Découverte et application du réarrangement inverse de Meisenheimer

Ce mémoire traite d’un nouveau sujet de recherche : le réarrangement inverse de Meisenheimer (RIM) ainsi que son application dans la synthèse d’un interrupteur moléculaire. Le premier chapitre fera état des différents plans de synthèse utilisés pour démontrer que le réarrangement de Meisenheimer est possible. Les hypothèses par rapport à cette réversibilité seront également exposées. Le deuxième chapitre portera sur l’application du réarrangement inverse de Meisenheimer pour la synthèse d’un interrupteur moléculaire. Les différents essais de synthèses seront décrits pour l’obtention du système cible, avec une justification des choix effectués. Par la suite, le RIM sera testé avec une variation de plusieurs paramètres. Les résultats obtenus seront discutés et les hypothèses qui peuvent en être tirées seront développées

Real exhange rate misalignment in Hungary: a fractionally integrated=20 threshold model

This paper proposes an estimate of the Hungarian real exchange rate=20 misalignments using fractionally integrated threshold models (FI-STARMA and=20= FI-TARMA=20 processes). This allows us to simultaneously take into account two types of=20 persistence: a long memory behavior due to the influence of real factors and= a=20 nonlinear behavior where persistence is associated with regime-dependent eff= ects.=20 Our results suggest that the regime-switching is instantaneous since the=20 FI-TARMA process is adequate to describe the misalignment of the Hungarian=20 Currency.

Module GYPTIS version 1.0 : contact unilatéral avec frottement en mécanique des structures, inéquations variationnelles

Le module GYPTIS permet de résoudre des problèmes de con- tact unilatéral avec frottement de Coulomb entre une structure et un obstacle fixe ou entre différents solides déformables. Le problème est ici posé et résolu pour de petites déformations élastiques. L'extension à la viscoélasticité, la viscoplasticité ou l'élastoplasticité en grandes déformations a été réalisée par ailleurs (...

Scanning tunneling microscopy simulations of poly(3-dodecylthiophene) chains adsorbed on highly oriented pyrolytic graphite

We report on a novel scheme to perform efficient simulations of Scanning Tunneling Microscopy (STM) of molecules weakly bonded to surfaces. Calculations are based on a tight binding (TB) technique including self-consistency for the molecule to predict STM imaging and spectroscopy. To palliate the lack of self-consistency in the tunneling current calculation, we performed first principles density-functional calculations to extract the geometrical and electronic properties of the system. In this way, we can include, in the TB scheme, the effects of structural relaxation upon adsorption on the electronic structure of the molecule. This approach is applied to the study of regioregular poly(3-dodecylthiophene) (P3DDT) polymer chains adsorbed on highly oriented pyrolytic graphite (HOPG). Results of spectroscopic calculations are discussed and compared with recently obtained experimental datComment: 15 pages plus 5 figures in a tar fil

Energy bands of atomic monolayers of various materials: Possibility of energy gap engineering

The mobility of graphene is very high because the quantum Hall effects can be observed even at room temperature. Graphene has the potential of the material for novel devices because of this high mobility. But the energy gap of graphene is zero, so graphene can not be applied to semiconductor devices such as transistors, LEDs, etc. In order to control the energy gaps, we propose atomic monolayers which consist of various materials besides carbon atoms. To examine the energy dispersions of atomic monolayers of various materials, we calculated the electronic states of these atomic monolayers using density functional theory with structural optimizations. The quantum chemical calculation software "Gaussian 03" was used under periodic boundary conditions. The calculation method is LSDA/6-311G(d,p), B3LYP/6-31G(d), or B3LYP/6-311G(d,p). The calculated materials are C (graphene), Si (silicene), Ge, SiC, GeC, GeSi, BN, BP, BAs, AlP, AlAs, GaP, and GaAs. These atomic monolayers can exist in the flat honeycomb shapes. The energy gaps of these atomic monolayers take various values. Ge is a semimetal; AlP, AlAs, GaP, and GaAs are indirect semiconductors; and others are direct semiconductors. We also calculated the change of energy dispersions accompanied by the substitution of the atoms. Our results suggest that the substitution of impurity atoms for monolayer materials can control the energy gaps of the atomic monolayers. We conclude that atomic monolayers of various materials have the potential for novel devices.Comment: This paper was first presented at the 14th International Conference on Modulated Semiconductor Structures (MSS14) held in Kobe, Japan, on 23 July 200

Structural classification of boron nitride twisted bilayers and ab initio investigation of their stacking-dependent electronic structure

Since the discovery of superconductive twisted bilayer graphene which initiated the field of twistronics, moir\'e systems have not ceased to exhibit fascinating properties. We demonstrate that in boron nitride twisted bilayers, for a given moir\'e periodicity, there are five different stackings which preserve the monolayer hexagonal symmetry (i.e. the invariance upon rotations of 120$^\circ$) and not only two as always discussed in literature. We introduce some definitions and a nomenclature that identify unambiguously the twist angle and the stacking sequence of any hexagonal bilayer with order-3 rotation symmetry. Moreover, we employ density functional theory to study the evolution of the band structure as a function of the twist angle for each of the five stacking sequences of boron nitride bilayers. We show that the gap is indirect at any angle and in any stacking, and identify features that are conserved within the same stacking sequence irrespective of the angle of twist.Comment: 16 pages (6.5 main text); 15 figures (5 in main); 5 tables (3 in main). Appendixes concatenated to main tex

Excitons in boron nitride single layer

Boron nitride single layer belongs to the family of 2D materials whose optical properties are currently receiving considerable attention. Strong excitonic effects have already been observed in the bulk and still stronger effects are predicted for single layers. We present here a detailed study of these properties by combining \textit{ab initio} calculations and a tight-binding-Wannier analysis in both real and reciprocal space. Due to the simplicity of the band structure with single valence ($\pi$) and conduction ($\pi^*$) bands the tight-binding analysis becomes quasi quantitative with only two adjustable parameters and provides tools for a detailed analysis of the exciton properties. Strong deviations from the usual hydrogenic model are evidenced. The ground state exciton is not a genuine Frenkel exciton, but a very localized "tightly-bound" one. The other ones are similar to those found in transition metal dichalcogenides and, although more localized, can be described within a Wannier-Mott scheme

Boron and nitrogen codoping effect on transport properties of carbon nanotubes

International audienceThis paper reports a theoretical study of the effect of boron and nitrogen codoping on the transport properties of carbon nanotubes (CNTs) at the mesoscopic scale. A new tight-binding parametrization has been set up, based on density functional theory calculations, that enables a reliable description of the electronic structure of realistic BN-doped CNTs. With this model, we have carried out a deep analysis of the electronic mean free path (MFP) exhibited by these nanostructures. The MFP is highly sensitive to the geometry of the scattering centers. We report that the relative distance between B and N atoms in the network influences drastically the electronic conduction. Moreover, we point out that the scattering induced by small hexagonal BN domains in the carbon network is less important than the BN-pair case