Engineering the properties of semiconductors by changing their crystalline phase is a technologically and economically relevant alternative to doping using foreign elements, with strong potential for photonic and electronic applications. Although major advances have been reported recently for crystal-phase engineering of III-V and group IV semiconductor nanowires, interfacing two mismatched crystalline phases in a nanostructure induces several deformation mechanisms, which remain largely unexplored. Here, using state-of-the-art synchrotron X-ray nanobeam diffraction and transmission electron microscopy, subtle twisting and bending is unveiled within an individual GaAs nanowire containing cubic and hexagonal segments. Their role is discussed in accommodating the inter-reticular spacing fluctuations, and their variations are correlated to the nanoscale phase distribution and to the effect of the NW support. This study brings direct evidence of a complex combination of deformation mechanisms in biphasic nanowires, which opens a new path to tune the nanowire properties with appealing perspectives for device engineering in nanophotonics and nanomechanics.

Recent advancements in organic photovoltaics (OPVs) have focused on improving both efficiency and mechanical robustness, yet critical insights into the structural and mechanical properties of the materials remain underexplored, particularly in the context of intrinsically stretchable OPVs. These devices hold great promise for applications in wearable and portable electronics, offering exciting possibilities for energy generation in innovative use cases. This study presents novel findings on the structural and mechanical behavior of PM6:Y12 blends, processed using a green solvent and two deposition techniques: spin-coating and blade-coating. We demonstrate that the blade-coating technique, performed in air, results in more ordered blend layers, with a significant increase in crystalline domain size from 67 & Aring; to 136 & Aring;. Additionally, we examine the effects of annealing and focus on the behavior of as-cast blend layers. In an original approach, we studied the mechanical response of these films by in situ GIXRD under tensile strain on stretchable TPU/PEDOT:PSS substrates, revealing that the as-cast PM6:Y12 blend can sustain up to 7% tensile strain. These findings provide valuable insights into the structural and mechanical properties of PM6:Y12 blends, providing a pathway for the development of stretchable OPVs.

X-ray photon correlation spectroscopy (XPCS) has become a pivotal technique for exploring nanoscale dynamic phenomena across various materials, facilitated by advancements in synchrotron radiation sources and beamline upgrades. The recent Extremely Brilliant Source (EBS) upgrade at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, has notably improved brilliance and coherence length, thereby enhancing the capabilities of XPCS and related techniques. Here, we present a dedicated setup on the D2AM beamline at the ESRF, enabling simultaneous XPCS and wide-angle X-ray scattering measurements. The setup developed and its performance are detailed in the first part. Then, the XPCS capabilities are evaluated by studying polymer-based materials, with particular attention to the effects of temperature, crystallinity and macromolecular orientation on polymer dynamics. The study on the influence of temperature revealed that XPCS in the case of entangled polymers is an efficient technique to probe the dynamics of the macromolecular network, complementary to classical spectroscopy techniques. In addition, in situ measurements during the polymer crystallization revealed that increased crystallinity slows down macromolecular dynamics. Conversely, studies on stretched samples indicate that macromolecular orientation accelerates these dynamics. This work represents a novel investigation into the effect of crystallinity on macromolecular dynamics using XPCS, opening new avenues for research in polymer science.

The development of Ge-rich GeSbTe (GGST) alloys significantly enhanced the high-temperature stability required for Phase-Change Memory technology. Previous studies on Ge enrichment in GeSbTe (GST) materials with Sb-over-Te ratio lower than one (Sb/Te<1) highlighted the segregation into cubic Ge and cubic GST phases. Such a segregated cubic GST phase is metastable and presents a polycrystalline structure with disordered grain boundaries that could lead to structural relaxation and then to drift phenomena. In this work, using resistivity measurements, Raman spectroscopy, and in situ x-ray diffraction analyses, we demonstrate for the first time to our knowledge that GGST with Sb/Te higher than one (Sb/Te>1) upon annealing leads to the direct formation of a GST hexagonal phase featuring a high growth speed, bypassing the cubic metastable phase. Combined with Ge enrichment, the increased value of the activation energy of the nucleation of Sb/Te>1 GGST alloys ensures a high stability of the amorphous phase. Finally, nitrogen introduction further stabilizes the system against the crystallization, without compromising the high crystalline growth speed and the formation of the stable GST hexagonal phase in alloys with Sb/Te>1. These results demonstrate the possibility to tune the crystalline structure of the segregated phases in Ge-rich GeSbTe alloys, combining the stability at high temperature of the amorphous phase with the high crystallization speed and uniformity (with larger grains) of a targeted GST phase.

Solid-state reactions play a key role in materials science. The evolution of the structure of a single 350 nm Ni3Fe nanoparticle, i.e., its morphology (facets) as well as its deformation field, has been followed by applying multireflection Bragg coherent diffraction imaging. Through this approach, we unveiled a demixing process that occurs at high temperatures (600 degrees C) under an Ar atmosphere. This process leads to the gradual emergence of a highly strained core-shell structure, distinguished by two distinct lattice parameters with a difference of 0.4%. Concurrently, this transformation causes the facets to vanish, ultimately yielding a rounded core-shell nanoparticle. This final structure comprises a Ni3Fe core surrounded by a 40 nm Ni-rich outer shell due to preferential iron oxidation. Providing in situ 3D imaging of the lattice parameters at the nanometer scale while varying the temperature, this study & horbar;with the support of atomistic simulations & horbar;not only showcases the power of in situ multireflection BCDI but also provides valuable insights into the mechanisms at work during a solid-state reaction characterized by a core-shell transition.

High-energy Bragg coherent diffraction imaging (BCDI)can enablethree-dimensional imaging of atomic structure within individual crystallitesin complex environments. Here, we show that sufficient coherent photonflux is available to extend the BCDI technique to higher energiesto (1) obtain improved strain information and sensitivity at the nanoscalewith higher order Bragg reflections, (2) exploit BCDI in embeddedmaterials or complex operando environments, (3) reduceX-ray induced sample modification, and (4) minimize dynamical scatteringeffects. We demonstrate the nanoscale imaging technique on the samesub-micrometer sized crystal at 8.5, 19.9, and 33.4 keV by takingadvantage of the brilliance and coherence of the fourth generationExtremely Brilliant Source of the ID01 beamline at ESRF - The EuropeanSynchrotron (Grenoble, France). The photon flux, data quality, resolutionand strain information are compared. We also show the first coherentdiffraction measurements performed at the ID31-EBS beamline at anenergy of 41 keV.

At the nanoscale, the properties of materials depend critically on the presence of crystal defects. However, imaging and characterizing the structure of defects in three dimensions inside a crystal remain a challenge. Here, by using Bragg coherent diffraction imaging, we observe an unexpected anomalous {110} glide plane in two Pt submicrometer crystals grown by very different processes and having very different morphologies. The structure of the defects (type, associated glide plane, and lattice displacement) is imaged in these faceted Pt crystals. Using this noninvasive technique, both plasticity and unusual defect behavior can be probed at the nanoscale.

Surface strain is widely employed in gas phase catalysis and electrocatalysis to control the binding energies of adsorbates on active sites. However, in situ or operando strain measurements are experimentally challenging, especially on nanomaterials. Here we exploit coherent diffraction at the new fourth-generation Extremely Brilliant Source of the European Synchrotron Radiation Facility to map and quantify strain within individual Pt catalyst nanoparticles under electrochemical control. Three-dimensional nanoresolution strain microscopy, together with density functional theory and atomistic simulations, show evidence of heterogeneous and potential-dependent strain distribution between highly coordinated ({100} and {111} facets) and undercoordinated atoms (edges and corners), as well as evidence of strain propagation from the surface to the bulk of the nanoparticle. These dynamic structural relationships directly inform the design of strain-engineered nanocatalysts for energy storage and conversion applications. Surface strain can be used in gas phase catalysis and electrocatalysis to control the binding energies of adsorbates on active sites, but in situ or operando strain measurements can be challenging. Coherent diffraction now allows strain inside individual Pt nanoparticles to be mapped and quantified under electrochemical control.

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Nanostructures with specific crystallographic planes display distinctive physico-chemical properties because of their unique atomic arrangements, resulting in widespread applications in catalysis, energy conversion or sensing. Understanding strain dynamics and their relationship with crystallographic facets have been largely unexplored. Here, we reveal in situ, in three-dimensions and at the nanoscale, the volume, surface and interface strain evolution of single supported platinum nanocrystals during reaction using coherent x-ray diffractive imaging. Interestingly, identical { hkl } facets show equivalent catalytic response during non-stoichiometric cycles. Periodic strain variations are rationalised in terms of O 2 adsorption or desorption during O 2 exposure or CO oxidation under reducing conditions, respectively. During stoichiometric CO oxidation, the strain evolution is, however, no longer facet dependent. Large strain variations are observed in localised areas, in particular in the vicinity of the substrate/particle interface, suggesting a significant influence of the substrate on the reactivity. These findings will improve the understanding of dynamic properties in catalysis and related fields.

Surface strain is widely used in gas phase catalysis and electrocatalysis to control the binding energies of adsorbates on metal surfaces. However, $in$ $situ$ or $operando$ strain measurements are experimentally challenging, especially on nanomaterials. Here, we take advantage of the 4$^{th}$ generation Extremely Brilliant Source at the European Synchrotron Radiation Facility (ESRF-EBS, Grenoble, France) to quantify the distribution of strain inside a Pt nanoparticle, and to determine its morphology in an electrochemical environment. Our results show for the first time evidence of heterogeneous and potential-dependent strain distribution between highly-coordinated ({100} and {111} facets) and under-coordinated atoms (edges and corners) as well as evidence of strain propagation from the surface to the bulk of the nanoparticle. These results provide dynamic structural insights to better simulate and design efficient nanocatalysts for energy storage and conversion applications.

Bragg coherent X-ray diffraction is a nondestructive method for probing material structure in three dimensions at the nanoscale, with unprecedented resolution in displacement and strain fields. This work presents Gwaihir, a user-friendly and open-source tool to process and analyze Bragg coherent X-ray diffraction data. It integrates the functionalities of the existing packages bcdi and PyNX in the same toolbox, creating a natural workflow and promoting data reproducibility. Its graphical interface, based on Jupyter Notebook widgets, combines an interactive approach for data analysis with a powerful environment designed to link large-scale facilities and scientists.

On one hand, coherent diffraction imaging (CDI) in Bragg geometry has emerged as a unique 3D microscopy of nanocrystals thanks to 3rd generation synchrotron sources.Away from absorption edges and at space-group allowed reflections, it provides not only the electronic density, but also, encoded in the phase, the atomic displacement field with respect to the mean lattice, which in turn reveals crystal strain, defects and domains [1][2][3].On the other hand, some crystal structures have crystallographic reflections which are forbidden by the spacegroup symmetry but can nevertheless be observed at a suitable X-ray absorption edge, due to the anisotropy of the tensor of scattering (ATS) [4].They are several orders of magnitude weaker than allowed reflections, but the absence of Thomson scattering allows the observation of various electronic phenomena related to electronic orders (magnetic, charge, orbital), as well as static and dynamic atomic displacements.The new generation of synchrotron sources, such as the ESRF "Extremely Bright Source", opens opportunities to perform CDI on such weak reflections.Here we report on the measurement of the ( 115) forbidden reflection of a GaN nanopillar at the Ga K edge (Figure 1).Sufficient statistics could be obtained in a total accumulation time of ~30 minutes for an entire rocking curve to retrieve the phase of the scattering function (Figure 2).Such measurement at high temperature would provide an image of the inhomogeneity of thermal motion in the crystal [5], which would be particularly interesting close to surfaces, inversion domain boundaries [3] and crystal defects.This proof-of-principle experiment demonstrates that forbidden reflections are a new opportunity for CDI with the new synchrotron sources.

published or not.The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

come from teaching and research institutions in France or abroad, or from public or private research centers.L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.In situ 3D observations of a core-shell volume transition in an Ni 3 Fe nanocrystal using Bragg coherent X-ray diffraction imaging

Variations in the interatomic distances lead to altered d-band centre for a given metal, and provide an elegant way to control its activity towards (electro)catalytic reactions (“strain-engineering” approach). The effect of strain was rationalized within the frame of the d-band theory of Hammer and Nørskov in the late 1990s [1,2]. The authors predicted that the rate of the sluggish oxygen reduction reaction (ORR) can be enhanced on catalysts binding *OH ca. 0.10 - 0.15 eV more weakly than Pt(111), [1, 2] and this prediction was experimentally verified using a Pt3Ni(111)-skin surface.[3] Nevertheless, these predictions hardly translated to nanomaterials, because of the wide variety of catalytic sites configurations. Also, the d-band theory mostly considers catalytic surfaces in vacuum, without any effect related to the electrical double layer and adsorption/desorption processes. Hence, an in situ picture of how strain develops on Pt-based surfaces is still lacking. In this contribution, we took benefit of recent advances in Bragg Coherent Diffraction Imaging (BCDI) [4, 5]and of the fourth generation Extremely Brilliant Source of the European Synchrotron (ESRF-EBS, Grenoble, France) to map strain over Pt nanoparticles in situ. Our results show that adsorption of anions causes appearance of compressive strain at under-coordinated (edges and corners) atoms and tensile strain at highly-coordinated ({001} and {111} facets) atoms. Strain heterogeneity increases with the electrode potential and reaches as large as 0.08 %. at ORR-relevant potential. These results provide direct insights into the dynamics of Pt nanoparticles in an electrochemical environment, and have direct consequences for electrocatalysis in general, and for ORR electrocatalysis in particular. Ackowledgements This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant n° 818823). FM acknowledges the financial support from the French National Research Agency in the frame of the BRIDGE project (grant n° ANR-19-ENER-0008-01). References [1] B. Hammer, J. K. Nørskov, Surf. Sci. 1995, 343, 211. [2] B. Hammer, Y. Morikawa, J. K. Nørskov, Phys. Rev. Lett. 1996, 76, 2141. [3] V. R. Stamenkovic, B. Fowler, B. S. Mun, G. Wang, P. N. Ross, C. A. Lucas, N. M. Markovic, Science 2007, 315, 493. [4] I. Robinson, R. Harder, Nat. Mater. 2009, 8, 291. [5] J. Carnis, A. R. Kshirsagar, L. Wu, M. Dupraz, S. Labat, M. Texier, L. Favre, L. Gao, F. E. Oropeza, N. Gazit, E. Almog, A. Campos, J.-S. Micha, E. J. M. Hensen, S. J. Leake, T. U. Schülli, E. Rabkin, O. Thomas, R. Poloni, J. P. Hofmann, M.-I. Richard, Nat. Commun. 2021, 12, 5385. Figure 1. Schematic representation of observed strain distribution over a Pt nanoparticle in 0.05 M H2SO4. Figure 1