M.A. Belkhir

Microstructure and crystallographic texture of Charonia lampas lampas shell

Charonia lampas lampas shell is studied using scanning electron microscopy and X-ray diffraction combined analysis of the preferred orientations and cell parameters. The Charonia shell is composed of three crossed lamellar layers of biogenic aragonite. The outer layer exhibits a 001 fibre texture, the intermediate crossed lamellar layer is radial with a split of its c-axis and single twin pattern of its a-axis, and the inner layer is comarginal with split c-axis and double twinning. A lost of texture strength is quantified from the inner layer outward. Unit-cell refinements evidence the intercrystalline organic influence on the aragonite unit-cell parameters anisotropic distortion and volume changes in the three layers. The simulation of the macroscopic elastic tensors of the mineral part of the three layers, from texture data, reveals an optimisation of the elastic coefficient to compression and shear in all directions of the shell as an overall.

Enhanced Light–Matter Interaction in Graphene/h-BN van der Waals Heterostructures

By investigating the optoelectronic properties of prototypical graphene/hexagonal boron nitride (h-BN) heterostructures, we demonstrate how a nanostructured combination of these materials can lead to a dramatic enhancement of light-matter interaction and give rise to unique excitations. In the framework of ab initio many-body perturbation theory, we show that such heterostructures absorb light over a broad frequency range, from the near-infrared to the ultraviolet (UV), and that each spectral region is characterized by a specific type of excitations. Delocalized electron-hole pairs in graphene dominate the low-energy part of the spectrum, while strongly bound electron-hole pairs in h-BN are preserved in the near-UV. Besides these features, characteristic of the pristine constituents, charge-transfer excitations appear across the visible region. Remarkably, the spatial distribution of the electron and the hole can be selectively tuned by modulating the stacking arrangement of the individual building blocks. Our results open up unprecedented perspectives in view of designing van der Waals heterostructures with tailored optoelectronic features.