Properties of methane adsorbed in confined geometries are interesting from both fundamental and practical points of view. At ambient temperatures adsorption at the supercritical conditions is usually studied, as it is interesting from the point of view of methane storage. At the same time, the analysis of low temperature adsorption properties is essential for understanding the mechanism of adsorption, as a function of temperature and the pore size. In this work we study phase diagram of methane confined in carbon slit pores of the width between 1nm and 4nm. We analyze the mechanism of the layering transition(s) and capillary condensation at subcritical conditions, for temperatures between 80 K and 180 K, then we study the pore s storage capacity, up to the room temperature. The mechanism of the layers formation is strongly temperature dependent, and changes from a sharp adsorption at low temperature to more continuous one at higher temperatures. The size of pore defines the number of layers adsorbed: 1 nm pore allows adsorbing 2 layers of methane molecules. Capillary condensation is observed in 4 nm pores.

Silicate glasses possess a central role in glass technology due to their multipleapplications ranging from optical devices to the immobilization of nuclear waste. In this context,an accurate theoretical modeling of their spectra can be proven to be invaluable in order tooptimize their performance and tailor their fabrication method to match requirements for futureapplications.The vibrational properties of silica glass have been intensively studied experimentallyand theoretically during the last four decades. However there are few theoretical studies of theevolution of the vibrational properties under pressure. We have calculated the parallel andperpendicular Raman spectra of the silica glass, within the density functional theory framework.At zero pressure, we have found a good agreement with the experimental spectra as well as toprevious calculations reported in the literature. Modifications of the Raman spectra underpressure have been found to be in agreement with experimental data.We will equally present preliminary results on simulated Raman spectra of a binary sodo-silicate glass. We focus on the effect of local structural units, such as SiO 4 tetrahedra and theirinterconnection, alongside the role of sodium atom content in order to assign the correspondingbands. The obtained information can be then used in order to help to interpret the experimentalspectra obtained for more complex silicate glasses.

The vibrational properties of silica glass have been intensively studied experimentally andtheoretically during the last four decades. However there are few theoretical studies of theevolution of the vibrational properties for more complex silicate glasses (binary, ternary etc...).In the first part of this talk, we will present the structural and vibrational properties a sodium silicateglass of composition 4Na 2 O-6SiO 2 (NS1.5). The study has been carried out using first principlescalculations within the density functional theory framework as implemented in the VASP code. Wehave studied the structural and vibrational properties of this glass, and we have identified thecontributions of the various species to the vibrational density of states (VDOS) as well as to the IRspectra. In particular we will discuss how the presences of the sodium atoms affect the relevantvibrational parameters: positions, shapes and intensities of the main peaks of the VDOS and IRspectra.In the second part, we will discuss the properties of several complex borosilicate glasses.Computing physical properties of complex glass compositions via numerical simulations oftensuffers of inaccurate predictions when using classical potentials, or it is excessively timeconsuming simulations when glass structures are obtained using ab-initio methods. The study hasbeen carried out by combining classical and ab initio molecular dynamics (MD) methods and byvarying the concentrations of SiO 2 , B 2 O 3 , Na 2 O, CaO, Al 2 O 3 and MgO. The classical MD includedliquid equilibration, quenching and preliminary relaxation, while ab initio method was used tofurther relax the samples. Two sets of effective potentials have been used for the classicalsimulations. This strategy allows of course a significant CPU time saving.We have compared the structural properties of the simulated samples and have found thatclassical MD simulations cannot provide reliable glass models for complex borosilicates (at leastwith the potentials we have chosed), especially for the peculiar aspect of Boron coordination. Theab initio simulations have corrected the unreliable classical simulated structures and providedresults in good agreement with previous studies of borosilicate glasses. We have also noticed thatthe presence of Al and Mg has influenced the fraction of 3-fold coordinated Boron, as expectedfrom experimental data. The vibrational properties have been equally studied within the ab initioapproach, and the contributions of the various species have been identified. We have found that 3-and 4-fold coordinated borons give rise to distinguished spectral features.

Overview of the Raman signatures of graphene and carbon nanotubes

Raman spectroscopy is a major characterization technique of carbon nanotubes and graphene. It is widely used to identify their structure, i.e. the diameter of single-walled carbon nanotubes (SWNT), or the number and orientation of layers of graphene, as well as the nature and density of defects. On the other hand, the Raman signatures of carbon nanomaterials are sensitive to electronic and mechanical perturbations, eg doping and strain, and to their dielectric/polar environment. Their orientation in anisotropic materials can be described from polarization studies. Raman studies can also be used to probe the properties of a substrate eg through interferences on thin films or surface-enhanced Raman spectroscopy (SERS) on plasmonic antennas.We will recall the main Raman signatures of SWNT and graphene, discuss the resonance phenomena, stress the limits and traps of Raman characterization, and review some recent and original Raman results from the literature.

The influence of growth direction on electrical and optical properties of GaN:Mg single crystals grown by High Nitrogen Pressure Solution method