Gilles Montagnac

Ultraviolet photoproduction of ISM dust Laboratory characterisation and astrophysical relevance

The production of a hydrogenated amorphous carbon polymer (a-C:H) via the photolysis of a series of organic molecule precursors at low temperature is described. Such amorphous material is synthesised under interstellar conditions (10 K and Lyman-α photons) and represents the best candidate to explain the Diffuse Interstellar Medium absorption observed in our Galaxy and in other galaxies. We perform a series of laboratory analyses (Infrared spectroscopy, µspectroscopy, Raman, Photoluminescence and UV-visible spectroscopy) which allow a full characterisation of such polymers. This allows us to assess the importance of the polymer and possible scenarios for its role in crucial aspects of the lifecycle of dust. Such material has implications for the carbon budget at galactic scales, hydrogen formation, extended red emission, as a PAH precursor, and in explaining the 2175 A extinction bump.

Deformation of (Mg0.9,Fe0.1)SiO3 Perovskite aggregates up to 32 GPa

Room temperature investigations on the shear stress and deformation mechanisms of (Mg0.9Fe0.1)SiO3 perovskite are performed in situ up to 32 GPa using radial X-ray diffraction and the diamond anvil cell as a deformation apparatus. The uniaxial stress supported by the perovskite aggregate is found to increase continuously with pressure up to 10.9(+/-1.9) GPa at 32(+/-1) GPa. Our measurements show no development of significant lattice preferred orientations in the sample, which indicates that deformation by dislocation glide is not the dominant deformation mechanism under these conditions. Assuming that the underlying cause for seismic anisotropy in the deep Earth is elastic anisotropy combined with lattice preferred orientation, our results indicate that silicate perovskite deformed under the conditions of this experiment would not be the source of seismic anisotropy

Pressure-induced exfoliation of inorganic fullerene-like WS2 particles in a Hertzian contact

Nanoparticles are potential additives for the improvement of lubricant properties, because of the structural modifications they undergo under high pressures in mechanical contacts. The behavior of inorganic fullerene-like WS2 nanoparticles (IF-WS2) under high isotropic pressures of up to 20GPa generated in a diamond anvil cell was studied and compared to the response of the lamellar 2H phase of WS2. The same materials were then subjected to static uniaxial pressures in a Hertzian contact in the GPa range. The evolution of the particles as a function of pressure was studied by in situ Raman spectroscopy and transmission electron microscopy at the end of the test. Data analysis shows that IF-WS2 particles resist high hydrostatic pressures well, but they are totally exfoliated by uniaxial compression in a Hertzian contact under low pressure. These results explain the excellent tribological properties at ambient temperature of IF-WS2 nanolubricant that have previously been attributed to the nested nanospheres...

Zinc phosphate chain length study under high hydrostatic pressure by Raman spectroscopy

The aim of this study is to combine a diamond anvil cell with in-situ Raman spectroscopy to simulate and analyze the effect of pure pressure on the length of phosphate chains in an antiwear film formed in a tribological contact. In-situ Raman spectra of Zn2P2O7 glass, α-Zn3(PO4)2, and γ−Zn2P2O7 crystals submitted to high hydrostatic pressure up to 20 GPa were recorded. Evolution of Raman spectra as a function of pressure was studied in the characteristic high frequency range of PO4 tetrahedra molecular resonance (650−1300 cm−1). When exposed to high pressure, the structure of the sample becomes less ordered. Phase transitions in α-Zn3(PO4)2 structure are observed during compression from ambient pressure to 3 GPa. The length of the phosphate chains is conserved up to 20 GPa when samples are subjected to hydrostatic pressure.The aim of this study is to combine a diamond anvil cell with in-situ Raman spectroscopy to simulate and analyze the effect of pure pressure on the length of phosphate chains in an antiwear film formed in a tribological contact. In-situ Raman spectra of Zn2P2O7 glass, α-Zn3(PO4)2, and γ−Zn2P2O7 crystals submitted to high hydrostatic pressure up to 20 GPa were recorded. Evolution of Raman spectra as a function of pressure was studied in the characteristic high frequency range of PO4 tetrahedra molecular resonance (650−1300 cm−1). When exposed to high pressure, the structure of the sample becomes less ordered. Phase transitions in α-Zn3(PO4)2 structure are observed during compression from ambient pressure to 3 GPa. The length of the phosphate chains is conserved up to 20 GPa when samples are subjected to hydrostatic pressure.

Pressure-induced Pbca-P21/c phase transition of natural orthoenstatite: Compositional effect and its geophysical implications

Abstract Raman spectroscopy has been employed to investigate possible compositional effects on the high-pressure phase transition of Mg-rich orthoenstatite to a newly discovered P21/c phase. Three natural orthoenstatite (OEN) samples were used in this study: near end-member Mg orthoenstatite (Zabargad Island, Egypt), Al-free, Fe-bearing orthoenstatite (Morogoro, Tanzania) and Al-rich, Fe,Ca-bearing orthoenstatite (Kilbourne Hole, New Mexico). Experiments were carried out at room temperature. For all samples, the high-pressure phase transition is characterized by a splitting of the 660-680 cm-1 doublet in the Raman spectrum into a triplet, with a corresponding change of peak intensities. These spectral changes are caused by the lowered symmetry of the high-pressure phase, as indicated by structural refinement from single-crystal X-ray diffraction results. The high-pressure phase of all samples appears to have space group P21/c. No evidence for a C2/c phase was observed. Our results indicate that upon compression, the presence of 10 mol% Fe decreases the onset pressure of formation of the high-pressure P21/c phase by about 1 GPa. Results for the Kilbourne Hole OEN show that upon compression, a combined enrichment of Al and Ca contents increases the onset pressure of formation of high-pressure clinoesntatite (HPCEN2) by over 3 GPa relative to Tanzania OEN. Upon decompression, all samples revert to single crystals of the orthoenstatite starting phase. Our measurements suggest that orthoenstatite is the prevalent phase of Mg-rich pyroxene throughout the uppermost mantle, whereas the newly discovered P21/c phase might be present near the bottom of uppermost mantle, slightly shallower than the top of the transition zone.

Mineral and Bacterial Diversities of Desert Sand Grains from South-East Morocco

Mineralogy and microbiology of sand from Merzouga (Morocco) were simultaneously characterized, with the purpose of contributing to a better understanding of the geomicrobiology of deserts. In spite of very low measured bacterial biomass, bacterial diversity on each of the five defined mineralogical classes, was found high. An original grain by grain cultivation method enabled to obtain bacterial isolates with an unusually high recovery rate. The results of this study show that the genus Arthrobacter is well adapted to this environment with a preference for grains other than the dominant mineral quartz, and that the genera Chelatococcus and Saccharotrix are strongly attached to the grains.

Measurement of water contents in olivine using Raman spectroscopy

Abstract We have measured the water contents in forsterites and olivines synthesized in the multi-anvil press using confocal Raman spectroscopy. These samples were previously characterized for water contents by polarized FTIR and contain from 75 to 1300 ppm wt H2O. We find that both forsterite and olivine follow the same trend in water content vs. integrated Raman OH/Si intensity. In addition three synthetic enstatites also display a linear trend in water vs. OH/Si integrated Raman intensity but with a different slope than for olivine, indicating that the calibration for measuring water by Raman is matrix dependent. Three glasses of different compositions (two rhyolites and one basalt) and different water contents were also analyzed. Comparison with the forsterites and olivines shows that the Raman cross-section of these glasses is very different and their intensities must be corrected by different factors. Therefore, to be able to use glasses as external calibrants, prior knowledge of their behavior compared to well-characterized NAM standards is necessary.

A Novel SERRS Sandwich-Hybridization Assay to Detect Specific DNA Target

In this study, we have applied Surface Enhanced Resonance Raman Scattering (SERRS) technology to the specific detection of DNA. We present an innovative SERRS sandwich-hybridization assay that allows specific DNA detection without any enzymatic amplification, such as is the case with Polymerase Chain Reaction (PCR). In some substrates, such as ancient or processed remains, enzymatic amplification fails due to DNA alteration (degradation, chemical modification) or to the presence of inhibitors. Consequently, the development of a non-enzymatic method, allowing specific DNA detection, could avoid long, expensive and inconclusive amplification trials. Here, we report the proof of concept of a SERRS sandwich-hybridization assay that leads to the detection of a specific chamois DNA. This SERRS assay reveals its potential as a non-enzymatic alternative technology to DNA amplification methods (particularly the PCR method) with several applications for species detection. As the amount and type of damage highly depend on the preservation conditions, the present SERRS assay would enlarge the range of samples suitable for DNA analysis and ultimately would provide exciting new opportunities for the investigation of ancient DNA in the fields of evolutionary biology and molecular ecology, and of altered DNA in food frauds detection and forensics.

Study of inorganic fullerenes and carbon nanotubes by in situ Raman tribometry

Nanoparticles such as inorganic fullerenes of metal dichalcogenides or carbon nanotubes have been recently used as lubricant additives and they present excellent tribological properties. Raman spectroscopy is a useful technique to follow modification of these two structures. We developed an original tribometer able to perform in situ Raman analyses during sliding steel on a sapphire flat. These analyses gave unique information on real-time structural changes of nanoparticles inside the contact area: inorganic fullerenes are tribologically active by a progressive exfoliation process and carbon nanotubes is changed to amorphous carbon. Lubrication mechanism of these particles are explained in the light of analytical results.

Detection of DNA Sequences Refractory to PCR Amplification Using a Biophysical SERRS Assay (Surface Enhanced Resonant Raman Spectroscopy)

The analysis of ancient or processed DNA samples is often a great challenge, because traditional Polymerase Chain Reaction – based amplification is impeded by DNA damage. Blocking lesions such as abasic sites are known to block the bypass of DNA polymerases, thus stopping primer elongation. In the present work, we applied the SERRS-hybridization assay, a fully non-enzymatic method, to the detection of DNA refractory to PCR amplification. This method combines specific hybridization with detection by Surface Enhanced Resonant Raman Scattering (SERRS). It allows the detection of a series of double-stranded DNA molecules containing a varying number of abasic sites on both strands, when PCR failed to detect the most degraded sequences. Our SERRS approach can quickly detect DNA molecules without any need for DNA repair. This assay could be applied as a pre-requisite analysis prior to enzymatic reparation or amplification. A whole new set of samples, both forensic and archaeological, could then deliver information that was not yet available due to a high degree of DNA damage.