Ref HAL: hal-03406977_v1
Ref Arxiv: 2101.01410
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The polarized fluorescence emission of organic fluorophores has been extensively studied in photonics and is increasingly exploited in single molecule scale bio-imaging. Expanding the polarization properties of compact molecular assemblies is, however, extremely challenging due to depolarization and quenching effects associated with the self-aggregation of molecules into the sub-nanometer scale. Here we demonstrate that Boron Nitride Nanotubes (BNNTs) can act as a 1D host-template for the alignment of encapsulated a-sexithiophene (6T) inside BNNTs, leading to an optically active 6T@BNNT nanohybrid. We show that the fluorescence from the nanohybrid is strongly polarized with extinction ratios as high as 700 at room temperature. A statistical analysis of the 6T orientation inside BNNTs with inner diameter up to 1.5 nm shows that at least 80% of the encapsulated 6Ts exhibit a maximum deviation angle of less than 10{\deg} with respect to the BNNT axis. Despite a competition between molecule-molecule and molecule-BNNT adsorption in larger BNNTs, our results also show that more than 80% of the molecules display a preferential orientation along the BNNT axis with a deviation angle below 45{\deg}.

Ref HAL: hal-03171300_v1
DOI: 10.3390/app11031229
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Even if on-board mm-wave/THz heterodyne receivers have been developed to measure greenhouse gases (GHGs) atmospheric profiles, rotational spectroscopy rests under-exploited for their monitoring unlike IR rovibrational spectroscopy. The present study deals with the ability of THz spectroscopy using long interaction path-lengths for GHG laboratory investigations. High-resolution THz signatures of non-polar greenhouse molecules may be observed by probing very weak centrifugal distortion induced rotational transitions. To illustrate, new measurements on CH4 and CF4 have been carried out. For CH4, pure rotational transitions, recorded by cw-THz photomixing up to 2.6 THz in a White type cell adjusted to 20 m, have allowed to update the methane line list of atmospheric databases. Concerning CF4, Fabry-Perot THz absorption spectroscopy with a km effective pathlength was required to detect line intensities lower than 10−27 cm−1/(moleccm−2). Contrary to previous synchrotron-based FT-FIR measurements, the tetrahedral splitting of CF4 THz lines is fully resolved. Finally, quantitative measurements of N2O and O3 gas traces have been performed in an atmospheric simulation chamber using a submm-wave amplified multiplier chain coupled to a Chernin type multi-pass cell on a 200 m path-length. The THz monitoring of these two polar GHGs at tropospheric and stratospheric concentrations may be now considered.

Ref HAL: hal-03406165_v1
DOI: 10.1117/12.2593589
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The terahertz absorption spectra of sodium magnesium chlorophyllin (Chl-Mg-Na) and sodium copper chlorophyllin (Cu-Chl), two major members of the chlorophyll derivative family, have been measured in the range 0.2−3.0 THz (6.6−100 cm-1), at room temperature. Additionally, surface-enhanced Raman scattering spectroscopy was used to supplement data in the higher frequency range. The capability of terahertz spectroscopy for quantitative characterization of Chl-Mg-Na intermolecular vibrations was investigated and the sensitivity of the 1.82-THz feature with degree of hydration by changes in the molecular environment was examined. For Cu-Chl derivative, a broad feature was observed around 1.8 THz which currently hinders clear Cu-Chl identification and quantification.

Ref HAL: tel-03396817_v1
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La mécanique statistique explique désormais les transitions de phase se produisant dans des substances simples à l'équilibre thermodynamique. Néanmoins, la transition vitreuse, observée universellement dès lors qu'un liquide est refroidi ou comprimé suffisamment rapidement pour éviter sa cristallisation, est toujours source d'intenses recherches. Dans l'approximation de champ moyen, le ralentissement des systèmes vitreux est la conséquence de l'émergence d'un paysage d'énergie libre rugueux avec un nombre exponentiellement grand de minima correspondant aux états métastables. Ces derniers dictent également les propriétés thermodynamiques des liquides surfondus ainsi que le comportement hors-équilibre des verres. Ils sont cependant mal définis au-delà du champ moyen : ils ont une durée de vie finie et une extension spatiale limitée. Le travail de cette thèse participe à l'effort de définir et de caractériser les états métastables en dimension finie par les simulations numériques et les travaux analytiques. Nous exploitons dans un premier temps la thermodynamique contrainte des liquides surfondus dans la construction de Franz et Parisi. La théorie champ moyen prédit que l'existence d’états métastables se manifeste par une ligne de transition de phase et un point critique dans un diagramme des phases étendu. Nous utilisons les simulations numériques et nous montrons que les résultats champ moyen survivent malgré l'introduction de fluctuations de dimension finie. Nous sommes capables de caractériser le point critique et d'en donner sa classe d'universalité ainsi que sa dimension critique inférieure. Nous étudions ensuite en détail la définition du paramètre d'ordre associé à cette transition analytiquement et numériquement pour orienter d'éventuelles futures études mais également pour mieux comprendre la structure gros-grains du paysage d’énergie libre de verres modèles. Finalement, nous nous intéressons à la thermodynamique des liquides surfondus en présence d'une contrainte thermodynamique locale et nous révélons d'importantes fluctuations spatiales. Dans un second temps, nous étudions la dynamique des liquides surfondus proches de leur transition vitreuse en mettant à profit un algorithme récent pour générer des configurations d'équilibre de liquides modèles à très basses températures. Nous montrons que la dynamique de relaxation résulte de l'apparition distribuée de régions mobiles qui croissent par facilitation. Dans un troisième temps, nous étudions les propriétés de verres hors-équilibre, et nous mettons en place des protocoles numériques qui permettent de générer des verres beaucoup plus stables que ceux obtenus usuellement en simulations par vieillissement.

Ref HAL: hal-03394606_v1
Ref Arxiv: 2110.06949
Ref INSPIRE: 1945075
DOI: 10.1007/JHEP12(2021)044
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We compute the contribution of Euclidean D-branes in type IIB string theory on Calabi-Yau threefolds to the metric on the hypermultiplet moduli space in the large volume, weak coupling limit. Our results are in perfect agreement with the predictions based on S-duality, mirror symmetry and supersymmetry.

Ref HAL: hal-03382355_v1
DOI: 10.3390/nano11092173
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Nanoporous carbons remain the most promising candidates for effective hydrogen storage by physisorption in currently foreseen hydrogen-based scenarios of the world’s energy future. An optimal sorbent meeting the current technological requirement has not been developed yet. Here we first review the storage limitations of currently available nanoporous carbons, then we discuss possible ways to improve their storage performance. We focus on two fundamental parameters determining the storage (the surface accessible for adsorption and hydrogen adsorption energy). We define numerically the values nanoporous carbons have to show to satisfy mobile application requirements at pressures lower than 120 bar. Possible necessary modifications of the topology and chemical compositions of carbon nanostructures are proposed and discussed. We indicate that pore wall fragmentation (nano-size graphene scaffolds) is a partial solution only, and chemical modifications of the carbon pore walls are required. The positive effects (and their limits) of the carbon substitutions by B and Be atoms are described. The experimental ‘proof of concept’ of the proposed strategies is also presented. We show that boron substituted nanoporous carbons prepared by a simple arc-discharge technique show a hydrogen adsorption energy twice as high as their pure carbon analogs. These preliminary results justify the continuation of the joint experimental and numerical research effort in this field.

Ref HAL: hal-03391523_v1
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We present a numerical approach for the solution of EM scattering from a dielectric cylinder partially covered with graphene. It is based on a classical Fourier-Bessel expansion of the fields inside and outside the cylinder to which we apply the ad-hoc boundary conditions in the presence of graphene. Due to the singular nature of the electric field at the ends of the graphene sheet, we introduce auxiliary boundary conditions to better take this reality into account. The result is a very simple and very efficient method allowing the study of diffraction from such structures.