Fonctionnalisation de graphene epitaxie : Greffage covalent de molécules, intercalation de terbiu, ingénieurie de défauts

The first chapter of this thesis explains the general motivation and problematic of graphene functionalization. It presents the state of the art of current research in this field. In the second chapter we discuss the experimental techniques in detail. Chapter 3 of this thesis work focuses on covalent modification of graphene by cycloaddition reaction of maleimide derivative molecules. In these studies we have confirmed the grafting of molecules on epitaxial defect free graphene on SiC and a tendency to open a gap with the help of Raman spectroscopy, XPS, ARPES and STM studies. An increase in the ID /IG ratio for Raman signature and sp3 bonding on the sample with increasing reaction time confirmed the reaction of molecules. By drawing an analogy with the standing waves obtained on armchair step edges of graphene and standing waves generated by molecules it was possible to determine the location of grafted molecules on the graphene lattice. In chapter 4, studies on terbium intercalation of epitaxial graphene are discussed. After intercalation a complex band structure was observed by ARPES with one spectra corresponding to highly n-doped graphene monolayer. We were able to isolate this highly n-doped graphene and confirmed its origin from decoupling of buffer layer and making it graphene like. These results are also supported by the XPS data. STM images on Terbium intercalated on buffer layer samples showed an interesting pattern of lines, atomic resolution scans at low bias voltage on these lines showed 6 atoms of hexagon confirming the transformation of buffer layer into graphene layer.Le premier chapitre de cette thèse présente l’intérêt et la problématique de la fonctionnalisation du graphène. L’état de l’art actuel de cette thématique est présenté. Dans un deuxième chapitre, nous discutons de façon détaillée des techniques expérimentales. Le chapitre 3 est centré sur la modification du graphène par réaction de cycloaddition par molécules dérivées de maleimides. Dans cette étude, nous démontrons le greffage covalent de molécules sur graphène épitaxié sans défaut sur SiC, ainsi qu’une tendance d’ouverture de bande interdite à l’aide de caractérisations par spectroscopie Raman, XPS, ARPS et STM. L’augmentation du rapport ID /IG des pics Raman et des liaisons sp3 sur l’échantillon en fonction de la durée de réaction chimique confirme le greffage. Par analogie avec les bords de marche de type « zigzag » ou « armchair », l’étude des ondes de densité de charge générées sur le graphène par les molécules permet de déterminer la nature des sous-réseaux mis en jeu lors du greffage. Dans le chapitre 4, nous étudions l’intercalation du terbium dans le graphène épitaxié. Après intercalation, l’ARPES montre une structure de bande complexe dont une composante correspond à une monocouche de graphène fortement dopée n. Nous avons pu isoler cette composante et montrer qu’elle provient du découplage de la couche tampon du substrat par le Terbium. Ces résultats sont confirmés par les données XPS. Le graphène avec Terbium intercalé produit également un réseau de lignes visibles par imagerie STM, qui a l’échelle atomique à basse tension montrent les 6 atomes de carbone de la structure en nid d’abeille, confirmant ainsi la transformation de la couche tampon en graphène

Enhanced Ammonia Gas Adsorption through Site-Selective Fluorination of Graphene

International audienceGraphene has been widely explored as an ideal platform for gas sensing owing to exceptional properties, such as its atom-thin two-dimensional conjugated structure and large specific surface area. Herein, we report that, by introducing covalent C-F bonds via site-selective ion-beam-induced fluorination, graphene sensing response to ammonia gas can be considerably improved due to the enhanced gas adsorption on the surface of fluorinated graphene. The response to the ammonia gas increased by a factor of eight together with the limit of detection approaching 65 ppb. The absorption kinetics between the ammonia gas and fluorinated graphene were analyzed by using the Langmuir isotherm model and the result shows that the enhanced sensitivity is mainly attributed to the strong binding energy of fluorinated graphene to ammonia gas molecules, which is consistent with previous theoretical predictions

Enhanced Ammonia Gas Adsorption through Site-Selective Fluorination of Graphene

Graphene has been widely explored as an ideal platform for gas sensing owing to exceptional properties, such as its atom-thin two-dimensional conjugated structure and large specific surface area. Herein, we report that, by introducing covalent C-F bonds via site-selective ion-beam-induced fluorination, graphene sensing response to ammonia gas can be considerably improved due to the enhanced gas adsorption on the surface of fluorinated graphene. The response to the ammonia gas increased by a factor of eight together with the limit of detection approaching 65 ppb. The absorption kinetics between the ammonia gas and fluorinated graphene were analyzed by using the Langmuir isotherm model and the result shows that the enhanced sensitivity is mainly attributed to the strong binding energy of fluorinated graphene to ammonia gas molecules, which is consistent with previous theoretical predictions

Functionalization of 2D materials by intercalation

International audienceSince the discovery of graphene many studies focused on its functionalization by different methods. These strategies aim to find new pathways to overcome the main drawback of graphene, a missing band-gap, which strongly reduces its potential applications, particularly in the domain of nanoelectronics, despite its huge and unequaled charge carrier mobility. The necessity to contact this material with a metal has motivated a lot of studies of metal/graphene interactions and has led to the discovery of the intercalation process very early in the history of graphene. Intercalation, where the deposited atoms do not stay at the graphene surface but intercalate between the top layer and the substrate, may happen at room temperature or be induced by annealing, depending of the chemical nature of the metal. This kind of mechanism was already well-known in the earlier Graphite Intercalation Compounds (GICs), particularly famous for one current application, the Lithium-ion Battery, which is simply an application based on the intercalation of Lithium atoms between two sheets of graphene in a graphite anode. Among numerous discoveries the GICs community also found a way to obtain graphite with superconducting properties by using intercalated alkali metals. Graphene is now a playground to “revisit” and understand all these mechanisms and to discover possible new properties of graphene induced by intercalation. For example, the intercalation process may be used to decouple the graphene layer from its substrate, to change its doping level or even, in a more general way, to modify its electronic band structure and the nature of its Dirac fermions. In this paper we will focus on the functionalization of graphene by using intercalation of metal atoms but also of molecules. We will give an overview of the induced modifications of the electronic band structure possibly leading to spin-orbit coupling, superconductivity, …We will see how this concept of functionalization is also now used in the framework of other 2D materials beyond graphene and of van der Waals heterostructures based on these materials

Electric-Field-Mediated Reversible Transformation between Supramolecular Networks and Covalent Organic Frameworks

status: publishe

Electric-Field-Mediated Reversible Transformation between Supramolecular Networks and Covalent Organic Frameworks

By using an oriented electric field in a scanning tunneling microscope, one can locally control the condensation of boronic acids at the liquid/solid interface. The phase transition between self-assembled molecular networks and covalent organic frameworks is controlled by changing the polarity of the applied bias. The electric-field-induced phase transformation is reversible under ambient conditions.status: publishe

Electric-Field-Mediated Reversible Transformation between Supramolecular Networks and Covalent Organic Frameworks

By using an oriented electric field in a scanning tunneling microscope, one can locally control the condensation of boronic acids at the liquid/solid interface. The phase transition between self-assembled molecular networks and covalent organic frameworks is controlled by changing the polarity of the applied bias. The electric-field-induced phase transformation is reversible under ambient conditions

Synthesis of Triply Fused Porphyrin-Nanographene Conjugates

Two unprecedented porphyrin fused nanographene molecules, 1 and 2, have been synthesized by the Scholl reaction from tailor-made precursors based on benzo[m]tetraphene-substituted porphyrins. The chemical structures were validated by a combination of high-resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (HR MALDI-TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV-vis-near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red-shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π-conjugated systems.status: publishe

Synthesis of Triply Fused Porphyrin-Nanographene Conjugates

Two unprecedented porphyrin fused nanographene molecules, 1 and 2, have been synthesized by the Scholl reaction from tailor-made precursors based on benzo[m]tetraphene-substituted porphyrins. The chemical structures were validated by a combination of high-resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (HR MALDI-TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV-vis-near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red-shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π-conjugated systems

Interface Chemistry of Graphene/Cu Grafted By 3,4,5-Tri-Methoxyphenyl

Chemical reaction with diazonium molecules has revealed to be a powerful method for the surface chemical modification of graphite, carbon nanotubes and recently also of graphene. Graphene electronic structure modification using diazonium molecules is strongly influenced by graphene growth and by the supporting materials. Here, carrying on a detailed study of core levels and valence band photoemission measurements, we are able to reconstruct the interface chemistry of trimethoxybenzenediazonium-based molecules electrochemically grafted on graphene on copper. The band energy alignment at the molecule-graphene interface has been traced revealing the energy position of the HOMO band with respect to the Fermi level.status: publishe