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À l'occasion du bicentenaire des découvertes d'André-Marie Ampère dans le domaine de l'électromagnétisme, le Musée Ampère, nommé déjà « Maison des Illustres » en 2013 par le ministère de la Culture, vient de recevoir le 6 octobre 2021 le label "EPS Historic Site". Le Musée Ampère est ainsi devenu le cinquième site français inscrit dans la liste des sites historiques de la physique européenne.

International audience; Cutting and folding 2D systems is one of the explored paths to tune physical and chemical properties in one-atom-thick matter. Contrary to graphene, boron nitride (BN) nanoribbons are difficult to obtain, and folded BN nanoribbon structures have not been reported yet. Here, we show that pressure application in multiwalled boron nitride nanotubes leads to different types of tube internal organizations including BN nanoribbon formation and folds. The new structures are associated with the breaking of a number of the internal tubes, leading to either nonorganized structures in the form of internal tube alveoli or an organized stacking of folded h-BN nanoribbons. Irreversible changes in the morphology of multiwalled BN nanotubes (MWBNNTs) take place from ∼7 GPa, and morphologically modified tubes could be observed up to pressures of at least 49 GPa. The experimental probes utilized included high-resolution transmission microscopy, electron tomography, and Raman spectroscopy. Atomistic modeling shows the formation of pinch structures along the tubes that favor pressure-induced bond-breaking and hybridization changes and confirm the folded structure. Both experiments and modeling show that tube polygonization is a prominent characteristic of MWBNNTs even at ambient pressure. Overall, the pressure evolution of MWBNNTs strongly differs from their carbon analogues. The high mechanical stability of BN tube geometry is of interest for composite-based structural materials. On the other side, the availability of h-BN nanoribbons and folded structures opens new prospects to produce physically modified BN properties.

Filling carbon nanotubes with molecules is a route for the development of electronically modified one-dimensional hybrid structures for which the interplay between the electronic structure of molecules and nanotubes is a key factor. Tuning these energy levels with external parameters is an interesting strategy for the engineering of new devices and materials. Here we show that the hybrid system composed by quaterthiophene (4T) molecules confined in single-walled carbon nanotubes, presents a piezo-Raman-resonance of the molecule vibrational pattern. This behavior manifests as a rapid pressure induced enhancement of the 4T Raman mode intensities compared to the tubes G-band Raman modes. Density functional theory calculations allow to explain the spectral behaviour through the pressure-enhanced quaterthiophene resonance evolution. By increasing pressure, the tube cross-section deformation leads to a reduction of the intermolecular distance, to the splitting of the molecular levels and then to an increase of resonance channels. Calculations and experiments converge to the 4T piezo-resonance scenario associated with the pressure-induced nanotube radial collapse observed at about 0.8 GPa. Our findings offer possibilities for the development of pressure transducers based on molecule-filled carbon nanotubes.

Human–elephant coexistence remains a major conservation and livelihood challenge across elephant Loxodonta africana range in Africa. This study investigates the extent of elephant crop damage on 66 farms in the Selous–Niassa corridor (Tanzania), to search for potential management solutions to this problem. We found that the relative abundance of highly preferred crops (area covered by preferred crops divided by the total area of each farm) was by far the most important factor determining crop damage by elephants. Eighteen crop types were ranked according to their preference by elephants. Sweet potatoes, bananas, peanuts, onions, pumpkins and maize were the most preferred crops, with maize the most common crop among those highly preferred. On average elephants damaged 25.7% of the cultivated farmland they entered. A beta regression model suggests that a reduction in the cultivation of preferred crops from 75 to 25% of the farmland area decreases elephant crop damage by 64%. Water availability (distance to the nearest waterhole) and the presence of private investors (mostly hunting tourism companies) were of lower importance in determining elephant crop damage. Thus, damage by elephants increased with shorter distances to waterholes and decreased in areas with private investors. However, further studies are required, particularly of the perceived costs and benefits of elephants to local communities. Farm aggregation and the use of non-preferred crops that also require less water would potentially reduce elephant damage but would be a major lifestyle change for some local communities.

International audience; Modulation of electronic properties of bilayer materials through the strain and doping mismatch between layers opens new opportunities in 2D material straintronics. We present here a new approach allowing to generate asymmetric strain or doping between layers and a method to quantify it using a supported isotopically labeled bilayer graphene studied by in situ Raman spectroscopy. Strain differences up to ∼0.1% between the two graphene layers have been obtained by applying pressures of up to 10 GPa with nonpolar solid environments. However, when immersed in a liquid polar environment, namely, a mixture of ethanol and methanol, a piezo-doping mismatch between layers is observed. This asymmetrical doping increases with pressure, leading to charge concentration differences between layers of the order of 1013 cm–2. Our approach thus allows disentangling strain and doping effects in high-pressure experiments evidencing the asymmetries of these phenomena and comforting isotopic bilayer graphene as a benchmark system for the study of asymmetric effects in devices or composite surfaces.

We have explored the effect of high pressure post-treatment in optimizing the properties of carbon nanotube yarns and found that the application of dry hydrostatic pressure reduces porosity and enhances electrical properties. The CNT yarns were prepared by the dry-spinning method directly from CNT arrays made by the hot filament chemical vapour deposition (HF-CVD) process. Mechanical hydrostatic pressure up to 360 MPa induces a decrease in yarn resistivity between 3% and 35%, associated with the sample’s permanent densification, with CNT yarn diameter reduction of 10%–25%. However, when increasing the pressure in the 1–3 GPa domain in non-hydrostatic conditions, the recovered samples show lower electrical conductivity. This might be due to concomitant macroscopic effects such as increased twists and damage to the yarn shown by SEM imaging (caused by strong shear stresses and friction) or by the collapse of the CNTs indicated by in situ high pressure Raman spectroscopy data.

In Mediterranean areas, severe drought events are expected to intensify in forthcoming years as a consequence of climate change. These events may increase physiological and reproductive stress of wild populations producing demographic changes and distribution shifts. We used retrospective life tables to understand demographic changes on a wild population after severe drought events. We studied the impact of two extreme events (2003 and 2005) on the population dynamics of our model species, the red deer (Cervus elaphus). During both years, population density was high (40 and 36 ind/100 ha, respectively). Thus, we reconstructed retrospectively the age structure of the female part of the population for the period 2000–2010 by using data of known‐age individuals culled during the period 2000–2019 (n = 4176). Also, based on previous study results, we aimed to validate this methodology. Both extremely dry years, 2003 and 2005, produced marked and lasting cohort effects on population demography. Age pyramid the following years (2004 and 2006) revealed that the extreme drought caused the female fawn cohort to be similar or even smaller than the yearling cohort. Furthermore, these cohort effects were still perceptible 3 years after these severe events. Results agree with previous findings that showed a negative effect of severe drought events on female pregnancy rates and conception dates. Although simple, this study provides an empirical quantification of the demographic effects of severe drought events for a wild population which might be useful to understand future demographic changes under the context of climate change., Retrospective life tables for wild populations of animals might be a useful tool to assess future demographic changes under the context of climate change. Using this methodology, we provided an empirical quantification of the demographic effects of severe drought events for a wild red deer population.

A diamond shatters easily, despite it being the hardest natural material. Atomically disordered forms of diamond made from buckyballs might not only overcome this problem, but also allow other properties to be optimized. Syntheses of amorphous and paracrystalline forms of diamond.

The classical buckling problem, studied by Euler himself, is still important in many fields where macroscale or nanoscale structures may fail under compression. The impact of discrete or atomic structure on the critical buckling load is of paramount interest, yet the physics is still insufficiently understood. This study combines experiment and theory to solve that enigma: Phonon dispersion relations are at the heart of the physics of the buckling of both discrete and continuous structures. This insight will have an impact on engineering solutions, from nanostructures where molecular details prevail, to medical stents that naturally feature discretized polygonal symmetry.

International audience; Carbon nanotubes have extraordinary mechanical properties, but modifications of their structure tend to weaken them. Here, we have studied by experiments and modelling the one-dimensional filling of single chirality (6,5) carbon nanotubes with iodine and water. We show that iodine-filling can enhance the pressure of radial collapse of these nanotubes by a factor 2 compared to the empty (6,5) tubes. For water filling, this enhancement factor reduces to 1.4. Our single-chirality study allows correlating the different Raman signatures of the radial collapsing process, which was not possible in samples with mixed chiralities. A clear spectroscopic signature of the collapse pressure can thus be given: it is the pressure at which the G-band frequency evolution with pressure softens while the radial breathing mode intensity vanishes. These new criteria for the detection of radial collapse allow correcting some existing discrepancies in the literature. Finally, we discuss the impact of molecular filling on the radial mechanical stability as a function of the tube diameter. It results that molecular filling allows for a superior stability effect than filling with tubes (i.e. multi-wall carbon nanotubes). The stability enhancement tends to grow with the tube diameter and depends strongly on the nature of the filling molecules.

Carbon nanotubes tend to collapse when their diameters exceed a certain threshold, or when a sufficiently large external pressure is applied on their walls. The radial stability of tubes has been studied in each of these cases, however a general theory able to predict collapse is still lacking. Here, we propose a simple model predicting stability limits as a function of the tube diameter, the number of walls and the pressure. The model is supported by atomistic simulations, experiments, and is used to plot collapse phase diagrams. We have identified the most stable carbon nanotube, which can support a maximum pressure of ∼ 18 GPa before collapsing. The latter was identified as a multiwall tube with an internal tube diameter of ∼ 12 nm and ∼ 30 walls. This maximum pressure is lowered depending on the internal tube diameter and the number of walls. We then identify a tube diameter domain in which the radial mechanical stability can be treated as equivalent to macroscopic tubes, known to be described by the canonical Levy-Carrier law. This multiscale behavior is shown to be in good agreement with experiments on the collapse of O-rings, proposed as a simple macroscopic parallel to nanotubes in this domain.

International audience; We perform a theoretical study of an atomically thin, two-dimensional layer obtained by positioning atoms at the vertices of the classical Pythagorean tiling. This leads to an unusual geometrical pattern that is only stable for the three halogens Cl, Br, and I. In this Pythagorean structure, halogen atoms are arranged in strongly bound diatomic units that bind together by weaker electrostatic bonds. The energy of these phases is competitive with those of the low-temperature phase of the halogens and the two-dimensional layer obtained by exfoliating it. The Pythagorean layers are semiconducting, with an unusual band structure composed of very mobile holes and extremely heavy electrons. They are also soft, exhibiting small values of the elastic constants and a very low energy flexural mode. Analysis of the allowed Raman transitions reveals breathing-like modes that might be used to fingerprint, experimentally, the Pythagorean structure. Finally, we present a series of substrates that, due to lattice matching and compatible symmetry, can be used to stabilize these peculiar two-dimensional layers.

International audience; Competition between microscopic point defect (vacancy and interstitial) configurations is inherent to crystalline phases of increased structural complexity. Phase transitions that preserve symmetry between them belong to a specific class of isostructural transitions. Type-I silicon clathrates are representatives of such structurally complex crystalline phases showing an intriguing structural transition at high pressure associated with an abrupt reduction of volume with no indication for any breakage of symmetry. Using isothermal high-pressure X-ray diffraction performed on a single crystal of the simplest representative type-I silicon clathrates, binary Ba 8 Si 46 , we confirm the isostructural character of the transition and identify the associated mechanism. A detailed analysis of the atomic structural parameters across the transition in combination with ab initio studies allow us to pinpoint a microscopic mechanism driven by a rearrangement of point defects initially present in the structure. An analysis based on the Landau theory gives a coherent description of the experimental observations. A discussion on the analogy between this transformation and liquid-liquid transitions is proposed.

International audience; Metallization and dissociation are key transformations in diatomic molecules at high densities particularly significant for modeling giant planets. Using X-ray absorption spectroscopy and atomistic modeling, we demonstrate that in halogens, the formation of a connected molecular structure takes place at pressures well below metallization. Here we show that the iodine diatomic molecule first elongates by ∼0.007 Å up to a critical pressure of Pc ∼ 7 GPa, developing bonds between molecules. Then its length continuously decreases with pressure up to 15–20 GPa. Universal trends in halogens are shown and allow us to predict for chlorine a pressure of 42 ± 8 GPa for molecular bond-length reversal. Our findings contribute to tackling the molecule invariability paradigm in diatomic molecular phases at high pressures and may be generalized to other abundant diatomic molecules in the universe, including hydrogen.

International audience; Nanoscale coal deformation affects thegeomechanics response of coal structure under external stress conditions. In this study, insitu small-angle neutron scattering (SANS) is used to characterize the evolution of nanopore structures under uni-axial compression on an Illinois coal specimen. Porod invariant mapping is used to estimate apparent porosities at different azimuthal angles. Structure-free orientation factors, including the alignment factor and Hermans’ orientation factor, are used to characterize orientation degree in nanopores quantitatively. The nanoscale pore deformation and evolution with stress have not been directly measured before, and the insitu SANS technique offers the unique capability to probe the nanoscale rock deformation. From the results, higher values of apparent porosities are shown near the coal bedding direction.At dif-ferent azimuthal angles, the apparent porosities increase with increasing uniaxial stress in the elastic deformation range (54–575bar) for the measured coal. The pore-scale degree of orientation is a size-dependent parameter, and pore orientation along the coal bedding generally increases as pore size increases. The degree of orientation in nanopores on average (in a size range between ~ 2 × 103Å and ~ 15Å) tends to increase first and then decreases with increasing stress loading, although different from that of macropores, indicating higher stresses on the nanopore edges along the bedding direction and then on the nanopore body along the normal direction. There is no distinct permanent change ofporosity within the measured stress range (0–575 bar)after the stress relief

The radial stability and the irreversible transformation of triple-wall carbon nanotubes (TWCNTs) bundles are investigated at high pressure conditions both experimentally and theoretically (exp. up 72 GPa). The tubes having a mean internal diameter of 0.83 nm and graphite-like intertube distance, show an onset of the radial collapse evidenced by the evolution of optical phonons. The nanotube collapse onset is observed at ∼ 22 GPa completes for the two external tubes at ∼ 29 GPa, however the innermost tube remains stable up to ∼ 37 GPa. Molecular dynamic calculations performed on smaller diameter TWCNTs bundles, as a model system, confirmed the multiple-stage pressure-induced collapse process. An analytical expression for the collapse pressure of carbon nanotubes having an arbitrary number of walls is proposed. Our experiments and modelling show that for pressures beyond ∼ 60 GPa an irreversible structural transformation of TWCNTs takes place. Ex situ transmission electron microscopy characterization on the recovered sample from 72 GPa revealed the mechanical failure of carbon nanotubes which evolve towards ribbon-like structures as corroborated by Raman spectroscopy. Modelling the tubes evolution at high pressure and high temperature showed the formation of new structures ranging from ribbon-like to graphite-like with either different degrees of amorphization or s p 3 interlinking.

Wild ungulate numbers are increasing and expanding across most woody systems of the Northern Hemisphere. Simultaneously, wildfire risk has risen considerably over the last decades due to anthropogenic climate change and the increasing continuity of heavier fuel loads. It is therefore imperative to evaluate how human-made structures aimed at wild ungulate management (e.g., supply points) and wildfire prevention and suppression (e.g., firebreaks) affect ungulate use and woody vegetation at increasing distances from the structures to manage forestland accordingly. This study investigates the use of firebreaks and artificial supply points by wild ungulates and the derived effects on woody vegetation (plant damage, fuel load, woody plant diversity and regeneration) along a distance gradient from the human-made structures. Particularly, we examine the effects of a large wild ungulate (Ammotragus lervia) on a highly diverse Mediterranean vegetation following a distance gradient (10–50–100 m) from supply points and firebreaks. Our results show that ungulate habitat use decreased with distance to structures. Both supply points and firebreaks also showed greater plant damage (browsing, trampling and rubbing) and lower fuel load as distance to structures decreased but effects were rather constant within 50 m (∼1 ha) around the structures, indicating a non-linear relationship along the distance gradient. Woody species richness also increased with distance to firebreaks and supply points but changes in plant composition (beta-diversity) were small (0.80–0.87 similarity), mostly due to limited regeneration and heavy use by ungulates along the gradient, which mostly favored the regeneration of ungulate-resistant plants (non-palatable or resprouting). Importantly, supply points showed significantly greater ungulate effects as compared to firebreaks at any distance for all the study variables. Thus, supply points showed, on average, 1.8 times greater browsing damage than firebreaks at any distance from the boundary. Similarly, fuel load between 100 and 10 m from the structures was reduced by 78% in supply points but only by 20% in firebreaks. Managers should carefully consider the location and distribution of firebreaks and supply points throughout the landscape given their differential capacity to attract ungulates and their associated effects on fuel load reduction and woody plant communities. Fire-prone areas within the landscape can benefit from the combined use of firebreaks and supply points to reduce fuel load at a low cost but regeneration of ungulate-sensitive and threatened taxa should be considered.

The effect of pressure – by definition a 3-dimensional concept – on 2-dimensional systems brings a number of fundamental questions, which have been partly answered through newly engineered samples and experimental setups. In this review of the high-pressure Raman studies of graphene, we will in particular underline the importance of the presence of a supporting substrate and its role for the production of biaxial strain conditions in high pressure experiments. Raman shifts observed during these experiments may be related to the strain induced by the substrate rather than by the applied pressure, graphene stress, and hydrostatic pressure not being straightforwardly equivalent in this case of a composite 2D-on-3D material. We will also consider the effects of the nature of the substrate surface, the nature of the pressure transmittingmedia, aswell as the effect of the number of layers on the high-pressure response of the 2D–system, by using the phonon behavior as strain probe as pressure is applied. The effects of adhesion and of strain transfer from the substrate to the 2D–system will be at the heart of our discussion.

Understanding the factors that lead to variation in the timing of breeding in widespread species such as red deer (Cervus elaphus) is crucial to predict possible responses of wild populations to different climate scenarios. Here, we sought to further understand the causes of inter-annual variation in the reproduction timing of female deer in Mediterranean environments. An integrative approach was used to identify the relative importance of individual, population and climate traits in the date of conception of free-ranging deer, based on a dataset of 829 hinds culled during 12 years. We found that a population trait, density, was the most important factor explaining the variation in conception dates, with greater densities causing later conception dates. Body mass was the second in importance, with heavier females conceiving earlier than lighter ones. Almost equally important was the spring real bioclimatic index, a measure of plant productivity, causing later conception dates in the least productive springs (drier and hotter). Another climatic component, the end of summer drought, showed that the sooner the autumn arrives (greater rainfalls and cooler temperatures) the earlier the conception dates. Interestingly, age class was found to be a minor factor in determining conception date. Only older females (≥10 years old) conceived significantly later, suggesting reproductive senescence. This study highlights not only the importance of population and individual traits but also the influence of climatic parameters on the deer reproductive cycle in Mediterranean environments, giving valuable insight into how reproductive phenology may respond to seasonality and global climate changes.

International audience; The evolution of the pore structure of compressed expanded vermiculite was investigated in situ under uniaxial stress up to 3200 bar using small-angle neutron and X-ray scattering. The studied samples have a lamellar texture in which the presence of oriented oblate pores was revealed by the anisotropic small-angle scattering patterns. The initial pore size distribution and the mechanical behaviour of the pellets at working pressure conditions are strongly related to the applied initial stresses used to pre-compact the vermiculite powder. Our study shows that the porous structure of the pellets was not modified under compression up to the pre-compaction pressure. Higher densification is associated with increasing anisotropy of the pore–matrix interface structure. The pore–matrix interface could be described with fractal geometry. The stress dependence of the system fractal dimension, apparent specific surface area and total porosity was determined and related to the meso- and macropore evolution under uniaxial stress.

Reflets de la Physique, Revue de la société française de Physique; International audience; Première femme à avoir accédé au rang de professeur titulaire au Massachussetts Institute of Technology (MIT),Mildred Spiewak Dresselhaus, ou simplement Millie pourla plupart de ses collègues, est l’exemple d’un engagement passionnel et infatigable pour la science en général, la physique en particulier, et pour la reconnaissancede la place des femmes en science.Sa disparition le 20 février 2017 à l’âge de 86 ans, en pleine activité scientifique, a très profondément marqué les communautés de chercheurs engagés dansles nanosciences. Ses contributions à la compréhension du couplage entre propriétés électroniques,vibrationnelles et structurales, dans les différentes formesde carbone sont au centre du développement des nanomatériaux carbonés et de leurs applications.

Rewilding and translocations of large herbivores for conservation purposes have increased in recent times, with numerous introductions inside and outside their native range. This study aims to analyze the use of threatened plant taxa as a possible ecological indicator of large herbivore introductions. We examined the effects of a threatened large ungulate, the Barbary sheep (Ammotragus lervia), on both endangered and vulnerable woody taxa after its introduction in 1970. Contrary to our hypothesis, the herbivore impact on threatened woody species was higher than that found on widespread woody plants. The results reveal that 35.7% of the threatened species showed the highest possible level of herbivore damage in contrast to 6.5% for the widespread species. Threatened species were preferred over common plants, probably due to their greater palatability. Overall plant cover, including neighboring species, was also an important factor determining browsing damage and, thus, habitats with low ground cover should be particularly considered in conservation plans. Herbivore damage on common taxa should be taken with caution since they could mask unsustainable herbivore densities for threatened woody taxa or protected habitats. The use of threatened woody taxa through the studied ecological indicators (herbivore damage, plant preferences, habitat use and regeneration success) represented a useful tool to assess the sustainability of large herbivores introductions and to establish a priority conservation ranking for threatened plant species. These findings highlight the deleterious effects of overabundant ungulate populations regardless its origin (exotic or native) and the need of monitoring threatened woody taxa to better estimate the suitability and sustainability of large herbivore introductions.

Scattered trees are considered keystone structures and play an important role in Mediterranean sylvopastoral systems. Such systems are associated with high biodiversity and provide important natural resources and ecosystem services. In this study, we measured the contribution of scattered trees and different grazing management (cattle, sheep and wildlife only) to the diversity of the grassland sward in a dehesa (open holm oak woodland) located in Central Spain. We analyzed alpha and beta diversity through measurement of species richness, Shannon-Wiener, and Whittaker indices, respectively; and the floristic composition of the herb layer using subplots within two adjacent plots (trees present vs. trees absent) under three different grazing management regimes, including wildlife only, during a year. We found a 20–30% increment in the alpha diversity of wooded plots, compared to those without trees, regardless of grazing management. All beta indices calculated showed more than 60% species turnover. Wooded plots were occupied by different herbaceous species in different heterogeneous microsites (under the canopy, in the ecotone or on open land) created by the trees. Livestock grazing modified species composition (e.g. more nitrophilous species) compared to wildlife only plots. In addition to all their other benefits, trees are important to maintaining grassland diversity in Mediterranean dehesas.

Mediterranean scattered oak woodlands support relatively high biological diversity, and provide important ecosystem services. However, there is still a lack of knowledge about livestock-tree-grassland relationships, knowledge necessary for effective conservation management in these systems. To address such lacuna, we measured the effects of scattered trees and grazing animals (livestock vs. wild ungulates, mostly deer) on biomass and diversity (and their relationship) of the herbaceous layer (understory) of open holm oak woodland (known as dehesa) in Central Spain, for two years. We located two 1-ha plots within three different grazing management schemes (cattle, sheep and wildlife only). Within each plot, we randomly selected four focal trees from which a subplot was established in two directions and three distances. In each subplot, we measured plant diversity and biomass, along with microclimatic variables across sites. We found rainfall variability affected herbaceous biomass and diversity in the dehesa system, and the effects were nuanced: in a dry year ( 600 mm annual rainfall) the effect was enhanced, as plots under livestock grazing exhibited even higher herbaceous biomass (42%). In addition, livestock, particularly cattle, generated a more diverse community (52 species m−2). Microsites created by trees generated high plant diversity among herbaceous communities, where alpha diversity was higher (20%) in ecotone and inter-tree gaps than under the canopies. In addition, species turnover was higher than 50% in all cases. Biomass was higher (15%) under the canopies only under humid conditions. Legume dry matter was positively related to plant diversity. We concluded that agroforestry management practices such as promoting tree development through silvicultural techniques to create different microsites, and maintaining livestock grazing are needed to preserve these emblematic ecosystems.

International audience; Pressure and temperature phase transitions of nanomaterials often differ significantly from those of their bulk parents, offering novel approaches for the engineering of original materials. The importance or even the dominance of surface atoms in the nanoworld enhances the effects of environment, geometry, and intercalation. In the present article, we explore the current knowledge of these effects, as evidenced in the high pressure phase diagrams of nanomaterials such as nanocrystals, carbon nanotubes, fullerites, graphene, and other 2D systems, as well as nanoporous structures like clathrates or zeolites. Recent advances and future challenges in the use of extreme thermodynamic conditions to develop new functional nanomaterials, composites, or devices will be reviewed, along with the specificities of the experimental environment required for these investigations.

International audience; When reducing the size of a material from bulk down to nanoscale, the enhanced surface-to-volume ratio and the presence of interfaces make the properties of nano-objects very sensitive not only to confinement effects but also to their local environment. In the optical domain, the latter dependence can be exploited to tune the plasmonic response of metal nanoparticles by controlling their surroundings, notably applying high pressures. To date, only a few optical absorption experiments have demonstrated this feasibility, on ensembles of metal nanoparticles in a diamond anvil cell. Here, we report a nontrivial combination between a spatial modulation spectroscopy microscope and an ultraflat diamond anvil cell, allowing us to quantitatively investigate the high-pressure optical extinction spectrum of an individual nano-object. A large tuning of the surface plasmon resonance of a gold nanobipyramid is experimentally demonstrated up to 10 GPa, in quantitative agreement with finite-element simulations and an analytical model disentangling the impact of metal and local environment dielectric modifications. High-pressure optical characterizations of single nanoparticles allow for the accurate investigation and modeling of size, strain, and environment effects on physical properties of nano-objects and also enable fine-tuned applications in nanocomposites, nanoelectromechanical systems, or nanosensing devices.

International audience; High-pressure resonance Raman experiments were performed on linear carbon chains Cn confined in double-wall carbon nanotubes (Cn@DWCNT). Our results indicate that the frequency of the chain mode undergoes a non-linear decreasing as pressure increases, in agreement with previous studies of the behavior of carbon chains into multi-wall carbon nanotubes. After the pressure cycle, the Cn modes present an irreversible frequency downshift together with an irreversible upshift (downshift) of the RBM modes (G+ band) of the inner tube. These spectral changes are interpreted as evidence of cross-linking between the carbon chain and the wall of the inner tube. Density functional theory (DFT) calculations were performed in order to shed light on the interpretation of the experimental data. The theoretical calculations show a pressure-induced charge transfer from the nanotube to the carbon chain, thus resulting in an increasing of the C≡C bond length, and consequently, a softening frequency of the Cn Raman mode. Furthermore, an irreversible cross-linking between the tube and Cn is observed when the maximum applied pressure is higher than the pressure of radial tube collapse is predicted by modelling, thus supporting the experimental results.

Barium silicides are versatile materials that have attracted attention for a variety of applications in electronics and optoelectronics. Using an unbiased structural search based on a particle-swarm optimization algorithm combined with density functional theory calculations, we investigate systematically the ground-state phase stability and the structural diversity of Ba-Si binaries under high pressure. The phase diagram turns out to be quite intricate, with several compositions stabilizing/destabilizing as a function of pressure. In particular, we identify novel phases of BaSi, BaSi2, BaSi3, and BaSi5 that might be synthesizable experimentally over a wide range of pressures. Our results not only clarify and complete the previously known structural phase diagram, but also provide new insights for understanding the Ba-Si binary system.

The ability of animals to find and consume hoarded seeds (i.e. seed recovery) is a key stage within the seed dispersal process. However, the ecology of seed recovery is still poorly understood. Here, we analyze the factors controlling seed recovery by scatter-hoarding rodents in an oak-dominated temperate forest. We examined the relative importance of intrinsic seed traits (i.e. plant-driven) and extrinsic seed factors (i.e. animal-driven) on the probability of seed recovery. We found that seed recovery is mainly driven by extrinsic seed factors, mostly related to animal behavior (pilfering frequency, microsite preference, predation risk, burial depth and cache size). Important intrinsic traits such as seed size, seed quality and seed-drop timing were, on average, of lower significance in the probability of seed recovery (2.8-times less important than extrinsic factors); only seed quality was an important intrinsic trait. On the other hand, larger and nutritionally more valuable seeds showed a removal–recovery tradeoff as they enhance seed removal and hoarding (increasing dispersal quality) but also favour seed recovery (increasing predation). We find that other mechanisms beyond seed traits (e.g. masting) are needed to decrease seed recovery and, thus, increase seed survival. We conclude that, as seed recovery is mostly driven by animal behavioural factors, it substantially differs from other previous stages of the seed dispersal process that are more dependent on seed traits. We argue that seed recovery needs further attention to advance our understanding of the ecology of seed dispersal and the role of secondary dispersers as a selective force for seeds.

International audience; AbstractKey messageSmall-scale forest interventions ( 130-cm high). Ungulates did not use the treated areas more often than the control plots but caused significantly greater rubbing damage in the treated areas. Silvicultural treatments did not have a significant effect on alpha woody plant diversity but did promote beta-diversity, with a 49.7% woody species turnover. We did not find any clear patterns indicating that the treated areas suffered heavier browsing damage across all woody plant species.ConclusionThis study highlights that small-scale forest interventions (

International audience; We study the pressure induced collapse of single-, double- and triple-wall carbon nanotubes. Theoretical simulations were performed using density-functional tight-binding theory. For tube walls separated by the graphitic distance, we show that the radial collapse pressure, Pc, is mainly determined by the diameter of the innermost tube, din and that its value significantly deviates from the usual Pc∝din−3 Lévy-Carrier law. A modified expression, Pcdin−3=α(1−β2∕din2) with α and β numerical parameters, which reduces the collapse pressure for low diameters is proposed. For din ≳ 1.5 nm an enhanced stability is found which may be assigned as due to the bundle intertube geometry-induced interactions. If the inner and outer tubes are separated by larger distances, the collapse process is found to be more complex. High-pressure resonant Raman experiments were performed in double-wall carbon nanotubes having inner and outer diameters averaging 1.5 nm and 2.0 nm, respectively. A modification in the response of the G-band and the disappearance of the radial breathing modes between 2 GPa and 5 GPa indicate the beginning and the end of the radial collapse process. Experimental results are in good agreement with our theoretical predictions, but do not allow to discriminate from those corresponding to a continuum mechanics model.

Aim of study: To present the evolution of the current multi-objective Spanish National Forest Inventory (SNFI) through the assessment of different key indicators on challenging areas of the forestry sector.Area of study: Using information from the Second, Third and Fourth SNFI, this work provides case studies in Navarra, La Rioja, Galicia and Balearic Island regions and at national Spanish scale.Material and methods: These case studies present an estimation of reference values for dead wood by forest types, diameter-age modeling for Populus alba and Populus nigra in riparian forest, the invasiveness of alien species and the invasibility of forest types, herbivore preferences and effects on trees and shrub species, the methodology for estimating cork production , and the combination of SNFI4 information and Airborne Laser Scanning datasets with the aim of updating forest-fire behavior assessment information with a high degree of accuracy.Main results: The results show the suitability and feasibility of the proposed methodologies to estimate the indicators using SNFI data with the exception of the estimation of cork production. In this case, additional field variables were suggested in order to obtain robust estimates.Research highlights: By broadening the variables recorded, the SNFI has become an even more important source of forest information for the development of support tools for decision-making and assessment in diverse strategic fields such as those analyzed in this study.

The stacking effect on the E12g and A1g vibrational modes of mechanically exfoliated MoS2 samples supported on SiO2 was investigated by onresonant Raman spectroscopy at high-pressure conditions. The split of E12g and A1g modes were observed for single- and bilayered samples whereas such splitting disappears for higher numbers of layers. The differences on the E12g pressure coefficients allowed us to interpret the observed splitting as due to the presence of two types of regions corresponding to a high and a low conformation of MoS2 to the substrate roughness. The difference in the pressure coefficient appears then as due to the biaxial stress introduced via the substrate compression. Such effects were not observed for the A1g mode due to its vibration symmetry. This out-of-plane vibration is mainly affected by the normal stress that corresponds to pressure transmitted by the pressure-transmitting medium.

International audience; The dependence of the radial breathing modes (RBMs) and the tangential mode (G-band) of triple-wall carbon nanotubes (TWCNTs) under hydrostatic pressure is reported. Pressure screening effects are observed for the innermost tubes of TWCNTs similar to what has been already found for DWCNTs. However, using the RBM pressure coefficients in conjunction with the histogram of the diameter distribution, we were able to separate the RBM Raman contribution related to the intermediate tubes of TWCNTs from that related to the inner tubes of DWCNTs. By combining Raman spectroscopy and high-pressure measurements, it was possible to identify these two categories of inner tubes even if the two tubes exhibit the same diameters because their pressure response is different. Furthermore, it was possible to observe similar RBM profiles for the innermost tubes of TWCNTs using different resonance laser energies but also under different pressure conditions. This is attributed to changes in the electronic transition energies caused by small pressure-induced deformations. By using Raman spectroscopy, it was possible to estimate the displacement of the optical energy levels with pressure.