[show abstract][hide abstract] 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
Journal of Physics Conference Series 05/2013; 425(13).
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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.
[show abstract][hide abstract] ABSTRACT: Using coherent x-ray scattering, we evidenced atomic step roughness at the  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  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 direction confirms the monoatomic step sensibility of the technique. This experiment opens the way towards studies of step dynamics on crystalline surfaces.
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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.
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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
[show abstract][hide abstract] 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.
[show abstract][hide abstract] ABSTRACT: A straightforward way of measuring X-ray intensity fluctuation spectroscopy in a small-angle X-ray scattering configuration is demonstrated using heterodyne techniques. Two examples are presented: the Brownian motion of latex spheres in glycerol, and a Doppler velocity experiment demonstrating the motion and the relaxation of carbon-black-filled elastomers after uniaxial stretching. In the latter case the effects of mechanical relaxation can be separated from those of aggregate diffusion. The results suggest that the dynamics of these filled elastomers are similar to the universal features observed in disordered jammed systems.
[show abstract][hide abstract] ABSTRACT: Small-angle X-ray scattering (SAXS) performed down to small q values (q <or= 10(-3) A(-1)) is a powerful method for investigating the arrangement of filler aggregates in filled elastomers under uniaxial strain. Meanwhile, for vulcanized samples, zinc oxide is used as an additive. Owing to their high contrast, the ZnO particles remaining in the manufactured composite are strong X-ray scatterers. In the low-q domain, their scattering hides that of filler aggregates (carbon black, pyrogenic silica) and must be quantified in order to be suppressed. To this end, anomalous SAXS (ASAXS) and small-angle neutron scattering (SANS) have been performed. It is shown that ASAXS measurements can be performed down to small q values (q <or= 10(-3) A(-1)). Therefore ASAXS is well adapted to separate the contributions of ZnO and filler scattering. For neutron scattering the contrast of the ZnO particles is similar to that of carbon. Because the amount of ZnO is much smaller than that of filler, ZnO scattering can be neglected. Owing to multiple scattering effects, however, SANS can only be used for very thin samples (less than about 0.25 mm). It is shown that, providing multiple scattering is avoided, ASAXS and SANS yield similar scattering curves for the filler aggregates.
[show abstract][hide abstract] ABSTRACT: We report on the dynamics of phason modes in the i-Al-Pd-Mn icosahedral quasicrystal, measured between room temperature and 650°C, using the X-ray Intensity Fluctuation Spectroscopy technique (XIFS). Up to 500°C, the auto-correlation function ℑ(q, t) displays almost no time evolution as expected for frozen-in phason fluctuations at low temperature. At higher temperatures, ℑ(q, t) follows a single exponential time decay from which the characteristic time τ c (q) is extracted. These results are compared with the expected shape of ℑ(q, t) as derived from the expressions of the eigenvalues and eigenvectors of the C ⊥⊥ (q) phason dynamical matrix. In agreement with the hydrodynamic theory of quasicrystals which predicts phasons with diffusive character, we find that τ c (q) varies linearly with q -2 at 650°C. The corresponding diffusion coefficient is 2.2(± 0.5)×10 -18 m².s -1 and the activation energy is estimated around 2.3(± 1) eV.