Recent advances in experimental and computational methods have opened up new directions in graphene fundamental studies. In addition to understanding the basic properties of this material and its quasi-one dimensional structures, significant efforts are devoted to describing their long ranged dispersive interactions. Other two-dimensional materials, such as silicene, germanene, and transition metal dichalcogenides, are also being investigated aiming at finding complementary to graphene systems with other "wonder" properties. The focus of this work is to utilize first principles simulations methods to build our basic knowledge of structure-interaction relations in two-dimensional materials and design their properties. In particular, mechanical folding and extended defects in zigzag and armchair graphene nanoribbons can be used to modulate their electronic and spin polarization characteristics and achieve different stacking patterns. Our simulations concerning zigzag silicene nanoribbons show width-dependent antiferromagnetic-ferromagnetic transitions unlike the case of zigzag graphene nanoribbons, which are always antiferromagnetic. Heterostructures, build by stacking graphene, silicene, and MoS$_2$, are also investigated. It is found that hybridization alters the electronic properties of the individual layers and new flexural and breathing phonon modes display unique behaviors in the heterostructure compositions. Anchored to SiC substrate graphene nanoribbons are also proposed as possible systems to be used in graphene electronics. Our findings are of importance not only for fundamental science, but they could also be used for future experimental developments.

This thesis covers the structural, electronic, magnetic, and vibrational properties of graphene and silicene. In Chapter I, we will start with an introduction to graphene and silicene. In Chapter II, we will briefly discuss about the methodology (i. e. density functional theory)In Chapter III, we will introduce band gap opening in graphene either by introducing defects/doping or by creating superlattices with h-BN substrate. In Chapter IV, we will focus on the structural and electronic properties of K and Ge-intercalated graphene on SiC(0001). In addition, the enhancement of the superconducting transition temperature in Li-decorated graphene supported by h-BN substrate will be discussed. In Chapter V, we will discuss the vibrational properties of free-standing silicene. In addition, superlattices of silicene with h-BN as well as the phase transition in silicene by applying an external electric field will be discussed. The electronic and magnetic properties transition metal decorated silicene will be discussed, in particular the realization of the quantum anomalous Hall effect will be addressed. Furthermore, the structural, electronic, and magnetic properties of Mn decorated silicene supported by h-BN substrate will be discussed. The conclusion is included in Chapters VI. Finally, we will end with references and a list of publications for this thesis.

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With the emergence of nanotechnology, mankind has obtained the capability to manipulate materials at nanoscale and this led to the invention of a new group of novel materials like carbon nanotubes, graphene and quantum nanodots. Silicene nanoribbons (SiNRs) are one of the newest members of this nanomaterial family which has been synthesized very recently by deposition on silver substrates. A SiNR sheet is made up of a layer of two dimensional honeycomb structure solely composed of silicon atoms. In this thesis, structural and mechanical properties of SiNR are being investigated with the help of classical empirical molecular dynamics simulation technique. In the first part of this thesis, structural properties of SiNR sheets have been investigated. This investigation has been carried out by performing classical molecular dynamics simulations using atomistic many-body potential energy functions at many different SiNR sheet lengths and widths, at low and room temperatures with and without periodic boundaries. It has been found that SiNR sheets do not have perfectly flat honeycomb geometry. It has also been found that finite length models are more likely to form tubular structures resembling distorted silicon nanotubes at room temperature. In the second part of this thesis, mechanical properties of SiNRs have been investigated. Mechanical properties of silicene nanoribbons of varying width have been investigated under 5% and 10% uniaxial strain via classical Molecular-Dynamics simulations at 1 K&deg / and 300 K&deg / temperatures by the aid of atomistic many-body potential energy functions. It has been found that under strain, SiNRs show such material properties: they are very ductile, they have considerable toughness and despite their low elasticity, they have a very long plastic range before fragmentation.

La physique des surfaces et nanosciences est une discipline qui permet la conception d’une diversité de matériaux innovants pour mieux répondre aux besoins de la technologie actuelle. Dans ce contexte, nous nous sommes intéressés à caractériser les propriétés de différentes structures 2D élaborées sur des substrats d’argent en combinant différentes techniques d'analyses de surface.D'une part nous avons étudié des films 2D auto-assemblés à base de phtalocyanine de cobalt adsorbées sur Ag(100). Au régime de la monocouche, deux phases ont été essentiellement observées : la (5x5) et la (7x7). La spectroscopie de pertes d'énergie nous a permis de mettre en évidence deux mécanismes de transfert de charge métal/molécule différents en raison des sites d'adsorption différents.D'autre part, nous avons synthétisé, par évaporation d'atomes de silicium sur de l'Ag(111), du silicene en monocouche et multicouche. Ainsi nous avons entrepris des mesures dans le but de comprendre les propriétés structurales du silicene en multicouche. Pour cela nous avons engagé des mesures par spectroscopie de photoémission et diffraction de photoélectrons, et comparé nos données avec des simulations réalisées dans le cadre la diffusion multiple. Plusieurs hypothèses concernant la nature de ce matériau ont pu être testées. Par ailleurs nous avons étudié la fonctionnalisation du silicene par hydrogénation et adsorption de molécules de F4TCNQ. / Nanosciences and surface science are key elements in the conception of a diversity of innovative materials designed to better cope with the needs of current technology. Within this context, we have resolved to characterise the properties of different two-dimensional structures grown on silver substrates with the help of several complementary techniques of surface analysis.Firstly, we have studied auto-assembled 2D films of cobalt phthalocyanine on Ag(100) substrates. In situations with coverages close to the monolayer, two phases were observed: the (5x5) and the (7x7). The electron energy loss spectroscopy has allowed us to support the existence of two inequivalent charge transfer mechanisms between the substrate and the molecules due to differences in the adsoprtion sites. Secondly, we have synthesised both monolayer and multilayer silicene by evaporating silicon atoms on Ag(111) substrates. We have decided to delve into the characteristics of multilayer silicene as it’s less well-known than its monolayer counterpart. With this aim, the system has been subjected to experiments of photoemission spectroscopy and diffraction. In this manner, several hypotheses on the very nature of this material have been tested. On another matter also related to silicene, we have studied its functionalization by adsorption of F4TCNQ molecules and atomic hydrogen.

Le silicène est l’équivalent du graphène pour le silicium avec une structure bidimensionnelle (2D). Il est supposé avoir des propriétés électroniques intéressantes comme les fermions de Dirac sans masse et présentant une grande mobilité des électrons. L’existence du silicène a été montrée récemment sur des substrats de métaux nobles comme l’argent ou l’or. Cependant les résultats montrent des interactions fortes entre la couche de silicène et le substrat métallique, ce qui a pour conséquence de détruire les propriétés électroniques intrinsèques du silicène. Dans le but de résoudre ce problème, nous proposons dans ce travail d’explorer d’autres substrats potentiels présentant de faibles interactions avec le silicène. Nous avons étudié la croissance de couches 2D de silicium sur un film mince isolant de NaCl. En effet, les métaux alcalins halogénés tel que NaCl offrent une solution avantageuse comme surface alternative puisqu'ils se comportent comme une couche diélectrique, permettant la caractérisation du silicène. Nous avons étudié les propriétés structurales et électroniques des couches de silicium 2D déposées sur un film mince de NaCl, lui-même déposé sur un substrat d’Ag(110). Une étude expérimentale a été réalisée combinant un grand nombre de techniques utilisées en science des surfaces telles que : « low energy electron diffraction » (LEED), « Auger electron spectroscopy » (AES), « scanning tunneling microscopy and spectroscopy » (STM/STS), «extended x-ray absorption fine structure » (EXAFS), « x-ray photoelectron spectroscopy » (XPS) et « angle resolved photoemission spectroscopy (ARPES) ». L’absorption d’atomes de silicium sur les films de NaCl révèle l’existence d’une couche de silicium 2D superficielle avec une structure très ordonnée en forme de nids d’abeilles. Cette couche présente une interaction faible avec le substrat tout en étant analogue au silicène. Enfin, des expériences préliminaires sur la croissance de silicene sur des films de NaCl dissociés sont présentées. L’effet de l’irradiation électronique du film de NaCl ainsi que des mesures d’ARPES sur le silicène intercalé sur Na sont présentées. / Silicene, the silicon-based analog of graphene which has a two-dimensional (2D) structure. It is expected to have attractive electronic properties such as massless Dirac fermions and high electron mobility. The existence of silicene has been shown recently on noble metal substrates such as Ag and Au. The results present strong interactions between the silicene adlayer and the metallic substrate which destroy the intrinsic electronic properties of silicene. In order to solve this problem, we propose in this work to explore other potential substrates that have weaker interactions with silicene. We studied the growth of a 2D silicon layer on insulating NaCl thin film. Indeed, Alkali metal halides such as NaCl offer a great solution as an alternative surface because they behave as a dielectric layer, allowing characterization of silicene material. We studied the structural and electronic properties of 2D silicon layer grown on a NaCl film deposited over Ag(110) substrate. A combined experimental investigation was performed with a large number of techniques which are used in surface science such as: low energy electron diffraction (LEED), auger electron spectroscopy (AES), scanning tunneling microscopy and spectroscopy (STM/STS), extended x-ray absorption fine structure (EXAFS), x-ray photoelectron spectroscopy (XPS) and angle resolved photoemission spectroscopy (ARPES). The adsorption of silicon atoms on NaCl films reveals the existence of a 2D silicon sheet adlayer with a highly ordered honeycomb-like structure. The silicon ad-layer has weak interactions with the substrate and it mimics the structure of silicene. Finally, preliminary experiments on the growth of silicene on dissociated NaCl films are presented. The effect of electron irradiation on the NaCl film and initial ARPES measurement on the silicone intercalated-Na atoms system are presented.

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L’objet de cette thèse est l’étude de la croissance de silicène sur des substrats d’argent,ainsi que l’étude de sa réactivité vis-à-vis de l’oxygène. La croissance a été réalisée sous ultra-vide et contrôlée par spectroscopie d’électrons Auger (AES) et par diffraction d’électrons lents (LEED). Les structures obtenues et leurs réactivités à l’oxygène ont été étudiées par microscopie à champ proche (STM et nc-AFM) et par spectroscopie de photoémission résolue en angle (ARPES). Nous avons étudié la structure interne des nano-rubans de silicène auto-assemblés sur un substrat d’Ag(110). Sur Ag(111) nous obtenons un feuillet de silicène qui présente différentes structures en fonction de la température du substrat. L’étude de la réactivité des rubans et des feuillets a montré que le silicène formé sur substrat d’argent est relativement stable vis-à-vis de l’oxygène ce qui ouvre des perspectives de fonctionnalisation du silicène. La dernière partie de cette thèse concerne la synthèse de feuillets de silicium par voie chimique. Nous avons mis au point une nouvelle méthode prometteuse de synthèse chimique qui nous a permis de synthétiser des feuillets de silicium de structure graphitique. / The objective of this thesis is the study of the growth of silicene on silver substrates as well as its reactivity towards the oxygen. The growth was performed under ultra-high vacuum and controlled by Auger electrons spectroscopy (AES) and low energy electrons diffraction (LEED). The obtained structures and their relativities towards the oxygen were studied by near field microscopy (STM and nc-AFM) and by angle resolved electrons photoemission spectroscopy (ARPES). We have studied the internal structure of the selfassembled silicene nanoribbons on Ag(110) substrate. On Ag(111), we have obtained a silicene sheet presenting different structures versus the temperature of the substrate. The reactivity of silicene nanoribbons and sheets grown on silver show that silicene is relatively stable towards the oxygen which opens a new perspectives of functionalization of the silicene. The last part of this thesis concerns the synthesis of silicone sheets by chemical process. We have develpped a new promising process of chemical synthesis which allowed us to synthesize silicon sheets with graphitic structure.