Since 2008, epitaxial graphene growth has been developed in terms of homogeneity and scale by using a 1 ATM argon pressure at high temperature (>1650°C). Until now, it still remains challenging to obtain films with different and controlled characteristics such as the number of graphene layers or the doping by tuning the growth parameters. Here, we optimized the epitaxial growth of monolayer graphene (1LG) on 4H-SiC (0001) under a low argon pressure of 10 mbar. This intermediate pressure allows growing a continued 1LG in a short process time ~1h30. First, we discuss the initial growth stages from buffer layer (BL) to 1LG as a function of annealing temperature (same heating rate). The combined Raman spectroscopy and atomic force microscopy analyses show that a BL, fully covering the Si-face of SiC, forms as the first step of growth. Subsequently, 1LG starts to grow at step edges and continue to cover the terraces with a step-flow growth mechanism, as demonstrated. Eventually, reproducible syntheses of 1LG films were achieved by this temperature-controlled growth process. Then, we investigate the structural and electronic properties of the 1LG films. The integrated intensity of G-band in Raman spectra normalized with respect to a HOPG reference, AG/AG-HOPG, of each spectrum in Raman map of our continued graphene film is very close to the experimental value reported for a 1LG, demonstrating the good homogeneity. Atomically resolved scanning tunnelling microscopy (STM) evidences a (6x6) superstructure, indicative of 1LG covering a reconstructed interface layer. Regarding the transport measurement, quantum Hall plateau values observed in our graphene layers confirmed both continuity and thickness of the 1LG film8. Moreover, we estimated by transport measurement and STM analysis a hole concentration of pHall~10^10 - 10^11 cm^-2 at 1.7 K in helium atmosphere. We ascribe this unusual doping type to an atmosphere contamination effect since we regain the typical n-doped graphene under vacuum.

Helium-4 atoms are bosons, with the capability to turn superfluid at very low temperature. Remarkably, this property is conserved even when the thickness of the Helium film is reduced down to few atoms thick only. The study of 2D helium films has led to several breakthrough in condensed matter physics including the study of third sound and topological phase transitions, the latter being rewarded by the 2016 Nobel Prize.In most experimental studies helium was adsorbed on large scale substrates, such as mm2 scale grafoil plates or Mylar. Recent advances in the field of optomechanics and nanomechanics now opens up the possibility to study fluids and superfluids of smaller dimensions.In this talk, we present our recent experiments on helium films probed through the mechanical vibrations of a carbon nanotube. We observed a strong discontinuity in the adsorption of He on the nanotube surface, that we attributed to a layering transition. In addition, the low-temperature dependence of the mechanical mode of the nanotube exhibit a mode softening. Thanks to the tunability of the nanotube resonator, we confirmed the spring nature of this effect and drawn a link with the propagation of third sound in He 2D films.

When cooling Helium-4 atoms at very low temperature the system becomes superfluid, a quantum state of matter. Remarkably, this property is conserved even when the thickness of the Helium film is reduced down to few atoms thick only. The study of 2D helium films has led to several breakthrough in condensed matter physics including the study of third sound and topological phase transitions, the latter being rewarded by the 2016 Nobel Prize.Up to now, most experimental studies focused on large scale substrates, such as mm2 scale grafoil plates or Mylar. Recent advances in the field of optomechanics and nanomechanics now opens up the possibility to study fluids and superfluids of smaller dimensions.I will present our recent experiments on helium films growed on individual carbon nanotube, and probed through the mechanical vibrations of the nanotube. We observed a strong discontinuity in the adsorption of He on the nanotube surface, that we attributed to a layering transition. In addition, the low-temperature dependence of the mechanical mode of the nanotube exhibit a mode softening. Thanks to the tunability of the nanotube resonator, we confirmed the spring nature of this effect and drawn a link with the propagation of third sound in He 2D films.

Some countries with rich textile industries are nowadays facing water quality issues as a consequence of impacting dye pollution. In addition to their inherent toxicity, dyes induce modification in water acidity or salinity which has harmful consequences on the photosynthesis of aquatic plants. As dye are hardly biodegradable, water treatment is necessary to get ride of them [1], and adsorption treatment appears as a good candidate with efficient low-cost adsorbents, such as clays [2]. As a matter of fact, lamellar materials are widely used for sorbtion of ions and molecules harmful for health and environment. In order to gain in efficiency in the use of such materials, it is essential to get a deeper understanding of the retention mechanisms at the interface solid/liquid. In this work, anionic clays, namely layered double hydroxides (LDH) have been chosen as model compounds in order to study sorption mechanism. The presence of charged layer induce strong anionic exchange capacity in these materials, moreover their composition and structual parameters are easily controled through mastered synthesis process [3]. This study work has been focused on the the mechanisms that can lead to the capture of polluting molecules. Several model dyes have been chosen (MethylOrange - MO, Carmen Indigo - CI et Orange G - OG) for their charge, symmetry and hydrophobicity. Parameters such as the solution concentration and the activity of the solvant, playing with the nature of ions, have also been explored.The work presented here rely on vibrational spectroscopies (Infrared and Raman spectroscopies) sensitive to the intermolecular interaction of the dye with its environment particularly at the interface solid/dye. In parallel, X-Ray Diffraction probes the structural modification in the clay during sorption.The experimental results interpreted though the help of simulations (Monte-Carlo, DFT), lead a fine description of ions sorption at the interfaces with these models lamellar materials.

Bridged silsesquioxane nanomaterials exhibit original mechanical properties thanks to the association of non-covalent and covalent interactions. Thanks to in situ high pressure spectroscopic studies, achieved in diamond anvil cells, the mechanical behavior of these materials was followed as a function of pressure. Figure 1: Schematic representation of bottom-up structuring in organic-inorganic hybrid silica through self-assembling process Vibrational studies on organic models coupled to ab-initio simulations show that H bond response to pressure is strengthening. In hybrid materials the H bond shows its ability to absorb the mechanical constrains by the modulation of H bond interactions. We thus show that the rigidity yielded by the inorganic polymerization is counterbalanced by the presence of the intermolecular H bond network. The hybrid materials have therefore a reversible behavior, thanks to h bonds behaving as molecular springs. For higher pressure ranges inorganic network start to be strongly impacted in a dominant way so that an irreversible loss of long range order within the organic network is observed.In a second time, the influence of the nature of the organic substructure (thiourea versus urea link, aryl versus aliphatic core) on this spring behavior is discussed.