Friction properties of fluorinated carbons

In boundary lubrication regime, friction reduction and antiwear processes are associated to the presence of additives in the lubricating oils or greases. These processes are due to the formation of protective tribofilms resulting from chemical reactions between the additives and the sliding surfaces, in the physico-chemical conditions of the sliding contact. Conventional antiwear additives mainly consist of transition metal organo phosphate or thiophosphates which present a remarkable efficiency in the case of contacts between ferrous alloys. In the case of non reacting surfaces, these additives become inactive. Recently developped lubrication strategies consist in the use of dispersion in oils of nano additives able to build the protective tribofilm in the sliding contact without reaction with the surfaces. Carbon fluorinated phases, due to their lamellar structure and their high chemical stability even at relatively high temperature (400°C) represent interesting candidates as lubricant nano-additives subjected to present friction reduction, anti wear and anti corrosion actions. This work presents the tribologic behaviour of some carbon fluorinated derivatives such as graphite fluorides, fluorinated carbon nanofibers, fluorinated carbon nanodiscs and fluorinated carbon blacks. The influence, on the tribologic performances, of the structure of the initial carbon phases, of the fluorination rate (0<F/C<1) and the structure of the fluorinated compounds is discussed

Pt nanoparticles by sputtering onto glycerol: effect of the argon pressure

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Laser-induced periodic surface structures formation on mesoporous silicon from nanoparticles produced by picosecond and femtosecond laser shots

International audienceThis paper deals with the formation of laser-induced periodic surface structures (LIPSS) on mesoporous silicon thin films induced by two laser regimes in the UV range: picosecond and femtosecond. Different LIPSS formation mechanisms from nanoparticles, mainly coalescence and agglomeration, have been evidenced by scanning electron microscopy analysis. The apparition of a liquid phase during both laser interaction at low fluence (20 mJ/cm2) and after a large number of laser pulses (up to 12,000) has been also shown with 100 nm size through incubation effect. Transmission electron microscopy analyses have been conducted to investigate the molten phase structures below and inside LIPSS. Finally, it has shown that LIPSS are composed of amorphous silicon when mesoporous silicon is irradiated by laser beam in both regimes. Nevertheless, mesoporous silicon located between LIPSS stays crystallized

Silicon exfoliation by hydrogen implantation: Actual nature of precursor defects

International audienceMeV energy hydrogen implantation in silicon followed by a thermal annealing is a very smart way to produce high crystalline quality silicon substrates, much thinner than what can be obtained by diamond disk or wire sawing. Using this kerf-less approach, ultra-thin substrates with thicknesses between 15 pm and 100 pm, compatible with microelectronic and photovoltaic applications are reported. But, despite the benefits of this approach, there is still a lack of fundamental studies at this implantation energy range. However, if very few papers have addressed the MeV energy range, a lot of works have been carried out in the keV implantation energy range, which is the one used in the smart-cut (R) technology. In order to check if the nature and the growth mechanism of extended defects reported in the widely studied keV implantation energy range could be extrapolated in the MeV range, the thermal evolution of extended defects formed after MeV hydrogen implantation in (100) Si was investigated in this study. Samples were implanted at 1 MeV with different fluences ranging from 6 x 10(16) H/cm(2) to 2 x 10(17) H/cm(2) and annealed at temperatures up to 873 K. By cross-section transmission electron microscopy, we found that the nature of extended defects in the MeV range is quite different of what is observed in the keV range. In fact, in our implantation conditions, the generated extended defects are some kinds of planar clusters of gas filled lenses, instead of platelets as commonly reported in the keV energy range. This result underlines that hydrogen behaves differently when it is introduced in silicon at high or low implantation energy. The activation energy of the growth of these extended defects is independent of the chosen fluence and is between (0.5-0.6) eV, which is very close to the activation energy reported for atomic hydrogen diffusion in a perfect silicon crystal. (C) 2017 Elsevier B.V. All rights reserved

Growth of Pt based nano-catalysts in vegetal glycerin liquid by magnetron sputtering

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Structural, Optical and Thermo-physical Properties of Mesoporous Silicon Layers: Influence of Substrate Characteristics

International audienceABSTRACT: In this paper, the structural, optical and thermal properties of n-type (100),p-type (100) and (111) mesoporous silicon (MePSi) are reported. The mesoporous silicon wasprepared by an electrochemical process from bulk silicon wafer. Depending on the etchingdepth, analyses show that the porosity of p-type (111) increased by 32 to 40% compared to p(100) which, in turn, increased by 22 to 48% compared to n-type (100). The structuremorphology and the abundance of Si-Ox and Si-Hy also depended heavily on the type andcrystal orientation of MePSi. The thermal properties of the MePSi layers such as thermalconductivity (κ), volumetric heat capacity (ρCp) and thermal contact resistance (Rth) weredetermined using the pulsed photothermal method. The thermal conductivity of bulk silicondropped sharply after etching, decreasing by more than twenty-fold in the case of n-type (100)and by over forty-five fold for p-type (100) and (111). According to the percolation modeldepending on both porosity and phonon confinement, the drop in thermal conductivity wasmainly due to the nanostructure formation after etching. Thermal investigations showed thatthe volumetric heat capacity (ρCp) followed the barycentric model which depends mainly onthe porosity. The thermal contact resistances of MePSi layers were estimated to be in therange of 1x10-8 to 1x10-7 K⋅m2⋅W-1

Synthesis of Platinum Nanoparticles by Plasma Sputtering onto Glycerol: Effect of Argon Pressure on Their Physicochemical Properties

International audiencePlatinum nanoparticles (Pt NPs) were synthesized in glycerol as a liquid substrate via a magnetron sputtering method at different argon pressures (1.0, 4.0, and 9.0 Pa). Then, Pt NPs were deposited onto a Vulcan XC-72 powder to form carbon-supported Pt NPs catalysts. Molecular dynamics (MD) simulations were carried out using parameters mimicking the deposition conditions of Pt in plasma sputtering experiments to determine key parameters for the growth of Pt NPs and to understand the growth mechanism at the atomic scale. MD simulations showed that Pt NPs growth depended on the kinetic energy of Pt atoms arriving onto the liquid substrate, which is related to the argon (Ar) pressure. The Pt NPs obtained for different Ar pressures and dispersed in glycerol were characterized by small-angle X-ray scattering (SAXS) to investigate the Ar pressure effect on Pt NPs size. Independently on the Ar pressure, SAXS results revealed the presence of two NPs populations. The first population is composed of isolated small NPs with an average diameter increasing from 1.8 to 3.2 nm with the pressure. Transmission electron microscopy (TEM) analysis performed on carbonsupported Pt NPs (Pt NPs/C) displayed the same diameter evolution, but the Pt NPs diameters were found to be slightly larger (from 2.5 to 3.7 nm) than those obtained by SAXS in glycerol. Both SAXS and TEM measurement revealed a second population of larger nano-objects that could correspond to agglomerates of individual small NPs from the first population formed either during the deposition in the liquid bulk or more probably at the liquid surface. The electrochemical behavior of the Pt NPs/C catalysts was studied in a conventional three-electrode electrochemical cell at room temperature in a N 2-saturated 0.50 mol L −1 H 2 SO 4 electrolyte. It was shown that the Pt NPs size increased with argon pressure, which further led to a decrease of the Pt electrochemical surface area

Potential for fossilization of an extremotolerant bacterium isolated from a past mars analog environment

In the context of astrobiological missions to Mars, the key question is what biosignatures to search for and how? lndigenous Martian organisms, if they existed or still exist, can be classified as extremophile per se. Following this precept the FP7-funded European MASE project (Mars Analogues for Space Exploration} is investigating various aspects of anaerobic life under Mars' extreme envrionmental conditions, including the potential for preservation over long geological time periods of certain strains. In this contribution, we report on the mineralisation and preservation of Yersinia sp. in silica and gypsum, two minerals that have been reported on Mars, in cold and anaerobic conditions, similar to Martian conditions. The organism, polyextremotolerant bacterium Yersinia sp. MASE-LG-1 (hereafter named Yersinia. sp.) was isolated from the lcelandic Graenavatn Lake, an acidic (pH3), cold and oligotrophic volcanic crater lake. These organisms have a strong tolerance to diverse Mars-like stresses (Rettberg et al., 2015). We also studied the effect of physiological status on mineralisation by exposing Yersinia to two common stresses thought to have increased du ring Mars history, desiccation and radiation. The mineralisation process has been studied using microbiological (microbial viability), morphological (scanning and transmission electron microscopy), biochemical (GC-MS, Rock-Eval) and spectroscopic (FTIR and RAMAN spectroscopy) methodologies. Based on these approaches, the potential of mineralised Yersinia sp. cells to be preserved over geological time scales is also discussed. Salient results include the fact that fossilisation in gypsum solutions is slower than in silica; not all cells were mineralised, even after 6-months in the fossilising solutions, although the FTIR, Raman and SOLID biomarker signatures were lost by this time period; Rock-Eval analysis suggests that the kerogen in the fossilised strain may not survive preservation over long geological periods, although carbon molecules preserved in fossil microbial traces up to ~3.45 Ga have been detected in the rock record