O. Fassi-Fehri’s research while affiliated with Faculté des Sciences de Meknès and other places

A comprehensive MD analysis of cracked and porous InX structures (X = Se, Te) is performed to elucidate the mechanical properties and fracture behavior. The results show that fracture stress degrades as crack length and pore diameter increase, inducing a power-law relationship between stress and structural integrity. The effect of nanoscale crack-pore (CP) and main crack-auxiliary crack (MC-AC) interactions shows that depending on the positions of pores/auxiliary cracks around the main crack, the ultimate tensile stress can decrease or amplify. The simulations demonstrate that the CP and AC lead to a stress reduction in the area near the crack tip, which retards the fracture process. The CP strategy can enhance fracture strength more efficiently than AC. Finally, the fracture mechanism highlights that branching predominates for applied tension in the zigzag direction. Such a study is an adequate framework towards the advanced stress-engineered based design of InX structures and their counterparts.

We predict a new 2D topological insulator, namely the half hydrogenated PbBi-H monolayer, with an intrinsic Dirac double cone using GGA corrected to Rashba spin splittings using HSE approximation. The results establish that without spin orbit coupling (SOC) correction, this system is a buckled hexagonal semi-conductor with a direct gap at 𝛤-point and strong structural stability. When the SOC is switched on, the upper valence and lower conduction bands form a double Dirac cone with a small gap energy of 20.51 meV, derived from GGA-PBE calculations. This generates the presence of Dirac fermions characterized by a high Fermi velocity along the 𝑘𝑥 - and 𝑘𝑦 -directions, respectively. Moreover, the invariant number Z2 = 1 as well as the gapless edge modes provide evidence for the non trivial topological phase of the PbBi-H material. Interestingly, the gap reaches 184 𝑚𝑒𝑉 using the HSE method and exhibits trivial topology (Z2 = 0). However, after applying a biaxial tensile strain of 𝜀 = 0.085, our system transforms into a topological insulator. The present findings confirm the potential use of 2D PbBi-H compound in nano-electronic devices.

Topological phase of matter has attracted a great deal of interest. Drawing inspiration from the recent advances in this field, we model the supersymmetric extension of the Altland-Zirnbauer (AZ) periodic table classifying the topological insulators and superconductors in tenfold way. We construct the five supercharges $\boldsymbol{Q}_{\textbf{k}}=\hat{F}_{ \textbf{k}}.\boldsymbol{q}_{\textbf{k}}.\hat{B}_{\textbf{k}}$ of super AZ matter describing the coupling between fermions $\hat{F}_{\textbf{k}}$ and bosons $\hat{B}_{\textbf{k}}$; and we analyse the induced supersymmetric 3D hamiltonians $\boldsymbol{H}_{\textbf{k}}.$ We also probe topological effects leading to remarkable properties like the supersymmetric gapless states living on the boundary. A discussion on super classes A, C and D and the corresponding symmetries is also given.

Using the field theory method and coherent spin state approach, we investigate properties of magnetic solitons in spacetime while focussing on 1D kinks, 2D and 3D skyrmions. We also study the case of a rigid skyrmion dissolved in a magnetic background induced by the electronic spins; and derive the effective rigid skyrmion equation of motion. We investigate as well the interaction between an electron and a 3D skyrmion.

Magnetic skyrmions have been subject of growing interest in recent years for their very promising applications in spintronics, quantum computation and future low power information technology devices. In this book chapter, we use the field theory method and coherent spin state ideas to investigate the properties of magnetic solitons in spacetime while focussing on 2D and 3D skyrmions. We also study the case of a rigid skyrmion dissolved in a magnetic background induced by the spin-tronics; and derive the effective rigid skyrmion equation of motion. We examine as well the interaction between electrons and skyrmions; and comment on the modified Landau-Lifshitz-Gilbert equation. Other issues, including emergent electrodynamics and hot applications for next-generation high-density efficient information encoding, are also discussed.

Polyamide-11 (PA11)/organoclay nanocomposites were prepared via melt compounding using silane grafted montmorillonites and Cloisite 20 A. Two graft procedures were used for clay modification. The first one provided a grafted 3-aminopropyltriethoxysilane (APTES) at clay surfaces, whereas the second led to intercalated structure in addition to grafted APTES at clay surface. X-ray diffraction and transmission electron microscopy confirmed the formation of the exfoliated nanocomposites at low clay loading (2 wt%) and a mixture of exfoliated and intercalated structures at higher clay contents. Thermogravimetric analysis, melt rheology as well as tensile tests showed that the degree of dispersion of clay within polymer matrix plays a vital role in property improvement. In addition, elongation at break was considerably enhanced in the case of silane grafted clay. This was attributed to hydrogen bonding between clay surfaces and PA11 via APTES.

The relationship between the morphological observations and the physical properties of polyamide 11 (PA11)/clay nanocomposites prepared by melt processing was investigated with a special interest on the use of various contents of silane modified PA11 (PA-m-Si). PA-m-Si was prepared using 1 wt% of 3-aminopropyltriethoxysilane (APTES) added to PA11 in reactive extrusion. The morphological observations by TEM and XRD are presented in conjunction with the rheological and mechanical properties of these nanocomposites. The addition of PA-m-Si generated a net favorable interaction with organoclay that permitted higher level of exfoliation/intercalation resulting from a balance of component interactions. XRD spectra of nanocomposites revealed that the increase of PA-m-Si induced a decrease in peak intensities at high clay loadings (≥5 wt%) which informed about a reduction of stacks intercalated structure leading to a higher degree of delamination and a larger increase of aspect ratio of clay. The rheological properties suggest that the extent of a percolation network can be enhanced by increasing the degree of exfoliation/intercalation at fixed clay content. The tensile and thermal properties were also found to be improved in all cases.

In the present work, five different atomic configurations of fully hydrogenated silicene/graphene hybrid sheet, namely chair, boat, zigzag, armchair and table have been studied. Using DFT-based calculations method, it was found that the arrangement of the absorbed hydrogen atoms influences significantly the structural and electronic properties of the hybrids. It was also demonstrated that the five structures are stable and that full hydrogenation of SiC in different configurations are exothermic adsorptions, except in table conformer. Charge density calculations revealed that a large amount of electric charge is condensed around C atoms, whose orbitals contribute mainly, with regard to H and Si atoms, in the energy gap of silicane-graphane conformers. The overall results of this work show that silicane-graphane hybrids is a promising potential candidate not only for nano-electronic applications but also for hydrogen storage.

Extrusion and injection processes have been used to successfully prepare two systems of composite, polypropylene (PP)/clay (E1) and compatibilized polypropylene (PP-SEBS-g-MA)/clay (E1) at various particles content (5, 10, 15, 20, 25, 30 wt.%). To enhance fillers wettability within the polymer, a coupling agent was added. The essential work of fracture (EWF) concept was successfully applied to the fracture toughness characterization of ductile composites. Moreover, tensile and dynamic mechanical analysis (DMA) tests were conducted for these composites to ascertain the influence of the material composition (E1 particles) on these mechanical parameters. The tensile properties results indicate that the Young's modulus has increased for whole systems reaching a gain of 60% and 23% in binary and ternary composites, respectively, at 30 wt.% particle. Clay (E1) addition markedly enhances the plastic work of fracture (W-e) and reduces the specific plastic work (B-wp). The thermal analysis shows an increase in initial thermal decomposition temperatures with addition of clay (E1), which normal with the addition of a high degradation temperature charge.

Using ab-initio density functional theory calculations, we investigate the effects of full and half fluorinations on the structure and properties of silicene/graphene (SG) hybrid sheets. The results indicate that full and half fluorinations reduce the gap energy of pure SG. The partial coverage of SG sheets reveals large differences between the structural and electronic properties of the two half-fluorinated conformers and exhibits unusual magnetic properties according to how the adsorption of F atoms is accomplished: on either Si sites or C sites. It is found that, although F bonding Si atoms give rise to an antiferromagnetic semiconductor, the hybrid presents nonmagnetic ordering when F atoms bond to C atoms. Stability analysis shows that the three fluorinated structures are stable and that F atoms prefer being adsorbed on Si atoms in terms of energy. Thus, chemical modification with F can control and tune the electronic and magnetic properties of SG, which opens a wide spectrum of possibilities for designing future SG-based nanodevices.