In situ nanoindentation of Au crystals imaged by Bragg coherent X-ray diffraction

The mechanical properties of micro- and nanostructures were demonstrated to vary significantly from their bulk counterparts. Despite numerous studies, plasticity at the nanoscale is, however, not fully understood yet. In situ experiments are perfectly suited for the fundamental understanding of the onset of dislocation nucleation. Recently, we developed a scanning force microscope (SFINX) which is compatible with 3rd generation synchrotron beamlines allowing for in situ nano-mechanical tests in combination with nano-focused X-ray diffraction [1] such as coherent X-ray diffraction imaging (CDI). This novel lensless imaging method retrieves the sample scattering function from a coherent X-ray diffraction data set using computational inversion algorithms, thus determining the phase of the scattered amplitude, which is not directly measured by a detector. In Bragg condition, the retrieved phase is directly related to the displacement field and, hence to the strain within a crystal. Please click Additional Files below to see the full abstract

In situ nano-mecanics studies of metallic nanostructures using synchrotron source

Dans cette thèse, le comportement nano-mécanique d’ilots d'Au sub-micrométriques est étudié par nano-indentation in-situ en utilisant le microscope à force atomique SFINX en combinaison avec la microdiffraction de Laue et l’imagerie par diffraction cohérente des rayons X en condition de Bragg (BCDI). Ces études de couplage des rayons X à la nano-indentation ont été menés sur des lignes synchrotron, les lignes ID01 et BM32 à l'ESRF (Grenoble). De nouvelles méthodes ont été développées dans le cadre de cette thèse : une nouvelle technique de mesure de la force appliquée in situ qui repose sur le mesure de la déflexion de la poutre AFM en silicium par microdiffraction de Laue fournissant une résolution de force de 90 nN. Une technique d'imagerie par diffraction cohérente des rayons X en condition de Bragg à plusieurs longueurs d'ondes (Multi Wavelength BCDI) qui permet un BCDI in situ réel pendant les tests nano-mécaniques. Les tests mécaniques couplés à la micro diffraction de Laue ont permis de déterminer la densité de dislocation dans un cristal d'or en fonction de la force appliquée mettant en évidence un recuit mécanique par la baisse de la densité des dislocations géométriquement nécessaires (GND). La technique de MW-BCDI a été utilisée lors de l'indentation in situ d'un mono cristal d'Au et a permis de visualiser en 3D l'évolution des dislocations. Elle a aussi montré la disparition des dislocations après un déchargement complet, laissant derrière elle un cristal d'or sans défaut. Ces expériences de couplage in situ permettent d'apporter de nouveaux éléments de réponse concernant la nucléation des premiers défauts dans des nano-structures métalliques CFCThe nano-mecanic behavior of Au sub-micronic islands has been studied by in situ nano-indentation using the atomic force microscope SFINX coupled with the Laue X ray microdiffraction and the Bragg coherent diffraction imaging (BCDI°techniques. These coupled studies have been led on synchrotron beamlines, ID01 and BM32 at the ESRF (France Grenoble). New methods have been developped during this PHD work : a mesure of the in situ applied force by measuring the deflexion of the AFM Si cantilever by Laue microdiffraction with a resolution of 90 nm. A brand new multi-wavelength BCDI approach allowing real in situ nano-mecanical tests coupled with X ray diffraction. The mecanical tests coupled with Laue microdiffraction led to the determination of defaults density in a Au nanocristal function of the applied force, which demonstrated a mecanical annealing by the drop of the GNDs. The mw-BCDI has also be coupled with nanoindentation tests on a Au nano-cristal, which allowed us to visualize in 3D the evolution and the nucleation of dislocations. It also showed the disapearing of the dislocations after a full unloading, leaving the nano-cristal with no defaults. These in situ coupled experiments will shed some new light about the nucleation of the first defaults in metalic FCC nanostructure

In Situ Coherent X-ray Diffraction during Three-Point Bending of a Au Nanowire: Visualization and Quantification

International audienceThe three-point bending behavior of a single Au nanowire deformed by an atomic force microscope was monitored by coherent X-ray diffraction using a sub-micrometer sized hard X-ray beam. Three-dimensional reciprocal-space maps were recorded before and after deformation by standard rocking curves and were measured by scanning the energy of the incident X-ray beam during deformation at different loading stages. The mechanical behavior of the nanowire was visualized in reciprocal space and a complex deformation mechanism is described. In addition to the expected bending of the nanowire, torsion was detected. Bending and torsion angles were quantified from the high-resolution diffraction data

In‐situ force measurement during nano‐indentation combined with Laue microdiffraction

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In Situ Nano-Indentation of a Gold Sub-Micrometric Particle Imaged by Multi-Wavelength Bragg Coherent X-ray Diffraction

International audienceThe microstructure of a sub-micrometric gold crystal during nanoindentation is visualized by in situ multi-wavelength Bragg coherent X-ray diffraction imaging. The gold crystal is indented using a custom-built atomic force microscope. A band of deformation attributed to a shear band oriented along the (221) lattice plane is nucleated at the lower left corner of the crystal and propagates towards the crystal center with increasing applied mechanical load. After complete unloading, an almost strain-free and defect-free crystal is left behind, demonstrating a pseudo-elastic behavior that can only be studied by in situ imaging while it is invisible to ex situ examinations. The recovery is probably associated with reversible dislocations nucleation/annihilation at the side surface of the particle and at the particle-substrate interface, a behavior that has been predicted by atomistic simulations. The full recovery of the particle upon unloading sheds new light on extraordinary mechanical properties of metal nanoparticles obtained by solid-state dewetting

Variable-wavelength quick scanning nano-focused X-ray microscopy for in situ strain and tilt mapping

International audienceCompression of micro-pillars is followed in situ by a quick nano-focused X-ray scanning microscopy technique combined with three-dimensional reciprocal space mapping. Compared to other attempts using 2 X-ray nanobeams, it avoids any motion or vibration that would lead to a destruction of the sample. The technique consists of scanning both the energy of the incident nano-focused X-ray beam and the in-plane translations of the focusing optics along the X-ray beam. Here, we demonstrate the approach by imaging the strain and lattice orientation of Si micro-pillars and their pedestals during in situ compression. Varying the energy of the incident beam instead of rocking the sample and mapping the focusing optics instead of moving the sample supplies a vibration-free measurement of the reciprocal space maps without removal of the mechanical load. The maps of strain and lattice orientation are in good agreement with the ones recorded by ordinary rocking-curve scans. Variable-wavelength quick scanning X-ray microscopy opens the route for in situ strain and tilt mapping towards more diverse and complex materials environments, especially where sample manipulation is difficult

Variable‐Wavelength Quick Scanning Nanofocused X‐Ray Microscopy for In Situ Strain and Tilt Mapping

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Simultaneous Multi-Bragg Peak Coherent X-ray Diffraction Imaging

International audienceThe simultaneous measurement of two Bragg reflections by Bragg coherent X-ray diffraction is demonstrated on a twinned Au crystal, which was prepared by the solid-state dewetting of a 30 nm thin gold film on a sapphire substrate. The crystal was oriented on a goniometer so thattwo lattice planes fulfill the Bragg condition at the same time. The Au 111 and Au 200 Bragg peaks were measured simultaneously by scanning the energy of the incident X-ray beam and recording the diffraction patterns with two two-dimensional detectors. While the former Bragg reflection is not sensitive to the twin boundary, which is oriented parallel to the crystal–substrate interface, the latter reflection is only sensitive to one part of the crystal. The volume ratio between the two parts of the twinned crystal is about 1:9, which is also confirmed by Laue microdiffraction of the same crystal. The parallel measurement of multiple Bragg reflections is essential for future in situ and operando studies, which are so far limited to either a single Bragg reflection or several in series, to facilitate the precise monitoring of both the strain field and defects during the application of external stimuli