Nano-Carbon |
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Under high pressure, graphite transforms into diamond, which is possibly the most famous transition between two solids. This transformation is associated to a change of dimensionality in the carbon bond from a planar (2D) phase to a 3D structure. How do evolve under pressure the carbon nanoforms having reduced diemensionality as nanotubes, graphene, fullerenes or other nano-cavities? Ca we guide such evolution in order to produce new nanomaterials able to provide better answers to the increasing societal requests for instance in the energy domain? This is the challenge of our research in which we try to understand how the dimensionality of these carbon forms evolve under extreme conditions and how we can take profit of this evolution to synthesize new materials which could excell in terms of superconductivity, thermoelectricity, super-capacitance, photovoltaic applications,… We are interested in the evolution of electronic and mechanical properties of carbon nano-forms in response to external stresses. Our research includes the study of the deformation of these structures, the development of electronic transport and coupling the evolution of electronic and mechanical properties under extreme stress. Coupling with various environments (nano-composites, biomolecules, ...) or the development of electromechanical devices (NEMS) constitute explored applications axes. These research is strongly supported by the efforts in nanofabrication (lithography, CVD, laser cutting, ...) coupled to the use of extreme conditions of pressure and temperature (Diamond anvil cells anvils, SPS ultra-high pressure, heating laser, ...). Study methods include optical spectroscopy (Raman, SMS ...), microscopic probes (AFM, TEM, SEM, ...) and the use of large instruments such as X-ray sources of synchrotron (ESRF, SOLEIL) or neutron reactors (ILL, LLB) for scattering experiments at small angles and X-ray absorption (XANES, EXAFS) among others.
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People: Alfonso San Miguel |
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News |
Collapse of nanopores under pressure in the expanded graphiteThe expanded graphite is a disordered form of graphite having a very high porosity. We have shown how the fractal dimension of the interface created by the pores with changing strain and showed a nanometric pore closure mechanism by irreversible collapse similar to that observed in the carbon nanotubes. Beyond the interest for the understanding of the mechanics of the expanded graphite which is used for example in the seals, this mechanism may be more general and apply for example to clays or other layered systems natural or artificial, subjected to high mechanical stress. |
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Collapse mechanism and irreversible division of the pores in the flexible graphite under the effect of uniaxial pressure. 'An in situ small angle neutron scattering study of expanded graphite under a uniaxial stress', Carbon (accepté); Félix Balima, Vittoria Pischedda, Sylvie Le Floch et Alfonso San Miguel en collaboration avec A. Brûlet (LLB, Saclay), P. Linder (ILL, Grenoble) et L. Duclaux (Université de Savoie). |
Collapse of pressurized carbon nanotubes.We conducted a theoretical study of the evolution of the Raman spectrum of single and double walled carbon nanotubes under pressure. Our results show, in agreement with the experiments, that evolution under pressure from the G band Raman spectrum is a good indicator to detect the collapse of the carbon nanotubes. A detailed analysis makes it possible to understand why. |
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The pressure Raman spectrum calculated for the G band (left panel) has contributions that depend on the zone of the tube which is given by the azimuth angle (right panel). A. L. Aguiar, Rodrigo B. Capaz, A. G. Souza Filho et A. San-Miguel, J. Phys Chem C, 116, 22637 (2012) |
