Academic literature on the topic 'Nanostructure - Graphene'

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Dissertations / Theses on the topic "Nanostructure - Graphene"

1

France-Lanord, Arthur. "Transport électronique et thermique dans des nanostructures." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS566/document.

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La miniaturisation continue des composants électroniques rend indispensable la connaissance des mécanismes de transport à l’échelle nanométrique. Alors que les processus simples de conduction dans les matériaux homogènes sont bien assimilés, la compréhension du transport à l’échelle nanométrique dans les systèmes hétérogènes reste à améliorer. Par exemple, le couplage entre courant, résistance et flux de chaleur dans des nanostructures doit être clarifié. Dans ce contexte, le sujet de thèse est centré autour du développement et de l’application de méthodes de calcul avancées pour la prédiction des propriétés de transport électronique et thermique à l’échelle nanométrique. Dans une première partie, nous avons paramétré un modèle de potentiel inter-atomique classique adapté à la description de systèmes multicomposants, afin de modéliser les propriétés structurelles, vibratoires et de transport de chaleur de la silice, ainsi que du silicium. Pour ce faire, une approche d’optimisation automatisée et reproductible a été mise en place. En guise d’exemple, nous avons calculé la dépendance en température de la résistance de Kapitza pour le système silice amorphe - silicium cristallin, ce qui a permis de souligner l’importance d’une description structurelle précise de l’interface. Dans une seconde partie, nous avons étudié la décomposition modale de la conductivité thermique du graphène supporté par un substrat de silice amorphe. Plus précisément, l’influence de l’état de surface (hydroxilation, etc) sur le transport thermique a été quantifiée. Le rôle déterminant des excitations collectives de phonons a été mis au jour. Finalement, dans une dernière partie, les propriétés de transport électronique du graphène supporté par une bi-couche de silice, système récemment observé expérimentalement, ont été étudiées. L’influence d’ondulations dans la couche de graphène ou dans le substrat, souvent présentes dans les échantillons réels et dont l’amplitude et la longueur d’onde peuvent être contrôlées, a été dégagée. Nous avons également modélisé le champ électrique généré par une grille, et déterminé son incidence sur le transport électronique<br>The perpetual shrinking of microelectronic devices makes it crucial to have a proper understanding of transport mechanisms at the nanoscale. While simple effects are now well understood in homogeneous materials, the understanding of nanoscale transport in heterosystems needs to be improved. For instance, the relationship between current, resistance, and heat flux in nanostructures remains to be clarified. In this context, the subject of the thesis is centered around the development and application of advanced numerical methods used to predict electronic and thermal conductivities of nanomaterials. This manuscript is divided into three parts. We begin with the parameterization of a classical interatomic potential, suitable for the description of multicomponent systems, in order to model the structural, vibrational, and thermal transport properties of both silica and silicon. A well-defined, reproducible, and automated optimization procedure is derived. As an example, we evaluate the temperature dependence of the Kapitza resistance between amorphous silica and crystalline silicon, and highlight the importance of an accurate description of the structure of the interface. Then, we have studied thermal transport in graphene supported on amorphous silica, by evaluating the mode-wise decomposition of thermal conductivity. The influence of hydroxylation on heat transport, as well as the significant role played by collective excitations of phonons, have come to light. Finally, electronic transport properties of graphene supported on quasi-two-dimensional silica, a system recently observed experimentally, have been investigated. The influence on transport properties of ripples in the graphene sheet or in the substrate, which often occur in samples and whose amplitude and wavelength can be controlled, has been evaluated. We have also modeled electrostatic gating, and its impact on electronic transport
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Celis, Retana Arlensiú Eréndira. "Gap en graphène sur des surfaces nanostructurées de SiC et des surfaces vicinales de métaux nobles." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS417/document.

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L'électronique basée sur le graphène fait face à un verrou technologique, qui est l'absence d'une bande interdite (gap) permettant une commutation entre les états logiques allumé et éteint. Les nano-rubans de graphène rendent possible l'obtention de ce gap mais il est difficile de produire de tels rubans avec une largeur précise à l'échelle atomique et des bords bien ordonnés. Le confinement électronique est une façon élégante d'ouvrir un gap et peut en principe être réglé en ajustant la largeur des nano-rubans. Cette thèse est consacrée à la compréhension de l'ouverture du gap par nano-structuration. Nous avons suivi deux approches: l'introduction d'un potentiel super-périodique sur le graphène par des substrats vicinaux de métaux nobles et le confinement électronique dans des nano-rubans sur des facettes artificielles du SiC. Des potentiels super-périodiques ont été introduits avec deux substrats nano-structurés: l'Ir(332) et un cristal courbé de Pt(111) multi-vicinale. Le graphène modifie les marches initiales des substrats et les transforme en une succession de terrasses (111) et de régions d'accumulation de marches, observés par STM. La nano-structuration du substrat induit alors un potentiel super-périodique dans le graphène entraînant l'ouverture de gaps sur la bande π du graphène observée par ARPES, ce qui est cohérent avec la périodicité structurale observé par STM et LEED. Les gaps peuvent être convenablement expliqués par un modèle de type hamiltonien de Dirac; ce dernier nous permet de retrouver la force du potentiel à la jonction entre les terrasses (111) et la région d'accumulation des marches. La force du potentiel dépend du substrat, de la périodicité associée à la surface et du type de bord des marches (soit type A ou B). Nous avons aussi changé le potentiel de surface en intercalant du Cu sur l'Ir(332), qui reste préférentiellement au niveau de l'accumulation des marches. La surface présente des régions dopées n alors que les régions non-intercalées restent dopées p, conduisant à une succession de rubans dopés n et p pour une même couche de graphène continue. La seconde approche pour contrôler le gap est par confinement électronique dans des nanorubans de graphène synthétisés sur du SiC. Ces rubans sont obtenus sur des facettes du SiC ordonnées périodiquement. Comme l'ouverture d'un gap d'origine inconnue avait été observée par ARPES, nous avons réalisé les premières études atomiquement résolues par STM. Nous démontrons la régularité et la chiralité des bords, nous localisons précisément les nanorubans de graphène sur les facettes et nous identifions des mini-facettes sur du SiC. Afin de comprendre le couplage entre le graphène et le substrat, nous avons étudié une coupe transversale par STEM/EELS, en complément des études par ARPES et STM/STS. Nous observons que la facette (1-107) où le graphène se trouve présente un sub-facettage sur les extrémités haute et basse. Le sub-facettage comprend des mini-terrasses (0001) et des mini-facettes (1-105). Le graphène s'étend tout au long du la région sub-facettée, et est couplé au substrat dans les mini-terrasses (0001), ce qui le rend semi-conducteur. En revanche, le graphène au-dessus des mini-facettes (1-105) est découplé du substrat mais présente un gap observé par EELS, et compatible avec les observations faites par ARPES. L'origine du gap est expliquée par le confinement électronique sur des nano-rubans de graphène de 1 - 2 nm de largeur localisés sur ces mini-facettes (1-105)<br>The major challenge for graphene-based electronic applications is the absence of the band-gap necessary to switch between on and off logic states. Graphene nanoribbons provide a route to open a band-gap, though it is challenging to produce atomically precise nanoribbon widths and well-ordered edges. A particularly elegant method to open a band-gap is by electronic confinement, which can in principle be tuned by adjusting the nanoribbon width. This thesis is dedicated to understanding the ways of opening band-gaps by nanostructuration. We have used two approaches: the introduction of a superperiodic potential in graphene on vicinal noble metal substrates and the electronic confinement in artificially patterned nanoribbons on SiC. Superperiodic potentials on graphene have been introduced by two nanostructured substrates, Ir(332) and a multivicinal curved Pt(111) substrate. The growth of graphene modifies the original steps of the pristine substrates and transforms them into an array of (111) terraces and step bunching areas, as observed by STM. This nanostructuration of the underlying substrate induces the superperiodic potential on graphene that opens mini-gaps on the π band as observed by ARPES and consistent with the structural periodicity observed in STM and LEED. The mini-gaps are satisfactorily explained by a Dirac-hamiltonian model, that allows to retrieve the potential strength at the junctions between the (111) terraces and the step bunching. The potential strength depends on the substrate, the surface periodicity and the type of step-edge (A or B type). The surface potential has also been modified by intercalating Cu on Ir(332), that remains preferentially on the step bunching areas, producing there n-doped ribbons, while the non-intercalated areas remain p-doped, giving rise to an array of n- and p- doped nanoribbons on a single continuous layer. In the second approach to control the gap, we have studied the gap opening by electronic confinement in graphene nanoribbons grown on SiC. These ribbons are grown on an array of stabilized sidewalls on SiC. As a band-gap opening with unclear atomic origin had been observed by ARPES, we carried-out a correlated study of the atomic and electronic structure to identify the band gap origin. We performed the first atomically resolved study by STM, demonstrating the smoothness and chirality of the edges, finding the precise location of the metallic graphene nanoribbon on the sidewalls and identifying an unexpected mini-faceting on the substrate. To understand the coupling of graphene to the substrate, we performed a cross-sectional study by STEM/EELS, complementary of our ARPES and STM/STS studies. We observe that the (1-107) SiC sidewall facet is sub-faceted both at its top and bottom edges. The subfacetting consists of a series of (0001) miniterraces and (1-105) minifacets. Graphene is continuous on the whole subfacetting region, but it is coupled to the substrate on top of the (0001) miniterraces, rendering it there semiconducting. On the contrary, graphene is decoupled on top of the (1-105) minifacets but exhibits a bandgap, observed by EELS and compatible with ARPES observations. Such bandgap is originated by electronic confinement in the 1 - 2 nm width graphene nanoribbons that are formed over the (1-105) minifacets
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3

Chernozatonskii, L. A., and V. A. Demin. "Nanotube Connections in Bilayer Graphene with Elongated Holes." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35460.

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Structures, stability and electronic properties of AA-stacking bigraphene with holes are studied using molecular mechanic and DFT method calculations. It has been shown the zig-zag edges of considered elon-gated holes lead to armchair sp2-nanotube-type connection between these two edges forming all sp2-structure. We consider similar periodic structures with (n,n) nanotubes formed among elongated holes and connected with bigraphene fragments, which edges are also closed edges. The stability and electronic prop-erties of these structures are investigated. Band structures of considered materials have energy gaps 0.20-0.27 eV in the direction of tube axes through jumpers on the connections, and Dirac-like point views in the opposite direction. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35460
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4

Das, Santanu. "Carbon Nanostructure Based Electrodes for High Efficiency Dye Sensitize Solar Cell." FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/678.

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Synthesis and functionalization of large-area graphene and its structural, electrical and electrochemical properties has been investigated. First, the graphene films, grown by thermal chemical vapor deposition (CVD), contain three to five atomic layers of graphene, as confirmed by Raman spectroscopy and high-resolution transmission electron microscopy. Furthermore, the graphene film is treated with CF4 reactive-ion plasma to dope fluorine ions into graphene lattice as confirmed by X-ray photoelectron spectroscopy (XPS) and UV-photoemission spectroscopy (UPS). Electrochemical characterization reveals that the catalytic activity of graphene for iodine reduction enhanced with increasing plasma treatment time, which is attributed to increase in catalytic sites of graphene for charge transfer. The fluorinated graphene is characterized as a counter-electrode (CE) in a dye-sensitized solar cell (DSSC) which shows ~ 2.56% photon to electron conversion efficiency with ~11 mAcm−2 current density. Second, the large scale graphene film is covalently functionalized with HNO3 for high efficiency electro-catalytic electrode for DSSC. The XPS and UPS confirm the covalent attachment of C-OH, C(O)OH and NO3- moieties with carbon atoms through sp2-sp3 hybridization and Fermi level shift of graphene occurs under different doping concentrations, respectively. Finally, CoS-implanted graphene (G-CoS) film was prepared using CVD followed by SILAR method. The G-CoS electro-catalytic electrodes are characterized in a DSSC CE and is found to be highly electro-catalytic towards iodine reduction with low charge transfer resistance (Rct ~5.05 Wcm2) and high exchange current density (J0~2.50 mAcm-2). The improved performance compared to the pristine graphene is attributed to the increased number of active catalytic sites of G-CoS and highly conducting path of graphene. We also studied the synthesis and characterization of graphene-carbon nanotube (CNT) hybrid film consisting of graphene supported by vertical CNTs on a Si substrate. The hybrid film is inverted and transferred to flexible substrates for its application in flexible electronics, demonstrating a distinguishable variation of electrical conductivity for both tension and compression. Furthermore, both turn-on field and total emission current was found to depend strongly on the bending radius of the film and were found to vary in ranges of 0.8 – 3.1 V/μm and 4.2 – 0.4 mA, respectively.
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5

Rhoads, Daniel Joseph. "A Mathematical Model of Graphene Nanostructures." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1438978423.

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6

Federspiel, Francois. "Etude optique du transfert d'énergie entre une nanostructure semiconductrice unique et un feuillet de graphène." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE015/document.

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Mes travaux de thèse portent sur l’interaction de type FRET (tranfert d’énergie résonant de Förster) entre une nanostructure semiconductrice colloïdale individuelle et le graphène. La première partie concerne l’établissement de la théorie du FRET et ce pour plusieurs types de nanostructures. Vient ensuite la partie expérimentale, à commencer par le montage optique ainsi que les méthodes d’analyse, tant pour la spectroscopie que pour la photoluminescence. Par la suite, nous décrivons les résultats obtenus pour divers types de nanocristaux sphériques en interaction directe avec le graphène (incluant des multicouches) : le transfert d’énergie a des effets drastiques sur la photoluminescence mais aussi sur le clignotement des nanocristaux. Puis nous étudions la dépendance du FRET avec la distance ; dans le cas des boîtes quantiques, nous observons une loi en 1/z^4. Par contre, dans le cas de nanoplaquettes, la fonction est plus complexe et dépend de la température<br>My PhD subject is the FRET interaction (Förster-like resonant energy transfer) between single colloidal semiconductor nanostructures and graphene. The first part is about the development of the interaction theory with the graphene for several types of nanostructures. Then comes the experimental part, and firstly the optical setup together with the analysis methods, for both spectroscopy and photoluminescence. After that, we describe our results about different types of spherical nanocrystals directly interacting with graphene (which can be multilayer) : the energy transfer has a huge effect on the photoluminescence, as well as the blinking behaviour of the nanocrystals. Then we measure the dependency of the energy transfer as a function the distance ; in the case of quantum dots, we observe a 1/z^4 law. On another hand, in the case of nanoplatelets, the function is more complex and depends on the temperature
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CURCIO, DAVIDE. "Growth and Properties of Graphene-Based Materials." Doctoral thesis, Università degli Studi di Trieste, 2017. http://hdl.handle.net/11368/2908114.

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In this thesis, I have focused on graphene-based nanostructures as a versatile means of manipulating the electronic properties of graphene, while working with objects perfect at the atomic level. This is the nanotechnological approach, where we exploit the infinite possibilities of making small things with new materials. For these reasons, I concentrated my research efforts to graphene-based nanomaterials, because graphene is one of the most exciting materials we have to date, and because manipulation of surfaces at the nano-level is what allows us to make new materials today. In this thesis, I will show how we have created and studied new graphene-based nanostructures by employing cutting-edge surface science techniques. Most of the experimental data we have acquired has been given a new light by powerful Density Functional Theory calculations, that allow for an approach where hardly accessible data (experimentally) becomes indirectly known through numerical calculations, while providing valuable feedback for further aimed calculations. I will show how we have undertaken a route that takes us from a detailed study of how carbon monomers, the building blocks of graphene, come to exist on an Ir(1 1 1) surface after ethylene dissociation. Next, simple nanostructures have been ex- ploited, so that the properties of a preexisting graphene layer are manipulated by intercalating different metals between graphene and the substrate. Then I will discuss an experiment where graphene was grown on a highly anisotropic substrate, Ru(1 0 1 0), which proved to be an extremely rich system, giving rise to several self-assembled graphene nanostructures, including nanoribbons and one-dimensional quasi free-standing graphene waves. Then, we will progress to what are commonly perceived as being proper graphene-based nanostructures. We have, in fact, managed to create size selected graphene nanodomes on Ir(1 1 1) using coronene as a precursor, and we have understood many details of the dynamics in the formation of these carbon-based nanostructures, discovering that in certain steps of the reaction they lift from the surface and rotate, before settling in the definitive adsorption position. Furthermore, while performing similar experiments on pentacene (a semiconducting molecule, used the fabrication of molecular FETs) on Ir(1 1 1), we have discovered that the molecules exhibit a reversible dehydrogenation, allowing for a switch between semiconducting molecules and minimalistic graphene nanoribbons, only one aromatic ring wide. Finally, a size-selected nanocluster source system will be described. In parallel with my research activity, I have been profoundly involved in the commissioning of such a machine that is currently capable of producing size selected nanoclusters.
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Seo, Michael. "Plasma-assisted nanofabrication of vertical graphene- and silicon-based nanomaterials and their applications." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/12285.

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Scarcity of physical resources, increasing concerns for safety and hazardous waste disposal which affects the environment drove the current nanoscience research to focus on developing low-cost, green and environmentally friendly method of obtaining nanomaterials. Yet, developing such smart and innovative processes is at premature stage. Over a few decades, many nanomaterials have been found and investigated. Amongst many nanomaterials, carbon and silicon nanomaterials attracted immense attention due to their abundance, low cost, unique and tunable properties which are promising for many applications. However, making nanostructure with uniformity and desirable properties is often difficult due to a lack of precise control which inherits from fabrication process. Furthermore, many techniques cannot satisfy green and environmentally friendly synthesis of mentioned nanomaterials. Therefore, efficient, effective and environmentally friendly way to create mentioned nanostructures with tunable properties remains a major challenge. Over a few decades, many investigations demonstrated that plasma technique can create uniform nanostructure in an environmentally friendly way which holds great promise as a versatile nanofabrication tool. Therefore, in this thesis, I investigate the plasma aided fabrication of Nobel Prize winning graphene related material called vertical graphenes will be discussed in details. Vertical graphene features are expected to be promising for a host of applications, from energy storage devices to gas detection. Therefore, I will explore the potential of vertical graphenes in diverse applications. Furthermore, green way of creating vertical graphenes using natural precursors from different states of matter will also be investigated. Following on from investigation of vertical graphenes, I will also demonstrate controllable, green synthesis of silicon based nanostructures without hazardous silicon precursor material using plasma-assisted methods.
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Kim, Junseok. "Improved Properties of Poly (Lactic Acid) with Incorporation of Carbon Hybrid Nanostructure." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/81415.

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Poly(lactic acid) is biodegradable polymer derived from renewable resources and non-toxic, which has become most interested polymer to substitute petroleum-based polymer. However, it has low glass transition temperature and poor gas barrier properties to restrict the application on hot contents packaging and long-term food packaging. The objectives of this research are: (a) to reduce coagulation of graphene oxide/single-walled carbon nanotube (GOCNT) nanocomposite in poly(lactic acid) matrix and (b) to improve mechanical strength and oxygen barrier property, which extend the application of poly(lactic acid). Graphene oxide has been found to have relatively even dispersion in poly(lactic acid) matrix while its own coagulation has become significant draw back for properties of nanocomposite such as gas barrier, mechanical properties and thermo stability as well as crystallinity. Here, single-walled carbon nanotube was hybrid with graphene oxide to reduce irreversible coagulation by preventing van der Waals of graphene oxide. Mass ratio of graphene oxide and carbon nanotube was determined as 3:1 at presenting greatest performance of preventing coagulation. Four different weight percentage of GOCNT nanocomposite, which are 0.05, 0.2, 0.3 and 0.4 weight percent, were composited with poly(lactic acid) by solution blending method. FESEM morphology determined minor coagulation of GOCNT nanocomopsite for different weight percentage composites. Insignificant crystallinity change was observed in DSC and XRD data. At 0.4 weight percent, it prevented most of UV-B light but was least transparent. GOCNT nanocomposite weight percent was linearly related to ultimate tensile strength of nanocomposite film. The greatest ultimate tensile strength was found at 0.4 weight percent which is 175% stronger than neat poly(lactic acid) film. Oxygen barrier property was improved as GOCNT weight percent increased. 66.57% of oxygen transmission rate was reduced at 0.4 weight percent compared to neat poly(lactic acid). The enhanced oxygen barrier property was ascribed to the outstanding impermeability of hybrid structure GOCNT as well as the strong interfacial adhesion of GOCNT and poly(lactic acid) rather than change of crystallinity. Such a small amount of GOCNT nanocomposite improved mechanical strength and oxygen barrier property while there were no significant change of crystallinity and thermal behavior found.<br>Master of Science
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Geng, Yan. "Preparation and characterization of graphite nanoplatelet, graphene and graphene-polymer nanocomposites /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20GENG.

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