Ref HAL: hal-01648032_v1
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I will discuss our recent studies showing that the optical response in hBN displays prominent evidence for phonon-assisted optical transitions. First of all, by two-photon spectroscopy, we have demonstrated that the intrinsic optical properties at the band edge are characteristic of an indirect bandgap material. I will further discuss our experimental evidence that transverse optical phonons at the K point of the Brillouin zone assist inter-K valley scattering in hexagonal boron nitride, thanks to the presence of a density of final electronic states coming from extended stacking faults. Finally, I will present our measurements of the vibronic spectrum in a point defect in hBN, displaying a remarkable mapping with the phonon density of states, and in particular a suppression of the phonon-assisted recombination signal at the phonon gap energy. I will discuss our recent studies showing that the optical response in hBN displays prominent evidence for phonon-assisted optical transitions. First of all, by two-photon spectroscopy, we have demonstrated that the intrinsic optical properties at the band edge are characteristic of an indirect bandgap material. I will further discuss our experimental evidence that transverse optical phonons at the K point of the Brillouin zone assist inter-K valley scattering in hexagonal boron nitride, thanks to the presence of a density of final electronic states coming from extended stacking faults. Finally, I will present our measurements of the vibronic spectrum in a point defect in hBN, displaying a remarkable mapping with the phonon density of states, and in particular a suppression of the phonon-assisted recombination signal at the phonon gap energy.

Ref HAL: hal-01645738_v1
Ref Arxiv: 1706.02738
DOI: 10.1103/PhysRevLett.119.188002
WoS: 000414137900014
Ref. & Cit.: NASA ADS
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48 Citations
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Glass films created by vapor-depositing molecules onto a substrate can exhibit properties similar to those of ordinary glasses aged for thousands of years. It is believed that enhanced surface mobility is the mechanism that allows vapor deposition to create such exceptional glasses, but it is unclear how this effect is related to the final state of the film. Here we use molecular dynamics simulations to model vapor deposition and an efficient Monte Carlo algorithm to determine the deposition rate needed to create ultra-stable glassy films. We obtain a scaling relation that quantitatively captures the efficiency gain of vapor deposition over bulk annealing, and demonstrates that surface relaxation plays the same role in the formation of vapor-deposited glasses as bulk relaxation does in ordinary glass formation.

Commentaires: Five pages and five figures. Data relevant to this work have been archived and can be accessed at https://doi.org/10.7924/G8P26W5G. Réf Journal: Phys. Rev. Lett. 119, 188002 (2017)

Ref HAL: hal-01643147_v1
DOI: 10.4028/www.scientific.net/MSF.897.731
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Ref HAL: hal-01643146_v1
DOI: 10.1063/1.4995630
WoS: 000411748100011
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1 Citation

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Ref Arxiv: 1705.06424
Ref INSPIRE: 1600255
DOI: 10.3842/SIGMA.2017.080
WoS: 000413172400001
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5 Citations
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We study integrable deformations of sine-Liouville conformal field theory. Every integrable perturbation of this model is related to the series of quantum integrals of motion (hierarchy). We construct the factorized scattering matrices for different integrable perturbed conformal field theories. The perturbation theory, Bethe ansatz technique, renormalization group and methods of perturbed conformal field theory are applied to show that all integrable deformations of sine-Liouville model possess non-trivial duality properties.

Ref HAL: hal-01632337_v1
DOI: 10.3390/ma10101191
WoS: 000414639000086
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3 Citations
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Colloidal suspensions of anisotropic nanoparticles can spontaneously self-organize in liquid-crystalline phases beyond some concentration threshold. These phases often respond to electric and magnetic fields. At lower concentrations, usual isotropic liquids are observed but they can display very strong Kerr and Cotton-Mouton effects (i.e., field-induced particle orientation). For many examples of these colloidal suspensions, the solvent is water, which hinders most electro-optic applications. Here, for goethite (α-FeOOH) nanorod dispersions, we show that water can be replaced by polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethylsulfoxide (DMSO), without loss of colloidal stability. By polarized-light microscopy, small-angle X-ray scattering and electro-optic measurements, we found that the nematic phase, with its field-response properties, is retained. Moreover, a strong Kerr effect was also observed with isotropic goethite suspensions in these polar aprotic solvents. Furthermore, we found no significant difference in the behavior of both the nematic and isotropic phases between the aqueous and non-aqueous dispersions. Our work shows that goethite nanorod suspensions in polar aprotic solvents, suitable for electro-optic applications, can easily be produced and that they keep all their outstanding properties. It also suggests that this solvent replacement method could be extended to the aqueous colloidal suspensions of other kinds of charged anisotropic nanoparticles.

Résumé:

Single-walled carbon nanotubes (SWCNTs) are functionalized with copper hexacyanoferrate (CuHCF) nanoparticles to prepare solid substrates for sorption of cesium ions (Cs+) from liquid outflows. The high mechanical resistance and large electrical conductivity of SWCNTs are associated with the ability of CuHCF nanoparticles to selectively complex Cs+ ions in order to achieve membrane-like buckypapers presenting high loading capacity of cesium. The materials are thoroughly characterized using electron microscopy, Raman scattering, X-ray photoelectron spectroscopy and thermogravimetric analyses. Cs sorption isotherms are plotted after having measured the Cs+ concentration by liquid phase ionic chromatography in the solution before and after exposure to the materials. It is found that the total sorption capacity of the material reaches 230 mg g1, and that about one third of the sorbed Cs (80 mg g1) is selectively complexed in the CuHCF nanoparticles grafted on SWCNTs. The quantification of Cs+ ions on different sorption sites is made for the first time, and the high sorption rates open interesting outlooks in the integration of such materials in devices for the controlled sorption and desorption of these ions.