Guillaume Geandier

Development of a synchrotron biaxial tensile device for in situ characterization of thin films mechanical response

We have developed on the DIFFABS-SOLEIL beamline a biaxial tensile machine working in the synchrotron environment for in situ diffraction characterization of thin polycrystalline films mechanical response. The machine has been designed to test compliant substrates coated by the studied films under controlled, applied strain field. Technological challenges comprise the sample design including fixation of the substrate ends, the related generation of a uniform strain field in the studied (central) volume, and the operations from the beamline pilot. Preliminary tests on 150 nm thick W films deposited onto polyimide cruciform substrates are presented. The obtained results for applied strains using x-ray diffraction and digital image correlation methods clearly show the full potentialities of this new setup.

Elastic-strain distribution in metallic film-polymer substrate composites

Synchrotron x-ray radiation was used for in situstrain measurements during uniaxial tests on polymer substrates coated by a metallic goldfilm 400 nm thick deposited without interlayer or surface treatment. X-ray diffraction allowed capturing both components elastic strains and determining how these were partitioned between the metallic film and the polymeric substrate. For strains below 0.8%, deformation is continuous through the metal-polymer interface while above, the onset of plasticity in the metallic film induces a shift between film and substrate elastic strains.

Benefits of two-dimensional detectors for synchrotron X-ray diffraction studies of thin film mechanical behavior

Performing a complete in situ mechanical property analysis of polycrystallinethin films using X-ray diffraction is time consuming with most standarddiffraction beamlines at synchrotron facilities and not realistic with laboratorydiffractometers. Two-dimensional detection is shown to enable relatively fastandreliableX-raystrainmeasurementsduringinsitutensiletestingofgoldfilmsdepositedonpolyimidesubstrates.Advantagesanddrawbacksintheuseoftwo-dimensional detectors for this type of analysis are discussed for two commonlyused geometries: reflection and transmission.1. IntroductionBoth theoretical and experimental studies have shown thatmaterials that have previously been examined at the micro-metre scale must be re-examined at the nanometre scale inorder to gain a full understanding of their physical properties.When grain sizes decrease to the nanometre scale, mechanicalproperties can be significantly altered from those of similarmicrometre-sized grains (Schiotz et al., 1999; Yip, 1998; VanSwygenhoven WCuenotetal.,2004; Spaepen& Yu, 2004). The processes responsible for these changes arebelieved to be caused mainly by an increase in grain-surfaceeffects and grain-boundary volumes, which become dominantover the bulk at the nanoscale. In a thin film, the changes canalso be caused either by the boundary conditions, whichbecome non-negligible for small film thicknesses at thesurface, at the film–substrate interface or at interfaces inmultilayers, or by constraints imposed by the substrate (Arzt,1998; Meyers et al., 2006). The study of elastic behaviorconsists in choosing a constitutive law using certain elasticconstants. X-ray diffraction is a well known technique used tomeasure very precisely elastic strains in crystalline materials(Hauk, 1997; Noyan & Cohen, 1987). By collecting individualdiffraction peaks or entire sections of diffraction patterns, it ispossible to obtain information about applied or residualmicro- and macro-strain as well as grain orientation (texture).As most crystalline materials are heterogeneous from themechanical point of view, X-ray strain measurements have tobe carried out for several directions, i.e. for different Braggpeaks or/and different lattice planes, to obtain reliable results.The diffractive determination of elastic constants using poly-crystallinesamplesrepresentstheinverseproblemtotheusualexperiment of classical X-ray diffraction residual-stressanalysis. Both problems are rather sensitive to the quality ofthe experimental data and to the micromechanical models.Micromechanical models, such as the self-consistent model,can predict inter-granular effects by accounting for themechanical anisotropy and the texture of the polycrystal(Matthies et al., 2001; Matthies & Humbert, 1995; Bunge et al.,2000). Grain interaction models can be relatively simple for atexture-free case and for a cubic crystal symmetry (Do¨lle,1979), and the so-called sin

Size effects on the Mechanical Behavior of Nanometric W/Cu Multilayers

The mechanical behavior of nanostructured stratified W/Cu composites prepared by ion beam sputtering has been investigated using a method combining X-ray diffraction and tensile testing. Tests were performed on a synchrotron light source to analyze the elastic response of the tungsten phase. Three different microstructures have been analyzed: the specimen composed of the thinner tungsten layers reveals an elastic behavior different from the one expected assuming bulk elastic constants. However, Transmission Electron Microscopy (TEM) and Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) measurements reveal discontinuities in the copper layers. As the strain in the related copper clusters as well grains boundary contributions are not experimentally accessible, atomistic calculation are of utmost importance. Polycrystalline materials have already been constructed through the Voronoi method and thanks to TEM observations. Atomistic simulation and calculation are underway to validation.

Synchrotron Radiation and Neutron Diffraction Study of Hydroxyapatite in Bone at the Interface with Implant

The quantitative evaluation of the preferential orientation of crystallites by the synchrotron and neutron diffraction techniques during regeneration at the interface with implant gives a good prediction of the mechanical properties of the bone. During the process of bone healing after implantation, the speed and quality of regeneration is affected by the nature of the implant surface. Titanium alloy (Ti-Al-4V) is currently coating with the hydroxyapatite (HAp), Ca10(PO4)6 (OH)2, in order to obtain a stable and functional direct connection between bone and implant. At the interface implant-bone, the new bone reconstituted after implantation must have the same mechanical properties of bone in order to accept the implant. Therefore, it is necessary to study by means of two non destructive techniques: neutron diffraction and synchrotron radiation, the crystal growth and texture of this new bone crystals reconstituted at the interface.