F Livet

University of Grenoble, Grenoble, Rhône-Alpes, France

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Publications (78)155.33 Total impact

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    ABSTRACT: The slow magnetic dynamics, from seconds to kiloseconds, of the canonical 3-k antiferromagnet USb have been probed, using X-ray photon correlation spectroscopy (XPCS). In this work, XPCS is combined with resonant X-ray diffraction to focus on scattering at an antiferromagnetic Bragg peak. High quality coherent magnetic diffraction patterns were recorded (speckle contrast of ~ 88%) and magnetic domains were observed; the number of domains increases on warming to T* ~ 160 K, where the spin waves soften to zero frequency, and again on warming to TN = 218 K. The intensity auto-correlation, g2(t), is primarily static over 1000 s, with a small dynamical process (change of ~ 0.4%) that increases in rate close to the transitions.
    Journal of Physics Conference Series 05/2014; 519(1):012010.
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    ABSTRACT: Tensile stress-relaxation measurements have been performed on a series of cross-linked filled elastomers. The fillers are chosen to investigate the effect of the filler–filler and the filler–matrix interactions on the time dependence of the tensile relaxation modulus E(t) after UP and DOWN jumps. For the carbon black-filled sample (strong filler–elastomer interaction) E(t) decreases as log(t) when the strain ε is strictly larger than 0.2 and reached by UP jumps. For the silica-filled samples in the same conditions, and for all samples after a DOWN jump, including ε = 0.2, the experimental data can be fitted with a power law equation characterized by the exponent m. Thus, in all cases, |dE(t)/dt| scales as t−α with α ⩵ m + 1. Pertinence of the soft glassy rheology model for interpreting these results is examined. It is shown that α could be equivalent to the effective noise temperature x and related to the polymer chain mobility. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014
    Journal of Polymer Science Part B Polymer Physics 04/2014; 52(9). · 2.22 Impact Factor
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    ABSTRACT: Coherent x-ray micro-diffraction and local mechanical loading can be combined to investigate the mechanical deformation in crystalline nanostructures. Here we present measurements of plastic deformation in a copper crystal of sub-micron size obtained by loading the sample with an Atomic Force Microscopy tip. The appearance of sharp features in the diffraction pattern, while conserving its global shape, is attributed to crystal defects induced by the tip.
    Journal of Physics Conference Series 05/2013; 425(13).
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    ABSTRACT: The strain field of individual epitaxial sub-micrometric copper islands is studied using coherent X-ray diffraction and finite element modelling. The strain inhomogeneity in each island is so large that the characteristic features of the island shape tend to disappear in the diffraction pattern, which is dominated by strain effects. The model confirms the tensile strain imposed to the island by the thermal mismatch occurring during the preparation of the samples. An evaluation of the residual strain is obtained by qualitatively fitting the diffraction data.
    Thin Solid Films 03/2013; 530:120 - 124. · 1.87 Impact Factor
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    Dataset: lebolloch
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    ABSTRACT: The complexity of the mechanical behavior of filled elastomers can be partly attributed to the fact that the duration of an applied strain plays a crucial role. In order to bring new insights into this still incompletely solved problem, we look for relationships between the macroscopic mechanical relaxation and the relaxation of the filler particles at the nano- to mesoscale. To this end, X-ray photon correlation spectroscopy (XPCS) in homodyne and heterodyne configurations combined with tensile stress relaxation is employed. The paper is devoted to the study of the role of the filler–filler and the filler–matrix interactions in a cross-linked elastomer on the aging mechanisms under strain. The fillers investigated are carbon black, as an example of strong filler–matrix interactions, and hydroxylated silica for which the filler–filler interaction is strong (H-bonds). Homodyne XPCS correlation reveals features of jammed systems (compressed exponential and ballistic motion) for both systems. The exponents characterizing the aging of the homodyne relaxation times are not the same in the carbon black and in the silica filled samples. For both systems, the decrease of the particle velocity determined by heterodyne detection with aging time follows a power law. The silica sample is characterized by a slow decrease of the velocity during aging. For the carbon black sample, the velocity remains small and decreases faster than for the silica sample. The reverse is observed for the behavior of the tensile force.
    Macromolecules 11/2012; 45(21):8691-8701. · 5.93 Impact Factor
  • Frédéric Livet, Mark Sutton
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    ABSTRACT: In a coherent x-ray scattering experiment, interference of the waves diffracted across the sample is observed. This gives a speckle pattern in the observed scattering intensity, whereas a standard experiment leads to diffuse intensity or to broadening of a Bragg peak. Speckles correspond to the disorder configuration of the irradiated volume and their dynamics provide microscopic information of the time evolution of the sample microstructure.After a brief description of the techniques used for the observation of speckles in an x-ray experiment, some examples of measured time dynamics are given. These concern reversible fluctuations and irreversible decomposition of unmixing or ordering alloys. A few experiments in defect imaging are described and the studies opened by free electron lasers are briefly discussed.RésuméEn conditions de diffraction cohérente des rayons X, on observe les interférences entre les ondes diffractées par lʼéchantillon. Cela conduit à lʼobservation de tavelures là où une expérience classique donne une intensité diffuse ou une raie de Bragg élargie. Les tavelures correspondent à la configuration locale du désordre dans le volume irradié.Dans cet article, après une brève description des techniques mises en oeuvre pour observer des tavelures dans une expérience de rayons X, quelques exemples dʼobservation de leur dynamique temporelle sont donnés. On discutera dʼabord le cas de fluctuations réversibles et ensuite de lʼutilisation de cette technique pour étudier la dynamique irréversible de la décomposition dʼalliages à démixtion ou à mise en ordre. On décrira quelque sepériences dʼimagerie des défauts et on discutera des voies ouvertes par lʼapparition des lasers à électrons libres.
    Comptes Rendus Physique 04/2012; 13(3):227–236. · 1.82 Impact Factor
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    ABSTRACT: A Reply to the Comment by L. Pizzagalli et al.
    Physical Review Letters 11/2011; 107(19):199602. · 7.73 Impact Factor
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    ABSTRACT: Using coherent x-ray scattering, we evidenced atomic step roughness at the [111] vicinal surface of a silicon monocrystal of 0.05 degree miscut. Close to the (1/2 1/2 1/2) anti-Bragg position of the reciprocal space which is particularly sensitive to the [111] surface, the truncation rod exhibits a contrasted speckle pattern that merges into a single peak closer to the (111) Bragg peak of the bulk. The elongated shape of the speckles along the[111] direction confirms the monoatomic step sensibility of the technique. This experiment opens the way towards studies of step dynamics on crystalline surfaces.
    Surface Science 02/2011; 605(3-4):390-395. · 1.87 Impact Factor
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    ABSTRACT: We report on a new approach to probe bulk dislocations by using coherent x-ray diffraction. Coherent x rays are particularly suited for bulk dislocation studies because lattice phase shifts in condensed matter induce typical diffraction patterns which strongly depend on the fine structure of the dislocation cores. The strength of the method is demonstrated by performing coherent diffraction of a single dislocation loop in silicon. A dissociation of a bulk dislocation is measured and proves to be unusually large compared to surface dislocation dissociations. This work opens a route for the study of dislocation cores in the bulk in a static or dynamical regime, and under various external constraints.
    Physical Review Letters 02/2011; 106(6):065502. · 7.73 Impact Factor
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    ABSTRACT: The use of coherent x-ray beams has been greatly developing for the past decades. They are now used by a wide scientific community to study biological materials, phase transitions in crystalline materials, soft matter, magnetism, strained structures, or nano-objects. Different kinds of measurements can be carried out: x-ray photon correlation spectroscopy allowing studying dynamics in soft and hard matter, and coherent diffraction imaging enabling to reconstruct the shape and strain of some objects by using methods such as holography or ptychography. In this article, we show that coherent x-ray diffraction (CXRD) brings a new insight in another scientific field: the detection of single phase defects in bulk materials. Extended phase objects such as dislocations embedded in the bulk are usually probed by electron microscopy or X-ray topography. However, electron microscopy is restricted to thin samples, and x-ray topography is resolution-limited. We show here that CXRD brings much more accurate information about dislocation lines (DLs) in bulk samples and opens a route for a better understanding of the fine structure of the core of bulk dislocations. Comment: Article is 8 pages, with 4 figures and 29 references; 6 pages of additional information together with 4 figures
    08/2010;
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    ABSTRACT: Bragg coherent X-ray diffraction imaging is demonstrated with a micro-focused illumination. The 2D projected density of the 3D nano-crystal is successfully retrieved from the inversion of its diffraction intensity pattern. The analysis of the phase field at the sample position, which holds in principle the strain information, emphasizes the high sensitivity of the technique with regard to the wavefront structure. The ptychography approach is a proposed solution to discriminate the wavefront function from the sample electron density distribution. It is based on a redundancy of the collected information obtained by measuring a series of diffraction patterns for different but overlapping beam positions onto the sample. Applicability to the Bragg geometry still needs to be demonstrated.
    Journal of Modern Optics 01/2010; · 1.16 Impact Factor
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    ABSTRACT: Using soft x-ray resonant magnetic scattering with a coherent beam, we find evidence for memory effects in the magnetic configuration of a periodic array of submicron ferromagnetic lines under external magnetic field. The memory effect is explained by the dipolar coupling between the lines which is lost when the sample is saturated by the external magnetic field.
    New Journal of Physics 11/2009; 11(11):113026. · 4.06 Impact Factor
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    ABSTRACT: A high resolution coherent x-ray diffraction experiment has been performed on the charge-density wave (CDW) system K0.3MoO3. The 2kF satellite reflection associated with the CDW has been measured with respect to external dc currents. In the sliding regime, the 2kF satellite reflection displays secondary satellites along the chain axis which corresponds to correlations up to the micrometer scale. This super long-range order is 1500 times larger than the CDW period itself. This new type of electronic correlation seems inherent to the collective dynamics of electrons in charge-density wave systems. Several scenarios are discussed.
    Physical Review Letters 04/2008; 100(9):096403. · 7.73 Impact Factor
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    ABSTRACT: Direct-illumination CCDs find increasing use in coherent X-ray imaging due to their good spatial resolution and signal-to-noise ratio. These CCDs offer a high quantum efficiency for soft X-rays near the $3d$ transition metal $L$ edges. We compare front- and back-illuminated CCDs and describe a method to obtain images with a large dynamic range (five orders of magnitude) and high spatial resolution. Back-illuminated CCDs are resistant to radiation damage at the soft X-ray energies and provide a true 13.5 $\mu$m pixel resolution. High quality diffraction images are obtained in magnetic studies from metallic multilayer structures in reflection geometry.
    The European Physical Journal Applied Physics 01/2008; · 0.71 Impact Factor
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    ABSTRACT: An experimental setup has been developed to perform soft x-ray coherent scattering at beamline ID08 of the European Synchrotron Radiation Facility. An intense coherent beam was obtained by filtering the primary beam with the monochromator and a circular pinhole. A pinhole holder with motorized translations was installed inside the UHV chamber of the diffractometer. The scattered intensity was recorded in reflection geometry with a back-illuminated charge coupled device camera. As a demonstration we report experimental results of resonant magnetic scattering using coherent beam. The degree of coherence is evaluated, and it is shown that, while the vertical coherence is much higher than the horizontal one at the source, the situation is reversed at the diffractometer. The intensity of the coherent beam is also discussed.
    Review of Scientific Instruments 09/2007; 78(9):093901-093901-11. · 1.60 Impact Factor
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    F. Livet
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    ABSTRACT: Erratum to Livet [Acta Cryst. (2007), A63, 63–87].
    Acta Crystallographica Section A Foundations of Crystallography 05/2007; · 2.24 Impact Factor
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    Frédéric Livet
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    ABSTRACT: Methods for carrying out coherent X-ray scattering experiments are reviewed. The brilliance of the available synchrotron sources, the characteristics of the existing optics, the various ways of obtaining a beam of controlled coherence properties and the detectors used are summarized. Applications in the study of the dynamics of speckle patterns are described. In the case of soft condensed matter, the movement of inclusions like fillers in polymers or colloidal particles can be observed and these can reflect polymer or liquid-crystal fluctuations. In hard condensed-matter problems, like phase transitions, charge-density waves or phasons in quasicrystals, the study of speckle fluctuations provides new time-resolved methods. In the domain of lensless imaging, the coherent beam gives the modulus of the sample Fourier transform. If oversampling conditions are fulfilled, the phase can be obtained and the image in the direct space can be reconstructed. The forthcoming improvements of all these techniques are discussed.
    Acta Crystallographica Section A Foundations of Crystallography 04/2007; 63(Pt 2):87-107. · 2.24 Impact Factor
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    ABSTRACT: Frozen-in phason fluctuations in single grains of icosahedral Al-Pd-Mn quasicrystals have been studied by high-resolution coherent X-ray scattering. Bragg peak widths scale as expected for a distribution of uniform phason strains. Strong relaxation of the uniform phason strain is observed after sample annealing. Large intensity fluctuations or speckle patterns are observed in the Bragg peaks due to the uniform phason strain distribution in the sample. Speckle patterns are also observed in the diffuse scattering located close to the Bragg reflections and are related to long-wavelength phason fluctuations taking place in the sample.
    EPL (Europhysics Letters) 01/2007; 54(6):753. · 2.26 Impact Factor
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    ABSTRACT: In a coherent X-ray small-angle experiment, heterodyning between the scattering amplitudes of two samples is obtained by stacking a static reference and a fluctuating sample. Results of homodyne and heterodyne measurements are compared in the case of 98 nm diameter latex particles in glycerol. The method is also used for the study of the slow relaxation process of carbon-black-filled ethylene–propylene elastomers corresponding to the relaxation of the carbon black skeleton after a 100% elongation. On the scale of the 10 µm coherent beam, heterodyning is used to separate fluctuations from long-term flowing of the sample. We show that this flow can be observed for about 10 h, with velocities of the order of nanometres per second. Random fluctuations are dominant in the speckle changes only for large values (q > 2 × 10−2 Å−1) and after a long relaxation time.
    Journal of Applied Crystallography 01/2007; 40. · 3.34 Impact Factor

Publication Stats

423 Citations
155.33 Total Impact Points

Institutions

  • 2014
    • University of Grenoble
      Grenoble, Rhône-Alpes, France
  • 2011
    • European Synchrotron Radiation Facility
      Grenoble, Rhône-Alpes, France
  • 2005–2011
    • Université Paris-Sud 11
      • Laboratoire de Physique des Solides
      Paris, Ile-de-France, France
  • 1996–2003
    • Grenoble Institute of Technology
      Grenoble, Rhône-Alpes, France
  • 2001
    • University Joseph Fourier - Grenoble 1
      • Laboratoire Interdisciplinaire de Physique
      Grenoble, Rhône-Alpes, France