... Emilie Bertrand, Christine Gonçalves, Ludivine Billiet, Jean Pierre Gomez, Chantal Pichon, He... more ... Emilie Bertrand, Christine Gonçalves, Ludivine Billiet, Jean Pierre Gomez, Chantal Pichon, Hervé Cheradame, Patrick Midoux, Philippe Guégan. Histidinylated linear PEI: a new efficient non toxic polymer for gene therapy". ChemCom. 2011, DOI: 10.1039/c1cc15716g (2011). ...
The tribological behaviour of Ti/TiN amorphous nanometric multilayers is reported in comparison w... more The tribological behaviour of Ti/TiN amorphous nanometric multilayers is reported in comparison with that of single Ti and TiN layers, in order to study the wear mechanism of nanostructures submitted to that one may call “macroscopic loading”. Ti/TiN nanolayers were deposited onto Si substrate by high vacuum diode r.f. sputtering assisted by in-situ kinetic ellipsometry. Transmission Electron Microscopy (T.E.M.) characterization exhibited the multilayered structure of the films, ascertained by grazing angle X-ray reflectometry and ellipsometry. Sliding wear tests against alumina in dry air showed the ceramic-typed behaviour of the multilayers, the wear of which was partly governed through a microfracture mechanism. Their wear lifetime was found to be higher than that of Ti and TiN single layers and increased with the number of layers.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2010
The effects of grain size on the nanomechanical properties of Ar-irradiated magnesium-aluminate s... more The effects of grain size on the nanomechanical properties of Ar-irradiated magnesium-aluminate spinels was studied. Spinel single crystals and ceramics of different grain size varying from ∼1μm up to few tens of micrometers were used in the experiments. The measurements were performed in both grain centers and grain boundaries and point to rapidly disappearing differences between bulk and boundaries in
ABSTRACT The possibility of a dislocation mechanism in the deformation process of nanocrystalline... more ABSTRACT The possibility of a dislocation mechanism in the deformation process of nanocrystalline materials is reviewed and analyzed. The present theoretical calculation, by taking the anisotropic characteristic of crystallographic symmetry and different choices of critical shear strength into account, results in a reasonable limit in grain size for applying dislocation pile-up theory to nanocrystalline materials. The deviation from the Hall—Petch relationship is rationalized in terms of a small number dislocation pile-up mechanism. A composite model is proposed to evaluate the strength of nanocrystalline materials. It is shown that this model can be used for interpreting the various cases observed in Hall—Petch studies. An analytical expression for assessing the creep rate of nanocrystalline materials by a diffusion mechanism, including triple line diffusion, is derived. It is predicted that the creep rate due to triple line diffusion will exhibit a stronger grain size dependence than that due to grain boundary diffusion.
Reflectivity measurements, at different fixed frequencies, have been performed on Bi2Sr2CaCu2O8 f... more Reflectivity measurements, at different fixed frequencies, have been performed on Bi2Sr2CaCu2O8 films as a function of temperature and magnetic field. Analysis of the data provides evidence for an order parameter 2-Delta(0) of about 3.3 k(B)T(c), although the variation of this order parameter with temperature is significantly different from that predicted by the weak-coupling BCS model.
ABSTRACT Detailed X-ray photoelectron spectra (XPS) have been obtained from BiSrCaCuO thin films ... more ABSTRACT Detailed X-ray photoelectron spectra (XPS) have been obtained from BiSrCaCuO thin films without lead doping (Tc = 86 °K, 2212 phase) and from thin films with lead doping (Tc = 107 °K, mainly 2223 phase). Films were prepared by single target sputtering and post-annealed to synthesize superconducting films1,2.The spectral features of the Cu 2p, O 1s, Sr 3p, Ca 2p and Bi 4f are considered in some detail. It is found that in general the XPS signatures of the Cu 2p peaks are consistent with the presence of a mixed oxide environment with a main contribution from a binding energy similar to that for CuO but also with a significant contribution from a component with a binding energy shifted up to 1.7 eV for the low Tc phase and to 2 eV for the high Tc phase consistent with some trivalent state of copper for lead doped films. The Cu 2p structure exhibits the main line and satellite peaks familiar from screening of the 2p hole by the two valence-band configurations 2p 3d10 and 2p 3d9 in the intensity ratio ~2:1. Line-shape decomposition of the O 1s emission suggests that the main line corresponds to emission from oxygen bonded to copper in the Cu-O planes while the satellite peak with the higher binding energy corresponds to oxygen bonded to bismuth in Bi-O planes. No oxygen species bonded to Ca and Sr is clearly identified by line-shape analysis. Such explanations agree with angular-resolved photoemission spectra on our c axis oriented thin films. The Ca 2p and Sr 3d core-level spectra do not exhibit two sets of doublets as reported in other papers but their corresponding binding energies are shifted in the opposite trend of that observed for oxides. The bismuth ionization state in unleaded films seems inert under different annealing conditions and is very similar to Bi2O3.It is equally shown that the valence band structures are quite sensitive to small changes of the surface conditions and lead doping. In essence, this strongly suggests that valence band spectra may be able to be used as a finger print for the surface of the superconducting films.
Résumé Des essais de nanoindentation instrumenté pour des chargements monotones et cycliques sur ... more Résumé Des essais de nanoindentation instrumenté pour des chargements monotones et cycliques sur deux verres métalliques massifs (VMM) à base Zirconium ont été réalisés à température ambiante et avec une vitesse de chargement qui varie de 250 à 2500 μN/s. ...
... Emilie Bertrand, Christine Gonçalves, Ludivine Billiet, Jean Pierre Gomez, Chantal Pichon, He... more ... Emilie Bertrand, Christine Gonçalves, Ludivine Billiet, Jean Pierre Gomez, Chantal Pichon, Hervé Cheradame, Patrick Midoux, Philippe Guégan. Histidinylated linear PEI: a new efficient non toxic polymer for gene therapy". ChemCom. 2011, DOI: 10.1039/c1cc15716g (2011). ...
The tribological behaviour of Ti/TiN amorphous nanometric multilayers is reported in comparison w... more The tribological behaviour of Ti/TiN amorphous nanometric multilayers is reported in comparison with that of single Ti and TiN layers, in order to study the wear mechanism of nanostructures submitted to that one may call “macroscopic loading”. Ti/TiN nanolayers were deposited onto Si substrate by high vacuum diode r.f. sputtering assisted by in-situ kinetic ellipsometry. Transmission Electron Microscopy (T.E.M.) characterization exhibited the multilayered structure of the films, ascertained by grazing angle X-ray reflectometry and ellipsometry. Sliding wear tests against alumina in dry air showed the ceramic-typed behaviour of the multilayers, the wear of which was partly governed through a microfracture mechanism. Their wear lifetime was found to be higher than that of Ti and TiN single layers and increased with the number of layers.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2010
The effects of grain size on the nanomechanical properties of Ar-irradiated magnesium-aluminate s... more The effects of grain size on the nanomechanical properties of Ar-irradiated magnesium-aluminate spinels was studied. Spinel single crystals and ceramics of different grain size varying from ∼1μm up to few tens of micrometers were used in the experiments. The measurements were performed in both grain centers and grain boundaries and point to rapidly disappearing differences between bulk and boundaries in
ABSTRACT The possibility of a dislocation mechanism in the deformation process of nanocrystalline... more ABSTRACT The possibility of a dislocation mechanism in the deformation process of nanocrystalline materials is reviewed and analyzed. The present theoretical calculation, by taking the anisotropic characteristic of crystallographic symmetry and different choices of critical shear strength into account, results in a reasonable limit in grain size for applying dislocation pile-up theory to nanocrystalline materials. The deviation from the Hall—Petch relationship is rationalized in terms of a small number dislocation pile-up mechanism. A composite model is proposed to evaluate the strength of nanocrystalline materials. It is shown that this model can be used for interpreting the various cases observed in Hall—Petch studies. An analytical expression for assessing the creep rate of nanocrystalline materials by a diffusion mechanism, including triple line diffusion, is derived. It is predicted that the creep rate due to triple line diffusion will exhibit a stronger grain size dependence than that due to grain boundary diffusion.
Reflectivity measurements, at different fixed frequencies, have been performed on Bi2Sr2CaCu2O8 f... more Reflectivity measurements, at different fixed frequencies, have been performed on Bi2Sr2CaCu2O8 films as a function of temperature and magnetic field. Analysis of the data provides evidence for an order parameter 2-Delta(0) of about 3.3 k(B)T(c), although the variation of this order parameter with temperature is significantly different from that predicted by the weak-coupling BCS model.
ABSTRACT Detailed X-ray photoelectron spectra (XPS) have been obtained from BiSrCaCuO thin films ... more ABSTRACT Detailed X-ray photoelectron spectra (XPS) have been obtained from BiSrCaCuO thin films without lead doping (Tc = 86 °K, 2212 phase) and from thin films with lead doping (Tc = 107 °K, mainly 2223 phase). Films were prepared by single target sputtering and post-annealed to synthesize superconducting films1,2.The spectral features of the Cu 2p, O 1s, Sr 3p, Ca 2p and Bi 4f are considered in some detail. It is found that in general the XPS signatures of the Cu 2p peaks are consistent with the presence of a mixed oxide environment with a main contribution from a binding energy similar to that for CuO but also with a significant contribution from a component with a binding energy shifted up to 1.7 eV for the low Tc phase and to 2 eV for the high Tc phase consistent with some trivalent state of copper for lead doped films. The Cu 2p structure exhibits the main line and satellite peaks familiar from screening of the 2p hole by the two valence-band configurations 2p 3d10 and 2p 3d9 in the intensity ratio ~2:1. Line-shape decomposition of the O 1s emission suggests that the main line corresponds to emission from oxygen bonded to copper in the Cu-O planes while the satellite peak with the higher binding energy corresponds to oxygen bonded to bismuth in Bi-O planes. No oxygen species bonded to Ca and Sr is clearly identified by line-shape analysis. Such explanations agree with angular-resolved photoemission spectra on our c axis oriented thin films. The Ca 2p and Sr 3d core-level spectra do not exhibit two sets of doublets as reported in other papers but their corresponding binding energies are shifted in the opposite trend of that observed for oxides. The bismuth ionization state in unleaded films seems inert under different annealing conditions and is very similar to Bi2O3.It is equally shown that the valence band structures are quite sensitive to small changes of the surface conditions and lead doping. In essence, this strongly suggests that valence band spectra may be able to be used as a finger print for the surface of the superconducting films.
Résumé Des essais de nanoindentation instrumenté pour des chargements monotones et cycliques sur ... more Résumé Des essais de nanoindentation instrumenté pour des chargements monotones et cycliques sur deux verres métalliques massifs (VMM) à base Zirconium ont été réalisés à température ambiante et avec une vitesse de chargement qui varie de 250 à 2500 μN/s. ...
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