We report the synthesis of Fe/N/C ORR electrocatalysts by an original collinear CO2 laser pyrolysis of liquid aerosol droplets in various configurations and compared them to a catalyst synthesized in the classical perpendicular one. While the precursors were always injected at the bottom side of the reactor, two collinear configurations of the laser entry into the reactor are considered: by the Top Side (T.S.) or by the Bottom Side (B.S.). The two corresponding catalysts sets show significant different ORR performances. An in-depth XPS analysis and fitting of the N1s spectra allowed for drawing the ORR performance as a function of FeNx sites components. An original approach considering the energy delivered to a quantity of precursors in J.g(-1), linked to the flame temperature feature, evidenced very different conditions for perpendicular CO2 laser pyrolysis and each of the two collinear configurations. This mass-weighted energy delivered in the classical perpendicular configuration is too low to allow for the formation of FeNx sites and the resulting ORR performance is extremely poor, suggesting a marginal role of nitrogen species without interaction with iron atoms. In contrast, the delivered mass-weighted energies are sufficient in both collinear configurations to produce FeNx sites. The ORR performance for catalysts produced in these both configurations is positively correlated with the amount of energy deposited on the precursors. The ORR performance in the T.S. laser configuration is positively correlated to the amount of FeNx sites. The best performing catalysts obtained in the B.S. configuration show an opposite variation. These trends, and the ORR performance degradation of B.S. catalysts under prolonged chronoamperometry are discussed in light of the effect of temperature on the formation of the various kind of FeNx sites. A tentative explanation is given, considering that N1s XPS fitting with a single FeNx component may hinder the fact that Pyridinic sites components may contain a part of FeNx sites, as suggested by theoretical calculation from the literature. The best catalysts obtained in this work by collinear configuration show similar performances to those obtained by double stage perpendicular pyrolysis previously reported with an ORR onset potential of similar to 860 mV.

The one-step catalytic chemical vapor deposition (CCVD) meets the requirements for large-scale production of vertically aligned carbon nanotubes (VACNTs) to enable their numerous applications. Its main advantage at standard temperatures around 800 degrees C is the absence of growth saturation thanks to the renewal of catalytic particles through the continuous supply of a metal precursor. However, at lower temperature to grow VACNTs on substrates affording only medium range temperatures (eg. aluminum), some saturation occurs, especially as long syntheses duration are required due to the reduced growth rate. We show here how to overcome this limitation and produce tall and dense VACNT carpets at 615 degrees C on various grades of aluminum flexible foils. Adding CO2 in the gas phase delays the saturation and avoid the degradation of the carpet for synthesis duration above 2 h. Results are consistently better on higher grade substrates, due to the impact of roughness on VACNT nucleation. The trade-off line between mass density and height often reported in the case of 2-steps CCVD does not affect the one-step process. On polished Al foils, VACNTs almost 1 mm-tall are obtained with densities greater than 100 mg/cm3. Growth rate and quality of VACNTs are at the state-of-the-art for syntheses at such moderate temperature.

New Target-Ion Source Systems combining a target and a catcher material are developed in the radioactive beam community, in particular at GANIL, in order to maximise the yield of very short lived atoms by minimizing the atom-to-ion transformation time. The aim of this study is to characterize the release properties of 81Rb collected on two graphite catchers and two carbon nanotube catchers. The release fractions were measured at various catcher-heating temperatures and then compared to the analytical expressions relevant to each catcher. This comparison led to the extraction of the pre-exponential factor (D0) and the activation energy (Eact) involved in the diffusion coefficient of Rb for three carbon microstructures. All these data allowed to define an ideal catcher which could be made of aligned carbon nanotubes of small diameter and oriented in order to collect all the 81Rb atoms produced by the target but also to release them efficiently.

We present 12C+12C direct fusion measurements with STELLA UKFATIMA, that reach into the region of astrophysics interest relevant to massive stars (M⊙ ≈ 25) using self-supporting thin rotating carbon foils [1]. We demonstrate that detecting gammas and light charged particles in coincidence with nanosecond timing is key for effective background reduction achieving reliable measurements in the sub-nanobarn range. We give details about core developments of the detection apparatus as well as the coincidence-analysis procedure of low count statistics. The present data largely follows the phenomenological hindrance interpolation and shows indication for resonant behaviour at the lowest energy explored.

The present work explores the role of the carbon source content and the Fe/C ratio on the synthesis of vertically aligned carbon nanotubes (VACNTs) by one-step aerosol-assisted CCVD operated at a medium temperature (615 °C) on aluminum substrates. The main objective was to overcome the limitations of VACNT growth, constituting a drawback for applications requiring thick VACNTs. By using acetylene as carbon feedstock and ferrocene as a catalyst precursor, we demonstrate that when acetylene content is reduced to 1.5 vol%, it is possible to grow VACNT carpets up to 700 µm thick while maintaining constant VACNT growth for a long duration (up to 160 min). The carbon conversion yield is significantly improved when the acetylene content reaches 1.5 vol%. The Al surface roughness also influences VACNT growth. An optimum Fe/C ratio of 0.8 wt.% coupled with a low acetylene content gives the highest growth rate (5.4 µm/min) ever reported for a thermal aerosol-assisted CCVD process operated at such a low temperature. The CNT number density can be controlled by varying the Fe/C ratio, enabling high density growth (e.g., 1.3 × 1011 CNT/cm2).

Introduction: Ultracarbonaceous Antarctic Micrometeorites (UCAMMs) are dominated by N-rich polyaromatic organic matter exhibiting large D enrichments [1-5]. The high abundance of organic matter exhibiting large D enrichment suggests a cometary origin for UCAMMs [1-3]. Three kinds of organic matter are identified in UCAMMs, with different nitrogen abundances and highly variable concentrations of small (typically 30-500 nanometer) mineral aggregates embedded in the organic matter [5-8]. We focus here on a mineral assemblage embedded in one UCAMM that exhibits evidence of ion irradiation, to get insight on the formation and evolution of this cometary particle. Sample and methods: A fragment of UCAMM DC06-06-43 (hereafter DC06-43) was carbon coated, observed by SEM/EDX, and a 100 nm thick FIB section of this fragment was made at IEMN Lille. The size of the initial UCAMM before fragmentation was ~ 25 x 30 µm. After STXM-XANES analysis, the mineralogy of the sample was investigated by TEM at UMET Lille using a FEI Tecnai G2 20 at 200 kV and FEI TITAN Themis at 300 kV [9]. Results : TEM examination reveals a large assemblage of crystalline minerals at the center of the DC06-43 UCAMM fragment, surrounded by organic matter (Figure 1) [9]. The assemblage consists of µm-to subµm sized Mg-rich pyroxenes, a large triskell-shaped Fe-sulfide, a few Mg-rich olivines, and minor Si-Al-Carich amorphous pockets and Fe-Ni metal. About 28 crystalline pyroxenes are identified whereas only 5 olivine crystals are observed in the section. GEMS are present embedded in the organic matter, close to the crystalline assemblage. We identified irradiation features (rims and tracks) in pyroxene grains. No rims or tracks were found in olivine. We observed irradiated rims around six pyroxenes at the top of the section (Figure 1, light blue labels). One pyroxene shows a continuous irradiated rim (Figure 2 top). Rim thicknesses range from 20 to 100 nm, with an average of 60 ± 20 nm (1σ) (Figure 2 bottom). Fe-rich deposits are occasionally found on top of irradiated rims. EDX mappings and profiles show that the rims are strongly depleted in Mg (Figure 3). The average track density in pyroxene grains measured over an area of 4.5 x 10-8 cm 2 is 1.3 x 10 10 cm-2 with one value at 3.8 x 10 9 cm-2 , the other values ranging from 9.5 x 10 9 to 3.2 x 10 10 cm-2 (Figure 4). Irradiation track lengths

Context. Interstellar space hosts nanometre- to micron-sized dust grains, which are responsible for the reddening of stars in the visible. The carbonaceous-rich component of these grain populations emits in infrared bands that have been observed remotely for decades with telescopes and satellites. They are a key ingredient of Galactic radiative transfer models and astrochemical dust evolution. However, except for C 60 and its cation, the precise carriers for most of these bands are still unknown and not well reproduced in the laboratory. Aims. In this work, we aim to show the high-energy mechanochemical synthesis of disordered aromatic and aliphatic analogues provides interstellar relevant dust particles. Methods. The mechanochemical milling of carbon-based solids under a hydrogen atmosphere produces particles with a pertinent spectroscopic match to astrophysical observations of aromatic infrared band (AIB) emission, linked to the so-called astrophysical polycyclic aromatic hydrocarbon hypothesis. The H/C ratio for the analogues that best reproduce these astronomical infrared observations lies in the 5 ± 2% range, potentially setting a constraint on astrophysical models. This value happens to be much lower than diffuse interstellar hydrogenated amorphous carbons, another Galactic dust grain component observed in absorption, and it most probably provides a constraint on the hydrogenation degree of the most aromatic carbonaceous dust grain carriers. A broad band, observed in AIBs, evolving in the 1350–1200 cm −1 (7.4–8.3 μ m) range is correlated to the hydrogen content, and thus the structural evolution in the analogues produced. Results. Our results demonstrate that the mechanochemical process, which does not take place in space, can be seen as an experimental reactor to stimulate very local energetic chemical reactions. It introduces bond disorder and hydrogen chemical attachment on the produced defects, with a net effect similar to the interstellar space very localised chemical reactions with solids. From the vantage point of astrophysics, these laboratory interstellar dust analogues will be used to predict dust grain evolution under simulated interstellar conditions, including harsh radiative environments. Such interstellar analogues offer an opportunity to derive a global view on the cycling of matter in other star forming systems.

Interstellar space hosts nanometre- to micron-sized dust grains. The carbonaceous-rich component of these grain populations emits in infrared bands, observed remotely for decades with telescopes and satellites. They are a key ingredient of astrochemical dust evolution. The precise carriers for most of these bands are still unknown and not well reproduced in the laboratory. In this work, we show the high-energy mechanochemical synthesis of disordered aromatic and aliphatic analogues provides interstellar relevant dust particles. The mechanochemical milling of carbon-based solids under a hydrogen atmosphere produces particles with a spectroscopic match to astrophysical observations of aromatic infrared band (AIB) emission. The H/C ratio for the analogues that best reproduce these astronomical infrared observations lies in the 5$\pm$2% range. This value is much lower than diffuse interstellar hydrogenated amorphous carbons, another Galactic dust grain component observed in absorption, and it most probably provides a constraint on the hydrogenation degree of the most aromatic carbonaceous dust grain carriers. A broad band, observed in AIBs, in the 7.4-8.3 $\mu$m range is correlated to the hydrogen content, and thus the structural evolution in the analogues produced. The mechanochemical process can be seen as an experimental reactor to stimulate local energetic chemical reactions. It introduces bond disorder and hydrogen chemical attachment on the produced defects, with an effect similar to the interstellar space very localised chemical reactions with solids. From the vantage point of astrophysics, these laboratory interstellar dust analogues will be used to predict dust grain evolution under simulated interstellar conditions, including harsh radiative environments. Such interstellar analogues offer an opportunity to derive a global view on the cycling of matter in other star forming systems.

Recently, we reported the use of CO2 laser pyrolysis for the synthesis of promising Fe/C/N electrocatalysts for Oxygen Reduction Reaction (ORR) in fuel cells. The set-up used single laser pyrolysis of an aerosolized solution of iron acetylacetonate in toluene with ammonia, both as laser energy transfer agent and nitrogen source. In the present paper, we investigate the effect of a second ammonia promoted CO2 laser pyrolysis on the feature and ORR activity of Fe/C/N electrocatalysts. Indeed, compared to single pyrolysis, the second ammonia promoted CO2 laser pyrolysis could be an interesting way to synthesize in one-step performing ORR electrocatalysts on a large scale. For this comparison, a two-stage reactor was built, allowing both single ammonia-induced CO2 laser pyrolysis as reported previously or double ammonia-induced CO2 laser pyrolysis. In the latter configuration, the catalyst nanopowder flow is formed at the first stage of the reactor, then mixed with a second ammonia flow and allowed to cross a second CO2 laser beam, thus undergoing a second ammonia-induced CO2 laser pyrolysis before being collected on filters. It is found that the second ammonia-induced CO2 laser pyrolysis significantly improves the ORR performances of the materials prepared by single CO2 laser pyrolysis. The effect is demonstrated for three different catalysts for which the onset potentials for the ORR from single-stage to double-stage configuration increase from 625 mV to 845 mV, 790 mV to 860 mV, and 800 mV to 885 mV, respectively. The selectivity of the ORR was determined at 600 mV/SHE and lie between 3.41 and 3.72. These promising performances suggesting potentialities for the one-step formation of highly active Fe/C/N ORR electrocatalysts are discussed, based on results of surface analysis by XPS, specific surface area measurements, and Raman spectroscopy.

The ^{12}C+^{12}C fusion reaction plays a critical role in the evolution of massive stars and also strongly impacts various explosive astrophysical scenarios. The presence of resonances in this reaction at energies around and below the Coulomb barrier makes it impossible to carry out a simple extrapolation down to the Gamow window-the energy regime relevant to carbon burning in massive stars. The ^{12}C+^{12}C system forms a unique laboratory for challenging the contemporary picture of deep sub-barrier fusion (possible sub-barrier hindrance) and its interplay with nuclear structure (sub-barrier resonances). Here, we show that direct measurements of the ^{12}C+^{12}C fusion cross section may be made into the Gamow window using an advanced particle-gamma coincidence technique. The sensitivity of this technique effectively removes ambiguities in existing measurements made with gamma ray or charged-particle detection alone. The present cross-section data span over 8 orders of magnitude and support the fusion-hindrance model at deep sub-barrier energies.

The one-step aerosol-assisted catalytic chemical vapor deposition (CCVD) process, when operated in a H-2-based carrier gas, is shown to be effective at an extremely low ferrocene content (0.1 wt% in toluene), which enables to efficiently prepare forests of vertically aligned multiwalled carbon nanotubes (VACNTs) with high purity and good crystalline level. The resulting iron content in VACNT sample is only 0.5 wt% corresponding to a high catalytic yield of 200 while the steady growth rate (20 mm/min) is maintained at a significant value. The iron content in the sample is found proportional to the ferrocene concentration in the precursor, and when it decreases, a noticeable reduction in the iron encapsulation frequency in the nanotube channel is plainly observed. Lowering the ferrocene concentration generates a reduction in the VACNT number density while the growth rate increases and CNT diameters and crystalline structure remain similar. Such significant purity and crystalline levels involves a high oxidation resistance of the VACNT forest. These results, together with the in-situ continuous growth feature of the one-step aerosol assisted CCVD process, open up towards a new VACNT range made of pure and well-crystallized multiwalled carbon nanotubes, which is of interest for industrial production and commercial applications. (C) 2020 Elsevier Ltd. All rights reserved.

ANTARCTIC MICROMETEORITE (UCAMM). C. Engrand, E. Charon, H. Leroux, C. Le Guillou, J. Duprat, E. Dartois, S. Bernard, B. Guérin, L. Delauche, M. Godard. CSNSM CNRS/Univ. Paris Sud, Univ. Paris-Saclay, 91405 Orsay Campus, France (cecile.engrand@csnsm.in2p3.fr), NIMBE, CEA, CNRS, Univ. Paris-Saclay, CEA Saclay 91191 Gif-sur-Yvette France. UMET Univ. Lille 1, 59650 Villeneuve d’Ascq, France. ISMO CNRS/Univ. Paris Sud, Univ. Paris-Saclay, 91400 Orsay, France. IMPMC, CNRS, Sorbonne Université, MNHN, 4 place Jussieu, 75005 Paris, France.

We constructed semiempirical breakdown curves (BDC) for C2N, C3N, C2N+ and C3N+ molecules. These BDC, which are energy dependent dissociation branching ratios (BR) curves, were used to predict products branching ratios for various processes leading to the formation of C2N(+) and C3N(+) excited adducts. These processes, of astrochemical interest, are neutral-neutral and ion-molecule reactions, dissociative recombination and charge transfer reactions with He+. Model predictions of BR are compared to the literature data and to reported values in the kinetic database for astrochemistry KIDA. With the new BR values, the CnN abundances in cold cores were simulated.

Context. UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) represent a small fraction of interplanetary dust particles reaching the Earth’s surface and contain large amounts of an organic component not found elsewhere. They are most probably sampling a contribution from the outer regions of the solar system to the local interplanetary dust particle (IDP) flux. Aims. We characterize UCAMMs composition focusing on the organic matter, and compare the results to the insoluble organic matter (IOM) from primitive meteorites, IDPs, and the Earth. Methods. We acquired synchrotron infrared microspectroscopy (μFTIR) and μRaman spectra of eight UCAMMs from the Concordia/CSNSM collection, as well as N/C atomic ratios determined with an electron microprobe. Results. The spectra are dominated by an organic component with a low aliphatic CH versus aromatic C=C ratio, and a higher nitrogen fraction and lower oxygen fraction compared to carbonaceous chondrites and IDPs. The UCAMMs carbonyl absorption band is in agreement with a ketone or aldehyde functional group. Some of the IR and Raman spectra show a C≡N band corresponding to a nitrile. The absorption band profile from 1400 to 1100 cm−1 is compatible with the presence of C-N bondings in the carbonaceous network, and is spectrally different from that reported in meteorite IOM. We confirm that the silicate-to-carbon content in UCAMMs is well below that reported in IDPs and meteorites. Together with the high nitrogen abundance relative to carbon building the organic matter matrix, the most likely scenario for the formation of UCAMMs occurs via physicochemical mechanisms taking place in a cold nitrogen rich environment, like the surface of icy parent bodies in the outer solar system. The composition of UCAMMs provides an additional hint of the presence of a heliocentric positive gradient in the C/Si and N/C abundance ratios in the solar system protoplanetary disc evolution.

Context. UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) represent a small fraction of interplanetary dust particles reaching the Earth’s surface and contain large amounts of an organic component not found elsewhere. They are most probably sampling a contribution from the outer regions of the solar system to the local interplanetary dust particle (IDP) flux. Aims. We characterize UCAMMs composition focusing on the organic matter, and compare the results to the insoluble organic matter (IOM) from primitive meteorites, IDPs, and the Earth. Methods. We acquired synchrotron infrared microspectroscopy ( μ FTIR) and μ Raman spectra of eight UCAMMs from the Concordia/CSNSM collection, as well as N/C atomic ratios determined with an electron microprobe. Results. The spectra are dominated by an organic component with a low aliphatic CH versus aromatic C=C ratio, and a higher nitrogen fraction and lower oxygen fraction compared to carbonaceous chondrites and IDPs. The UCAMMs carbonyl absorption band is in agreement with a ketone or aldehyde functional group. Some of the IR and Raman spectra show a C≡N band corresponding to a nitrile. The absorption band profile from 1400 to 1100 cm -1 is compatible with the presence of C-N bondings in the carbonaceous network, and is spectrally different from that reported in meteorite IOM. We confirm that the silicate-to-carbon content in UCAMMs is well below that reported in IDPs and meteorites. Together with the high nitrogen abundance relative to carbon building the organic matter matrix, the most likely scenario for the formation of UCAMMs occurs via physicochemical mechanisms taking place in a cold nitrogen rich environment, like the surface of icy parent bodies in the outer solar system. The composition of UCAMMs provides an additional hint of the presence of a heliocentric positive gradient in the C/Si and N/C abundance ratios in the solar system protoplanetary disc evolution.

Introduction: Ultracarbonaceous Antarctic Micrometeorites (UCAMMs) are dominated by a polyaromatic organic matter globally N-enriched showing bulk D enrichments, with heterogeneous distributions of the D/H and 15 N/ 14 N isotopic ratios [1-6]. The abundant organic matter of UCAMMs contains amorphous and crystalline mineral components [7-9]. This high abundance of organic matter is reminiscent of the CHON particles detected in comet 1P/Halley [10, 11], although the size of CHONs was estimated to be on the micrometer to sub-micrometer size, while UCAMMs from the Concordia collection range in size from ~ 30 µm to ~ 200 µm [12]. They most probably originate from the outer regions of the protoplanetary disk, from the cometary reservoir [1, 3, 4], thus we aim at comparing their composition with that of dust particles from comet 67P/Churyumov-Gerasimenko (hereafter 67P) measured by Ro-setta/COSIMA [13-15]. A recent summary of the general UCAMM characteristics can be found in [12]. Methods: UCAMMs from the Concordia collection were identified by SEM/EDX, and complementary UCAMM fragments were analyzed by synchrotron-based Fourier transform infrared (FTIR) microscopy at SOLEIL/SMIS, electron microprobe analysis (EMPA) at the CAMPARIS facility (Paris), transmission electron microscopy (TEM) at UMET (Lille), STXM-XANES analyses at synchrotron facilities (ALS Berkeley and SOLEIL/HERMES), NanoSIMS at MNHN Paris and Institut Curie Orsay [1, 3-6, 12, 16, 17]. Recent STXM-XANES analyses were performed at the SOLEIL/HERMES beamline on 4 additional UCAMMs. Results and discussion: The additional STXM-XANES measurements of 4 UCAMM fragments in FIB-sections confirmed the presence of 3 organic phases in UCAMMs : i) an extended (up to tens of µm) smooth N-rich organic phase with a low O content, which is devoid of crystalline phases but can occasionnaly contain Glass Embedded with Metal and Sulfides (GEMS) inclusions; ii) an organic phase similar to the insoluble organic matter (IOM) extracted from carbonaceous chondrites (with a lower N/C ratio and a O content higher than for the smooth N-rich phase mentioned above), which contains minerals, including crystalline ones; iii) an organic phase associated with dusty-patches, which also has a low N concentration, but contains less O and shows a higher aromaticity than the previous IOM-like organic phase. UCAMMs analysed so far exibit various proportions of these 3 organic phases, thus showing variable bulk N contents [4, 12]. The N/C atomic ratios of individual UCAMMs varies from ~0.05 to ~ 0.20. The average N/C atomic ratio calculated from 5 UCAMMs is 2 to 3 times that of chondritic IOM. The N/C value calculated for dust particles from 67P is 0.035 ± 0.011 [14], i.e. lower than the average value of UCAMMs but still in the range of the UCAMMs with the lowest N/C atomic ratio. The C/Si atomic ratio of 67P is compatible with that of Halley dust particles and with the solar value [15]. This may indicate that the dust particles from these comets have well preserved their initial composition in semi-volatile elements. The C/Si of UCAMMs is higher than that of 67P, Halley and the Sun [4, 12], suggesting a local accumulation process of organic matter in the formation process of UCAMMs, such as irradiation of volatile ices in the external and cold regions of the protoplanetary disk, as proposed for the formation of the N-rich organic matter in UCAMMs [18]. The O/Si atomic ratio in UCAMMs is variable, but the average value is a good match to the solar value. The O/Si measured in UCAMMs is generally dominated by the minerals embedded in its organic matter. This similarity in O/Si atomic ratios suggests that the UCAMM mineral component is representative of the composition of the inner solar nebula. Irradiation tracks observed in pyroxenes in one UCAMM (DC060443) [17], indeed supports an origin of these minerals from the inner solar nebula. UCAMMs thus contain materials formed in the inner regions of the solar system and transported outward, mixed with material likely formed in situ in the outer regions of the protoplanetary disk.

Background: Carbon nanotubes (CNT) can interact with the biological environment, which could participate in their associated toxicity. We recently demonstrated that pH is an important player of CNT fate inside macrophages. We wanted to further characterize such process, and therefore designed a study dedicated to decipher CNT biodegradation by macrophages, as a function of two major physico-chemical properties in regard with nanotoxicology; length and degree of functionalization. To achieve our aim, we synthesized, following a single initial production process, four MWCNT differing in length and/or surface chemistry: S-CNT (short), SF-CNT (short functionalized), L-CNT (long) and LF-CNT (long functionalized).Results: Raman spectroscopy analysis performed on CNT recovered after exposure of RAW 264.7 macrophages for 6, 24, or 48 h demonstrate that CNT show early signs of biodegradation over time inside macrophages. The modulation of CNT length and functionalization, resulting in the modification of iron accessibility, both represent critical determinants of the biodegradation process; short pristine CNT were more prone to biodegradation than long CNT (pristine or functionalized), while short functionalized CNT were protected. Incubation of cells with Concanamycin completely prevents CNT from being modified, demonstrating that this biodegradation process is dependent on an intracellular pH-dependent mechanism. Interestingly, and despite evidence of degradation via Raman spectroscopy, the CNT length and diameter were not altered during the course of the study.Conclusions: In conclusion, our results identify a new mechanism of CNT biodegradation inside macrophages. This could give new insights for the understanding of CNT-associated toxicity, and represent important tools to develop safe(r)-by-design nanomaterials.