Strains Induced by Point Defects in Graphene on a Metal

Strains strongly affect the properties of low-dimensional materials, such as graphene. By combining in situ, in operando, reflection high energy electron diffraction experiments with first-principles calculations, we show that large strains, above 2%, are present in graphene during its growth by chemical vapor deposition on Ir(111) and when it is subjected to oxygen etching and ion bombardment. Our results unravel the microscopic relationship between point defects and strains in epitaxial graphene and suggest new avenues for graphene nanostructuring and engineering its properties through introduction of defects and intercalation of atoms and molecules between graphene and its metal substrate

Local deformations and incommensurability of high quality epitaxial graphene on a weakly interacting transition metal

We investigate the fine structure of graphene on iridium, which is a model for graphene weakly interacting with a transition metal substrate. Even the highest quality epitaxial graphene displays tiny imperfections, i.e. small biaxial strains, ca. 0.3%, rotations, ca. 0.5^{\circ}, and shears over distances of ca. 100 nm, and is found incommensurate, as revealed by X-ray diffraction and scanning tunneling microscopy. These structural variations are mostly induced by the increase of the lattice parameter mismatch when cooling down the sample from the graphene preparation temperature to the measurement temperature. Although graphene weakly interacts with iridium, its thermal expansion is found positive, contrary to free-standing graphene. The structure of graphene and its variations are very sensitive to the preparation conditions. All these effects are consistent with initial growth and subsequent pining of graphene at steps

Topography of the graphene/Ir(111) moiré studied by surface x-ray diffraction

International audienceThe structure of a graphene monolayer on Ir(111) has been investigated {\it in situ} in the growth chamber by surface x-ray diffraction including the specular rod, which allows disentangling the effect of the sample roughness from that of the nanorippling of graphene and iridium along the moiré-like pattern between graphene and Ir(111). Accordingly we are able to provide precise estimates of the undulation associated with this nanorippling, which is small in this weakly interacting graphene/metal system and thus proved difficult to assess in the past. The nanoripplings of graphene and iridium are found in phase, i.e. the in-plane position of their height maxima coincide, but the amplitude of the height modulation is much larger for graphene ($0.379 \pm 0.044$ \AA) than, {\it e.g.}, for the topmost Ir layer ($0.017 \pm 0.002$ \AA). The average graphene-Ir distance is found to be $3.38 \pm 0.04$ \AA

Bioinspired Design for Lightweighting and Vibration Behavior Optimization in Large-Scale Aeronautical Tooling: A Comparative Study

A comparative study is presented, focusing on three different bioinspired design methodologies applied to a large-scale aeronautical tooling use case. The study aims to optimize the structure in terms of the first vibration mode, minimizing mass, and supporting operational loads. The development of lightweight metallic components is of great importance for industries such as aerospace, automotive, and energy harvesting, where weight reduction can lead to significant improvements in performance, efficiency, and sustainability. Bioinspired design offers a promising approach to achieving these goals. The study begins with an introduction to natural selection and various bioinspired concepts. It proceeds with a thorough review of the selected bioinspired design methodologies and tools, which are then applied to the chosen use case. The outcomes for each methodology were explored with respect to the design requirements. Subsequently, the most suitable design was selected according to the success criteria defined and its validation is explained. The manufacturing of this design was carried out using an advanced and novel approach specifically tailored to accommodate the large dimensions and complexity of the structure. Finally, modal testing was performed to validate the entire process, and the results obtained demonstrate the potential effectiveness of bioinspired design methodologies in achieving lightweighting and optimizing vibration modes for large-scale aeronautical tooling.The Government of the Basque Country and the Aquitane Euskadi Network in Green Manufacturing and Ecodesign (LTC ÆNIGME) are acknowledged for their support through the project EKOHEGAZ, grant KK-2021/00092. In the same way, the OASIS consortium in the frame of the European Union’s Horizon 2020 research and innovation programme under grant agreement No 814581 is acknowledged for support through the project BioFLY

Full reciprocal-space mapping up to 2000 K under controlled atmosphere: the multipurpose QMAX furnace

We acknowledge the ESRF and the French Collaborating Research Group (F-CRG) for provision of synchrotron radiation facility beamtime. H. Song is thanked for his work on the preliminary thermomechanical calculations and the general sizing of the furnace. The building of the furnace has been realized under the technical supervision of D. de Barros. The experiments on the sapphire vicinal surfaces and on the IUCr zirconia powder were realized with the valuable help of C. Matringe (IRCER) and J. B. Marijon (PIMM), respectively. The authors are thankful to I. Cabodi and O. Bories (Saint-Gobain CREE) for the supply of the bulk-zirconia-based materials. M. Huger and F. Gouraud from the IRCER laboratory and T. O¨ rs and V. Michel from the PIMM labora-tory are strongly thanked for their involvement during these experiments. The oxidation experiments were realized in the frame of a research program funded by the CEA Paris–Saclay Centre in collaboration with R. Guillou, M. Lesaux, D. Menut and J. L. Bechade, who are also gratefully acknowledged.A furnace that covers the temperature range from room temperature up to 2000 K has been designed, built and implemented on the D2AM beamline at the ESRF. The QMAX furnace is devoted to the full exploration of the reciprocal hemispace located above the sample surface. It is well suited for symmetric and asymmetric 3D reciprocal space mapping. Owing to the hemispherical design of the furnace, 3D grazing-incidence small- and wide-angle scattering and diffraction measurements are possible. Inert and reactive experiments can be performed at atmospheric pressure under controlled gas flux. It is demonstrated that the QMAX furnace allows monitoring of structural phase transitions as well as microstructural evolution at the nanoscale, such as self-organization processes, crystal growth and strain relaxation. A time-resolved in situ oxidation experiment illustrates the capability to probe the high-temperature reactivity of materials.The QMAX furnace has been designed and built as part of the QMAX Project No. ANR-09-NANO-031 funded by the French National Research Agency (ANR). Experiments on the bulk-zirconia-based samples were done in the frame of the ASZTECH research program funded by the ANR (ANR-12-RMNP-0007)

Revealing hidden species diversity in closely related species using nuclear SNPs, SSRs and DNA sequences - a case study in the tree genus Milicia

Background: Species delimitation in closely related plant taxa can be challenging because (i) reproductive barriers are not always congruent with morphological differentiation, (ii) use of plastid sequences might lead to misinterpretation, (iii) rare species might not be sampled. We revisited molecular-based species delimitation in the African genus Milicia, currently divided into M. regia (West Africa) and M. excelsa (from West to East Africa). We used 435 samples collected in West, Central and East Africa. We genotyped SNP and SSR loci to identify genetic clusters, and sequenced two plastid regions (psbA-trnH, trnC-ycf6) and a nuclear gene (At103) to confirm species’ divergence and compare species delimitation methods. We also examined whether ecological niche differentiation was congruent with sampled genetic structure. Results: West African M. regia, West African and East African M. excelsa samples constituted three well distinct genetic clusters according to SNPs and SSRs. In Central Africa, two genetic clusters were consistently inferred by both types of markers, while a few scattered samples, sympatric with the preceding clusters but exhibiting leaf traits of M. regia, were grouped with the West African M. regia cluster based on SNPs or formed a distinct cluster based on SSRs. SSR results were confirmed by sequence data from the nuclear region At103 which revealed three distinct ‘Fields For Recombination’ corresponding to (i) West African M. regia, (ii) Central African samples with leaf traits of M. regia, and (iii) all M. excelsa samples. None of the plastid sequences provide indication of distinct clades of the three species-like units. Niche modelling techniques yielded a significant correlation between niche overlap and genetic distance. Conclusions: Our genetic data suggest that three species of Milicia could be recognized. It is surprising that the occurrence of two species in Central Africa was not reported for this well-known timber tree. Globally, our work highlights the importance of collecting samples in a systematic way and the need for combining different nuclear markers when dealing with species complexes. Recognizing cryptic species is particularly crucial for economically exploited species because some hidden taxa might actually be endangered as they are merged with more abundant species

Human ectoparasites and the spread of plague in Europe during the Second Pandemic

Plague, caused by the bacterium Yersinia pestis, can spread through human populations by multiple transmission pathways. Today, most human plague cases are bubonic, caused by spillover of infected fleas from rodent epizootics, or pneumonic, caused by inhalation of infectious droplets. However, little is known about the historical spread of plague in Europe during the Second Pandemic (14-19th centuries), including the Black Death, which led to high mortality and recurrent epidemics for hundreds of years. Several studies have suggested that human ectoparasite vectors, such as human fleas (Pulex irritans) or body lice (Pediculus humanus humanus), caused the rapidly spreading epidemics. Here, we describe a compartmental model for plague transmission by a human ectoparasite vector. Using Bayesian inference, we found that this model fits mortality curves from nine outbreaks in Europe better than models for pneumonic or rodent transmission. Our results support that human ectoparasites were primary vectors for plague during the Second Pandemic, including the Black Death (1346-1353), ultimately challenging the assumption that plague in Europe was predominantly spread by rats

Laue microdiffraction on polycrystalline samples above 1500 K achieved with the QMAX-µLaue furnace

MRSEI-HoTMIXX-ray Laue microdiffraction aims to characterize microstructural and mechanical fields in polycrystalline specimens at the sub-micrometre scale with a strain resolution of ∼10−4. Here, a new and unique Laue microdiffraction setup and alignment procedure is presented, allowing measurements at temperatures as high as 1500 K, with the objective to extend the technique for the study of crystalline phase transitions and associated strain-field evolution that occur at high temperatures. A method is provided to measure the real temperature encountered by the specimen, which can be critical for precise phase-transition studies, as well as a strategy to calibrate the setup geometry to account for the sample and furnace dilation using a standard α-alumina single crystal. A first application to phase transitions in a polycrystalline specimen of pure zirconia is provided as an illustrative example

Mitogen‐activated protein kinase activity drives cell trajectories in colorectal cancer

In colorectal cancer, oncogenic mutations transform a hierarchically organized and homeostatic epithelium into invasive cancer tissue lacking visible organization. We sought to define transcriptional states of colorectal cancer cells and signals controlling their development by performing single-cell transcriptome analysis of tumors and matched non-cancerous tissues of twelve colorectal cancer patients. We defined patient-overarching colorectal cancer cell clusters characterized by differential activities of oncogenic signaling pathways such as mitogen-activated protein kinase and oncogenic traits such as replication stress. RNA metabolic labeling and assessment of RNA velocity in patient-derived organoids revealed developmental trajectories of colorectal cancer cells organized along a mitogen-activated protein kinase activity gradient. This was in contrast to normal colon organoid cells developing along graded Wnt activity. Experimental targeting of EGFR-BRAF-MEK in cancer organoids affected signaling and gene expression contingent on predictive KRAS/BRAF mutations and induced cell plasticity overriding default developmental trajectories. Our results highlight directional cancer cell development as a driver of non-genetic cancer cell heterogeneity and re-routing of trajectories as a response to targeted therapy