Monte Carlo Simulations

We report single-crystal X-ray diffuse scattering measurements on C-60.C8H8 fullerene-cubane showing that the C-60 molecules are orientationally disordered at 300 and 150K and get ordered at low temperatures. Monte Carlo simulations provide further insight in the orientational behavior of both C-60 and C8H8 molecules; low-temperature molecular orientations are predicted