I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.

In this talk, I will discuss the striking co-existence of a high internal quantum efficiency and an indirect bandgap in hexagonal boron nitride.

Interactions and assemblies of wheat proteins

Structuring and degrading polymer gels via catalytic reactions. Réunion plénière du GDR SLAMM (Solliciter LA Matière Molle)

Chalcogenide glasses exhibit remarkable properties, which could be used in the development of electrical memory susceptible to replace the current flash memories. During the last decades, a strong interest has been focused on superionic Ag-Ge-Se glasses for their high ionic conductivity, a property that could be used to develop ionic Conductive-Bridging Random Access Memories (CB-RAM). Bulk Ag-Ge-Se glasses have already been widely studied for their electrical, structural and thermal properties. In particular it was shown that the conductivity of phase separated Agx(Ge0.25Se0.75)100-x glasses increases suddenly by seven to eight orders of magnitude at 7-10 at.%Ag. The percolation of the Ag-rich phase was at the origin of this sudden jump in conductivity. Despite a convergence on the inhomogeneous nature of these glasses, some questions remain open such as the composition of the Ag-rich and Ag-poor phases, size and shape of the different phases. These questions has hardly been treated in literature to date. In this talk, investigations on bulk Agx(Ge0.25Se0.75)100-x glasses will be performed focusing on the inhomogeneous nature of the glasses. Macroscopic and local studies of vibrational and mechanical properties will conduct using Raman (mapping) spectroscopy, Vickers microhardness and Contact Resonance Atomic Force Microscopy (CR-AFM). For the glass containing 10 at. % in Ag, Raman mapping will give evidence of a phase separation for through continuous interpenetrating phases in the spinodal decomposition process. Combined mechanical characterizations will indicate that the microhardness and rigidity modulus decrease with the silver content in the glass. At nanoscale level, CR-AFM measurements will highlight a modulation of the rigidity with Ag content. The structural origin of these changes will be confirmed using Raman mapping evidencing modifications in the tetrahedral network between two phases. The results could suggest a different Ge/Se ratio in Ag-poor and Ag-rich phases.

In this communication, we report direct and unambiguous evidence of the existence of inner semiconducting tube photoluminescence (PL) from measurements performed on four individual freestanding index-identified double-walled carbon nanotubes (DWNTs). Based on thorough Rayleigh scattering, Raman scattering, and PL experiments, we are able to demonstrate that the innersemiconducting tube PL is observed with a quantum yield estimated to be a few 10-6 independent of the semiconducting or metallic nature of the outer tube. This result is mainly attributed to ultrafast exciton transfer from the inner to outer tube. Furthermore, by carrying out PL excitation experiments on the (14,1)@(15,12) DWNT, we show that the inner semiconducting tube PL can be detected through the optical excitation of the outer tube, indicating that the exciton transfer can also occur in theopposite way.