Infrared response on a carbon nanotube is weak because this homonuclear allotrope of carbon does not bear permanent dipoles. Here, we report the discovery of an exaltation of the infrared absorption response in single-walled carbon nanotubes from dye molecule interactions. A study performed on dimethylquaterthiophene confined into the hollow core of single-walled carbon nanotubes or π-stacked at the outer surface of the latter leads to a symmetry breaking, allowing us to probe interactions between both subsystems. The nature of these interactions is discussed taking into account the tube diameter. This new phenomenon opens a new route to detect weak vibrations thanks to a confinement effect.

Despite the wealth of research conducted the last three years on hybrid organic perovskites (HOP), several questions remain open including: to what extend the organic moiety changes the properties of the material as compared to all-inorganic (AIP) related perovskite structures. To ultimately reach an answer to this question, we have recently introduced two approaches that were designed to take the stochastic molecular degrees of freedom into account, and suggested that the high temperature cubic phase of HOP and AIP is an appropriate reference phase to rationalize HOP's properties. In this paper, we recall the main concepts and show recent molecular dynamic results (figure 1) to discuss more specifically the various possible couplings between charge carriers and low energy excitations such as acoustic and optical phonons. As available experimental or simulated data on low energy excitations are limited, we also present preliminary neutron and Brillouin scattering, as well as ultrasonic measurements obtained on freshly prepared single crystals of CH 3 NH 3 PbBr 3.

In this paper, we examine recent theoretical investigations on 3D hybrid perovskites (HOP) that combine concepts developed for classical bulk solid-state physics and empirical simulations of their optoelectronic properties. In fact, the complexity of HOP calls for a coherent global view that combines usually disconnected concepts, related to classical semiconductors, perovskites and plastic crystals1. For the pseudocubic high temperature reference perovskite structure that plays a central role for 3D HOP, we introduce a new tight-binding Hamiltonian, which specifically includes spin-orbit coupling. The resultant electronic band structure is compared to that obtained using state of the art density functional theory (DFT). Possible plastic crystal and orientational glass behaviors of HOP will be discussed, building on Car-Parrinello molecular dynamics simulations and symmetry analyses of the cation stochastic reorientations. As available experimental or simulated data on low energy structural excitations are limited, large single crystals of MAPbBr3 have been grown and used to perform neutron and Brillouin scattering and ultrasonic characterization of low frequency acoustic phonons, as well as relaxation modes in different energy ranges. Neutron scattering experiments further reveal that the MAPbBr3 crystal presents a coexistence of crystalline domains below the cubic to tetragonal phase transition at Tc=225K. This observation is consistent with the improper ferroelastic character of the phase transition as predicted from the symmetry analysis of phonon and molecular relaxational modes. [1]Even, J., Carignano, M. & Katan, C. “Molecular disorder and translation/rotation coupling in the plastic crystal phase of hybrid perovskites.” Nanoscale DOI: 10.1039/C5NR06386H, (2016)

We propose a model taking into account the periodic spatial modulation of a doped graphene sheet conductivity influenced by a dielectric grating. We obtain the dispersion relation through the Fourier Modal Method (FMM) and study the excitation of surface plasmons on such structures. We compute and study the spatially localized fields on the graphene sheet.

We derive the explicit expression for the Casimir energy between a sphere and a 1D grating under thermal equilibrium, in terms of the sphere and grating reflection matrices, and valid for arbitrary materials, sphere radius, and grating geometric parameters.

Behind the appellation “modal methods”, for diffraction gratings, one can find a variety of methods sharing in common the development of the fields in terms of basis functions that can be either Fourier exponentials hence the name Fourier Modal Method (FMM), or polynomials leading to the family of Polynomial Modal Methods (Legendre, Tchebychev, and Gegenbauer). These approaches may not behave in the same way when dealing with gratings with extreme features such as a very low or very high filling ratios. In the present work, we address such a problem and compare the performances of the different Modal Methods.

We synthesized KC8 by simply mixing molten potassium and graphite at 180 °C under inert atmosphere. The KC8 showstypical shiny bronze color, Raman characteristics and XRD pattern of an efficiently intercalated stage 1 GIC, and is ofsufficient quality to produce fully exfoliated graphenide solutions in tetrahydrofuran (THF) and subsequently single layer graphene in water as “eau de graphene” (EdG). The evolution of absorption and Raman spectroscopic signatures of the EdGas a function of processing conditions give key indications on the number of layers of the graphene flakes dispersed in EdG.