Дисертації з теми "Nanostructure - Graphene"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Nanostructure - Graphene.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Nanostructure - Graphene".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
France-Lanord, Arthur. "Transport électronique et thermique dans des nanostructures." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS566/document.
Повний текст джерелаАнотація:
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 électroniqueThe 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
2
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.
Повний текст джерелаАнотація:
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)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
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.
Повний текст джерелаАнотація:
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
4
Das, Santanu. "Carbon Nanostructure Based Electrodes for High Efficiency Dye Sensitize Solar Cell." FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/678.
Повний текст джерелаАнотація:
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.
5
Rhoads, Daniel Joseph. "A Mathematical Model of Graphene Nanostructures." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1438978423.
Повний текст джерела
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.
Повний текст джерелаАнотація:
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 températureMy 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
7
CURCIO, DAVIDE. "Growth and Properties of Graphene-Based Materials." Doctoral thesis, Università degli Studi di Trieste, 2017. http://hdl.handle.net/11368/2908114.
Повний текст джерелаАнотація:
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.
8
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.
Повний текст джерелаАнотація:
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.
9
Kim, Junseok. "Improved Properties of Poly (Lactic Acid) with Incorporation of Carbon Hybrid Nanostructure." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/81415.
Повний текст джерелаАнотація:
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.Master of Science
10
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.
Повний текст джерела
11
Garcia, Ana Maria Valencia. "Estudo ab initio de nanoestruturas de grafeno: defeitos intrínsecos e interação com água." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-21112017-170853/.
Повний текст джерелаАнотація:
Neste trabalho utilizamos métodos computacionais ab initio, baseados na Teoria do Funcional da Densidade (DFT), para simular em nível atomístico propriedades estruturais, eletrônicas e magnéticas de nanoestruturas de grafeno. Estudamos nanoflocos de grafeno (GNFs) em estado pristino e GNFs com defeitos intrínsecos (monovacância, divacância e Stone-Wales). Escolhemos GNFs com diferentes terminações e formas, e estudamos também empilhamentos duplos - biflocos - em diferentes composições. Empregamos dois enfoques diferentes de DFT, a aproximação de gradiente generalizado simples no nível teórico de Perdew-Burke-Ernzerhof (PBE), e PBE híbrida (PBEh), incorporando uma fração de troca de Hartree-Fock. Todos os cálculos foram realizados através do código all-electron AIMS, incluindo correções de van der Waals. Nossos GNFs foram escolhidos com simetrias específicas: D2h, D3h e D6h, e com diferentes bordas, armchair (AC), zigue-zague (ZZ) e misturas das duas. Os flocos hexagonais D6h apresentam um gap de energia e nao apresentam spin, enquanto flocos perfeitos com bordas zigue-zague e mistas apresentam spin intrínseco. Esse spin não nulo é devido à diferença no numero de átomos entre uma e outra subrede do grafeno (Liebs imbalance). Defeitos em materiais de carbono sao frequentes, e tem sido estudados experimental e teoricamente. Aqui, estudamos a monovaçancia, através de modelos de cluster e supercélulas, e obtemos para esse defeito o momento magnético de = 2B, (B ´e o magneton de Bohr). Mostramos que as diferenças entre resultados anteriores são oriundas do erro de auto-interação presente na DFT simples, amenizado através do uso de PBEh. Através da mesma metodologia estudamos a interação de nanoestruturas de grafeno com moléculas de água, focalizando em propriedades estruturais. A grafite é um material hidrofóbico, mas a nanoestrutura poderia favorecer a interação com a água. Obtemos que pequenos agregados de água são adsorvidos na superfície de GNFs e biflocos, entretanto a inclusão desses agregados na região interna dos biflocos é altamente desfavorável. Assim podemos esperar que essas nanoestruturas empilhadas sejam também hidrofóbicas.In this work, computational ab initio methods based on density functional theory (DFT) are used to simulate on an atomistic level the structural, electronic and magnetic properties of graphene nanostructures. We study pristine graphene nanoflakes (GNFs), and GNFs with intrinsic defects (monovacancy, divacancy, Stone-Wales). We design GNFs with different terminations and shapes and also studied stacked forms -biflakes- in different compositions. We employed two DFT approaches, plain generalized gradient approximation in the Perdew-Burke-Ernzerhof (PBE) level of the theory, and hybrid PBE (PBEh) incorporating a fraction of Hartree-Fock exchange. All calculations were performed with the all-electron code AIMS, including van der Waals corrections. Our GNFs were chosen from three symmetry groups: D2h, D3h and D6h, and with different edges, armchair (AC), zigzag (ZZ) and a mixture of both. Our chosen D6h- hexagonal flakes present an energy gap and no spin, while perfect trigonal zigzag and mixed edges GNFs have an intrinsic spin. This non-zero spin is due to the graphene sublattice imbalance (Liebs imbalance). Defects are common in carbon materials, and have been experimentally and theoretically studied in graphene. Here, the single vacancy in graphene was studied, by cluster and supercell approaches, finding that the vacancy induces a magnetic moment = 2B (Bohr magneton). We show that conflicting results for the magnetic moment coming from theoretical studies come from the self-interaction error present in plain PBE, cured through the use of PBEh. Using the same methodology we studied the interaction of carbon nanostructures with water molecules, focusing on structural properties. Graphite is a hydrophobic material but nanostructuring could favor the interaction with water. We obtained that small water groups are adsorbed on the surface of GNFs and biflakes, however the inclusion of these groups in the internal region of biflakes is highly unfavorable, thus we can expect these stacked nanostructures to be also hydrophobic.
12
Li, Yanguang. "Nanostructured Materials for Energy Applications." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275610758.
Повний текст джерела
13
Poole, Timothy. "Acoustoelectric properties of graphene and graphene nanostructures." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/29838.
Повний текст джерелаАнотація:
The acoustoelectric effect in graphene and graphene nanoribbons (GNRs) on lithium niobate surface acoustic wave (SAW) devices was studied experimentally. Monolayer graphene produced by chemical vapour deposition was transferred to the SAW devices. The photoresponse of the acoustoelectric current (Iae) was characterised as a function of SAW frequency and intensity, and illumination wavelength (using 450 nm and 735 nm LEDs) and intensity. Under illumination, the measured Iae increased by more than the measured decrease in conductivity, while retaining a linear dependence on SAW intensity. The latter is consistent with the piezoelectric interaction between the graphene charge carriers and the SAWs being described by a relatively simple classical relaxation model. A larger increase in Iae under an illumination wavelength of 450 nm, compared to 735 nm at the same intensity, is consistent with the generation of a hot carrier distribution. The same classical relaxation model was found to describe Iae generated in arrays of 500 nm-wide GNRs. The measured acoustoelectric current decreases as the nanoribbon width increases, as studied for GNRs with widths in the range 200 – 600 nm. This reflects an increase in charge carrier mobility due to increased doping, arising from damage induced at the nanoribbon edges during fabrication. 2 Lastly, the acoustoelectric photoresponse was studied as a function of graphene nanoribbon width (350 – 600 nm) under an illumination wavelength of 450 nm. Under illumination, the nanoribbon conductivity decreased, with the largest percentage decrease seen in the widest GNRs. Iae also decreased under illumination, in contrast to the acoustoelectric photoresponse of continuous graphene. A possible explanation is that hot carrier effects under illumination lead to a greater decrease in charge carrier mobility than the increase in acoustoelectric attenuation coefficient. This causes the measured decrease in Iae.
14
Vieitas, de Amaral Dias Ana Inês. "Plasma based assembly and engineering of advanced carbon nanostructures." Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2019/document.
Повний текст джерелаАнотація:
L’environnement réactif du plasma constitue un outil puissant dans la science des matériaux, permettant la création de matériaux innovatifs et l'amélioration de matériaux existants qui ne serait autrement pas possible.Le plasma fournit simultanément des fluxes de particules chargées, des molécules chimiquement actives, des radicaux, de la chaleur, des photons, qui peuvent fortement influencer les voies d'assemblage à différentes échelles temporelles et spatiales, y compris à l’échelle atomique.Dans cette thèse de doctorat, des méthodes tenant pour base des plasmas micro-ondes ont été utilisées pour la synthèse de nanomatériaux de carbone, y compris graphène, graphène dopé à l'azote (N-graphène) et structures de type diamant.À cette fin, ce travail est lié à optimisation de la synthèse de nanostructures 2D du carbone, comme graphène et N-graphène par la poursuite de l'élaboration et du raffinement de la méthode développée en Plasma Engineering Laboratory (PEL). La synthèse de graphène de haute qualité et en grandes quantités a été accomplie avec succès en utilisant des plasmas d'Ar-éthanol à ondes de surface dans des conditions de pression ambiante. De plus, le N-graphène a été synthétisé par un procédé en une seule étape, de l'azote a été ajouté au mélange d’Ar-éthanol, et par un procédé en deux étapes, en soumettant des feuilles de graphène préalablement synthétisées ont été exposées à un traitement plasma argon-azote à basse pression. Les atomes d'azote ont été incorporés avec succès dans le réseau de graphène hexagonal, formant principalement liaisons pyrroliques, pyridiniques et quaternaires. Un niveau de dopage de 25 at.% a été atteint.Différents types de nanostructures de carbone, y compris du graphène et des structures de type diamant, ont été synthétisées au moyen d'un plasma d’argon en utilisant du méthane et du dioxyde de carbone comme précurseurs du carbone.De plus, des plasmas à couplage capacitif ont également été utilisés pour la fonctionnalisation du graphène et pour la synthèse de nanocomposites, tels que les composites de Polyaniline (PANI)-graphène. Les utilisations potentielles de ces matériaux ont été étudiées et les deux structures ont démontré avoir des attributs remarquables pour leur application aux biocapteursPlasma environments constitute powerful tools in materials science by allowing the creation of innovative materials and the enhancement of long existing materials that would not otherwise be achievable. The remarkable plasma potential derives from its ability to simultaneously provide dense fluxes of charged particles, chemically active molecules, radicals, heat and photons which may strongly influence the assembly pathways across different temporal and space scales, including the atomic one.In this thesis, microwave plasma-based methods have been applied to the synthesis of advanced carbon nanomaterials including graphene, nitrogen-doped graphene (N-graphene) and diamond-like structures. To this end, the focus was placed on the optimization of the production processes of two-dimensional (2D) carbon nanostructures, such as graphene and N-graphene, by further elaboration and refinement of the microwave plasma-based method developed at the Plasma Engineering Laboratory (PEL). The scaling up of the synthesis process for high-quality graphene using surface-wave plasmas operating at atmospheric pressure and argon-ethanol mixtures was successfully achieved. Moreover, N-graphene was synthetized via a single-step process, by adding nitrogen to the argon-ethanol mixture, and via two-step process, by submitting previously synthetized graphene to the remote region of a low-pressure argon-nitrogen plasma. Nitrogen atoms were usefully incorporated into the hexagonal graphene lattice, mainly as pyrrolic, pyridinic and quaternary bonds. A doping level of 25% was attained.Different types of carbon nanostructures, including graphene and diamond-like nanostructures, were also produced by using methane and carbon dioxide as carbon precursors in an argon plasma.Additionally, capacitively-coupled radio-frequency plasmas have been employed in the functionalization of graphene and in the synthesis of Polyaniline (PANI)-graphene composites. The potential uses of these materials were studied, with both showing favourable characteristics for their applicability in biosensing applications
15
Pijeat, Joffrey. "Anthracenylporphyrin based building blocks for the bottom-up fabrication of nitrogen-doped graphene nanostructures." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS346/document.
Повний текст джерелаАнотація:
La synthèse de graphène par approche « bottom-up » fait l’objet de nombreux travaux de recherche ayant pour but de contrôler les propriétés électroniques et optiques de ce matériau par la fabrication de nanostructures avec une précision atomique. D’autre part, le contrôle de dopant dans le graphène permettant d’en moduler les propriétés suscite un grand intérêt et dans ce contexte l’utilisation de porphyrines avec un taux d’azote contrôlé est attrayante. Par leurs ressemblances structurelles, les porphyrines π-étendues peuvent être considérées comme des nanoparticules de graphène dopées à l’azote (GQDs) présentant de fortes propriétés infrarouge tandis que les briques de construction à base de porphyrines peuvent être utilisées pour la synthèse sur surface de deux type de nanoarchitectures de graphene appélées nanorubans (GNRs) et nanomèches (GNMs). Cette thèse a pour objectif de développer la synthèse de porphyrines à base d’anthracenes et de les utiliser comme précurseurs pour la fabrication de nanostructures. La première partie de cette thèse est dédiée à la synthèse organique de différentes anthracenylporphyrines et à l’étude de leurs assemblages sur surface dans la chambre d’un microscope à effet tunnel. La seconde partie est dédiée à l’étude de formation de porphyrines π-étendues via une méthode pyrolyse flash pouvant activer thermiquement des réactions de couplage par déhydrogenation entre des hydrocarbures aromatiques polyycliques (PAHs) et des porphyrines. La dernière partie est dédiée à la modification post synthétique d’une tetrabromoanthracenylporphyrine par addition de PAHs via la réaction de couplage de Suzuki-Miyaura et à la caractérisation des propriétés optiques de ces porphyrines nouvellement forméesThe synthesis of graphene via bottom-up approach is a hot topic of research that aims to control the electronic and optical properties of this material by the fabrication of atomically precised nanostructures. Moreover, the control of dopant in graphene is of great interest to modulate the properties of the material. In this context, the contribution of porphyrins with a controlled content of nitrogen is attractive in this context. Because of structural similarities with graphene quantum dots (GQDs), π-extented porphyrins can be regarded as nitrogen-doped GQD with promising NIR properties. Porphyrins are convenient building blocks for the synthesis on surface of nanoarchitectures of graphene called nitrogen-doped Graphene Nanoribbons (GNRs) and Graphene NanoMeshes (GNMs). This thesis aims to develop the synthesis of symmetrical and robust porphyrins with anthracenes and to use them as precursors for the fabrication of nanostructures. The first part of this thesis is dedicated to the organic synthesis of variety of anthracenylporphyrins and the study of their assemblies on surface in a chamber of a Scanning Tunneling Microscope. The second part is dedicated to the study of formation of π-extended porphyrins via a method of flash pyrolysis able to thermally activate dehydrogenative coupling reactions between Polycyclic Aromatic Hydrocarbons (PAHs) and porphyrins. The last part is dedicated to the post synthetic modification of a tetrabromoanthracenylporphyrin with additional PAHs via Suzuki-Miyaura coupling and the characterization of the optical properties of the resulting porphyrins
16
Chu, Hua-Wei. "Development of solution-processed methods for graphene synthesis and device fabrication." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44738.
Повний текст джерелаАнотація:
Various solution-processed methods have been employed in this work. For the synthesis of graphene, a chemical exfoliation method has been used to generate large graphene flakes in the solution phase. In addition, chemical or electro polymerization has been used for synthesizing polyanthracene, which tends to form graphene nanoribbon through cyclodehydrogenation. For the device fabrication, graphene oxide (GO) thin films were deposited from solution phase on the vapor-silanzed aminosilane surface to make semiconducting active layer or conducting electrodes. Gold nanoparticles (AuNPs) were selectively self-assembled from solution phase to pattern nanowires.
17
Risley, Mason J. "Surfactant-assisted exfoliation and processing of graphite and graphene." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/48980.
Повний текст джерелаАнотація:
Surfactant assisted solution exfoliation of expanded graphite by means of sonication was carried out in an attempt to produce non-covalent charge functionality on the surface of graphene for the directed self assembly of graphene films on patterned substrates via electrostatic interactions. This thesis includes the results of experimental research associated with: 1) quantifying the effectiveness of various di-functionalized dithienothiophene surfactant small molecules, 2) further understanding the surface affinity and interaction mechanism between these surfactant molecules and the surface of expanded graphite and graphene and 3) experimentally testing the feasibility of the directed self-assembly of graphene films by means of charge functionalization of graphene by the surfactant molecules adsorbed onto the surface of exfoliated graphene.
18
Hong, Jeongmin. "Characteristics of graphitic films for carbon based magnetism and electronics." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1957308731&SrchMode=2&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1269014102&clientId=48051.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 19, 2010). Includes bibliographical references. Also issued in print.
19
Belchi, Raphaëlle. "Architectures à base de nanostructures de carbone et TiO₂pour le photovoltaïque." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS329/document.
Повний текст джерелаАнотація:
Le photovoltaïque est une énergie renouvelable pouvant aider à lutter contre le réchauffement climatique et l’épuisement des ressources fossiles utilisées pour la production d’énergie. La filière émergente à base de matériaux pérovskites (photovoltaïque de 3ème génération) est très prometteuse car elle utilise des matériaux abondants et faciles à mettre en œuvre (technologie bas-coût) et a montré de plus des rendements record compétitifs en peu de temps. Il reste cependant des verrous technologiques à lever afin de pouvoir développer cette technologie à grande échelle. L’un deux consiste à améliorer la couche de TiO₂ qui transporte les électrons et dont les défauts limitent les performances et la durée de vie des cellules photovoltaïques pérovskites. Ce travail propose l’utilisation de matériaux à base de nanostructures de carbone et de TiO₂ pour améliorer le transport et la collecte des électrons au sein de ces cellules photovoltaïques et ainsi améliorer leur rendement. Pour cela, la pyrolyse laser, technique singulière de production continue de nanoparticules, a été adaptée pour l’élaboration de nanocomposites TiO₂/graphène aux propriétés contrôlées. Ces matériaux ont été caractérisés puis intégrés aux cellules photovoltaïques pérovskites qui ont démontré une meilleure efficacité en présence de graphène. Par ailleurs, ce travail présente une architecture innovante à base de nanotubes de carbone alignés verticalement, en vue d’une application pour la collecte des électrons photo-générés des cellules photovoltaïques pérovskites. Les matériaux carbonés présentent donc de fortes potentialités pour l’optoélectronique, et plus particulièrement pour le photovoltaïque de 3ème générationPhotovoltaic is a promising renewable energy to tackle global warming and the depletion of fossil resources. The emerging field of perovskite solar cells (3rd generation photovoltaic) is very attractive because it uses abundant and easy-processing materials (low-cost technology) and provides competitive efficiencies.Still, efforts remain to be performed to develop this technology, especially concerning the improvement of efficient and reliable charge transporting electrodes. Titanium dioxide layer, commonly used for electron extraction, presents defects that limit the performance and lifetime of the perovskite solar cells.This work proposes the use of materials based on TiO₂ and carbon nanostructures to improve the electron transport and collection within the solar cells, in order to enhance the power conversion efficiency. The singular technique of laser pyrolysis, which is a continuous process of nanoparticles synthesis, was adapted to produce TiO₂/graphene nanocomposites with well-controlled properties. These materials have been characterized and integrated into perovskite solar cells that demonstrate an improved efficiency in presence of graphene.Besides, this work presents an innovating architecture based on vertically aligned carbon nanotubes for the electron collection of a perovskite solar cell. We show then the strong potential of carbon materials for optoelectronic, especially 3rd generation photovoltaic
20
Song, Zhimin. "Fabrication and Characterization of Nanopatterned Epitaxial Graphene Films for Carbon Based Electronics." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13943.
Повний текст джерелаАнотація:
In this thesis, we show that planar graphene ribbons have properties similar to those of nanotubes. Both exhibit semiconducting or metallic properties depending on crystal orientation. The band gap varies approximately as the inverse of the ribbon width. Both can be doped and gated. Due to these similarities, the patterned graphene also has nanotube like transport properties, which include coherent transport, ballistic transport, and high current capabilities. In essential contrast to nanotubes, graphene ribbons can be rationally patterned using standard electron beam lithography methods; functional graphene devices could be fabricated eliminating the need for metal interconnects on the wafer. This would remove many obstacles faced by carbon nanotubes, while retaining the benefits of high carrier mobility and quasi-1D transport.
We have produced ultrathin epitaxial graphite films on single-crystal silicon carbide by vacuum graphitization, which show remarkable 2D electron gas (2DEG) behavior. The most highly ordered samples exhibit Shubnikov-de Haas oscillations that correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nanopatterned epitaxial graphene (NPEG) with the potential for large-scale integration. The research created a foundation for graphene science and technology and established a path toward graphene-based nanoelectronics.
21
Rodriguez-Nieva, Joaquin F. (Joaquin Francisco). "Novel electronic behaviors in graphene nanostructures." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107041.
Повний текст джерелаАнотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 167-185).
Recently, it has been shown that graphene can be combined with a variety of nanoscale systems, such as other two-dimensional crystals, to form novel electronic nanostructures. These systems inherit the unique characteristics of graphene, such as high mobility, Berry phase, photoresponse mediated by hot carriers, and at the same time acquire new features due to nanoscale heterogenities. In this thesis, I explore the novel electronic behaviors which emerge in this fashion. I focus on two types of systems: (i) vertically-stacked structures in which graphene layers are interspaced with insulating materials and (ii) in-plane structures formed by spatially-varying electrostatic potentials in graphene. The outline of this thesis is as follows: first, I show that the vertical structures grant access to distinct transport behaviors and new kinds of photoresponse. Those include, in particular, photo-induced negative differential resistance, bistability, and hysteretic I-V characteristics. This wide variety of behaviors is enabled by a number of interesting physical phenomena which can be accessed in these structures, such as resonant tunneling, thermionic emission and field emission. I explore the different knobs which are available to control these phenomena and new ways to employ them to design the I-V response. Second, I study in-plane nanostructures such as pn junction rings induced by local charges, and show that they enable confinement of electronic states in graphene. Confined states in these graphene quantum dots arise due to constructive interference of electronic waves scattered at the pn junction and inward-reflected from the ring by the so-called Klein scattering process. Key fingerprints of confined states are resonances appearing periodically in scanning tunneling spectroscopy maps. Besides the novel mechanism for confinement, I also demonstrate that graphene quantum dots can be exploited for accessing exotic and potentially useful behavior which is not available in conventional quantum dots. An example of such behavior is a giant non-reciprocal effect of quantum dot resonances which is induced by the Berry phase. Third, I study manifestations of defects in the Raman spectral maps of disordered graphene systems. Two salient Raman features, namely the D and D' bands, provide useful information about the nature of defects. I perform a detailed analysis of the origin of the Raman scattering cross section which is routinely measured in experiments and discuss how it can be used to obtain information about defects. Overall, this thesis demonstrates the versatility of graphene nanostructures. This is manifested in numerous phenomena which have implications both in basic science, e.g. Berry phase effects, as well as in applied research, e.g. photodetection in graphene Schottky junctions. Furthermore, several of the ideas discussed here can be extended to achieve other interesting and potentially useful effects, such as localized valley-polarized states in graphene quantum dots and exciton confinement.
by Joaquin F. Rodriguez-Nieva.
Ph. D.
22
Hu, Tao. "Non-covalent functionalization of carbon nanostructures : a DFT study." Thesis, Toulouse, INSA, 2013. http://www.theses.fr/2013ISAT0011/document.
Повний текст джерелаАнотація:
Le dopage non covalent de nanostructures carbonées par transfert de charge depuis/vers des molécules donneuses ou acceptrices (EDA) ou bien par des molécules d’acide sulfurique H2SO4, est considéré comme potentiellement intéressant pour de nombreuses applications. Parmi celles-ci on peut citer: capteur chimique, transistor à effet de champ, et d’autre l'électronique. Cependant, d'un point de vue théorique, on en sait peu au sujet de ces processus de transfert de charge par électrons ou par trous.Dans un premier temps, nous nous sommes intéressés à l’interaction entre des molécules d’acide sulfurique et des nanostructures modèles, car elles sont capables de doper des nanotubes, de s’intercaler dans le graphite et même d’aligner les tubes dans une phase nématique, ce qui pourrait mener à la création de matériaux composites à forte valeur ajoutée.Bien que certaines études théoriques DFT ont été menées récemment, leurs résultats restent source de confusion. Par exemple, même s’il est rapporté un transfert de charge entre une molécule de H2SO4 et un plan de graphène, tous nos efforts pour reproduire ces calculs ont été infructueux. Nous proposons dans ce travail de thèse, un mécanisme de réaction qui expliquent la "protonation" des parois du tube, tel que proposé dans la littérature. Enfin nous proposons un scénario possible pour une meilleure compréhension de la structuration à grande échelle des molécules d'acide autour de points d'ancrage, telles que des défauts, de la structure carbonéeNon-covalent doping of carbon nanostructures by charge transfer from/to donor/acceptor molecules (EDA) or by H2SO4 molecules, be it with holes or electrons, is usually thought as potentially interesting for many applications of carbon based nano-devices. However, from a theoretical point of view, little is known about such “charge transfer” processes.Employing first-principles method based on Density Functional Theory (DFT), we have studied in details, and proposed a model to rationalize, the interaction between a prototypical donor molecule the tetrathiafulvalene (TTF), a standard acceptor organic molecule, tetracyanoethylene (TCNE) and carbon nanostructures: graphene layer and SWNTs with various chiral indices. Main results concern structural and thermodynamic aspects including dispersion forces effects, and evidently electronic structure modifications of the nanostructures. Various adsorption modes and concentration effects have been investigated. At very low coverage values, we have reported a charge transfer between graphene and TCNE or TTF. Moreover, we have shown that the charge transfer can be enhanced by increasing the concentration of those two EDA molecules, as it has been demonstrated experimentally. Those results are beneficial for comprehending the nonchemical doping mechanism in graphene structure by means of charge transfers. Considering the interaction between these prototypical molecules and carbon nanotubes, we have found that charge transfers tend to decrease while the curvature of nanotube is increasing. Besides, a strong influence of the metallic/semi-conductor character of the SWNTs can be observed and be explained by the change of polarisability of the curved carboneous substrates. Additionally, we have studied the adsorption properties of sulfuric acid molecules, in its non-hydrated form, on carboneous nanostructures. Against the common believe, no charge transfer is observed in the H2SO4@graphene or H2SO4@CNTs cases, even at very high concentrations. Instead, in order to elucidate the origin of p-doping observed experimentally, we have proposed that molecule is responsible of the reversible doping. Besides we have shown that a proton transfer could cause the experimental phenomenon of crystallization of H2SO4 molecules on SWNT’s surface. Finally in such process, defects like vacancy are of first importance, since they could provide anchorage points for hydrogen atoms. The results of the present work will certainly help to understand the charge transfer and doping mechanism of carbon nanostructures by means of non-covalent functionalization, which is a promising method for their future applications
23
Gao, Pengcheng. "Matériaux carbonés nanostructurés pour supercapacités électrochimiques." Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20028/document.
Повний текст джерелаАнотація:
Différents matériaux carbonés nanostructurés ont été synthétisés et mis en oeuvre comme matériaux supercapacitifs à double couche électrochimique (EDLC) ou comme substrats de matériaux pseudocapacitifs avec pour objectif d'augmenter leur densité de puissance. Nous avons ainsi développé une méthode de synthèse simple et originale de carbures de silicium (SiC) qui procède par une réduction topotactique d'un composite silice/carbon par le magnésium. Du fait de la température de synthèse inférieure à 800°C, SiC résultant conserve la morphologie et/ou la structure poreuse du précurseur composite. Par cette approche, nous pouvons moduler la structure poreuse ordonnée de SiC à façon, développer des porosités hiérarchiques méso/macro, préparer des feuillets ou des fibres de SiC. Les différentes formes de SiC ont été converties par chloration en autant de carbones, opération introduisant une microporosité supplémentaire. En électrolyte organique, ces carbones à porosité hierarchique combinent à la fois des capacités importantes issues de la microporosité mais également des performances inégalées en terme de puissance du fait de la méso ou macro-porosité associée. Dans une approche différente, des feuillet de graphène ont été décorés par voie sol-gel non-hydrolytique (micro-onde en milieu alcool benzilique) par des nanoparticules de FeOx. Le composite FeOx/graphene résultant combine simultanément les comportements EDLC et pseudocapacitif du graphène et de FeOx. Du fait de sa structure particulière, le composite FeOx/graphene conserve les performances en puissance du graphène auxquelles s'ajoutent celles d'énergie de FeOx. Nous avons également décoré des nanofibres de carbone avec des carbones mésoporeux. Après dépôt de MnO2 birnessite, les composites gagnent à la fois en capacité et en puissance en particulier avec des carbones présentant des pores supérieurs à 10nmVarious nanostructured carbon materials were synthesized and further served as active materials of electrical double layer capacitor or substrates of pseudocapacitive materials in order to improve power capability of corresponding supercapacitor. On the one hand, a simple synthesis of porous silicon carbides (SiCs) was achieved by performing a topotactic thermal reduction by magnesium (Mg) of a silica/ carbon composite. Thanks to the low synthetic temperature (below 800 ºC), the SiCs well preserved the pristine skeletons of their silica/carbon precursors. Successively, the SiCs with diverse porous structures from their silica/carbon precursor emerged, e.g. ordered tunable mesoporous SiCs, 3D-hierarchical meso and macroporous SiC, SiC nanosheet and SiC nanofiber. Furthermore, the porous SiCs derived from magnesio-thermal reduction were reduced to hierarchical carbons with newborn narrow distributed microporosity by chlorination. In an organic electrolyte, the hierarchical carbon combines the high specific capacitance from narrow distributed microporosity and the outstanding rate capability from ordered-arranged meso or macroporosity that make it promising for high power and energy density capacitor. On the other hand, a “benzyl alcohol route” has been used to decorate RGO nanosheets with FeOx nanoparticles. The resulting FeOx/ RGO composite, due to their hybrid nanostructure, combine both EDLC capacitive and pseudocapacitive bahaviors of RGO and FeOx, respectively. Thanks to the laminated RGO and nano FeOx particles film, the resulting composite gains the same power capability as RGO and a higher energy density than raw FeOx. Furthermore, mesoporous carbon was introduced to adorn the CNF surface through self-assemble of resol, carbon nanofiber(CNF) and Pluronic@127. After further coating with birnessite-MnO2, the composite electrode gains extra capacitance and power improvement in presence of superficially coating mesoporous carbon with pore size larger than 10nm
24
Förster, Georg Daniel. "Modélisation atomique de nanoparticules métalliques sur substrats carbonés et graphène épitaxié sur métaux." Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10150/document.
Повний текст джерелаАнотація:
Les applications des nanoparticules métalliques nécessitent des assemblées monodisperses et stables sur un substrat tel que le graphène ou le graphite. Le graphène épitaxié sur métal (GEM) est étudié, car il facilite l'auto-organisation des adsorbats. La différence entre les mailles du graphène et du métal conduit à un effet de moiré contenant certaines régions favorables de l'adsorption. Ce travail est consacré surtout aux systèmes Ru-C et Pt-C où nous nous sommes intéressé au substrat du GEM nu, des agrégats y etant deposés et des agrégats métalliques sur graphite. Les potentiels d'ordre de liason permettent de mener des études en dynamique moléculaire sur des systèmes de taille réaliste à température finie. Dans le cas du système Pt-C une paramétrisation est disponible dans la littérature. Cependant, pour le système du Ru-C une paramétrisation sur la base de données DFT était nécessaire. Ce modèle atomistique néglige les forces de dispersion importantes pour des milieux étendus. Basé sur les modèles de Grimme, nous avons développé une description implicite tenant compte de la structure du substrat et son extension semi-infinie. De plus les effets d'écrantage importants pour des milieux métalliques sont pris en compte. Basé sur ce champ de force nous montrons des propriétés des adsorbats sur des substrats carbonés où nous évaluons le modèle de forces de dispersion. Grâce à des simulations de dynamique moléculaire, la stabilité des adsorbats et du graphène a été étudié dans le contexte de la dynamique vibrationnelle et de diffusion. En accord avec les expériences, la mobilité des adsorbats sur graphite s'avère élevée en comparaison avec des adsorbats sur GEMApplications of metal nanoparticles require monodisperse and stable assemblies on a substrate such as graphene or graphite. Epitaxial graphene on metal (GOM) has attracted research interest because it contributes to the self-organisation of adsorbates. The difference in the lattice constants of graphene and metal leads to a moiré that contains certain regions that are favorable for adsorption. This work is mainly concerned with the Ru-C and Pt-C systems where we were interested in the bare substrate of GOM, adsorbates deposited thereon and metal clusters on graphite. Bond order potentials allow to carry out molecular dynamics studies for systems of realistic size and at finite temperature. In the case of the Pt-C, a parametrization is available in the literature. However, for Ru-C systems a custom parametrization effort based on data from electronic structure calculations was necessary. This atomistic model neglects long ranged dispersion forces that are important for adsorption phenomena on extended substrates. Based on the Grimme models, we developed an implicit description that takes the layered structure and the semi-infinite extension of the substrate into account. Also, screening effects that are important for metal materials are taken into account. Based on this force field, we show results concerning the properties of adsorbates on carbon substrates while evaluating the dispersion model. With the help of molecular dynamics simulations, the stability of adsorbates and graphene has been studied in the context of vibrational and diffusion dynamics. In agreement with experiments, the mobility of the adsorbates on graphite is high in comparison with adsorbates on GOM
25
Huppert, Simon. "Transport non-linéaire et génération Terahertz dans des systèmes bidimensionnels sous forte irradiation optique." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066217/document.
Повний текст джерелаАнотація:
Cette thèse traite de comportements non-linéaires dans deux types de systèmes bidimensionnels différents: les hétérostructures semiconductrices ainsi qu'un matériau monocouche, le graphène. Elle comporte deux axes principaux: l'étude de la quantification de Wannier-Stark dans les super-réseaux de puits quantiques biaisés électriquement, et la modélisation d'effets nouveaux pour la génération de rayonnement électromagnétique dans le domaine Terahertz. Dans les super-réseaux de puits quantiques soumis à une tension externe, le champ électrique induit un confinement bidimensionnel des porteurs de charge nommé quantification de Wannier-Stark. On modélise deux conséquences originales de cette quantification: d'une part, les fortes non-linéarités de photocourant dans un super-réseau placé entre deux barrières tunnel épaisses, et d'autre part, la possibilité de contrôler électriquement le couplage lumière-matière et le gain dans la gamme Terahertz dans un super-réseau biaisé couplé à une microcavité planaire. Dans un second temps, on étudie quantitativement deux effets non-linéaires nouveaux pour la génération Terahertz. Le premier est l'exaltation de l'émission Terahertz dans un système polaritonique en régime de laser à polaritons. On modélise précisément cet effet et on propose un nouveau dispositif utilisant une microcavité double et permettant de réduire très significativement les pertes par diffusion. Le second effet étudié est le transfert d'impulsion photonique dans le graphène sous excitation impulsionnelle. On construit un modèle microscopique prédictif de ce phénomène qui permet de déterminer les paramètres importants pour l'optimisation de l'impulsion Terahertz générée. Ce travail théorique a été mené en étroite collaboration avec plusieurs équipes expérimentalesThis thesis treats of nonlinear behaviors in two different types of bidimensional systems: semiconductor heterostructures as well as a monolayer material, graphene. It consists into two main parts: the study Wannier-Stark quantification in electrically biased quantum well superlattices, and the modelling of new effects for electromagnetic wave generation in the Terahertz range. In quantum well superlattices under an external voltage, the electric field induces bidimensional confinement of the charge carriers, this effect is known as Wannier-Stark quantification. We examine two interesting consequences of this confinement: the strong photocurrent nonlinearities induced when the superlattice is placed between thick tunnel barriers, and the possibility to control light-matter coupling as well as Terahertz gain in superlattices coupled to a semiconductor microcavity. In a second part of this work, we study quantitatively two new nonlinear effects for Terahertz generation. The first one is Terahertz emission exaltation in a polaritonic system reaching the polariton lasing regime. We model precisely this effect and suggest a new scheme using a double microcavity and providing very significant reduction of the diffusion losses. The second effect is photon drag in graphene under pulsed excitation. We build a microscopic and predictive model for this phenomenon which provides a comprehensive insight on the relevant parameters for the optimisation of the Terahertz generation. This theoretical work was done in tight collaboration with several experimental groups
26
Musheghyan, Avetisyan Arevik. "Synthesis and characterization of multilayer graphene nanostructures." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667645.
Повний текст джерелаАнотація:
The goal of the present investigation is to examine the processing-structure-property relationships of multilayer graphene nanowall materials. Various plasma enhanced chemical vapor deposition (PECVD) processing parameters were altered to control the structure and morphology of the material. Growth parameters and substrate material were the major structural features studied, and these were characterized by spectroscopic techniques. The direct synthesis of graphene without catalysis on dielectric substrates, compatible with the complementary metal oxide semiconductor technology, is a stimulating but complex task.
The goal of the thesis has different tasks consisting of:
a) The design and construction of a new inductively coupled plasma remote chemical vapor deposition reactor in the PECVD-FEMAN laboratory of the Universitat de Barcelona.
b) Fabrication of vertical graphene nanostructures at low temperature on different conductive and nonconductive substrates.
c) Characterization of the vertical graphene obtained through different synthesis parameters in order to optimize their physical and surface properties; such as structural and morphological studies by Raman spectroscopy, SEM and TEM.
d) Functionalization of MLGNWs by MnO nanoparticles for hybrid supercapacitor systems.
The thesis consists of the following main parts:
In the first part of the thesis provides a brief introduction of carbon materials, graphene, graphene nanowalls and their history, discovery, outstanding properties and all the technologies that prompted their development during these years until the first application. Moreover, in this section the methods for the synthesis of carbon nanostructures and brief explanation of the fundamentals of each technique explains.
In the second part the concepts and technologies of plasma, plasma enhanced chemical vapor deposition (PECVD) and PECVD related techniques are exposed. In addition, in this section a deposition reactor designed by us are described, where all experiments carried out during this thesis took place. Also, the basics and work principles of different characterization techniques are briefly described. Furthermore, this part discusses the growth mechanism of MLGNWs synthesized by PECVD.
In the third part, which is the main results part, discusses the study of growing material along the entire length of the tube and the importance of sample location inside a tubular quartz reactor. The influence of the substrate material, growth time and growth temperature on the MLGNWs growth process have been examined by field emission scanning electron microscopy (FESEM),
transmission electron microscopy (TEM) and high resolution TEM (HRTEM) techniques. The chemical characteristics of as grown structures were studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectrometer. The hydrogen and carbon contents in grown samples were determined by elemental analysis (EA). To study the photoluminescent properties of the carbon structure grown in the whole length of the tubular reactor, the room temperature PL spectra were conducted. In addition, the chemical reactions inside the tube under plasma deposition were controlled by optical emission spectroscopy (OES).
Also, in the part of results synthesis and characterization of MLGNWs/CNTs hybrid structure are discussed. The goal of MLGNWs/CNTs hybrid structure is increased chemical activity of CNTs. The morphological and structural characterization was carried out using SEM, High resolution TEM and Raman scattering analysis. Electrochemical properties of transferred MLGNWs/CNTs were studied by CV and charge/discharge measurements.
The last section of the part of the results are exposed information about application of MLGNWs in supercapacitors, in particular, supercapacitive performance of manganese dioxide/ graphene nanowalls electrodes deposited on stainless steel current collectors and annealing temperature effect are discussed. Composite electrodes MLGNWs/MnO2 were characterized by FESEM and Raman shift spectroscopy. The electrochemical properties of the MLGNWs/MnO2 for supercapacitor applications were investigated by cyclic voltammetry (CV), charge/discharge and electrochemical impedance spectroscopy (EIS). The influence of annealing temperature on the electrochemical performance has been studied as well.El grafeno, como material basado en el carbono, es un logro del desarrollo y los avances de la Nanotecnología. La síntesis directa de grafeno sin catálisis sobre sustratos dieléctricos, compatible con la tecnología de los semiconductores complementarios de óxido metálico, es una tarea estimulante pero compleja. La técnica PECVD, permite la síntesis directa de nanoestructuras de carbono a temperaturas más bajas y es el método principal utilizado en esta tesis. El objetivo de esta tesis es la síntesis y optimización de nanoparedes verticales de grafeno y su posible extensión a aplicaciones en sistemas que requieran superficies macroscópicas. Para ello, se han realizado diferentes tareas: a) Se ha diseñado y construido un reactor prototipo con plasma remoto en el laboratorio PECVD-FEMAN de la Facultad de Física (Universidad de Barcelona) con el fin último de crecer grafeno en forma de paredes/tabiques verticales nanométricos mediante la técnica PECVD. b) Se ha desarrollado un proceso PECVD modificado con el fin de mejorar los resultados actuales en términos de: 1) el tiempo de crecimiento, 2) la temperatura, 3) la naturaleza del substrato, 4) la presión, y 5) la cantidad de gas precursor para crecer grafeno vertical. Las muestras obtenidas fueron caracterizadas mediante microscopía TEM, SEM, XPS, XRD y mayormente mediante espectroscopia Raman, con el objetivo de optimizar el proceso y las propiedades físico-químicas y del grafeno vertical. c) Se ha desarrollado una estructura híbrida con nanoparedes y nanotubos de carbono. Para ello, se utilizaron tres equipos: el reactor “PEDRO” para la preparación del substrato, el reactor “CNTs” para el crecimiento de nanotubos de carbono y el reactor ICP-CVD para el crecimiento de nanoparedes de grafeno. En esta tesis se investigaron las caracterizaciones morfológicas y electroquímicas, pero aún se necesitan más estudios para confirmar posibles futuras aplicaciones. d) Para mejorar las propiedades de los supercapacitores basados en los electrodos desarrolladas con nanoparedes de grafeno y acero inoxidable, se ha realizado el crecimiento de capas delgadas de MnO2 mediante el método de electrodeposición. El efecto de la temperatura de recocido (annealing) en las propiedades electroquímicas de las muestras se ha estudiado en el rango de 70° C a 650° C.
27
Poole, Christopher J. "Electronic and transport properties of graphene nanostructures." Thesis, Lancaster University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.654742.
Повний текст джерела
28
MANGADLAO, JOEY DACULA. "Multifunctional Materials from Nanostructured Graphene and Derivatives." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1448279230.
Повний текст джерела
29
Zedan, Abdallah. "GRAPHENE-BASED SEMICONDUCTOR AND METALLIC NANOSTRUCTURED MATERIALS." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/457.
Повний текст джерелаАнотація:
Exciting periods of scientific research are often associated with discoveries of novel materials. Such period was brought about by the successful preparation of graphene which is a 2D allotrope of carbon with remarkable electronic, optical and mechanical properties. Functional graphene-based nanocomposites have great promise for applications in various fields such as energy conversion, opteoelectronics, solar cells, sensing, catalysis and biomedicine. Herein, microwave and laser-assisted synthetic approaches were developed for decorating graphene with various semiconductor, metallic or magnetic nanostructures of controlled size and shape. We developed a scalable microwave irradiation method for the synthesis of graphene decorated with CdSe nanocrystals of controlled size, shape and crystalline structure. The efficient quenching of photoluminescence from the CdSe nanocrystals by graphene has been explored. The results provide a new approach for exploring the size-tunable optical properties of CdSe nanocrystals supported on graphene which could have important implications for energy conversion applications. We also extended this approach to the synthesis of Au-ceria-graphene nanocomposites. The synthesis is facilely conducted at mild conditions using ethylenediamine as a solvent. Results reveal significant CO conversion percentages between 60-70% at ambient temperatures. Au nanostructures have received significant attention because of the feasibility to tune their optical properties by changing size or shape. The coupling of the photothermal effects of these Au nanostructures of controlled size and shape with GO nanosheets dispersed in water is demonstrated. Our results indicate that the enhanced photothermal energy conversion of the Au-GO suspensions could to lead to a remarkable increase in the heating efficiency of the laser-induced melting and size reduction of Au nanostructures. The Au-graphene nanocomposites are potential materials for photothermolysis, thermochemical and thermomechanical applications. We developed a facile method for decorating graphene with magnetite nanocrystals of various shapes (namely, spheres, cubes and prisms) by the microwave-assisted-reduction of iron acetylacetonate in benzyl ether. The shape control was achieved by tuning the mole ratio between the oleic acid and the oleyamine. The structural, morphological and physical properties of graphene-based nanocomposites described herein were studied using standard characterization tools such as TEM, SEM, UV-Vis and PL spectroscopy, powder X-ray diffraction, XPS and Raman spectroscopy.
30
Berrahal, Quentin. "Étude par STM de nanostructures métalliques dans le graphène : croissance, propriétés et défauts induits." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7030.
Повний текст джерелаАнотація:
Le graphène, premier cristal purement bidimensionnel à avoir été obtenu, possède des propriétés électroniques uniques grâce à sa structure de bande en « cône de Dirac ». Au-delà des modifications et du contrôle de ses propriétés intrinsèques, il est aujourd’hui crucial d’étudier ses interactions avec divers environnements afin de créer de nouvelles applications : fonctionnalisation par des molécules, utilisation en tant que substrat pour des molécules ou des atomes métalliques, création de défauts structuraux ou chimiques, élaboration de multicouches à l’aide d’autres matériaux quasi-bidimensionnels (hétérostructures de type Van der Waals)Graphene, the first purely bidimensionnal crystal to be obtained holds unique electronic properties thanks to its "Dirac cones" band structure. Beyond the possible modifications of its intrinsic properties, it is now crucial to study its interactions with a diverse set of environments to create new applications: molecules functionnalization, as a substrate for molecules or metal adatoms, chemical or structural defect engineering or crafting of multilayered new materials such as van der Waals heterostructures.From a fundamental point of view, graphene synthesised on silicon carbide (SiC) is ideal. It provides a subtrate suited for scanning tunneling microscopy (STM) and physical deposition of metals as its synthesis takes place under vacuum through the evaporation of silicon.We studied the Gr/SiC(000-1) (carbon-rich face) at the local scale using STM and tunnel spectroscopy (STS) to analyse on one hand the effect of metal deposition on the graphene as a substrate and on the other hand the effects of the same deposition before the synthesis on the creation of defects in the graphene
31
Ghosh, Suchismita. "Thermal conduction in graphene and graphene multilayers." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1957308711&SrchMode=2&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1268427434&clientId=48051.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 12, 2010). Includes bibliographical references (p. 96-107). Also issued in print.
32
Espeland, Erlend. "Gold Nanostructures on Graphite." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22433.
Повний текст джерелаАнотація:
Gold nanoparticles supported on a graphite substrate are prepared by thermal evaporation, and subsequently studied by X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) of carbon monoxide and scanning electron microscopy (SEM).Increasing the amount of gold deposited leads to a shift of the desorption peak to higher temperatures, and the gold particles become larger.Depositing approximately the same amount of gold at different evaporation ratios does not seem to affect the desorption.Triangularly shaped gold particles appeared at higher evaporation rates.This is thought to be caused by diffusion effects dominating the formation of the particles.
33
Gong, Chuncheng. "Atomic structure and dynamics study of defects in graphene by aberration-corrected transmission electron microscope." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:53bd9a04-71ad-4da8-b982-cb45a005e791.
Повний текст джерелаАнотація:
Graphene has grabbed enormous research attention due to its multiple unique properties. These properties, however, can be strongly influenced by lattice imperfections. Aberration corrected transmission electron microscopy (AC-TEM) is one of the leading methods to image two-dimensional materials at the atomic level. This thesis addresses the issue of structure and dynamics characterization of dislocations and grain boundaries (GBs) in graphene with single atom sensitivity using the state-of-the-art AC-TEM in Department of Materials, University of Oxford. My first goal is to understand the interaction between dislocation and the edge of graphene. When a dislocation is located near an edge, a decrease in the rippling and increase of the in-plane rotation occurs relative to the dislocations in the bulk. The increased in-plane rotation near the edge causes bond rotations at the edge of graphene to reduce the overall strain in the system. Dislocations are highly stable and remain fixed in their position even when located within a few lattice spacings from the graphene edge. With the aid of an in situ heating holder, the high temperature behavior of dislocations is then investigated. Control of temperature enables the differentiation of electron beam induced effects and thermally driven processes. An analysis of the dislocation movement shows both climb and glide processes, including new complex pathways for migration and large nanoscale rapid jumps between fixed positions in the lattice. The improved understanding of the high temperature dislocation movement provides insights into annealing processes in graphene and the behavior of defects with increased heat. The in situ heterogeneous nucleation and growth of graphene are also studied within the AC-TEM. The growth mechanism consists of alternating carbon cluster attachment and indentation filling to maintain a uniform growth front of lowest energy. The highly polycrystalline graphene seed is found to evolve with time into a higher order crystalline structure. The motion of GBs is discontinuous and mediated by both bond rotation and atom evaporation. These results provide insights into the formation of crystalline seed domains that are generated during bottom-up graphene synthesis. Finally, the formation, reconfiguration and annihilation of GB loops are demonstrated. It is shown that the GB loop cannot fully relaxed under electron beam irradiation with its terminal state being isolated dislocations far apart from each other. Line defects composed of several adjacent excess-atom defects can be found during the reconfiguration process. This work gives detailed information about the stability and behavior of large GB loops in two dimensional materials.
34
Jean, Fabien. "Growth and structure of graphene on metal and growth of organized nanostructures on top." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY097/document.
Повний текст джерелаАнотація:
Le graphène, une monocouche de graphite, est composé d'atomes de carbone avec une structure en nid d'abeilles. Ses propriétés exceptionnelles ont attiré un intérêt mondial, dont le Prix Nobel de Physique en 2010. Le graphène épitaxié sur métal à rapidement été identifié comme un moyen de production de graphène de haute qualité de taille métrique, et est le sujet d'intenses activités de recherche en sciences de surface pour caractériser ses propriétés. En outre, ces études concernent aussi des systèmes plus complexes avec pour base le graphène, par exemple les réseaux ordonnés de nanoparticules à sa surface. Tout cela a mené à l'étude de la croissance, de la structure et des défauts du graphène épitaxié avec un grande variété de techniques expériementales, tel que la microscopie par effet tunnel, spectroscopie par photo-émission résolue en angle ou encore la microscopie électronique à basse énergie. Ce travail de recherche se concentre sur le graphène obtenu par croissance sur la surface (111) d'un monocristal d'iridium dans des conditions d'ultra vide et étudié avec plusieurs techniques de mesure par diffraction (diffraction de surface des rayons X, diffraction des rayons X en incidence rasante, réflectivité des rayons X et diffraction des électrons à haute énergie en réflexion). Ces expériences ont été faites au synchrotron européen ESRF à Grenoble, en France. La première partie de cette étude a été de déterminer la structure du graphène à l'échelle atomique. Le système montre une tendance à la commensurabilité, mais sa structure précise dépend fortement des conditions de préparation et de la température appliqué au système. En outre, en combinant des techniques de diffraction à haute résolution, une caractérisation précise de la structure, qui fait débat dans la littérature, est dévoilée. Le système étudié présente aussi une surperstructure, typique du graphène épitaxié, nommé moiré pour ses similarités avec l'effet optique du même nom. Celle-ci est utilisée comme gabarit pour faire croître des nanoparticules monodisperses à la surface en réseau auto-organisé. Durant cette étude, trois types de nanoparticules ont été examinés, des particules de platine de deux tailles différentes et des particules composées de platine et de cobalt. Ces systèmes hybrides présentent un fort degré d'organisation, partiellement hérité de la superstructure du moiré. Les nanoparticules forme une interaction forte avec leur support et elles subissent des contraintes de surface causées par leurs petites tailles. Par ailleurs, les nanoparticules de platine-cobalt, dont la croissance est en deux étapes, gardent une structure en couche et non une structure d'alliage métalliqueGraphene, a monolayer of graphite, is composed of carbon atoms arranged in a honeycomb lattice. Its exceptional properties have attracted a worldwide interest, including the Novel Prize in Physics in 2010. Epitaxial graphene on a metal was rapidly identified as an efficient method for large-area production of high quality graphene, and also was the matter of intense activities exploiting surface science approaches to address the various properties of graphene and of advanced systems based on graphene, for instance ordered lattice of metal nanoparticles on graphene. This resulted in the study of growth, structure and defects of epitaxial graphene on a wide variety of substrates with various techniques such as scanning tunneling microscopy, angle-resolved photoemission spectroscopy or low-energy electron microscopy. This work focuses on graphene grown on the (111) surface of iridium in ultra-high vacuum conditions and studied with several diffraction techniques (surface X-ray diffraction, grazing incidence X-ray diffraction, X-ray reflectivity, and reflection-high energy electron diffraction). These experiments were performed at the European Synchrotron Radiation Facility in Grenoble, France. The first step in our study was to determine the structure of graphene at the atomic scale. The system was found to have a tendency to commensurability, but that the precise structure depends on temperature and on preparation conditions. Moreover, with the combination of high resolution diffraction techniques, a precise characterization about the debated structure of graphene perpendicular to the surface was unveiled. The system, exhibits a superstructure, typical of epitaxial graphene, called a moiré, as an equivalent of the moiré effect in optics. This is used as a template to grown nanoparticles on top of the system to achieve the self-organisation of monodisperse nanoparticles. In this study, three type of nanoparticles were investigated, two different size of pure platinum ones and bimetallic ones, platinum and cobalt. These hybrid systems show very high degree of order, partly inherited by the superstructure lattice. The nanoparticles were found to strongly bond to their support, experience substantial surface strain related to their small size, and that bimetallic ones grown in a sequential manner retain a chemically layered structure
35
Mazaleyrat, Estelle. "Croissance, structure et propriétés électroniques du graphène épitaxié sur rhénium, vers une plateforme bidimensionnelle et supraconductrice." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY079.
Повний текст джерелаАнотація:
La réalisation de structures hybrides à base de graphène, dans lesquelles le graphène est associé à d'autres matériaux, constitue une piste prometteuse pour l'étude de nombreux phénomènes. En particulier, il est possible de cette façon d'induire des propriétés dans le graphène via des effets de proximité. Ici, le système cible que nous avons considéré consiste en une plateforme de graphène quasi-flottant, au caractère supraconducteur induit, et qui est placée à proximité d'impuretés magnétiques. A la lecture d'articles théoriques parus récemment, il semble qu'un tel échantillon pourrait présenter des états de Yu-Shiba-Rusinov (YSR) non conventionnels.Bien que le système cible n'ait pas encore été fabriqué, les trois ingrédients nécessaires à sa réalisation (graphène quasi-flottant, caractère supraconducteur induit et proximité à des impuretés magnétiques) ont été abordés, et ce à l'aide d'outils de la science des surfaces.Comme cela a pu être démontré précédemment, le graphène peut être rendu supraconducteur lorsqu'il est crû directement sur un matériau supraconducteur tel que le rhénium. Des aspects structuraux liés au graphène crû sur Re(0001) ont été explorés. En particulier, nous avons montré qu'augmenter le nombre de cycles de recuit contribue positivement à la croissance de domaines de graphène étendus et de bonne qualité. La structure d'un carbure de surface du rhénium, habituellement mal comprise, a également fait l'objet d'une étude.De plus, nous avons examiné un défaut présent dans le graphène crû sur des métaux interagissant fortement, tels que le Re(0001) et le Ru(0001). Dans la structure ondulée à l'échelle nanométrique du graphène, ce défaut apparaît sous la forme d'une dépression. Sa présence a été attribuée à des défauts d'empilement se trouvant soit dans le graphène, soit dans le substrat métallique.En prenant le graphène supraconducteur crû sur Re(0001) comme point de départ pour la fabrication de notre système cible, nous avons recouvré le caractère quasi-flottant du graphène (perdu à cause de sa forte interaction avec le substrat de rhénium) via l'intercalation d'une sub-monocouche ou de quelques couches d'atomes d'or. La présence d'une forte densité de défauts, observée dans le graphène sur Re(0001) intercalé à l'or, a été attribuée au processus d'intercalation lui-même. Par ailleurs, nous avons démontré que le caractère supraconducteur du graphène, induit par le rhénium, n'est pas affecté par l'intercalation d'or. A ce stade, deux des trois conditions prévues pour la réalisation du système cible étaient remplies.A condition d'amener des impuretés magnétiques à proximité immédiate d'un tel échantillon, des états de YSR étendus sur plusieurs nanomètres devraient être observables. Des résultats préliminaires impliquant deux composés magnétiques de type verdazyl ont été présentés. L'un de ces deux composés fut déposé sur un système modèle : le Cu(111). Avant de considérer l'usage du graphène quasi-flottant et supraconducteur comme substrat-hôte de ces composés magnétiques, des études complémentaires sur des systèmes modèles sont nécessaires. Et pour cause, nous n'avons pas encore réussi à résoudre la structure exacte des assemblées moléculaires observées sur la surface de Cu(111) ; la stabilité thermique de ces composés a été mise en causeThe realization of graphene-based hybrid structures, where graphene is associated with other materials, offers a promising avenue for testing a variety of phenomena. In particular, one can induce properties in graphene by proximity effects. Here, the targeted graphene-based system consists of a quasi free-standing graphene platform with induced superconducting character and in close vicinity to magnetic impurities. According to recent theoretical articles, such a sample could exhibit unconventional Yu-Shiba-Rusinov (YSR) states.Although the targeted graphene-based system was not fabricated yet, we have addressed, with the help of surface science tools, all three ingredients required for its realization (quasi-free standing graphene, induced superconducting character and proximity to magnetic impurities).As previously demonstrated, graphene can be rendered superconducting by growing it directly on top of a superconducting material such as rhenium. Structural aspects related to graphene grown on Re(0001) were investigated. In particular, we showed that increasing the number of annealing cycles positively contributes to growing high-quality extended graphene domains. The structure of a surface rhenium carbide, which constitutes a usually ill-characterized object, was studied as well.Additionnally, a defect appearing as a depression in the nanorippled structure of graphene on strongly interacting metals such as Re(0001) and Ru(0001) was investigated and ascribed to stacking faults either in graphene or in the metal substrate.Using superconducting graphene grown on Re(0001) as a starting point for the fabrication of the targeted graphene-based system, we recovered the quasi free-standing character of graphene (lost due to its strong interaction with the rhenium substrate) via intercalation of sub-monolayer to few layers of gold atoms. A high density of defects observed in gold-intercalated graphene on Re(0001) was attributed to the intercalation process itself. Besides, we demonstrated that the rhenium-induced superconducting character in graphene was not affected by gold intercalation. At this point, two of the three requirements for realizing the targeted graphene-based system were fulfilled.Provided that we bring magnetic impurities in close proximity to such a sample, few-nanometers extended YSR states could be observed. Preliminary results involving two original magnetic verdazyl compounds were presented, one of which was deposited on a model system, namely Cu(111). Before turning to quasi-free standing superconducting graphene as a hosting material for these magnetic compounds, further investigations on model systems are needed. Indeed, we could not resolve the precise structure of the molecular assemblies covering the Cu(111) surface yet, and the thermal stability of the compounds was discussed
36
Droth, Matthias [Verfasser]. "Spins and Phonons in Graphene Nanostructures / Matthias Droth." Konstanz : Bibliothek der Universität Konstanz, 2015. http://d-nb.info/1081551984/34.
Повний текст джерела
37
Mayorov, Alexander. "Tunnelling and noise in GaAs and graphene nanostructures." Thesis, University of Exeter, 2008. http://hdl.handle.net/10036/46914.
Повний текст джерелаАнотація:
Experimental studies presented in this thesis have shown the first realisation of resonant tunnelling transport through two impurities in a vertical double-barrier tunnelling diode; have proved the chiral nature of charge carriers in graphene by studying ballistic transport through graphene $p$-$n$ junctions; have demonstrated significant differences of $1/f$ noise in graphene compared with conventional two-dimensional systems. Magnetic field parallel to the current has been used to investigate resonant tunnelling through a double impurity in a vertical double-barrier resonant tunnelling diode, by measuring the current-voltage and differential conductance-voltage characteristics of the structure. It is shown that such experiments allow one to obtain the energy levels, the effective electron mass and spatial positions of the impurities. The chiral nature of the carriers in graphene has been demonstrated by comparing measurements of the conductance of a graphene $p$-$n$-$p$ structure with the predictions of diffusive models. This allowed us to find, unambiguously, the contribution of ballistic resistance of graphene $p$-$n$ junctions to the total resistance of the $p$-$n$-$p$ structure. In order to do this, the band profile of the $p$-$n$-$p$ structure has been calculated using the realistic density of states in graphene. It has been shown that the developed models of diffusive transport can be applied to explain the main features of the magnetoresistance of $p$-$n$-$p$ structures. It was shown that $1/f$ noise in graphene has much more complicated concentration and temperature dependences near the Dirac point than in usual metallic systems, possibly due to the existence of the electron-hole puddles in the electro-neutrality region. In the regions of high carrier concentration where no inhomogeneity is expected, the noise has an inverse square root dependence on the concentration, which is also in contradiction with the Hooge relation.
38
Gorbachev, Roman. "Fabrication and transport properties of graphene-based nanostructures." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/89275.
Повний текст джерелаАнотація:
In this work fabrication and studies of transistor structures based on an atomic sheet of graphite, graphene, are described. Since graphene technology is in its early stages, the development and optimisation of the fabrication process are very important. In this work the impact of various fabrication conditions on the quality of graphene devices is investigated, in particular the effects on the carrier mobility of the details of the mechanical exfoliation procedure, such as environmental conditions and humidity, source of graphite and wafer cleaning procedure. In addition, a comparison is made between the conventional e-beam lithorgaphy and lithography-free fabrication of samples. It was also demonstrated that water and other environmental species play an important role in graphene-to-substrate adhesion and can also contribute to the carrier scattering in graphene. A technique for creating suspended metal gates was developed for the fabrication of graphene p-n-p structures, and charge transport has been studied in such top-gated graphene devices. Depending on the relation between the carrier mean free path and the length of the top-gate we have realized three distinct transport regimes through the p-n-p structure: a) diffusive across the structure; b) ballistic in the regions of p-n junctions but diffusive in the n-region; c) ballistic across the whole p-n-p structure. The second regime has revealed the chiral nature of carriers in graphene. This was demonstrated by comparing the experimental resistance of a single p-n junction with results of electrostatic modeling in the diffusive model. In the third regime we have observed oscillations of the device resistance as a function of carrier concentration in the n-region, which are also dependent on magnetic field. These oscillations have been demonstrated to be a direct consequence of a Fabri-Perot-like interference effect in the graphene p-n-p structures.
39
Wu, Ying. "Computational studies of graphene on nanostructured ionic substrates." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683543.
Повний текст джерелаАнотація:
This work studies graphene on nanostructured ionic substrates using density functional theory (DFT) and the density functional tight binding (DFTB). Flat ionic substrates can provide graphene with a mechanical support without compromising its electronic properties, while the nanostructures can modify the electron behaviour in graphene sheets and potentially create devices such as on-sheet junctions. Previous to the calculations, we extend the self-consistent charge DFTB method (SCC-DFTB) to a self-consistent charge and dipole DFTB scheme (SCCD-DFTB), which allows atomic dipoles to be considered self-consistently. This new scheme is implemented and its parametrisation discussed. Assessment is made based upon calculations of some electronic properties of Carbon-based systems including fullerenes, nanotubes and graphenes. Studies of graphene on ionic substrates confirm that flat ionic substrates do not influence the electronic structure of graphene in the vicinity of Dirac points. In the case of nanostructured surfaces, it is identified that steps or pits with divalent impurity and cation vacancy pair with possible relaxations are the key to introducing sizeable electrostatic potential variations on graphene layers that can cause changes of the electronic structures of graphene at the low energy range recently observed in experiments.
40
Mishra, Shantanu, Thorsten G. Lohr, Carlo A. Pignedoli, Junzhi Liu, Reinhard Berger, JoséI Urgel, Klaus Müllen, Xinliang Feng, Pascal Ruffieux, and Roman Fasel. "Tailoring Bond Topologies in Open-Shell Graphene Nanostructures." ACS Publications, 2018. https://tud.qucosa.de/id/qucosa%3A36585.
Повний текст джерелаАнотація:
Polycyclic aromatic hydrocarbons exhibit a rich spectrum of physicochemical properties depending on the size and, more critically, on the edge and bond topologies. Among them, open-shell systems - molecules hosting unpaired electron densities - represent an important class of materials for organic electronic, spintronic, and optoelectronic devices, but remain challenging to synthesize in solution. We report the on-surface synthesis and scanning tunneling microscopy- and spectroscopybased study of two ultralow-gap open-shell molecules, namely peri-tetracene, a benzenoid graphene fragment with zigzag edge topology, and dibenzo[a,m]dicyclohepta-[bcde,nopq]rubicene, a nonbenzenoid nonalternant structural isomer of peri-tetracene with two embedded azulene units. Our results provide an understanding of the ramifications of altered bond topologies at the single-molecule scale, with the prospect of designing functionalities in carbon-based nanostructures via engineering of bond topology.
41
Frizera, Borghi Fabricio. "Fabrication And Biological Applications Of Graphene-Based Nanostructures." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15657.
Повний текст джерелаАнотація:
Graphene received increasing attention for sensing and biomedical applications due to its properties. However, the current production methods are resource consuming, struggle to integrate these films into devices, and hardly produce graphene nanostructures (GN) that improve desired film properties like surface area and reactivity. This thesis aims to use a plasma-enhanced technique to produce GN and to explore their potential biological applications. The control of GN using the plasma-enhanced chemical vapour deposition (PECVD) was investigated. Growth parameters were related with the nanostructures properties as well as to the occurrence of the chemical-free transfer (CFT). The ability of GN to induce cellular response was investigated. The biocompatibility of GN was tested and found to be able to support fibroblasts viability at or above 70%. Cell proliferation was correlated to the density of different GN. While the density of horizontal GN had no influence on cell viability, a higher density of vertical GN yielded higher levels of cell viability. Furthermore, proliferation assays showed the ability of the GN surfaces to support bone-cells adhesion and growth. We also demonstrated improvement on mineral deposition that indicates the capability of GN to induce cell differentiation via morphological cues. The GN were also used for biosensing, where different morphologies were optimized to provide extras binding. Horizontal and vertical GN were produced by PECVD and assembled into electrodes via the CFT. The electrochemical sensing shows that both nanostructures perform highly selective measurements with a low limit of detection (picomolar) in a complex biological environment. Furthermore, the sensitivity relied on the density of the GN. This work suggests that plasma techniques are a feasible solution for the production challenges and graphene-based nanostructures are promising for biological applications.
42
Mendes, Rafael Gregorio. "Synthesis, characterization and toxicological evaluation of carbon-based nanostructures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-186839.
Повний текст джерелаАнотація:
The synthesis, characterization and biological evaluation of different graphene-based nanoparticles with potential biomedical applications are explored. The results presented within this work show that eukaryotic cells can respond differently not only to different types of nanoparticles, but also identify slight differences in the morphology of nanoparticles, such as size. This highlights the great importance of the synthesis and thorough characterization of nanoparticles in the design of effective nanoparticle platforms for biological applications. In order to test the influence of morphology of graphene-based nanoparticles on the cell response, nanoparticles with different sizes were synthesized and tested on different cells. The synthesis of spherical iron-oxide nanoparticles coated with graphene was accomplished using a colloidal chemistry route. This synthesis route was able to render nanoparticle samples with narrow size distributions, which can be taken as monodispersed. Four different samples varying in diameter from 10 to 20 nm were produced and the material was systematically characterized prior to the biological tests. The characterization of the material suggests that the iron oxide nanoparticles consist of a mix of both magnetite and maghemite phases and are coated with a thin graphitic layer. All samples presented functional groups and were similar in all aspects except in diameter. The results suggest that cells can respond differently even to small differences in the size of the nanoparticles. An in situ study of the coating of the iron-oxide nanoparticles using a transmission electron microscope revealed that it is possible to further graphitize the remaining oleic acid on the nanoparticles. The thickness of the graphitic coating was controlled by varying the amount of oleic acid on the nanoparticles. The in situ observations using an electron beam were reproduced by annealing the nanoparticles in a dynamic vacuum. This procedure showed that it is not only possible to coat large amounts of iron oxide nanoparticles with graphene using oleic acid, but also to improved their magnetic properties for other applications such as hyperthermia. This study therefore revealed a facile route to grow 2D graphene takes on substrates using oleic acid as a precursor. The synthesis of nanographene oxide nanoparticles of different sizes was in a second approach accomplished by using the Hummers method to oxidize and expand commercially available graphite. The size of the oxidized graphite was adjusted by sonicating the samples for different periods of time. The material was also thoroughly characterized and demonstrated to have two distinctive average size distributions and possess functional groups. The results suggest that different size flakes can trigger different cell response. The synthesis, characterization and biological evaluation of graphene nanoshells were performed. The graphene nanoshells were produced by using magnesia nanoparticles as a template to the graphene nanoshells. The coating of magnesia with graphene layers was accomplished using chemical vapor deposition. The nanoshells were obtained by removing the magnesia core. The size of the nanoshells was determined by the size of the magnesia nanoparticles and presented a broad size distribution since the diameter of the magnesia nanoparticles could not be controlled. The nanoshells were also characterized and the biological evaluation was performed in the Swiss Federal Laboratories for Materials Science and Technology (EMPA), in Switzerland. The results suggest that despite inducing the production of reactive oxygen species on cells, the nanoshells did not impede cell proliferationDie Herstellung, Charakterisierung und biologische Auswertung von verschiedenen Graphen-basierten Nanopartikeln mit einer potenziellen biomedizinischen Anwendung wurden erforscht. Die vorgestellten Ergebnisse im Rahmen dieser Arbeit zeigen, dass eukaryotische Zellen unterschiedlich reagieren können, wenn sie mit Nanopartikeln unterschiedlicher Morphologie interagieren. Die Zellen können geringe Unterschiede in der Morphologie, insbesondere der Größe der Nanopartikeln, identifizieren. Dies unterstreicht den Einfluss der Herstellungsmethoden und die Notwendigkeit einer gründlichen Charakterisierung, um ein effektives Design von Nanopartikeln für biologische Anwendungen zu erreichen. Um den Einfluss der Größe von Graphen-basierten Nanopartikel auf das Zellverhalten zu erforschen, wurden verschiedene Graphen-beschichte Eisenoxid-Nanopartikelproben durch eine kolloidchemische Methode hergestellt. Dieses Herstellungsverfahren ermöglicht die Synthese von Nanopartikeln mit engen Größenverteilungen, die als monodispers gelten können. Vier Proben mit unterschiedlichen Durchmessern (von 10 bis 20 nm) wurden hergestellt und vor den biologischen Untersuchungen systematisch charakterisiert. Die Probencharakterisierung deutet auf eine Mischung aus Magnetit- und Maghemit-Kristallphasen hin, außerdem besitzen die Nanopartikel eine dünne Graphitschicht. Die spektroskopischen Ergebnisse auch zeigen außerdem, dass alle Proben funktionelle Gruppen auf ihrer Oberfläche besitzen, sodass sie in allen Aspekten, außer Morphologie (Durchmesser), ähnlich sind. Die biologischen Untersuchungen deuten darauf hin, dass Zellen unterschiedliche Größen von Eisenoxid-Nanopartikeln reagieren können. Ein in situ Untersuchung der Beschichtung der Eisenoxid-Nanopartikel wurde mit einem Transmissionelektronenmikroskop durchgeführt. Die Ergebnisse zeigen, dass eine dünne Schicht von Ölsäure aus dem Syntheseprozess auf den Nanopartikeln verbleibt. Diese Schicht kann mit einem Elektronstrahl in Graphen umgewandelt werden. Die Dicke der Graphitschicht auf den Nanopartikeln kann durch die Menge der eingesetzten Ölsäure kontrolliert werden. Die in situ Beobachtungen der Graphenumwandlung konnte durch erhitzen der Nanopartikeln in einem dynamischen Vakuum reproduziert werden. Das Brennen der Eisenoxid-Nanopartikel ermöglicht nicht nur die Graphitisierung der Ölsäure, sondern auch eine Verbesserung der magnetischen Eigenschaften der Nanopartikel für weitere Anwendungen, z. B. der Hyperthermie. Die Umwandlung der Ölsäure in Graphen konnte so als relativ einfaches Verfahren der Beschichtung von zweidimensionalen (2D) Substraten etabliert werden. Die Herstellung von Nanographenoxid mit unterschiedlichen Größen wurde mit der Hummers-Method durchgeführt. Die unterschiedlichen Größen der Nanographenoxidpartikel wurde durch eine Behandlung in Ultraschallbad erreicht. Zwei Proben mit deutlicher Verteilung wurden mit mehreren Verfahren charakterisiert. Beide Proben haben Nanographenoxid Nanoteilchen mit verschiedenen funktionellen Gruppen. Die biologische Charakterisierung deutet darauf hin, dass unterschiedliche Größen des Nanographens ein unterschiedliches Zellverhalten auslösen. Abschließend, wurde die Herstellung, Charakterisierung und biologische Auswertung von Graphen-Nanoschalen durchgeführt. Die Graphen-Nanoschalen wurden mit Magnesiumoxid-Nanopartikeln als Template hergestellt. Die Beschichtung des Magnesia mit Graphen erforgte durch die chemische Gasphasenabscheidung. Die Nanoschalen wurden durch Entfernen des Magnesia-Kerns erhalten. Die Größe der Nanohüllen ist durch die Größe der Magnesia-Kerns bestimmt und zeigt eine breite Verteilung, da der Durchmesser der Magnesiumoxid-Nanopartikel gegeben war. Die Nanoschalen wurden ebenfalls mit Infrarot- und Röntgen Photoemissionspektroskopie charakterisiert und die biologische Bewertung wurde im Eidgenössische Materialprüfungs- und Forschungsanstalt (EMPA) durchgeführt, in der Schweiz. Die Ergebnisse zeigen, dass zwar die Produktion von reaktiven Sauerstoffspezies in den Zellen ausgelöst wird, diese sich aber weiterhin vermehren können
43
Calizo, Irene Gonzales. "Raman nanometrology of graphene." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3359892.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 8, 2010). Includes bibliographical references (p. 59-64). Also issued in print.
44
Faizy, Namarvar Omid. "Structure électronique et transport quantique dans les nanostructures de Graphène." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00870405.
Повний текст джерелаАнотація:
Le graphène est un matériau constitué d'une seule couche atomique de carbone et représente un sujet majeur de la physique de la matière condensée. Le graphène possède de nombreuses propriétés remarquables : structure électronique décrite par une equation de Dirac sans masse, forte mobilité électronique, effet Hall quantique anormal, résistance ,rigidité et conductivité thermique élevée. Cette these concerne la structure électronique et le transport dans le graphène. Nous considérons en particulier le cas des bicouches tournées de graphène. Ces systèmes ont été découverts en particulier dans le graphène produit sur le carbure de silicium et présentent des propriétés originales par rapport aux bicouches dans l' empilement AB qui existe par exemple dans le graphite. Nous analysons au moyen d'une théorie perturbative et aussi par des approches numériques la densité d'états dans ces systèmes.Nous montrons que la densité d'états présente des oscillations avec la même période que celle du Moiré produit par ces bicouches. Nous analysons aussi le rôle des défauts sur les propriétés de transport en particulier dans le cas ou les défauts sont répartis uniquement sur une des deux couches. Ici aussi notre approche combine théorie perturbative du couplage interplans et approches purement numérique en liaisons fortes. Nous considérons aussi le role joué par les adatomes comme l'hydrogène par exemple. Nous analysons la modification de la densité d'états induite autour de l'adatome et les variations correspondantes de densité de charge et de potentiel électrostatique. Ces systèmes tendent à produire des états resonants près de l'énergie de Dirac qui dependent beaucoup aussi de la position top ou hollow de l' adsorbat. Pour des orbitales de type "s" la resonance est plus marquée si l'adatome est en position hollow. Nous montrons que l'image par experience STM (microscopie à effet tunnel) depend beaucoup de la distance entre l'adsorbat et la pointe du STM. Dans un régime de champ proche la résonance de l'adsorbat peut même apparaître comme un creux dans le signal dI/dV du STM.
45
Solouki, Bonab Vahab. "Polyurethane (PU) Nanocomposites; Interplay of Composition, Morphology, and Properties." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1542634359353501.
Повний текст джерела
46
Milana, Silvia. "Light interaction with graphene, related materials and plasmonic nanostructures." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708643.
Повний текст джерела
47
Tahmassebi, Amirhessam. "Fluid Flow Through Carbon Nanotubes And Graphene Based Nanostructures." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1436545689.
Повний текст джерела
48
Dragomirova, Ralitsa L. "Spin-dependent shot noise in semiconductor and graphene nanostructures." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 140 p, 2009. http://proquest.umi.com/pqdweb?did=1674099571&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Повний текст джерела
49
DI, PIERRO ALESSANDRO. "Computational modeling of thermal interfaces in graphene based nanostructures." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2742543.
Повний текст джерела
50
Wang, Shu Jun. "Applications of graphene for transparent conductors and polymer nanocomposites /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20WANGS.
Повний текст джерела