Le graphène épitaxié sur des substrats métalliques est un modèle prometteur pour le développement de nouveaux systèmes hybrides, dans lesquelles les effets d'interface peuvent être exploités pour concevoir de nouvelles propriétés. L'insertion d'espèces entre le graphène et son substrat, une opération connues sous le nom d'-«intercalation», est une approche très puissante à cet égard. Avec l'aide des outils de la physique des surfaces, nous avons étudié trois systèmes graphène/métal, dont deux sont des systèmes hybrides intercalés, et l'autre est un candidat pour un tel système : (i) le graphène/Ir(111) intercalé avec un oxyde ultra-mince, (ii) graphène/Ir(111) intercalé avec des couches sub-atomiques du cobalt et (iii) de graphène sur Re(0001). Nous avons montré que certains défauts, en particulier les ridules (délamination du graphène de son substrat) et d'autres régions courbées du graphène, jouent un rôle crucial, non anticipé, dans le processus d'intercalation. Nous avons également observé que l'intercalation se déroule d'une manière nettement différente sous ultravide et à pression atmosphérique. Dans le premier système, des espèces contenant de l'oxygène entrent à l'extrémité ouverte des ridules et diffusent au long de ces ridules pour former des nano-rubans d'oxyde. Ces rubans modifient le dopage électronique du graphène, ce qui se traduit également par des changements substantiels dans la réponse optique inélastique (Raman) du graphène. Dans le second système, l'efficacité de l'intercalation est apparue dépendante de l'interaction graphène-métal, laquelle varie entre les domaines de graphène orientés différemment sur_(111). Dans ce système, les sites d'entrée pour les espèces intercalées, des régions courbées dans le graphène, ont pu être identifiés grâce à l'observation in_operando (en cours de croissance) du processus. Enfin, la croissance de graphène dans un troisième système (graphène/Re(0001)), a été étudiée afin de permettre le développement de futurs systèmes graphène/Re hybrides supraconducteurs. Dans ce système, nous avons proposé deux voies de croissance, l'une étant basé sur un processus de croissance en surface d'un monocristal massif de Re(0001), l'autre reposant sur la ségrégation en surface, activée thermiquement, du carbone dissout à haute température dans des films minces de Re sur saphir. / Epitaxial graphene grown on metal substrates is a promising platform for developing new hybrid systems, in which interface effects can be exploited to engineer novel properties. The insertion of foreign species between graphene and its substrate, referred to as “intercalation”, was shown very powerful in this respect. With the help of surface science tools, we have studied three graphene/metal systems, two of which are intercalated hybrid systems, and the other is a candidate for such a system: (i) graphene/Ir(111) intercalated with an ultrathin oxide, (ii) graphene/Ir(111) intercalated with cobalt (sub) atomic layers, and (iii) graphene on Re(0001). We found that some defects, especially wrinkles (linear delaminations of graphene from its substrate) and other curve graphene regions, play a crucial, yet unanticipated role in the intercalation process. We also found that the intercalation proceeds in a markedly different fashion under ultra-high vacuum and under atmospheric pressure. In the first system, oxygen-containing species were found to intercalate via the open end of wrinkles, to diffuse along then, and to form oxide nanoribbons along wrinkles accordingly. These ribbons modify the charge density of graphene, which also translates into substantial changes in the inelastic (Raman) optical response of graphene. In the second system, the efficiency of intercalation proved to be dependent on the graphene-metal interaction, which varies between differently oriented graphene domains on Ir(111). In this systems the entry sites for intercalated species could be identified, thanks to in operando observation of the process, as curved regions in graphene. Finally, graphene growth in a third system, graphene on Re(0001), was addressed in order to enable the future development of graphene/Re superconducting hybrids. In this system, we proposed two growth routes, one being a surface-confined process, on bulk single-crystal Re(0001), and the other being a temperature-induced segregation of carbon dissolved at high temperature in thin Re(0001) films on sapphire.

Cette thèse présente une étude du graphène complète depuis sa synthèse par dépôt de vapeur chimique (CVD), la fonctionnalisation de sa surface, jusqu'aux mesures à basse températures des propriétés de supraconductivité. Je présente tout d'abord une nouvelle technique de croissance CVD basée sur une injection impulsionnelle du gaz précurseur en présence constante d'hydrogène. Cette technique permet de s'affranchir de la présence de multicouches de graphène aux points de nucléation, un type de défaut connu qui avait limité jusqu'à présent les applications électroniques et optiques de ce matériau. Les dispositifs flexibles et optiquement transparents obtenus à partir de ce matériau présentent des caractéristiques améliorées par rapport à l'état de l'art notamment une homogénéité améliorée et une mobilité électronique dépassant 8,000 cm^2/V/s. Un traitement chimique est ensuite introduit et nous montrons par diverses techniques microscopiques, spectroscopiques optiques et électroniques qu'il est possible de contrôler précisément la densité de défauts dans le graphène par voie chimique. Cette thèse s'achève sur une étude à très basse température (<1K) des propriétés de transport électronique d'un nouveau type de systèmes basé sur un réseau de plots d'étain déposé sur un transistor en graphène. Ce type de système hybrides s'avère être un système modèle pour l'étude des transitions de phase quantique supra/isolant et supra/métal. Les résultats présentés sur les réseaux réguliers et dilués sont en bon accord avec les modèles théoriques prédisant un état métallique subsistant jusqu'à température nulle. / This thesis presents a wide range of graphene activity: from chemical vapor deposition (CVD) of graphene growth on Cu surface, to two dimensional mesoscopic graphene devices for superconductivity studies. I first show that, in the CVD process of fabricating graphene, a cyclic injection of carbon feedstock under a constant hydrogen background allows to suppress the formation of multilayer graphene, which has plagued this fabrication method since its early days. With the CVD grown graphene,I demonstrate applications such as flexible transparent electrodes. Mobility of our CVD graphene at 4 K temperature reaches as high as 8,000 cm^2/V/s. Chemical treatment studies based on copper etchant show that control of the density of defects in CVD graphene can be precisely achieved by a chemical route. This thesis finishes at sub 1 K temperature transport measurements of a new type of superconducting array decorated graphene transistor. This type of hybride system is a prototypical model for quantum phase transition studies. I then show that the experimental observations are in good agreement with the predicted superconductor-to-metal quantum phase transition at the zero-temperature limit.

Made available in DSpace on 2014-06-11T19:30:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-07-07Bitstream added on 2014-06-13T18:47:33Z : No. of bitstreams: 1 ribeiro_av_me_bauru.pdf: 3385358 bytes, checksum: 8e2e43e5facbedc0c7e25a21e63fe6ac (MD5) / São calculadas as estruturas eletrônicas de arranjos atômicos periódicos unidimensionais, bidimensionais e tridimensionais, através do método de combinação linear de orbitais atômicos (método tight binding). Esses orbitais correspondem aos átomos isolados das espécies químicas que compõem o arranjo atômico sob investigação. Combinações lineares deles, com coeficientes apropriados, aproximam a forma das funções de onda eletrônicas do arranjo atômico. Nos casos em que a sobreposição dos orbitais é desprezada, a contribuição de cada orbital atômico para função de Bloch é mostrada nas representações gráficas das estruturas de bandas calculadas. Após uma brve apresentação do método tight binding, são calculadas as estruturas de bandas de cadeias lineares de átomos de Carbono que têm um ou dois átomos por célula unitária. Essas cadeias são chamadas de cumuleno e poliino, respectivamente. Dentre os arranjos atômicos bidimensionais de interesse, é calculada a estrutura de bandas do grafeno. Essas energias são comparadas com resultados disponíveis na literatura. Para este material é realizada uma breve discussão sobre as bandas 'pi' provenientes de orbitais 'p IND. z' e sobre como a sobreposição dos orbitais atômicos afeta a forma das bandas. O método também é aplicado na modelagem de cristais tridimensionais. São calculadas as estruturas de bandas doo diamante, Germânio (com estrutura de diamente), Arseneto de Gálio (com estrutura zincblend) e Nitreto de Gálio (com estrutura de wurtzita). Os resultados obtidos são comparados com aqueles reportados por outros autores que usaram métodos ab initio / The eletronic structures of periodic arrangements of atoms in one, two and three dimensions are calculated by a linear combinations of atomic orbitals (tight binding method). Those orbitals correspond to the isolated atoms of the chemical species composing the atomic arrangement under investigation. Suitable linear combinations of such states approximate the shape of the eletronic wave functions of the atomic arrangement. When the overlapping of the atomic orbitals is disregarded, the contribution of each orbital to the Bloch state is displayed in the graphs of the band structures. After a brief description of the tight binding method, the band structures of linear chains of Carbon atoms are calculated. The cases of one and two atoms per unit cell are considered. They correspond to cumulene and polyyne, respectively. Among the two-dimensional atomic arrangements of interest, we focus the calculation of the band structure of graphene. The calculated bands are compared with available results. Some attention is devoted to the 'pi' bands associated to the 'p IND. z' orbitals is presented. The effects of the overlapping of the atomic orbitals are discussed. The method is also applied to model three-dimensional crystels. The band structures of diamong, germanium (with diamond structure), Gallium Arsenide (with zincblende structure) and Gallium Nitride (with wurtzite structure) are obtained. The results are compared with those reported by other authors who applied ab initio methods

abstract: This dissertation presents research findings on the three materials systems: lateral Si nanowires (SiNW), In₂Se₃/Bi₂Se₃ heterostructures and graphene. The first part of the thesis was focused on the growth and characterization of lateral SiNW. Lateral here refers to wires growing along the plane of substrate; vertical NW on the other hand grow out of the plane of substrate. It was found, using the Au-seeded vapor &ndash; liquid &ndash; solid technique, that epitaxial single-crystal SiNW can be grown laterally along Si(111) substrates that have been miscut toward [11&minus; 2]. The ratio of lateral-to-vertical NW was found to increase as the miscut angle increased and as disilane pressure and substrate temperature decreased. Based on this observation, growth parameters were identified whereby all of the deposited Au seeds formed lateral NW. Furthermore, the nanofaceted substrate guided the growth via a mechanism that involved pinning of the trijunction at the liquid/solid interface of the growing nanowire. Next, the growth of selenide heterostructures was explored. Specifically, molecular beam epitaxy was utilized to grow In₂Se₃ and Bi₂Se₃ films on h-BN, highly oriented pyrolytic graphite and Si(111) substrates. Growth optimizations of In₂Se₃ and Bi₂Se₃ films were carried out by systematically varying the growth parameters. While the growth of these films was demonstrated on h-BN and HOPG surface, the majority of the effort was focused on growth on Si(111). Atomically flat terraces that extended laterally for several hundred nm, which were separated by single quintuple layer high steps characterized surface of the best In₂Se₃ films grown on Si(111). These In₂Se₃ films were suitable for subsequent high quality epitaxy of Bi₂Se₃ . The last part of this dissertation was focused on a recently initiated and ongoing study of graphene growth on liquid metal surfaces. The initial part of the study comprised a successful modification of an existing growth system to accommodate graphene synthesis and process development for reproducible graphene growth. Graphene was grown on Cu, Au and AuCu alloys at varioua conditions. Preliminary results showed triangular features on the liquid part of the Cu metal surface. For Au, and AuCu alloys, hexagonal features were noticed both on the solid and liquid parts. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2014

Depuis sa découverte expérimentale en 2004, le graphène a émergé comme un matériau potentiel pour les technologies de nouvelle génération. Le graphène était le premier matériau 2D produit et l’intérêt et qu’il suscite provient de ses remarquables propriétés: il possède d’importants coefficients de mobilité électronique et de conductivité thermique, il est également le matériau le plus solide et léger connu. Pour permettre le développement d’applications à l’ échelle industrielle, des technologies de structuration à l’ échelle submicronique sont nécessaires.Cette thèse se concentre sur l’exploration de l’ablation par laser femtoseconde en tant que technique de structuration rapide et peu coûteuse de structuré graphène obtenu par technique CVD (Chemical Vapor Deposition). L’utilisation d’impulsions laser ultra brèves est a priori intéressante en raison de la capacité des impulsions laser ultra brèves à déposer au sein des matériaux une quantité élevée d’ énergie dans un volume extrêmement confiné.Nous avons réalisé un ensemble d’expériences à partir de faisceaux non-diffractants pour caractériser les paramètres requis pour contrôler l’ablation à l’ échelle sub-micronique. Nous avons déterminé les caractéristiques de l’ablation en régime mono-coup pour le graphène CVD, tels que le seuil d’ablation et la probabilité d’ablation. Pour cela, nous avons développé une nouvelle technique de mesure indépendante du seuil indépendante de la taille de la zone ablatée. Nous avons ainsi pu mettre en évidence un écart par rapport au modèle classique d’ablation, l’effet des différents substrats diélectriques, ainsi que le rôle des joints de grain.Nos résultats montrent que l’ablation mono-coup par impulsion femtoseconde est une technique efficace pour des structures au-delà d’une taille caractéristique de 1 _m, mais en dessous de cette dimension, de nouvelles stratégies d’illuminations se révèlent encore nécessaires. / Since its isolation in 2004, graphene has emerged has a potential material for next generation technologies.Graphene was the first truly 2D material produced. The interest in this material is due to its outstandingproperties: graphene is the lightest and strongest material known. It has a large electronic mobility andthermal conductivity. To enable the development of technological applications at industrial scale, fast patterningtechniques, operable at sub-micron scale are needed.This thesis focuses on the requirement of a fast, easily reconfigurable, low cost method to pattern graphene.The aim of our research is to determine the possibilities and constraints of ultrafast laser ablation of CVDgraphene at sub-micron scale. Using ultrafast laser to pattern graphene layers is interesting due to the abilityof femtosecond laser pulses to accurately depositing a high energy density in confined regions.We performed a set of experiments using non-diffractive shaped-beams to characterize the parametersrequired to control laser material processing at such small scale. We determined laser patterningcharacteristics on CVD monolayer graphene such as the ablation threshold and the ablation probability. To thisaim, we have developed a novel technique to measure ablation threshold that is independent of the ablated sizeand reported unexpected deviation from the threshold model, we also investigated the influence of differentdielectric substrates and the effect of the presence of graphene grain boundaries. From our experimentalresults we conclude that direct single shot laser patterning is a very effective method to pattern features above 1 µm, but below this dimension, novel illumination strategies are needed

Nesta tese investigamos a partir de cálculos de primeiros princípios, dispositivos e componentes de dispositivos baseados em grafeno. Abordamos os campos da nanoeletrônica e da spintrônica. Dentro da nanoeletrônica investigamos: (i) propriedades de transporte de um nanotransistor de bicamada de grafeno na presença de um gate duplo. Demonstramos que sobre a ação de um campo elétrico externo, mesmo utilizando um gate da ordem de 10 nm, à temperatura ambiente e 4.5K uma corrente nula nunca é exibida. Esses resultados são explicados por um regime de tunelamento; (ii) propriedades eletrônicas e de transporte de multicamadas de grafeno em função do número de camadas e tipo de empilhamento entre elas. Mostramos que a estrutura eletrônica do sistema depende fortemente desse novo grau de liberdade de empilhamento. Na presença de um campo elétrico externo aplicado perpendicular ao sistema, o empilhamento do tipo Bernal nunca exibe um gap de energia, ao contrário do empilhamento romboédrico que exige um gap ajustável através da intensidade do campo. Mostramos também que é possível diferenciar os tipos de empilhamentos através da resistência do sistema e variando-se a temperatura; (iii) dentro das componentes de um nanotransistor mais realista, estudamos as propriedades eletrônicas e estruturais de: (a) bicamadas de grafeno sobre um substrato de nitreto de boro hexagonal. Neste sistema o limite de voltagens que podem ser aplicadas depende fortemente do número de camadas de h-BN e da direção do campo, onde quanto menos camadas maior é a voltagem que pode ser aplicada; (b) heteroestruturas compostas de bicamadas de grafeno, nitreto de boro hexagonal e cobre. Demonstramos que para uma aplicação direta em um dispositivo a configuração com uma bicamada de grafeno depositada sobre um substrato de h-BN e este conjunto sobre a superfície de cobre é a mais favorável. Nessa configuração é possível tanto controlar o gap na bicamada como a dopagem do sistema, sem a abertura de canais de condução através do dielétrico (h-BN). Dentro do campo da spintrônica estudamos: (i) propriedades de transporte das nanofitas de grafeno (GNR) (3,0) pristinas e dopadas com boro e nitrogênio. Para as GNR pristinas mostramos com os eletrodos em um alinhamento de spin anti-paralelo o sistema apresenta um comportamento de filtro de spin, onde para tensões de bias positivos/negativos somente o canal up/down conduz. Para as GNR dopadas com boro e nitrogênio, mostramos que as correntes para os diferentes canais de spin são não degeneradas ao longo de todo o intervalo de tensões aplicadas, apresentando desse modo um comportamento de filtro de spin; (ii) finalmente estudamos as propriedades de transporte de uma junção túnel magnética, composta de GNR intercaladas por uma nanofita de nitreto de boro hexagonal. Mostramos que esse sistema pode ser utilizado tanto como filtros de spin como elementos para dispositivos de magnetoresistência gigante, onde para este último a sua eficiência é muito mais pronunciada. / In this thesis we investigated by first principle calculations, devices and components of devices based on graphene. We covered the fields of nanoelectronics and spintronics. On the field of nanoelectronics we investigated: (i) the transport properties of a dual gate bilayer graphene nanotransistor. We showed that under the action of an external electrical field, even with a gate length of 10 nm, at room temperature and 4.5K a zero current is never exhibited. These results could be explained by a tunneling regime; (ii) the electronic and transport properties of few layer graphene, as function of the number and type of stacking of the layers. We show that the electronic structure strong deppends of the stacking order. On the presence of a external electrical field applied to the system, the Bernal stacking never presents a gap, contrary to the rombohedrical one, that posses a tuneable energy gap. Also we showed that is possible to differentiate the types of stacking by the resistance of the system and varying the temperature;(iii) for the components of a more realistic nanodevice, we study the structural and electronic properties of: (a) bilayer graphene over a hexagonal boron nitride substrate. We show that the voltages that could be applied to the system strongly depends of the number 0 layers and the direction of the field, where with more layers, smaller is the field; (b) heterostructures composed with bilayer graphene, hexagonal boron nitride and cooper. We show that for a direct application on a device, the better configuration is with a bilayer graphene over the hexagonal boron nitride, and this set over a cooper. In this configuration is possible to control both the gap and the doping of the system, without the creation of conducting channels through the dielectric (h-BN). On the field of spintronics, we study: (i) the transport properties (3,0) graphene nanoribbons pristines and doped with nitrogen and boron. For the pristine GNR we show that for the electrodes in an anti-parallel alignment the system presents a spin filter behavior, where for positive/negative bias the transport is only by up/down channel. For the GNR doped with nitrogen and boron we show that the current is non-degenerated in all range of voltages applied, presenting a spin filter behavior; (ii) finally, we study the transport properties of a magnetic tunnel junction, consisting of a GNR intercalated with a hexagonal boron nitride nanoribbon. We show that such system could be used both as a spin filter as a device that uses the the giant magnetoresistance effect, where for the last the system if more efficient.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-08-18T15:18:04Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TESE-BAGR.pdf: 9049017 bytes, checksum: af3edd6dce7e702e64d600bace79a1e9 (MD5) / Made available in DSpace on 2016-08-18T15:18:04Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) TESE-BAGR.pdf: 9049017 bytes, checksum: af3edd6dce7e702e64d600bace79a1e9 (MD5) Previous issue date: 2015-04-08 / CNPq / Atualmente o grafeno tem sido considerado uma nanoestrutura ideal para diversas aplicações, porém o processo de síntese em longa escala ainda é um desafio, sendo o grafeno oxidado (GO) uma possível solução para obter o grafeno em grande quantidade. Neste trabalho sintetizamos GO utilizando método de Hummers ao qual introduzimos modificações de modo a diminuir os gases tóxicos produzidos durante a síntese. De modo a não alterar as propriedades do grafeno devido à introdução de grupos funcionais existentes no GO utilizamos dois processos de redução, um químico e outro térmico. O grafeno obtido por ambos processos foi caracterizado do ponto de vista estrutural, morfológico e óptico. Os resultados revelaram que o grafeno reduzido (RGO) apresentava na forma de bicamada, com uma alta área superficial (500 m2 g-1). Foi observado também no espectro UV-Vis, um deslocamento de comprimento de onda da ordem de 40 nm para energias maiores e uma diminuição de 50% do número de defeitos em relação ao GO, devido a eliminação de grupos funcionais, pelo processo de redução. Utilizamos o mesmo processo de síntese do RGO para produzir nanofitas de carbono. As nanofitas apresentam propriedades similares ao grafeno, embora estas não dependam somente do número de folhas, como no caso do grafeno. As propriedades elétricas das nanofitas dependem fortemente de sua largura. Assim, para o controle da largura das nanofitas, utilizamos o método de Tour para a abertura de nanotubos de carbono de múltiplas camadas (MWCNTs). As nanofitas sintetizadas possuem comprimentos em torno de 5 μm e larguras em torno de 150 nm, e com número de folhas menor ou igual a 5. Além da síntese do grafeno e das nanofitas utilizamos nanopartículas magnéticas para decorar estas nanoestruturas, visando obter materiais com propriedades catalíticas, magnéticas e biocompatíveis. Utilizamos essas nanoestruturas para estudar suas possíveis aplicações no desenvolvimento de capacitores, na remoção de corantes e como sensor de biomoléculas. / Synthesis and characterization of graphene oxide and graphene nanoribbons Due to its excellent properties graphene has been established as a very good candidate in many potential applications. However, one of the main challenge for achivieving that is the massive producution of this material. Graphene oxide (GO) has been suggested as a possible route to face this concern taking the great advantage of its large scale production. In this work, we synthetise GO using the well-known Hummers method with some modifications in order to reduce the production of toxic gases. Futhermore, reduction of GO was performed to keep physical properties to be the most closest to graphene by eliminating funtional groups attached to the GO. Then, the obtained reduced graphene oxide (RGO) was characterized structural and morphologically. Those studies reveal that the RGO has at least 2 sheets, a high surface area (500 m2g-1) and a reduction of defects very close to a half of that in GO. Synthesis of graphene nanoribbons was also explored using the Tour procedure. Our results suggest the sucessful synthesis of nanoribbons with typical dimensions of 5 um in length, witdth of 150 nm and composed of less than 5 sheets. Decoration of graphene and graphene nanorribons with magnetic particles was achieved to study biocompatibility, catalityc and magnetic properties. Finally, some applications with the synthetized materials are developed in the field of capacitors, colorant removal and biosensors.

Made available in DSpace on 2018-06-27T18:56:33Z (GMT). No. of bitstreams: 3 Fabricio Andre Dutra.pdf: 2324263 bytes, checksum: d976987810d5ee8632aeb3895a29aaee (MD5) Fabricio Andre Dutra.pdf.txt: 94667 bytes, checksum: 3ec4dfa78936dd7176d06ab5f58e1a7a (MD5) Fabricio Andre Dutra.pdf.jpg: 3282 bytes, checksum: 74e36c65b551d6f29699776af43cf2a7 (MD5) Previous issue date: 2010-07-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The graphene is a two-dimensional network composed of carbon atoms arranged in hexagonal rings; characterized as "thinner material of the universe", which exhibits high crystal quality and ballistic electrical transport at low temperatures. This material presents electronic properties and large surface area that are interesting to adsorb or substitut aminoacids, to increase the hydrophilicity of the structure originally constituted only of carbon atoms and then enable the development of new sensors with high molecular sensitivity. This work aim to evaluate the structural and electronic properties of the grapheme interacting with the aminoacid cysteine, and the type of interaction established between this and monolayer graphene perfect or structural defect. These properties are investigated through computer simulation from first principles methods using the density functional theory that indicate the electronic and structural properties of the resulting systems. We found that the binding energy between the amino and graphene monolayer varies, being totally dependent on the reaction site and among the three sites considered (carboxyl, amine and thiol), both, in considering the perfect layer of graphene or with as structural defect, present the thiol group with a stronger interaction. In the electronic properties, we demonstrate little interaction between the systems, because the levels of isolated systems appear clearly in the structures of interacting systems, which demonstrates the low binding energy found. Thus, this study demonstrated, the properties associated with the interaction of amino acids adsorbed on graphene encouraging potential technological application of this innovative material as a sensor of more complex molecules. / O grafeno consiste numa rede bidimensional, composta unicamente de átomos de carbono dispostos em anéis hexagonais; sendo recentemente caracterizado como material mais fino do universo , o qual exibe alta qualidade cristalina e transporte elétrico balístico em baixas temperaturas. Neste material as propriedades eletrônicas e a grande área superficial são algumas das propriedades mais interessantes de modo que podem ser adsorvidos ou substituídos aminoácidos, visando aumentar a hidrofilicidade da estrutura originalmente constituída apenas de átomos de carbono. Neste trabalho visamos avaliar as propriedades estruturais e eletrônicas resultantes da adsorção ou substituição de átomos de carbono pelo aminoácido cisteína, bem como investigar o tipo de interação estabelecida entre este e a monocamada de grafeno perfeita ou com defeito estrutural. Avaliamos estas propriedades por meio de simulação computacional de primeiros princípios utilizando a Teoria do Funcional da Densidade. Indicamos as propriedades eletrônicas e estruturais de aminoácidos substituindo átomos de carbono na estrutura do grafeno ou adsorvendo na superfície. Constatamos que a energia de ligação entre o aminoácido e a monocamada de grafeno varia, sendo totalmente dependente do sítio reacional que aproximamos, sendo que dentre os três sítios considerados (carboxila, amino e tiol), tanto na aproximação da camada de grafeno perfeita quanto da camada com defeito estrutural, o grupo tiol foi o que demonstrou uma interação mais forte com o grafeno, além de apresentar também uma menor distância de ligação entre a monocamada e a molécula de aminoácido. Nas estruturas de bandas, demonstramos a pouca interação entre os sistemas, pelo fato de os níveis dos sistemas isolados aparecerem claramente nas estruturas dos sistemas interagentes, o que evidencia a baixa energia de ligação encontrada. Desta forma, este trabalho demonstrou, de forma inédita, as propriedades associadas com a interação da cisteína adsorvida no grafeno fomentando o potencial de aplicação tecnológica deste material inovador como sensor de moléculas mais complexas.

Submitted by MARCIA ROVADOSCHI (marciar@unifra.br) on 2018-08-15T13:37:56Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_FabricioAndreDutra.pdf: 2597820 bytes, checksum: b29ce7e5a23a5e29c3f38199420d805a (MD5) / Made available in DSpace on 2018-08-15T13:37:56Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_FabricioAndreDutra.pdf: 2597820 bytes, checksum: b29ce7e5a23a5e29c3f38199420d805a (MD5) Previous issue date: 2010-07-30 / The graphene is a two-dimensional network composed of carbon atoms arranged in hexagonal rings; characterized as "thinner material of the universe", which exhibits high crystal quality and ballistic electrical transport at low temperatures. This material presents electronic properties and large surface area that are interesting to adsorb or substitut aminoacids, to increase the hydrophilicity of the structure originally constituted only of carbon atoms and then enable the development of new sensors with high molecular sensitivity. This work aim to evaluate the structural and electronic properties of the grapheme interacting with the aminoacid cysteine, and the type of interaction established between this and monolayer graphene perfect or structural defect. These properties are investigated through computer simulation from first principles methods using the density functional theory that indicate the electronic and structural properties of the resulting systems. We found that the binding energy between the amino and graphene monolayer varies, being totally dependent on the reaction site and among the three sites considered (carboxyl, amine and thiol), both, in considering the perfect layer of graphene or with as structural defect, present the thiol group with a stronger interaction. In the electronic properties, we demonstrate little interaction between the systems, because the levels of isolated systems appear clearly in the structures of interacting systems, which demonstrates the low binding energy found. Thus, this study demonstrated, the properties associated with the interaction of amino acids adsorbed on graphene encouraging potential technological application of this innovative material as a sensor of more complex molecules. / O grafeno consiste numa rede bidimensional, composta unicamente de átomos de carbono dispostos em anéis hexagonais; sendo recentemente caracterizado como “material mais fino do universo”, o qual exibe alta qualidade cristalina e transporte elétrico balístico em baixas temperaturas. Neste material as propriedades eletrônicas e a grande área superficial são algumas das propriedades mais interessantes de modo que podem ser adsorvidos ou substituídos aminoácidos, visando aumentar a hidrofilicidade da estrutura originalmente constituída apenas de átomos de carbono. Neste trabalho visamos avaliar as propriedades estruturais e eletrônicas resultantes da adsorção ou substituição de átomos de carbono pelo aminoácido cisteína, bem como investigar o tipo de interação estabelecida entre este e a monocamada de grafeno perfeita ou com defeito estrutural. Avaliamos estas propriedades por meio de simulação computacional de primeiros princípios utilizando a Teoria do Funcional da Densidade. Indicamos as propriedades eletrônicas e estruturais de aminoácidos substituindo átomos de carbono na estrutura do grafeno ou adsorvendo na superfície. Constatamos que a energia de ligação entre o aminoácido e a monocamada de grafeno varia, sendo totalmente dependente do sítio reacional que aproximamos, sendo que dentre os três sítios considerados (carboxila, amino e tiol), tanto na aproximação da camada de grafeno perfeita quanto da camada com defeito estrutural, o grupo tiol foi o que demonstrou uma interação mais forte com o grafeno, além de apresentar também uma menor distância de ligação entre a monocamada e a molécula de aminoácido. Nas estruturas de bandas, demonstramos a pouca interação entre os sistemas, pelo fato de os níveis dos sistemas isolados aparecerem claramente nas estruturas dos sistemas interagentes, o que evidencia a baixa energia de ligação encontrada. Desta forma, este trabalho demonstrou, de forma inédita, as propriedades associadas com a interação da cisteína adsorvida no grafeno fomentando o potencial de aplicação tecnológica deste material inovador como sensor de moléculas mais complexas.

O grafeno, material com duas dimensões (2D), formado por átomos de carbono hibridizados em sp2, tem atraído muita atenção da comunidade científica devido às propriedades elétricas, térmicas e mecânicas excepcionais que este material apresenta. Nanopartículas (NPs) de metais e de óxidos metálicos têm sido incorporadas sobre a estrutura do grafeno com o objetivo de obter materiais compósitos. Este trabalho teve por objetivo principal desenvolver uma nova rota para a preparação de compósitos de grafeno/NPs metálicas e de óxidos metálicos pelo método do poliol modificado, em etapa única. O óxido de grafeno (GO) foi sintetizado pelo método Hummers modificado e reduzido e esfoliado pelo processo pioliol modificado para obtenção do grafeno. Ajustou-se a metodologia proposta para que o GO obtido pudesse ser utilizado diretamente no meio reacional do processo poliol sem a necessidade de secagem e redispersão. Foram testadas diversas condições de síntese do grafeno variando-se a presença e tipo de surfactante, o solvente e diferentes condições de aquecimento. As variações de síntese permitiram observar que a presença do surfactante oleilamina aumenta a capacidade redutora do sistema e inibe a formação de outras estruturas de carbono além do grafeno e taxas de aquecimento menores favorecem a formação de grafeno em detrimento destas outras estruturas, enquanto patamares de temperatura intermediários levam à formação dessas estruturas secundárias de carbono. As sínteses foram também adaptadas para a obtenção de compósitos de grafeno/NPs de FePt e Fe3O4. Estas sínteses foram realizadas de duas maneiras: com os precursores metálicos e o GO presentes no balão desde o início da síntese e com os precursores metálicos presentes no balão desde o início da síntese e hot injection do GO. Para os compósitos, as sínteses realizadas em benzil éter (BE) favoreceram a formação de partículas. Para os compósitos de grafeno/NPs de Fe3O4, observou-se que a quantidade de precursor de Fe é crucial para a formação das NPs. Os resultados indicaram que a metodologia empregada foi muito eficiente para produção de grafeno e de compósitos de grafeno/NPs em etapa única e o processo poliol se mostrou muito versátil, de maneira que os resultados obtidos indicam que é possível obter compósitos de grafeno com qualquer sistema de NPs que venham a ser sintetizadas pelo processo poliol, apenas pelo ajuste das condições de síntese, em etapa única. / Graphene, a two dimensional material, composed only by sp2 hybridized carbon atoms, have attracted much attention of the scientific comunity due to the exceptional electrical, thermal and mechanical properties this material presents. Metallic and metal oxide nanoparticles (NPs) have been incorporated over graphene structure in order to obtain composite materials. The main goal of this work was to develop a new synthetic route to obtain graphene and metallic and metal oxide NPs composites, in one step. Graphene oxide (GO) was sinthesized by the modified Hummers method and exfoliated and reduced by the modified polyol process to obtain graphene. The proposed methodology was adjusted for the obtained GO to be used directly in the polyol process reactional means, not being necessary to dry and to redisperse the material. Several synthesis conditions were tested to obtain graphene, varying the presence of the surfactant and its type, solvent and heating rates. The synthesis diversity let us observe that the presence of oleylamine improved the reducing capacity of the system and it inhibited other carbon structures formation besides graphene. Also, smaller heating rates favor graphene formation to the detriment of these other structures, whereas intermediate temperature plateaus lead to the formation of carbon secondary structures. The synthesis were also adapted in order to obtain graphene/NPs of FePt and Fe3O4 composites. These synthesis were performed in two ways: both metallic precursors and GO present in the flask since the begining of the synthesys and only methalic precursors present in the flask since the begining of the synthsys, with a GO hot injection. Regarding the composites, synthesis performed in benzyl ether (BE) favor the particles formation. And specifically on the graphene/NPs of Fe3O4 composites, it was observed that Fe precursor quantity is decisive on the NPs formation. The results indicated that the employed methodology was very efficient to produce graphene and graphene/NPs composites in one step. And the polyol process proved to be very versatile, thereby the obtained results indicate it\'s possible to obtain graphene/NPs composites, in one step, with any NPs system that can be synthesized by the polyol process, only by adjusting the synthesis condition.