Few Graphene layer/Carbon-Nanotube composite Grown at CMOS-compatible Temperature

We investigate the growth of the recently demonstrated composite material composed of vertically aligned carbon nanotubes capped by few graphene layers. We show that the carbon nanotubes grow epitaxially under the few graphene layers. By using a catalyst and gaseous carbon precursor different from those used originally we establish that such unconventional growth mode is not specific to a precise choice of catalyst-precursor couple. Furthermore, the composite can be grown using catalyst and temperatures compatible with CMOS processing (T < 450\degree C).Comment: 4 pages, 4 figure

Gas-solid carbonation of Ca(OH)2 and CaO particles under non-isothermal and isothermal conditions by using a thermogravimetric analyzer: Implications for CO2 capture

International audienceThe gas-solid carbonation of alkaline sorbents has been actively investigated as an alternative method to CO2 capture from industrial combustion sources and CO2 contained in the air. This study has a two-fold objective: firstly, quantify the gas-solid carbonation extent and the carbonation kinetics of Ca(OH)2 and CaO; and secondly, propose a reaction mechanism of gas-solid carbonation for CaO under dry conditions (relative humidity close to 0), i.e., when the action of water is negligible. The main results of our study have revealed that a high proportion of Ca(OH)2 nanoparticles were transformed into CaCO3 particles by gas-solid carbonation (carbonation extent, >0.94) under non-isothermal conditions. Moreover, this gas-solid reaction requires low activation energy (Ea≈6kJ/mol) at a constant heating rate of 5 or 10K/min. A similar carbonation extent was determined for gas-solid carbonation of in-situ synthesized CaO under non-isothermal conditions. However, the gas-solid carbonation of CaO takes place in a broader temperature range, implying a more complex thermokinetic behavior (overlapping of carbonation regimes or steps). Concerning the gas-solid carbonation of Ca(OH)2 and CaO under isothermal conditions, a high carbonation extent (>0.9) was determined for CaO at 600 (873K) and 800°C (1073K). Conversely, the gas-solid carbonation of Ca(OH)2 particles was relatively low (<0.56) at 400°C (673K) after 6h of reaction. This case is in agreement with the formation of a dense non-porous layer of carbonate mineral around the core of the reacting Ca(OH)2 particles, thereby limiting the transfer of CO2. Finally, an alternative reaction mechanism is proposed for the gas-solid carbonation of CaO, when the relative humidity is close to 0. This macroscopic control at high temperature avoids CO2 dissociation with molecular water at the CaO-CO2 interface. For these specific conditions, the mineralization of adsorbed CO2 on CaO particles implies a solid state transformation, i.e., CaCO3 formation from CaO-CO2 interactions. This could be explained by an atomic excitation than at high temperature allows the local migration of one oxygen atom from the solid towards the adsorbed CO2 leading to its mineralization into carbonate (porous or non-porous layer) around the reacting particles; chemically the mineralization of CO2 also implies the breaking of one covalent bond in the CO2 molecule

Electron transport through antidot superlattices in Si/SiGeSi/SiGe heterostructures: new magnetoresistance resonances in lattices with large diameter antidots

In the present work we have investigated the transport properties in a number of Si/SiGe samples with square antidot lattices of different periods. In samples with lattice periods equal to 700 nm and 850 nm we have observed the conventional low-field commensurability magnetoresistance peaks consistent with the previous observations in GaAs/AlGaAs and Si/SiGe samples with antidot lattices. In samples with a 600 nm lattice period a new series of well-developed magnetoresistance oscillations has been found beyond the last commensurability peak which are supposed to originate from periodic skipping orbits encircling an antidot with a particular number of bounds.Comment: To appear in EuroPhys. Let

Experimental microstylolites in quartz and modelling of natural stylolitic structures

International audienceExperimental microstylolites have been observed at stressed contacts between quartz grains loaded for several weeks in the presence of an aqueous silica solution, at 350 8C and 50 MPa of differential stress. Stereoscopic analysis of pairs of SEM images yielded a digital elevation model of the surface of the microstylolites. Fourier analyses of these microstylolites reveal a self-affine roughness (with a roughness exponent H of 1.2). Coupled with observations of close interactions between dissolution pits and stylolitic peaks, these data illustrate a possible mechanism for stylolite formation. The complex geometry of stylolite surfaces is imposed by the interplay between the development of dissolution peaks in preferential locations (fast dissolution pits) and the mechanical properties of the solid-fluid-solid interfaces. Simple mechanical modeling expresses the crucial competition that could rule the development of microstylolites: (i) a stress-related process, modeled in terms of the stiffness of springs that activate the heterogeneous dissolution rates of the solid interface, promotes the deflection. In parallel, (ii) the strength of the solid interface, modeled in terms of the stiffness of a membrane, is equivalent to a surface tension that limits the deflection and opposes its development. The modeling produces stylolitic surfaces with characteristic geometries varying from conical to columnar when both the effect of dissolution-rate heterogeneity and the strength properties of the rock are taken into account. A self-affine roughness exponent (Hz1.2) measured on modeled surfaces is comparable with natural stylolites at small length scale and experimental microstylolites

The three-dimensional roughness of stylolites in limestones: roughness analysis and possible genetic implications

International audienceStylolites are dynamic roughly planar surfaces formed by pressure solution of blocks of rocks into each other. The three-dimensional geometry of 12 bedding-parallel stylolites in several limestones was measured using laser and mechanical profilometers, and statistical characteristics of the surfaces were calculated. All the stylolites analyzed turn out to have self-affine fractal roughness with a well-characterized crossover length scale separating two self-affine regimes. Strikingly, this characteristic length scale falls within a very narrow range for all the stylolites studied, regardless of the microstructure sizes. To explain the data, we propose a continuous phenomenological model that accounts for the development of the measured roughness from an initially flat surface. The model postulates that the complex interface morphology is the result of competition between the long-range elastic redistribution of local stress fluctuations, which roughen the surface, and surface tension forces along the interface, which smooth it. The model accounts for the geometrical variability of stylolite surfaces and predicts the dependence of the crossover length scale on the mechanical properties of the rock

Renal Angiomyolipoma Associated with Inferior Vena Cava Thrombus

A 57-year-old woman was found to have an inferior vena cava involvement of a known sinusal angiomyolipoma incompletely resected three years beforehand. Intravascular extension into the IVC of angiomyolipoma has rarely been reported. We present a new case and reconsider the literature about this uncommon complication of a benign renal tumor

Roughness of fault surfaces over nine decades of length scales

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