A comprehensive model of the optical spectra of carbon nanotubes on substrate by polarized microscopy

Polarized optical microscopy and spectroscopy are progressively becoming key methods for the high-throughput characterization of individual carbon nanotubes (CNTs) and other one-dimensional nanostructures, on substrate and in devices. The optical response of CNTs on substrate in cross polarization experiments is usually limited by the polarization conservation of the optical elements in the experimental setup. We developed a theoretical model taking into account the depolarization by the setup and the optical response of the substrate. We show that proper modelization of the experimental data requires to take into account both non-coherent and coherent light depolarization by the optical elements. We also show how the nanotube signal can be decoupled from the complex reflection factor of the anti-reflection substrate which is commonly used to enhance the optical contrast. Finally, we describe an experimental protocol to extract the depolarization parameters and the complex nanotube susceptibility, and how it can improve the chirality assignment of individual carbon nanotubes in complex cases.Comment: 10 pages, 7 Figures, submitted to PRB. A supplementary information completes this pape

Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica

This series discusses the origin of sound damping and dispersion in glasses. In particular, we address the relative importance of anharmonicity versus thermally activated relaxation. In this first article, Brillouin-scattering measurements of permanently densified silica glass are presented. It is found that in this case the results are compatible with a model in which damping and dispersion are only produced by the anharmonic coupling of the sound waves with thermally excited modes. The thermal relaxation time and the unrelaxed velocity are estimated.Comment: 9 pages with 7 figures, added reference

Démarche qualité en recherche publique

If the quality approach is a concept that was formalized since the beginning of the twentieth century in the industry, its deployment in public research is more recent. Its implementation in the research community is very specific as shown by different actions led in recent years in different organizations. It usually responds to different challenges (scientific, economic, financial...). The specificities of the research should stop its deployment but also promote it.Si la démarche qualité est un concept qui s'est formalisé depuis le début du XXe siècle dans le milieu industriel, son déploiement dans la recherche publique est plus récent. Sa mise en œuvre dans le milieu de la recherche est très particulière comme le démontrent certaines actions menées ces dernières années dans les différents organismes. Elle répond, généralement et à la fois, à des enjeux scientifiques, économiques et financiers... Les spécificités liées à la recherche peuvent constituer un frein à son déploiement mais aussi en être le moteur

Démarche qualité en recherche publique

If the quality approach is a concept that was formalized since the beginning of the twentieth century in the industry, its deployment in public research is more recent. Its implementation in the research community is very specific as shown by different actions led in recent years in different organizations. It usually responds to different challenges (scientific, economic, financial...). The specificities of the research should stop its deployment but also promote it.Si la démarche qualité est un concept qui s'est formalisé depuis le début du XXe siècle dans le milieu industriel, son déploiement dans la recherche publique est plus récent. Sa mise en œuvre dans le milieu de la recherche est très particulière comme le démontrent certaines actions menées ces dernières années dans les différents organismes. Elle répond, généralement et à la fois, à des enjeux scientifiques, économiques et financiers... Les spécificités liées à la recherche peuvent constituer un frein à son déploiement mais aussi en être le moteur

Anomalous elastic behavior of vitreous silica under high pressure and high temperature

International audienc

Anomalous elastic behavior of vitreous silica under high pressure and high temperature

International audienc

Dynamical origin of anomalous temperature hardening of elastic modulus in vitreous silica

International audienceHigh-resolution Brillouin scattering experiments are performed under hydrostatic pressures ranging from 0 to 10 GPa in vitreous silica. The hypersound-attenuation coefficient exhibits a sharp maximum located at 2 GPa, which appears to coincide with the well-known minimum in sound velocity. Two main processes contribute to sound damping: the thermal relaxation of local defects and the anharmonic interactions with thermal vibrations. By analyzing the temperature dependence of the velocity and subtracting the changes produced by the above mechanisms, the unrelaxed velocity is found. It is constant at low temperatures and increases anomalously above a temperature onset.We show that the onset strongly depends on pressure, which is in agreement with a dynamical origin of the structural changes that produce the hardening