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1
Piastek, Jakub. "Příprava grafenových vrstev pokrytých Ga atomy a charakterizace jejich elektrických vlastností." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231957.
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This master's thesis deals with the study of electric properties of graphene layers covered by Ga atoms in UHV conditions. The substrates were prepared by using laser litography and the graphene layer was prepared by using chemical vapor deposition (CVD). Dependence of Dirac point location on gallium atoms deposition time and influence of electrical properties of graphene on hydrogen atoms deposition time were studied. Experimental results and their evaluation are discussed.
2
Skulason, Helgi. "Optical properties of few and many layer graphene flakes." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=67024.
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This thesis reports, for the first time, measurements of optical properties of graphene as a function of layer number up to 700 layers. Optical reflection, optical transmission and atomic force microscopy was performed on graphene exfoliated on glass. Universal optical conductance of graphene arising from pi−pi^* interband transitions was used to identify and count up to 9 layer graphene samples with optical reflection microscopy alone. The optical properties of graphene are best described by refractive index of 1.88−1.59i at 550 nm up to 90 layers. For thicker graphene flakes, we present a model for calculating conductance due to sigma−sigma^* transitions. Incorporating both transitions, we find a refractive index of 2.70−1.11i at 550 nm, which shows good agreement to 250−700 layer graphene flakes.Cette thèse rapporte, pour la première fois, des mesures des propriétés optiques du graphene en fonction du nombre de couches et ce allant jusqu'à 700 couches. La réflexion et la transmission optique ainsi que la microscopie par force atomique ont été utilisés sur du graphene déposé sur de la vitre. La conductance optique universelle du graphene provenant des transitions entre les bandes pi-pi^* a été utilisée afin de compter jusqu'à 9 couches de graphene avec seulement la microscopie à réflexion optique. Les propriétés optiques du graphene sont bien décrites par un index de réfraction de 1.88-1.59i à 550 nm et ce jusqu'à 90 couches. Pour des échantillons plus épais, nous présentons un modèle servant à calculer la conductance causée par les transitions entre les bandes sigma-sigma^*. En incorporant les deux transitions, nous trouvons un index de 2.70-1.11i à 550 nm, ce qui démontre un bon accord avec les échantillons de graphene de 250-700 couches.
3
Khrapach, Ivan. "Engineering the electrical properties of graphene materials." Thesis, University of Exeter, 2012. http://hdl.handle.net/10871/8168.
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In this thesis the properties of graphene and its few-layers are engineered to make them highly conductive. Two different approaches were implemented to achieve this goal. One approach was to increase the concentration of charge carriers by intercalation of acceptor FeCl3 molecules between graphene planes. This resulted in a highly conductive yet transparent material which can be useful for applications. Another approach was to increase the mobility of carriers by means of removing surface contamination in the current annealing process. Optimal annealing parameters were found and a reproducible cleaning method was suggested.
4
Khodkov, Tymofiy. "Probing the electrical properties of multilayer graphene." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/4352.
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Graphene is a new two-dimensional (2D) material with unique electrical transport, optical and mechanical properties. However, monolayer graphene (MLG) is a gapless semiconductor, which limits its relevance for transistor applications where a large on/off ratio of the current is required. In this work the investigation of transport properties of few-layer graphene (FLG) is presented. These 2D electronic systems offer a novel solution to the problem concerned the absence of an energy gap in single layer graphene, since they exhibit an electric field and stacking-dependent band gap in the energy dispersion. Thus far, a clear observation of a band-gap in multilayer graphene (e.g. Bernal-stacked bilayers) in transport measurements was hindered by the presence of disorder. Here we develop a reliable and effective method of fabrication of high-quality suspended double-gated graphene devices, which are of crucial importance for probing the low energy dispersion of few-layer graphene. The current annealing technique, described in details, improves transport characteristics like carrier mobility, which is typically higher than ∼ 104 cm2/Vs for our multilayer devices. Electrical transport experiments on suspended dual-gated ABC-stacked trilayer are performed. We report the direct evidence of the opening of a tunable band-gap with an external perpendicular electric field, ranging from 0 meV up to 5.2 meV for an electric field of 117 mV/nm. Thermally activated transport is observed in these samples over the temperature range 0.5 - 80 K. The values of energy gap extracted from both temperature dependence of minimum conductivity measurements and non-linear I –V characteristics correlate well. Our experimental results are in a good agreement with theoretical approximation, based on self-consistent tight-binding calculations. The high quality of our ABC trilayer samples is also demonstrated by a particularly high on/off ratio of the current (250 at applied electrical displacement as low as 80 mV/nm), which makes these devices promising for future semiconductor electronics. FLG samples with reduced disorder allow us to observe quantum Hall effect (QHE) at magnetic field as low as 500 mT. We present the first study of electric field- induced new QH states in ABC trilayer graphene (TLG). The transitions between spin-polarized and valley polarized phases of the sample at the charge neutrality point are investigated. Resolved novel broken symmetry states along with observed Lifshitz transition in rhombohedral TLG display exciting phenomena attributed to rich physics in these interactive electronic systems.
5
Bryan, Sarah Elizabeth. "Structural and electrical properties of epitaxial graphene nanoribbons." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47583.
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The objective of this research was to perform a systematic investigation of the unique structural and electrical properties of epitaxial graphene at the nanoscale. As the semiconductor industry faces increasing challenges in the production of integrated circuits, due to process complexity and scaling limitations, new materials research has come to the forefront of both science and engineering disciplines. Graphene, an atomically-thin sheet of carbon, was examined as a material which may replace or become integrated with silicon nanoelectronics. Specifically, this research was focused on epitaxial graphene produced on silicon carbide. This material system, as opposed to other types of graphene, holds great promise for large-scale manufacturing, and is therefore of wide interest to the academic and industrial community.
In this work, high-quality epitaxial graphene production was optimized, followed by the process development necessary to fabricate epitaxial graphene nanoribbon transistors for electrical characterization. The structural and electrical transport properties of the nanoribbons were elucidated through a series of distinct experiments. First, the size-dependent conductivity of epitaxial graphene at the nanoscale was investigated. Next, the alleviation of the detrimental effects revealed during the size-dependent conductivity study was achieved through the selective functionalization of graphene with hydrogen. Finally, two techniques were developed to allow for the complementary doping of epitaxial graphene. All of the experiments presented herein reveal new and important aspects of epitaxial graphene at the nanoscale that must be considered if the material is to be adopted for use by the semiconductor industry.
6
Smith, Anderson David. "Strain Effects on Electrical Properties of Suspended Graphene." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-52913.
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Graphene is an extraordinary material which shows tremendous potential as a replacement for silicon in many electronic applications. However, one major drawback to graphene is its zero band gap. Previous research in tight binding models have predicted band gap opening in graphene under tensile strain. New experimental tight binding models were formulated and compared to previous models in order to determine the strains necessary to induce a band gap in graphene. Using CVD graphene, a transfer method and etching method were successfully devised in order to fabricate future graphene devices. These devices were conceptualized such that they could be strained in order to experimentally confirm band gap openings. Future work will consist of further perfecting the graphene fabrication techniques and performing electrical testing on CVD graphene devices which could have wide ranging transistor and sensor applications.
7
Jones, Jason David. "Modification of Graphene Properties: Electron Induced Reversible Hydrogenation, Oxidative Etching and Layer-by-layer Thinning." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc115101/.
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In this dissertation, I present the mechanism of graphene hydrogenation via three different electron sources: scanning electron microscopy, e-beam irradiation and H2 and He plasma irradiation. in each case, hydrogenation occurs due to electron impact fragmentation of adsorbed water vapor from the sample preparation process. in the proposed model, secondary and backscattered electrons generated from incident electron interactions with the underlying silicon substrate are responsible for the dissociation of water vapor. Chemisorbed H species from the dissociation are responsible for converting graphene into hydrogenated graphene, graphane. These results may lead to higher quality graphane films having a larger band gap than currently reported. in addition, the dissertation presents a novel and scalable method of controllably removing single atomic planes from multi-layer graphene using electron irradiation from an intense He plasma under a positive sample bias. As the electronic properties or multi-layer graphene are highly dependent on the number of layers, n, reducing n in certain regions has many benefits. for example, a mask in conjunction with this thinning method could be used for device applications.
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Marashdeh, Wajeeh. "Relaxation Behavior and Electrical Properties of Polyimide/Graphene Nanocomposite." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1595850361812632.
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Ryan, Shawn David. "Bifurcation and Boundary Layer Analysis for Graphene Sheets." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1239646272.
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Malekpour, Hoda. "Optothermal Raman Studies of Thermal Properties of Graphene Based Films." Thesis, University of California, Riverside, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10252873.
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Efficient thermal management is becoming a critical issue for development of the next generation of electronics. As the size of electronic devices shrinks, the dissipated power density increases, demanding a better heat removal. The discovery of graphene’s unique electrical and thermal properties stimulated interest of electronic industry to development of graphene based technologies. In this dissertation, I report the results of my investigation of thermal properties of graphene derivatives and their applications in thermal management. The dissertation consists of three parts. In the first part, I investigated thermal conductivity of graphene laminate films deposited on thermally insulating polyethylene terephthalate substrates. Graphene laminate is made of chemically derived graphene and few layer graphene flakes packed in overlapping structure. Two types of graphene laminate were studied: as deposited and compressed. The thermal conductivity of the laminate was found to be in the range from 40 W/mK to 90 W/mK at room temperature. It was established that the average size and the alignment of graphene flakes are parameters dominating the heat conduction. In the second part of this dissertation, I investigated thermal conductivity of chemically reduced freestanding graphene oxide films. It was found that the in-plane thermal conductivity of graphene oxide can be increased significantly using chemical reduction and temperature treatment. Finally, I studied the effect of defects on thermal conductivity of suspended graphene. The knowledge of the thermal conductivity dependence on the concentration of defects can shed light on the strength of the phonon - point defect scattering in two-dimensional materials. The defects were introduced to graphene in a controllable way using the low-energy electron beam irradiation. It was determined that as the defect density increases the thermal conductivity decreases down to about 400 W/mK, and then reveal saturation type behavior. The thermal conductivity dependence on the defect density was analyzed using the Boltzmann transport equation and molecular dynamics simulations. The obtained results are important for understanding phonon transport in two-dimensional systems and for practical applications of graphene in thermal management.
11
Smith, Jacob A. "Electrical Performance of Copper-Graphene Nano-Alloys." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1550675878730599.
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Sokmen, Gokce. "Molecular Dynamics Investigation Of Moire Patterns In Double-layer Graphene." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614751/index.pdf.
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Before Moire patterns are discovered in graphene, graphene was assumed to be found in only the rhombohedral form in nature. After transfer of graphene layer over another substrate
was achieved by Andre Geim and Konstantin Novoselov, studies on graphene gained momentum. Following this, moire paterns were observed by scanning tunelling microscopy (STM) and high resolution transmision electron microscopy (HR-TEM). However, stability of these structures are still unknown. In this thesis, for the first time in literature, molecular dynamics of double layer graphene based Moire patterns are investigated as a result of the
rotation of two graphene layers with LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) which has a GNU general public license. To model the two graphene layers,
hexagonal graphene layers are generated by home writen Octave code. Then, periodicity condition for the Moire patterns are derived in chapter 2 according to rotation of graphene layers around their central axis, perpendicular to the layers. Then these layers with different angles or temperature or size are simulated by LAMMPS. There are 4 kind of molecular dynamics simulations studied according to modeled flakes.
These are grouped under the name of &rsquoExperiment #&rsquo
according to the modeling structure. Experiment-1 simulates double layer hexagonal flakes of graphene at a temperature of 0.1K. Experiment-2 simulates periodic moire patterns under periodic boundary conditions and represents the infinitely large graphene layers at 10K. Experiment 3 is dierent version of the experiment 1 but at higher temperature (10K). Finally, experiment 4 is modeled to show the behaviour of the graphene flake on a growth or attached region. The atoms around the flakes are modeled as a rigid body and constructs some stress on the graphene flakes.
13
Wang, Zegao, Pingjian Li, Yuanfu Chen, Jiarui He, Wanli Zhang, Oliver G. Schmidt, and Yanrong Li. "Pure thiophene–sulfur doped reduced graphene oxide: synthesis, structure, and electrical properties." Royal Society of Chemistry, 2014. https://tud.qucosa.de/id/qucosa%3A36294.
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Here we propose, for the first time, a new and green ethanol-thermal reaction method to synthesize highquality and pure thiophene–sulfur doped reduced graphene oxide (rGO), which establishes an excellent platform for studying sulfur (S) doping effects on the physical/chemical properties of this material. We have quantitatively demonstrated that the conductivity enhancement of thiophene–S doped rGO is not only caused by the more effective reduction induced by S doping, but also by the doped S atoms, themselves. Furthermore, we demonstrate that the S doping is more effective in enhancing conductivity of rGO than nitrogen (N) doping due to its stronger electron donor ability. Finally, the dye-sensitized solar cell (DSCC) employing the S-doped rGO/TiO₂ photoanode exhibits much better performance than undoped rGO/TiO₂, N-doped rGO/TiO₂ and TiO₂ photoanodes. It therefore seems promising for thiophene–S doped rGO to be widely used in electronic and optoelectronic devices.
14
Noël, Amélie. "Electrical properties of film-forming polymer/graphene nanocomposites : Elaboration through latex route and characterization." Thesis, Saint-Etienne, EMSE, 2014. http://www.theses.fr/2014EMSE0767/document.
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Les dispersions de nanocomposite à base aqueuse sont produites pour des applications diverses telles que les adhésifs, les revêtements et plus récemment les encres. Ce projet consiste à réaliser des encres conductrices nanocomposites comprenant des particules de polymère (latex) à basse température de transition vitreuse, Tg, pour la formation de films à température ambiante, et des plaquettes de graphène, en raison de leurs excellentes propriétés conductrices. Les charges conductrices, appelées multi-feuillets de graphène, sont réalisées par broyage en voie aqueuse de graphite (1-10 µm) stabilisées par différents tensio-actifs et/ou stabilisants. Cette méthode sans solvant et à bas coût permet de produire des suspensions de multi-feuillets (1-10 feuillets) de graphène. Les particules de polymères utilisées sont synthétisées par polymérisation en émulsion de monomères acrylates. Dans un second temps, des mélanges physiques de suspensions de graphène et de latex acrylates ont permis d’obtenir des encres nanocomposites. L’ajout de graphène permet l’obtention d’un seuil de percolation à bas taux de charge et une nette amélioration des propriétés électriques et du renfort. Le diamètre des billes de latex a une influence importante sur ces propriétés et a également été étudié. Afin d’augmenter la stabilité des suspensions et les interactions graphène/latex, des nanocomposites structurés ont été synthétisés par polymérisation in situ en émulsion, miniemulsion ou dispersion en présence de graphène. Les excellentes propriétés électriques associées à leur flexibilité font de ces matériaux des candidats adaptés pour la réalisation d’encres conductrices pour impression sur textilePrinted electronics, particularly on flexible and textile substrates, raised a strong interest during the past decades. This project presents a procedure that provides a complete and consistent candidate for conductive inks based on a graphene/polymer nanocomposite material. It consists in the synthesis of conductive inks nanocomposites comprising polymer particles (latex) with low glass transition temperature, Tg, and graphene platelets, for the conductive properties. The conductive particles, named Nanosize Multilayered Graphene (NMG), are prepared by wet grinding delamination of micro-graphite suspensions stabilized by various surfactants and/or polymeric stabilizers. This solvent-free procedure allows the formation of NMG suspensions with low thickness (1-10 sheets). Polymer particles are synthetized by surfactant-free emulsion polymerization with acrylates monomers.Physical blending of latex particles and NMG platelets are performed to obtain conductive nanocomposites inks. Adding NMG induce a low percolation threshold and a sharp increase of the electrical and mechanical properties of the nanocomposites. Moreover, the polymer particles diameters have an impact on these properties.To increase the formation of a well-defined cellular microstructure, the nanocomposites are also synthetized by in situ polymerization in presence of NMG platelets, using emulsion, miniemulsion or dispersion polymerization. The excellent electrical properties of these nanocomposites associated to their flexibility make these materials suitable candidates for the production of conductive inks for textile printing applications
15
Luo, Wen. "Tuning the redox properties of cobalt particles supported on oxides by an In-between graphene layer." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAF007/document.
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L'interaction métal-support (MSI) joue un rôle important dans la catalyse hétérogène. La compréhension et la modification du MSI sont des étapes essentielles pour développer catalyseurs de haute performance. Dans cette thèse, un nouveau concept, qu’il s’agit de recouvrir le support l'oxyde avec un revêtement mono-couche de graphène, a été proposé pour modifier le MSI. L'influence de la couche de graphène sur les interactions de métal (Co et Co-Pt) - oxyde (ZnO et SiO2) et sur les propriétés d'oxydo-réduction des particules métalliques ont été évaluées via des systèmes catalytiques de modèle. Les résultats ont montré que la mono-couche de graphène peut influencer considérablement les états d'oxydation et les morphologies des Co monométallique et Co-Pt bimétallique par rapport aux ceux résultent d’un dépôt direct sur les oxydes nus. En particulier, par calcination sous vide, le graphène protége Co d'être oxydé par ZnO, ce qui conduit à la formation d’un mélange métallique Co-Pt. Co interagit avec les substrats d'oxydes pour former des particules plates qui sont facilement oxydés par O2 en pression faible, tandis que l'insertion d'une couche intermédiaire de graphène entre la couche supérieure métallique et le supporte d’oxyde entraîne la formation des nanoparticules de Co en état très dispersés, qui sont résistants à l'oxydation. Sous la condition de réduction par H2, le graphène favorise clairement la réduction de Co. La quantité de dépôt de Co, le substrat d'oxyde, la température de calcination et l'environnement ont été prouvés pour pouvoir influencer la stabilité de graphène. Ces résultats ouvrent des nouvelles voies possibles d'utiliser le graphène comme promoteur dans des réactions catalytiques à l'avenirThe metal-support interaction (MSI) plays an important role in heterogeneous catalysis. Understanding and tuning the MSI are essential steps for developing catalysts with high performance. In this thesis, a new concept, which is coating the oxide supports with a single layer graphene, was introduced to modify the MSI. The influence of graphene layer on the metal (Co and Co-Pt) – oxide (ZnO and SiO2) interactions and on the redox properties of metal particles were evaluated through model catalyst systems. The results showed that single layer graphene can significantly influence the oxidation states and morphologies of both mono Co and bimetallic Co-Pt as compared to the one after direct deposition on bare oxides. In particular, under vacuum annealing, graphene protects Co from being oxidized by ZnO and results in Co-Pt metallic mixture. Co interacts with oxide substrates forming flat particles which are easily oxidized by low pressure O2, while insertion of a graphene interlayer between the metal overlayer and the oxide supports leads to the formation of highly dispersed Co nanoparticles, which are resistant to oxidation. Under H2 reduction condition, graphene evidently facilitates the reduction of Co. The deposition amount of Co, the oxide substrate, the annealing temperature and the environment were proved to influence the stability of graphene. These results explore new directions for the possible future of using graphene as a promoter in catalytic reactions
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Seifert, Christian. "Control of the Electrical Transport through Single Molecules and Graphene." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21647.
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Der Erste dieser Arbeit befasst sich mit der STM Untersuchung einer Grenzschicht in umgebender Atmosphäre, welche sich durch die Adsorption von Graphen auf einer Glimmeroberfläche ausbildet. Durch die umgebene Luftfeuchtigkeit interkalieren Wassermoleküle in diese Grenzschicht. Durch die Variation der relativen Luftfeuchtigkeit gibt diese Wasser ab bzw. nimmt auf, und es manifestieren sich sternförmig wachsende Fraktale, in denen Graphen etwa um den Durchmesser eines Wassermoleküls an Höhe absinkt. Die STM Untersuchung, welche primär sensitiv auf die Zustandsdichte von Graphen reagiert, zeigte, dass sich anders als in den SFM Untersuchungen, zusätzliche signifikante Höhenänderungen von Graphen innerhalb der Fraktale bildeten. Dieses deutet auf eine Wasserschicht hin, welche Domänen mit signifikant unterscheidbaren Polarisationsrichtungen aufweisen, welche die Zustandsdichte von Graphen verändern kann. Dies ist aber gleichbedeutend mit der Annahme, dass sich in jener Grenzschicht mindestens zwei oder mehr lagen Wasser bilden müssen.
Der zweiten Teil befasst sich mit der STM Untersuchung einer funktionalisierten Oberfläche die charakterisiert ist durch eine leitende Oberfläche (Graphen und HOPG) adsorbierten funktionalisierte Dyade an einer Fest-Flüssig Grenzfläche. Diese Dyade besteht im Wesentlichen aus einem Zink-Tetraphenylporphyrin (ZnTPP) und mit diesem über einem flexiblen Arm verbundenen Spiropyranderivat. Letztere ändert seine Konformation durch die Einstrahlung mit Licht geeigneter Wellenlänge, womit sich das Dipolmoment stark ändert. Es zeigte sich, dass das Schaltverhalten auf einen Graphen mit dem Schaltverhalten einer Dyade in Lösung vergleichbar ist. Dieses lässt den Schluss zu, dass das Schalteigenschaften einer einzelnen Dyade auf das adsorbierte Kollektiv übertragen werden kann, da es keine signifikanten beeinflussenden Wechselwirkungen durch die leitende Oberfläche und der benachbarten Dyaden auswirkte.The first of this two-part work deals with the STM investigation of an interface in the surrounding natural atmosphere, which is formed by the adsorption of the conductive graphene onto the mica surface. In this interface, water molecules may intercalate by the surrounding humidity. By varying the relative humidity, the interface is rewetted, respectively, dewetted and it manifests itself in a star shape growing fractals, where the height of graphene is decreased by approximately the diameter of one water molecule. The STM investigation - which is primarily sensitive to the density of states of graphene - shows that additional significant changes in the height of graphene are formed within the fractal, unlike in the SFM investigations. This suggests that there is a water layer by which the density of graphene is differently affected by domains with significant distinguishable polarisation alignments. However, this is equivalent to the assumption that there are two or more water layers exist within the interface. The second part of this work deals with the STM investigation of a functionalized surface characterised by a functionalized dyad adsorbed onto a conductive surface (graphene and HOPG) at a solid-liquid interface. This dyad essentially comprises a zinc-tetraphenylporphyrin (ZnTPP) and is connected with a spiropyran derivative via a flexible linker. This changes its conformation through irradiation with light with a suitable wavelength, by which the dipole moment is also strongly changed. It was found that the switching behaviour of a graphene-based conductive surface is comparable with the switching behaviour of a dyad, which itself can move freely in solution. This leads to the conclusion that the switching properties of a single dyad can be transmitted to its collective because it affected no significant influence interactions by the conductive surface and the adjacent dyads.
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Holliday, Nathan. "Processing and Properties of SBR-PU Bilayer and Blend Composite Films Reinforced with Multilayered Nano-Graphene Sheets." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1458300045.
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Kumar, Priyank Vijaya. "Enhanced electrical, optical and chemical properties of graphene oxide through a novel phase transformation." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98736.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 86-98).
Graphene oxide (GO) is a versatile, solution-processable candidate material for next-generation, large-area, ultrathin electronics, optoelectronics, energy conversion and storage technologies. GO is an atom-thick sheet of carbon functionalized with several oxygen-containing groups dominated by the epoxy and hydroxyl functional groups on the basal plane, with carboxyls and lactols at the sheet edges. It is well known that reduction of GO at temperatures > 150°C leads to the removal of oxygen atoms from the carbon plane, leading to the formation of reduced GO (rGO) structures. Although GO has been utilized for multiple applications in the last decade, our understanding of the structure-property relationships at the atomic-level has still been lacking owing to the amorphous nature and chemical inhomogeneity of GO, which has in turn limited our ability to design and tailor GO nanostructures for high-performance applications. In particular, the material's structure and its structural evolution at mild annealing temperatures (< 1000°C) has been largely unexplored. In this thesis, we use a combination of first-principles computations, classical molecular dynamics simulations based on reactive force fields and experiments to model realistic GO structures and develop a detailed understanding of the relationship between the carbon-oxygen framework and the sheet properties, at the atomic level. Based on our understanding, we demonstrate a new phase transformation in GO sheets at mild annealing temperatures (50-80°C), where the oxygen content is preserved and as-synthesized GO structures undergo a phase separation into prominent oxidized and graphitic domains facilitated by oxygen diffusion. Consequently, as-synthesized GO that absorbs mainly in the ultraviolet region becomes strongly absorbing in the visible region, photoluminescence is blue shifted and electronic conductivity increases by up to four orders of magnitude. We then use this novel phase transformation to improve two sets of applications. 1) We demonstrate that cell capture devices making use of phase transformed-GO substrates have higher capture efficiencies compared to devices making use of as-synthesized GO substrates. 2) We show that the reduction of phase transformed-GO leads to better electrical properties of rGO thin films. Our results fill an important gap and establish a complete theory for structural evolution of GO over the entire range of temperatures, i.e. from room temperature to ~1000°C. Taken together, this structural transition in GO enables us to predict and control the sheet properties in new ways, as opposed to reduction, which is till date the only handle to control the structure of GO. This could potentially open the door for completely new applications or for enhancing the performance of existing applications based on GO.
by Priyank Vijaya Kumar.
Ph. D.
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Liang, Qizhen. "Preparation and properties of thermally/electrically conductive material architecture based on graphene and other nanomaterials." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44846.
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With excellent electrical, thermal and mechanical properties as well as large specific surface area, graphene has been applied in next-generation nano-electronics, gas sensors, transparent electrical conductors, thermally conductive materials, and superior energy capacitors etc. Convenient and productive preparation of graphene is thereby especially important and strongly desired for its manifold applications.
Chemically developed functionalized graphene from graphene oxide (GO) has significantly high productivity and low cost, however, toxic chemical reduction agents (e.g. hydrazine hydrate) and raised temperature (400-1100°C) are usually necessary in GO reduction yet not preferred in current technologies. Here, microwaves (MW) are applied to reduce the amount of graphene oxide (GO) at a relatively low temperature (~165°C). Experimental results indicate that resurgence of interconnected graphene-like domains contributes to a low sheet resistance with a high optical transparency after MW reduction, indicating the very high efficiency of MW in GO's reduction.
Moreover, graphene is usually recumbent on solid substrates, while vertically aligned graphene architecture on solid substrate is rarely available and less studied. For TIMs, electrodes of ultracapacitors, etc, efficient heat dissipation and electrical conductance in normal direction of solid surfaces is strongly desired. In addition, large-volume heat dissipation requires a joint contribution of a large number of graphene sheets. Graphene sheets must be aligned in a large scale array in order to meet the requirements for TIM application. Here, thermally conductive fuctionalized multilayer graphene sheets (fMGs) are efficiently aligned in a large scale by vacuum filtration method at room temperature, as evidenced by SEM images and polarized Raman spectroscopy. A remarkably strong anisotropy in properties of aligned fMGs is observed. Moreover, VA-fMG TIMs are prepared by constructing a three-dimensional vertically aligned functionalized multilayer graphene architecture between contact Silicon/Silicon surfaces with pure Indium as a metallic medium. Compared with their counterpart from recumbent A-fMGs, VA-fMG TIMs have significantly higher equivalent thermal conductivity and lower contact thermal resistance.
Electrical and thermal conductivities of polymer composite are also greatly interested here. Previous researches indicated that filler loading, morphology of fillers, and chemical bonding across filler/polymer interfaces have significant influence on electrical/thermal conductivity of polymer composite. Therefore, the research also pays substantial attention to these issues. First, electrical resistivity of CPCs is highly sensitive on volume or weight ratio (filler loading) of conductive fillers in polymer matrix, especially when filler loading is close to percolation threshold (pc). Thermal oxidation aging usually can cause a significant weight loss of polymer matrix in a CPC system, resulting in a filler loading change which can be exhibited by a prompt alteration in electrical resistivity of CPCs. Here, the phenomena are applied as approach for in-situ monitoring thermal oxidation status of polymeric materials is developed based on an electrical sensors based on conductive polymeric composites (CPCs). The study developed a model for electrical resistivity of sensors from the CPCs as a function of aging time at constant aging temperature, which is in a good agreement with a Boltzmann-Sigmoidal equation. Based on the finding, the sensors show their capability of in-situ in-situ monitor and estimate aging status of polymeric components by a fast and convenient electrical resistance measurement.
Second, interfacial issues related to these thermal conductive fillers are systemically studied. On the one hand, the study focuses on relationship between morphology of h-BN particles and thermal conductivity of their epoxy composites. It is found that spherical-agglomeration of h-BN particles can significantly enhance thermal conductivity of epoxy resin, compared with dispersed h-BN plates, by substantially reducing specific interfacial area between h-BN and epoxy resin. On the other hand, surface of high thermal conductive fillers such as SiC particles and MWNTs are successfully functionalized, which makes their surface reactive with bisphenol A diglycidyl ether and able to form chemical bonding between fillers and epoxy resin. By this means, thermal conductivity of polymer composites is found to be significantly enhanced compared with control samples, indicating the interfacial chemical bonding across interface between thermal conductive fillers and polymer matrix can promote heat dissipation in polymeric composites. The finding can benefit a development of high thermal conductive polymer composites by interfacial chemical bonding enhancement to meet the demanding requirements in current fine pitch and Cu/low k technology.
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Wang, Zhenping [Verfasser]. "Investigation of electrical properties of monolayer oxo-functionalized graphene-based two-dimensional materials / Zhenping Wang." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1212031997/34.
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Wasala, Milinda. "ELECTRONIC AND OPTO-ELECTRONIC TRANSPORT PROPERTIES OF FEW LAYER INDIUM SELENIDE FETS." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/dissertations/1704.
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Layered Van der Waals solids, due to their highly anisotropic structure as well as their availability in mono, few and multi-layer form constitute a perfect playground, where a variety of possibility in structural variation as well as functionalities are expected. This potentially gives rise to a library of unique and fascinating 2D materials systems. These systems appear to demonstrate some spectacular variety of fundamental physics as well as indicate that some of these systems can be beneficial for several niche applications directly or indirectly resulting from their electrical and optical properties.
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Zhou, Ruiping. "Structural And Electronic Properties of Two-Dimensional Silicene, Graphene, and Related Structures." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1341867892.
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Maneshian, Mohammad Hassan. "The Influence of Ohmic Metals and Oxide Deposition on the Structure and Electrical Properties of Multilayer Epitaxial Graphene on Silicon Carbide Substrates." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc68009/.
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Graphene has attracted significant research attention for next generation of semiconductor devices due to its high electron mobility and compatibility with planar semiconductor processing. In this dissertation, the influences of Ohmic metals and high dielectric (high-k) constant aluminum oxide (Al2O3) deposition on the structural and electrical properties of multi-layer epitaxial graphene (MLG) grown by graphitization of silicon carbide (SiC) substrates have been investigated. Uniform MLG was successfully grown by sublimation of silicon from epitaxy-ready, Si and C terminated, 6H-SiC wafers in high-vacuum and argon atmosphere. The graphene formation was accompanied by a significant enhancement of Ohmic behavior, and, was found to be sensitive to the temperature ramp-up rate and annealing time. High-resolution transmission electron microscopy (HRTEM) showed that the interface between the metal and SiC remained sharp and free of macroscopic defects even after 30 min, 1430 °C anneals. The impact of high dielectric constant Al2O3 and its deposition by radio frequency (RF) magnetron sputtering on the structural and electrical properties of MLG is discussed. HRTEM analysis confirms that the Al2O3/MLG interface is relatively sharp and that thickness approximation of the MLG using angle resolved X-ray photoelectron spectroscopy (ARXPS) as well as variable-angle spectroscopic ellipsometry (VASE) is accurate. The totality of results indicate that ARXPS can be used as a nondestructive tool to measure the thickness of MLG, and that RF sputtered Al2O3 can be used as a (high-k) constant gate oxide in multilayer grapheme based transistor applications.
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Littlejohn, Samuel David. "Electrical properties of graphite nanoparticles in silicone : flexible oscillators and electromechanical sensing." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.600642.
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This thesis reports the discovery of a wide negative di↵erential resistance (NDR) region in a graphite-silicone composite that was utilized to create a strain-tuned flexible oscillator. Encoding the strain into frequency mimics the behavior of mechanoreceptor neurons in the skin and demonstrates a flexible and electronically active material suitable for state of the art bio-electronic applications. The NDR was investigated over a range of composite filling fractions and temperatures; alongside theoretical modelling to calculate the tunneling current through a graphite-silicone barrier. This led to the understanding that the NDR is the result of a semi-metal to insulator transition of embedded graphene bilayers within the graphite nanoparticles. The transition, brought about by a transverse bias across specifically orientated particles, opens a partial band-gap at the Fermi level of the bilayer. NDR in a flexible material has not been observed before and has potential for creating a flexible active device. The electromechanical properties of the composite were considered through a bend induced bilayer strain. The piezoresistance was found to be dominated by transient resistance spiking from the breaking of conduction lines, which then reform according to the viscoelasticity of the polymer matrix. The resistance spiking was embraced as a novel method for sensitive di↵erential pressure detection, used in the development of two applications. Firstly, it was employed for the detection of ultrasound waves and found to have an acoustic pressure detection threshold as low as 48 Pa. A commensurability was observed between the composite width and ultrasound wavelength which was shown to be consistent with the formation of standing waves, described by Bragg’s law. Secondly, a differential pressure array of 64 composite pixels was fabricated and demonstrated to image pressures under 3.8 kPa at a resolution of 10 dpi. The NDR active region was incorporated into an LC circuit where it was demonstrated to sustain oscillations of up to 12.5 kHz. The composite was then strained and an intrinsic frequency was observed which had a linear dependence on the strain with a frequency shift of 84 Hz / % strain. Lastly the composite was used in a strain-tuned amplifier circuit and shown to provide a gain of up to 4.5. This thesis provided the groundwork for a completely flexible electronically active device for futuristic bio-electronic skins with resolutions and sensitivities rivalling those of human tactile sensing.
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Sreenivasan, Raghavasimhan. "Metal-gate/high-k dielectric stack engineering by atomic layer deposition : materials issues and electrical properties /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Nittala, Aditya Kameshwara. "Electrical and Mechanical Performance of Aluminum Alloys with Graphite Nanoparticles." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1554117521295178.
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Pirondelli, Andrea. "Production and Electrical Characterization of Low Density Polyethylene-based Micro- and Nano-dielectrics containing Graphene Oxide, Functionalized Graphene and Carbon Black additives." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textAbstract:
Oggigiorno la ricerca di nuovi materiali per gradatori di campo da impiegarsi in accessori di cavi ha iniziato a studiare alcuni materiali nano dielettrici con proprietà elettriche non lineari con la tensione ed aventi proprietà migliorate rispetto al materiale base. Per questo motivo in questo elaborato si sono studiati materiali nanostrutturati a base di polietilene a bassa densità (LDPE) contenenti nano polveri di grafene funzionalizzato (G*), ossido di grafene (GO) e carbon black (CB). Il primo obiettivo è stato quello di selezionare e ottimizzare i metodi di fabbricazione dei provini. La procedura di produzione è suddivisa in due parti. Nella prima parte è stata utilizzatala tecnica del ball-milling, mentre nella seconda un pressa termica (thermal pressing). Mediante la spettroscopia dielettrica a banda larga (BDS) si sono misurate le componenti reali e immaginarie della permettività e il modulo della conducibilità del materiale, in tensione alternata. Il miglioramento delle proprietà rispetto al provino di base composto dal solo polietilene si sono ottenute quando il quantitativo delle nanopolveri era maggiore. Le misure sono state effettuate sia a 3 V che a 1 kV. Attraverso misurazioni di termogravimetria (TGA) si è osservato l’aumento della resistenza termica di tutti i provini, soprattutto nel caso quando la % di nanopolveri è maggiore. Per i provini LDPE + 0.3 wt% GO e LDPE + 0.3 wt% G* si è misurata la resistenza alle scariche parziali attraverso la valutazione dell’erosione superficiale dei provini. Per il provino contenente G* è stato registrato una diminuzione del 22% del volume eroso, rispetto al materiale base, mentre per quello contenente GO non vi sono state variazioni significative. Infine si è ricercata la resistenza al breakdown di questi ultimi tre provini sopra citati. Per la caratterizzazione si è fatto uso della distribuzione di Weibull. Lo scale parameter α risulta aumentare solo per il provino LDPE + 0.3 wt% G*.
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Foster, Mark Joseph. "Modeling Conductive Properties of Highly Aligned Single-Walled Carbon Nanotube and Graphene Thin Films." Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1627748724986992.
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Chiou, Chuang-Fu, and 邱創富. "Electrical and humidity sensing properties of reduced graphene oxide thin film fabricated by layer-by-layer covalently anchoring on flexible substrate." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/06803273987508265099.
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碩士中國文化大學
化學系應用化學碩士班
102
Novel flexible humidity sensors were fabricated by layer-by-layer (LBL) covalently bonding graphene oxide (GO) to a gold electrode on a plastic substrate using a peptide chemical protocol and then reducing in-situGO film to a partially reduced GO film. The effect of the duration of reduction of GO film on the electrical and humidity propertiesof the reduced GO film was investigated. This flexible impedance-type humidity sensor exhibited a strong water resistance, a wide working range of humidities, a short response/recovery time, a weak dependence on temperature and good long-term stability. The different complex impedance plots obtained at low and high relative humidity indicated that the ions dominate the conductance of the anchored partially reduced GO film.
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Huang, Jian-Wei, and 黃建維. "High quality few-layer graphene grown by Chemical Vapor Deposition and electric properties." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/96683676240128329954.
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WANG, PIN-HAN, and 王彬翰. "The effect of electric field on the electronic properties of few layer graphene nanoribbons:A first-principle study." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/21600007157235912586.
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碩士國立中正大學
物理學系暨研究所
103
The purpose of this thesis was to use Density Functional Theory (DFT) to determine both geometry and electric properties of few-layer graphene nanoribbons and applied an electric field to study the influence of electric properties. More than two layer Zigzag graphene nanoribbon will make the structure bend.If fit the structure in Z-Y plane, we will get a quadratic linear regression model and it’s equation (z=a+by+cy^2 ).Then,we can judge the curvature by magnitude of c. Results indicate that wider width of Zigzag graphene nanoribbon got lower magnitude of c. Different stack of few-layer Zigzag graphene nanoribbon have different electric properties.Two-layer Zigzag graphene nanoribbon magnetic moment will vanish, and its bandgap decrease into zero. AAA-stack Zigzag graphene nanoribbon band structure cross through fermi level and change into a metal-semiconductor. Same result appearin ABC’A and AAAA-stack of Zigzag graphene nanoribbon. Armchair graphene nanoribbon more than two layer did not bend. Different layer-stack Armchair graphene nanoribbon got different electric properties. When layer increase, Armchair graphene nanoribbon band gap will decrease for N=3p and 3p+1. In order to get the relation between width and electric field with different stack,we applied an electric field on Zigzag graphene nanoribbon. The calculation show that some value of electric field will made moment vanish or total moment unequal zero. Causing the band structure irregular vary. The effective electric field alter the band cross fermi level,and causes the metal-semiconductor transition. Electric field cause no apparent change to Armchair graphene nanoribbon,N=3pwill tiny decrease band gap when electric field increase.
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Lin, Ming-Chou, and 林銘洲. "On Friction Properties of Fe-Al-(C)/Graphite Hybrid Hard Layer at 6082 Al Alloy by Electrical Discharge Alloying Process via. Internal Grinder Machine and Infrared Thermograph." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/jr2y86.
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碩士國立中興大學
材料科學與工程學系所
106
ABSTRACT This study experimentally investigates the surface modification of 6082 Al alloy by the electrical discharge alloying EDA process. EDA process is the reverse-electrode method of electric discharge machine. pure iron was used as negative electrode in this process to improve friction properties of AA6082 alloy. Samples were analyzed by internal grander machine and infrared thermograph. The internal grinder experimental result show the base metal (6082 Al alloy) on the wear-resisting is rated current 5.6 A of 12 % (friction current 0.672 A) and electric power is 147 W. The general hard anodizing and super hard anodizing of specimen, the wear-resisting is show rated current 5.6 A of 11% (friction current 0.616 A) and electric power is 135 W. EDA alloyed layer of the wear-resisting is show rated current 5.6 A of 10% (friction current 0.56 A) and electric power is 123 W. EDA alloyed layer the specimen surface due to has pyrolytic graphite, can effectively reduce the wear-resisting and friction current, according to the reference, graphite have excellent lubricating performance. Then, the infrared thermography experimental result show the friction temperature on base metal (6082 Al alloy) is 29.46 degrees. Hard anodizing of the friction temperature is 31.41 degrees. super hard anodizing of the friction temperature is 32.46 degrees . EDA alloyed layer the specimen the friction temperature dropped to 27.91 degrees. The infrared thermography of EDA alloyed layer was evidently lower than that of the base metal (6082 Al alloy) and hard and super hard anodizing of specimen. Among the experimental result, pyrolytic graphite can effectively improve the friction properties of AA6082 alloy with the collocation of the hard alloyed layer and the excellent lubrication effect of graphite.
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Huang, Yu-ping, and 黃雨平. "Study of Electrical Properties of Strained Graphene." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/13365914109552496619.
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碩士國立中央大學
物理學系
102
In this thesis, the graphene were grown by chemical vapor deposition. And using wet transfer that graphene were transferred from copper to PET. Then strain exerted to graphene by bending the PET substrate. The electrical property of graphene was measured by Hall measurement system. The sheet resistivity of graphene was increased rapidly that strain exerted on graphene at first. When the strain exerted on graphene released, the sheet resistivity of graphene was not changed. In the second times and third times that strain exerted on graphene, the sheet resistivity of graphene was not changed. When the strain exerted on graphene bigger than last times, the sheet resistivity of graphene was higher than last times. For the graphene with various initial sheet resistivity`s, the sheet resistivity of graphene were changes with square of the change in sample length. The reason is that the length of graphene was changed with the length of sample was changed. The change in length of graphene, due to the defects of graphene increased. The defects of graphene increase, the sheet resistivity of graphene increased. The mobility of graphene is increased with the defects increased. The carrier scattering of graphene were increased with the defects of graphene increased. The carrier concentration of graphene is increased with the graphene be strained. The carrier concentration of graphene is return to initial with the strain of graphene release.
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Ying-HuaWu and 吳盈樺. "Effects of Random Potential on the Electronic Properties of Graphene Layer and Graphene Isles." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/43414450672600269482.
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碩士國立成功大學
物理學系碩博士班
100
Due to its promising potential as a candidate for the post-silicon electronic material, single-layer graphite structure (Known as graphene) hade became a hot research topics in the recent decade. In this work, we investigate the effects of random potential on the optical and electronic properties for both single-layer graphene and small graphene isles. For small graphene isles (preserved the C6v symmetry), we calculated the eigen levels using tight-binding method. Each level was assigned an irreducible notation to indicate its symmetry. We then derive the selection rule for optical transition between the symmetries of the empty and the occupied levels. The selection rule greatly simplified the absorption spectrum. After applied random potential to the isles, the peak position of the spectrum didn’t move apparently, but the width broadened. The extent of broadening can be used to indicate the strength of random potential. For a single-layer graphene, we adopt a large super-cell (e.g. 11x13) to impose the random potential. We first demonstrated to unfold the band structure in the small super-Brillouin zone into the original first Brillouin zone, using the projection method proposed by Tu. The existence of the random potential broke the honey-comb structure symmetry of graphene. It opened a gap at the Dirac point. The band structure possessed the parabolic shape at the very vicinity of Dirac point, and restore back to the linear band. We employed the average density of states to illustrate the parabolic to linear behaviors of the band structure.
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Chien, Yuan-hung, and 錢遠鴻. "The optical and electrical properties of multilayer graphene." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/89423513136455328377.
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碩士國立中央大學
物理研究所
100
In this thesis, high quality monolayer graphene were grown on Cu foil by chemical vapor deposition, and we manufacture multilayer graphene by stacking monolayer graphene. The propose of stacking multilayer graphene is to obtain optimum condition both in optical and electrical properties. According to the results of Raman spectrum measurement, the full width at half maximum of G band and 2D band peaks are both smaller than 40 cm-1 and the ratio of 2D/G is larger than 1.5, which means the transferred graphene is monolayer. The average sheet resistivity of transferred graphene, which is measured by Hall measurement system, are about 2000 ohm/sq. For the optical and electrical properties of stacked multilayer graphene, the transmittance, Raman spectrum, and Hall measurement were taken. The Raman spectrum results shows that the peak positions of G and 2D band didn’t shift and the 2D/G ratio were almost the same between one and stacked multilayer graphene. In addition, no shoulders were observed in the 2D peak of Raman spectrum that means there should be no interactions between layers. In the optical transmittance results, the absorption of multilayer graphene is about 3.1%/layer at 555 nm wavelength. The transmittance of three layers graphene is about 90%. In electrical properties, the sheet resistivity of graphene were decreased to 50% and 75% with stacked layer number was two and three layers, respectively. When the layer number was increased more than five layers, the sheet resistivity of multilayer graphene was close to HOPG. In the thesis, we successfully manufacture certain layers graphene by stacking monolayer graphene. The sheet resistivity of stacked graphene was decreased and the optical transmittance of stacked graphene was above 90%.
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Hsieh, Yun-Lien, and 謝昀璉. "Electrical conduction properties of chemical vapor deposited graphene." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/80574758566779667022.
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碩士國立中興大學
物理學系所
101
Graphene, an isolated single atomic layer of graphite, spotlights the practicability of the quantum confined systems. Here we report the optical and electric properties of graphene synthesized by chemical vapor deposition(CVD) on copper foils. The copper foil is etched by 0.25M ferric nitrate solution or 0.1M ammonium persulfate(APS) solution from backside. The graphene is transferred (assisted by PMMA)onto Si3N4/Si and SiO2/Si substrates, respectively. The Si3N4/Si substrates with Si3N4 membrane which thickness of 30nm, 75nm and 100nm . Through Raman spectrum mapping (with 488nm excitation laser), carbon signals are revealed an enhancement larger than 50% in D-band (1360cm-1) , G-band(1580cm-1) and 2D-band (2700cm-1) when the graphene was on sub-micrometer membranes. For studying their charge transport property, the grpaphene were transferred onto SiO2/Si substrates, followed by the fabrication of Al top gates. By modulating the gate voltage, we observed an ambipolar field effect and determined the Dirac point. The hole and the electron mobility both are on the order of 102cm2/V‧s . With sufficient magnetic field modulated, we observe Anderson localization at several temperatures.
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Ku-YuChen and 陳谷宇. "Electrical Properties of Graphene on β phase silicon nitride." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/y5sq4e.
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碩士國立成功大學
物理學系
103
Abstract Graphene is a rising star in both science and technology due to its unique electronic, thermal, and mechanical properties. However, graphene family is generally supported on silicon dioxide substrates; strong impurity scatterings at the interface obscure the study of the fundamental physics in graphene systems. Although suspending graphene and boron nitride [BN] as the substrate lead to a substantial improvement, these methods are unsuitable for massive production and thus their implications are severely limited. In principle, epitaxial monocrystalline β-silicon nitride [β-Si3N4] substrates match graphene lattice, which reduce interfacial strain like graphene/BN devices, and exhibit higher-κ dielectric constant than that on BN substrates. Graphene family on epitaxial β-Si3N4/Si substrates may be a promising structure in 2D-material integrated circuits on wafer scale. Here, we demonstrate the carrier mobility of single-layer graphene/β-Si3N4 devices is higher than 5000 cm^2⁄(v.s) before using the annealing process. In our experimental result, we report on the characterization of magnetotransport measurements in the graphene’s devices.
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Yang, Yu-Jhe, and 楊育哲. "Electrical and Optical Properties of Plasma Reduced Graphene Oxide." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/9454vk.
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碩士國立中興大學
光電工程研究所
101
In recent years, graphene is a unique two-dimensional structure with good electrical conductivity and thermal conductivity. However graphene oxide has attracted considerable attention because it has tunable surface chemical properties, electrical and optical properties. Many reduction approaches have been developed and most of reduction processes have abundant defects. In study, CH4 plasma treatment could reduce the graphene oxide and help defects repair. So we studied plasma reduction and decreased defects at the same time by the three kinds of the gas plasma such as H2, CH4 and H2+CH4 and compared their electrical and optical properties. Here we used plasma to reduce graphene oxide by PECVD. FTIR and XPS are used to know functional groups of graphene oxide, Raman is used to know molecular structure of graphene oxide and the two analysis methods can be used to know reduction level. In this thesis, we know H2+CH4 plasma treatment to reduce graphene oxide is outstanding, so we studied the relationship of transmittance and energy band gap, electrical properties, and the difference of exposure before and after reduction. We discover reduction level advance with the plasma treatment time increasing, so conductivity is increasing, too. Then, the samples were exposed by different light. Especially exposure to UV light, the measure results prove the current is apparent decreasing at low voltage.
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Wu, Chrng-Fang, and 吳承芳. "Thickness dependence of electrical properties of reduced graphene oxides." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/24643515613430215781.
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碩士國立交通大學
電子物理系所
101
The unique electrical properties of a real two-dimensional material, graphene, have attracted a lot of attentions since it was realized in 2004. The evolution from graphite to graphene has also been an interesting subject. Atomic force microscopy (AFM) and Raman spectrum have been, so far, the only two standard methods to identify layer number of the few-layer graphene (FLG). In this study, we use two different methods of electrical measurement for the determination of the layer number of FLG. We have observed a variation of resistivity at different temperature and conductivity at different bias voltage, and have investigated changes of physical properties with an increase of the layer number. Before the device fabrication, AFM is used to measure the thickness of the FLG for the estimation of the layer number. We use electron-beam lithography to make two types of devices for different electrical measurements. Type I devices are purely Ohmic-contacted devices. The metal electrodes are made by radio-frequency sputtering deposition. Type II devices are tunneling devices with a 8-nm thick aluminum oxide layer between metal (platinum) electrodes and a FLG. Resistivities of Type I devices are measured in the temperature range from 300 K to 30 K and the data are analyzed in accordance with the simple two band (STB) model. The layer dependent properties have been extracted through our analyses. When the layer number increases, the effective carrier mass, the electron-phonon interaction, and the density of state at Fermi level increase whereas the band overlap is kept constant. By analyzing our data from electrical measurements with the theoretical model, we have discovered alternatively other physical parameters which dependent strongly on the layer number of the FLG.
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Saha, Srijan Kumar. "Structural, Electronic And Vibrational Properties Of n-layer Graphene With And Without Doping : A Theoretical Study." Thesis, 2010. http://etd.iisc.ernet.in/handle/2005/1273.
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Graphene – a two-dimensional honeycomb lattice of sp2-bonded carbon atoms – has been attracting a great deal of research interest since its first experimental realization in 2004, due to its various novel properties and its potential for applications in futuristic nanodevices. Being the fundamental building block for carbon allotropes of other dimensionality, it can be stacked to form 3d graphite or rolled into 1d nanotube. Graphene is the thinnest known material in the universe, and one of the strongest materials ever measured in terms of its in-plane Young modulus and elastic stiffness. The charge carriers in graphene exhibit giant mobility as high as 20 m2/Vs, have almost zero effective mass, and can travel for micrometers without scattering even at ambient conditions. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and renders easy accessibility to optical probes. Electron transport in graphene is described by a Dirac-type equation, which allows the investigation of “relativistic” quantum phenomena in a benchtop experiment. This results in the observation of a number of very peculiar electronic properties from an anomalous quantum Hall effect to Kien paradox and the absence of localization.
All these enticing features make this material an excellent candidate for application in various electronic, photonic and optoelectronic devices. For instance, its ballistic ambipolar transport and high carrier mobility are the most useful traits for making ultrafast and low-power electronic devices. Its high surface area shouldmake it handy in manufacturing tough composite materials. The extreme thinness of graphene could also lead to more efficient field emitters that release electrons in the presence of strong electric
fields. Its robustness and light weight are useful for micromechnical resonators. The tunability of its properties could make it possible to build so-called spin-valve transistors, as well as ultra-sensitive chemical detectors.
Many of such applications of graphene require tuning of its properties, which can be achieved by varying the number of layers or/and by doping. There are several ways to dope graphene: (i)electrochemically gated doping, (ii)molecular charge-transfer doping, and (iii) substitutional doping by atoms like Boron or Nitrogen.Moreover, for graphene, a zero band gap semiconductor in its pristine form, to become a versatile electronic device material it is mandatory to find means to open up a band gap and tune the size of the band gap. Several strategies have been adopted to engineer such a band gap in graphene in a controlled way. Some of these are based on the ability to control the geometry of graphene layers, some use graphene-substrate interactions, while others are based on chemical reactions of atoms or molecules with the graphene layer.
Motivated by these considerations, in this thesis we present a systematic and thorough study of the structural, electronic and vibrational properties of graphene and their dependence on the number of layers, and on doping achieved electrochemically, molecularly and substitutionally, using first principles density functional theory (DFT).
In Chapter 1, we give an introduction to the hitherto beguiling world of graphene. Here, we briefly discuss the structure, novel properties and potential applications of graphene, and the motivation for this thesis.
In Chapter 2, an overview of the DFT formalism adopted here is given. We clearly state the theorems of the formalism and the approximations used when performing calculations. We succinctly explain how the various quantities like total energies, forces, stresses etcetera are calculated within this formalism. We also discuss how phonon frequencies, eigenvectors, electron-phonon couplings are obtained by using density functional perturbation theory (DFPT), which calculates the full dynamical matrices through the linear response of electrons to static perturbations induced by ionic displacements. Calculations are done first using a fully ab-initio approach within the standard Born-Oppenheimer approximation, and then time-dependent perturbation theory is used to explore the effects of dynamic response.
In Chapter 3, using such first-principles density-functional theory calculations, we determine the vibrational properties of ultra-thin n(1,2,...,7)-layer graphene films and present a detailed analysis of their zone-center phonons. We present the results (including structural relaxations, phonons, mode symmetries, optical activities) for bulk Graphite, single-layer graphene and ultrathin n-layer graphene films. and discuss the underlying physics of our main results together with a pictorial representation of the phonon modes. We demonstrate that a low-frequency (∼ 112 cm−1 ) optical phonon with out-of-plane displacements exhibits a particularly large sensitivity to the number of layers, although no discernible change in the interlayer spacing is found as n varies. Frequency shifts of the optical phonons in bilayer graphene are also calculated as a function of its interlayer separation and interpreted in terms of the inter-planar interaction.
The surface vibrational properties of n-layer graphene films are presented in Chapter 4, which renders a detailed and thorough analysis of all the surface phonon modes by determining, classifying and identifying them accurately. The response of surface modes to the presence of adsorbed hydrogen molecules is determined. As an illustrative adsorbate, hydrogen is chosen here mainly because of its huge importance in fuel cell technology and as a molecular sensor. We demonstrate that a doubly degenerate surface phonon mode with low-frequency (~ 35cm−1)exhibits a particularly large sensitivity to the adsorption of hydrogen molecules, as compared to other surface modes. Futhermore, we show that a low-frequency (108.8 cm−1)bulk-like phonon with out-of-plane displacements is also very sensitive and gets upshifted by as much as 21 cm−1 due to this adsorption.
In Chapter 5, we determine the adiabatic frequency shift of the and phonons in a monolayer graphene as a function of both electron and hole doping. The doping is simulated here to correspond to electrochemically gated graphene. Compared to the results for the E2g -Γ phonon (Raman G band), the results for the phonon are dramatically different, while those for the phonon are not so different. Furthermore, we calculate the frequency shifts, as a function of the charge doping, of the (K + ΔK) phonons responsible for the Raman 2D band –a key finger print of graphene, where [ΔK] is determined by the double resonance Raman process.
Doping graphene with electron donating or accepting molecules is an interesting approach to introduce carriers into it, analogous to electrochemical doping accomplished in graphene when used in a field-effect transistor. In Chapter 6, we use first-principles density-functional theory to determine changes in the electronic structure and vibrational properties of graphene that arise from the adsorption of aromatic molecules such as aniline and nitrobenzene. Identifying the roles of various mechanisms of chemical interaction between graphene and the adsorbed molecules, we bring out the contrast between electrochemical and molecular doping of graphene. Our estimates of various contributions to shifts in the Raman active modes of graphene with molecular doping are fundamental to the possible use of Raman spectroscopy in (a)characterization of the nature and concentration of carriers in graphene arising from molecular doping, and (b) graphene-based chemical sensors.
Graphene doped electrochemically or through charge-transfer with electron-donor and acceptor molecules, shows marked changes in electronic structure, with characteristic signatures in the Raman spectra. Substitutional doping, universally used in tuning properties of semiconductors, could also be a powerful tool to control the electronic properties of graphene. In Chapter 7, we present the structure and properties of boron and nitrogen doped graphenes, again using first-principles density functional theory. We demonstrate systematic changes in the carrier-concentration and electronic structure of graphenes with B/N-doping, accompanied by a stiffening of the G-band and change of the defect related D-band in the Raman spectra. Such n/p -type graphenes obtained without external fields or chemical agents should find device applications.
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Lee, Chao-Yu, and 李兆育. "Fabricate p-/n-type graphene via physical doping andInvestigate electrical properties of doping graphene." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/g2k234.
Full textAbstract:
碩士國立臺灣大學
光電工程學研究所
106
Study and develop 2D-materials devices have been the aim of scientists due to excellent conductivity and highly transparent properties. Since the discovery of graphene, graphene is becoming a rapidly growing and enormously promising field, and have great potential for wide applications. However, conduction band and valance band of intrinsic graphene is meeting at Fermi level, and implies that the carrier for conducting is insufficient. In this thesis, we demonstrate two methods for graphene doping, and analyze the results to make sure that the Fermi level could tune to suitability. The first method is molecular doping from substrate surface by modifying the SiO2/Si substrate surface with self-assembled molecule (SAM). When depositing graphene on SAM layer, the p-doping effect from silicon dioxide would be decreasing. The function groups of SAM would also dope the intrinsic graphene. However, the few H2O molecule between SAM layer and graphene would make serious impression on graphene. In our results, we found the results of SAM layer doping effect by measuring transfer curve are opposite totally of ultraviolet photoelectron spectroscopy. When few H2O molecule adsorb between SAM layer and graphene, the charge would transfer from H2O to graphene while the O atom of H2O head to the graphene surface. On the other hand, the charge would transfer from graphene to H2O when the H atom head to the graphene surface. The unexpected type of doping and high quality requirment of graphene and self-assembled layer make this method worthless. Thus, an easy and efficient method is desirable. Second method is vapor doping. We kept graphene in a place with vapor of dopant fill. Finally, graphene will be doped by adsorbing molecules on its surface. We found that the dominant mechanism of doping could be charge transfer between adsorbate and graphene. Besides, graphene could optimize by doping within certain degree. Finally, we also study the hysteresis of g-FET on different SAM-substrate and vapor doping graphene. In previous reports, the hysteresis of g-FET might originate from transfer and capacitive gating of H2O and SiO2 substrate, and compete with each other. In our study, we found the sweeping rate of measurement is not comparable to the life time of capacitive gating and the influence of capacitive gating is lower than that of charge transfer. For that result, charge transfer dominate the effect.
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Chiu, Yu-Huang, and 邱裕煌. "Electronic and Optical Properties of a Single-layer Graphene in Modulated Fields." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/40368023964011189990.
Full textAbstract:
博士國立交通大學
物理研究所
96
The π-electronic structures and optical absorption spectra of a single-layer graphene in spatially modulated magnetic and electric fields are studied by the tight-binding model and gradient approximation. For modulated magnetic fields, they could strongly affect the low-energy electronic properties, i.e., the dimensionality, energy dispersions, extra band-edge states, asymmetry, state degeneracy, and anisotropy of energy bands. There are partial flat bands at Fermi level and one-dimensional parabolic bands at others. The two kinds of bands make density of states (DOS) exhibit a delta-function-like structure and asymmetric prominent peaks, respectively. Each parabolic band owns one original and four extra band-edge states, and their energy dependences on the period and strength are investigated in detail. In the optical absorption spectra, the absorption peaks originating in original band-edge state and extra band-edge states obey different selection rules because their wave functions present different features. It is noted that the anisotropic absorption spectra are induced by different mod-ulated directions and electric polarization directions. For modulated electric fields, they could drastically change the low-frequency electronic and optical properties. Each energy band displays oscillatory energy dispersions and several band-edge states near original band-edge state. The doubly degenerate parabolic bands become nondegenerate. DOS shows many prominent asymmetric peaks mainly owing to the band-edge states. The finite DOS at Fermi level means that there are free carriers, i.e., a modulated electric field could change a semiconducting graphene into a semimetallic one. The optical absorption spectra demonstrate rich peaks resulting from band-edge states, and reveal the anisotropy in the modulated direction. Such absorption peaks could not be ascribed to an obvious selection rule.
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Yuan, Hui-Ching, and 袁惠卿. "Investigation on the Thermal Properties of Nanodiamond/Thin-layer Graphene Composite films." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/5ycza8.
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Kan, Zhe. "Electrical properties of carbon structures : carbon nanotubes and graphene nanoribbons." 2013. http://liblink.bsu.edu/uhtbin/catkey/1741647.
Full textAbstract:
Graphene is a one-atom thick sheet of graphite which made of carbon atoms arranged in a hexagonal lattice. Carbon nanotubes and graphene nanoribbons can be viewed as single molecules in nanometer scale. Carbon nanotubes are usually labeled in terms of the chiral vectors which are also the directions that graphene sheets are rolled up. Due to their small scale and special structures, carbon nanotubes present interesting electrical, optical, mechanical, thermal, and toxic properties. Graphene nanoribbons can be viewed as strips cut from infinite graphene. Graphene nanoribbons can be either metallic or semiconducting depending on their edge structures. These are robust materials with excellent electrical conduction properties and have the potential for device applications. In this research project, we present a theoretical study of electrical properties of the carbon structures. Electronic band structures, density of states, and conductance are calculated. The theoretical models include a tight-binding model, a Green’s function methodology, and the Landauer formalism. We have investigated the effects of vacancy and weak disorder on the conductance of zigzag carbon nanoribbons. The resulting local density of states (LDOS) and conductance bands show that electron transport has interesting behavior in the presence of any disorder. In general, the presence of any disorder in the GNRs causes a decrease in conductance. In the presence of a vacancy at the edge site, a maximum decrease in conductance has been observed which is due to the presence of quasi-localized states.Theory -- Band structure and density of states of carbon nanotubes -- Band structure and density of states of graphene nanoribbons -- Quantum conductance of zigzag graphene nanoribbons -- Quantum conductance of a zigzag graphene nanoribbon with defects.
Department of Physics and Astronomy
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Jewell, Ira. "Electrical characterization of thermally reduced graphite oxide." Thesis, 2010. http://hdl.handle.net/1957/16436.
Full textAbstract:
This thesis describes the transport properties observed in thermally treated graphite oxide (GO), which holds promise as an economical route to obtaining graphene. Graphene is a material consisting of a single atomic plane of carbon atoms and was first isolated as recently as 2004. Several isolation techniques have been investigated, including mechanical exfoliation, chemical vapor deposition, and the reduction (by various methods) of chemically synthesized graphite oxide.
Two fundamental questions are pursued in this work. The first is concerned with the maximum electrical conductivity that can be achieved in atomically thin reduced graphite oxide samples (rGO). As produced, GO is insulating and of little use electronically. By heating and exposure to reducing atmospheres, however, the conductivity can be increased. Through the lithographic definition and fabrication of four-point contact structures atop microscopic samples of GO, the resistance of the sample can be monitored in situ as the reduction process takes place.
It was discovered that the resistance of few-layer GO could be decreased by an order of magnitude when heated to 200 °C and subsequently cooled back to room temperature in forming gas. Final resistivities were on the order of 0.5 Ω-cm. An ambipolar field effect was observed in the thermally treated samples, with resistance decreasing by up to 16 % under a substrate bias of ±20 V. Mobilites were inferred to
be on the order of 0.1 cm²/V-s. It was also found that the presence of forming gas during reduction decreased the resistance of the GO samples by roughly one half.
The second question that this work begins to answer is concerned with the distance that electrons can travel in such thermally-reduced GO before spin-randomizing scattering. The answer can be elucidated with the aid of magnetoresistance measurements using ferromagnetic contacts to inject a spin-polarized current through the sample. The observation of the magnetoresistive effect with the contacts separated by a certain distance can be taken as evidence of a spin coherence length in the material of at least that distance.
Though this experiment has not yet been carried out, progress has been made toward its possibility; specifically in the fabrication and characterization of independently switchable magnetic contacts. By exploiting magnetic shape anisotropy, contact pairs have been fabricated and demonstrated to differ in magnetic coercivity by up to 8 Oe.Graduation date: 2011
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Chiu, Ta-Wei, and 邱達偉. "Electrical and thermoelectric transport properties in few-layer MoS2." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/he8p4k.
Full textAbstract:
碩士國立交通大學
電子物理系所
105
In recent years, many studies have concentrated on electrical and optoelectronic properties of few-layer MoS2. The thermoelectric properties are, however, still not well studied yet. In this study, we designed a pattern of current leads integrated with heater to investigate electrical and thermoelectric transport properties in few-layer MoS2 flakes in the temperature range from 80 to 600 K. The transport properties are different in different temperature regimes. We separated temperature behaviors into three different regimes for detailed discussions. At temperatures below 200 K, the temperature behavior of resistance (R) and Seebeck coefficient (S) can be described by the equations of R~exp(〖(T_0/T)〗^(1/3)) and S~T^(1/3), respectively, indicating that both electrical and thermoelectric transport satisfies with the two-dimensional variable-range hopping (2D-VRH) transport. In the temperature range from 300 to 460 K, the electron transport behavior changes from 2D-VRH to thermally activated transport and the thermoelectric transport changes to linear behavior as described by the equation S~T^1. At temperatures above 460 K, the electron transport behavior changes from insulating to metallic behavior whereas the thermoelectric transport still follows the relation of S~T^1. Additionally, we observed hysteresis and step-like feature in current-voltage loops in both electrical and thermoelectric data. The thickness-dependent and gate-dependent thermoelectric power factor (PF=S^2 σ) are studied and a maximum PF of 1.7 mW/m·K2 is measured at VG= 60 V in single layer MoS2 flakes. Our research results help to understand the electrical and thermoelectric characteristics in MoS2, and to show a high PF value that has potential for future applications of thermoelectric devices.
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Anicic, Rastko. "Effects of the Dielectric Environment on the Electrical Properties of Graphene." Thesis, 2013. http://hdl.handle.net/10012/7804.
Full textAbstract:
This thesis provides the study of graphene’s electrostatic interaction with the substrate surrounding it. Mathematical models based on current experimental configurations of graphene field-effect transistors (FET) are developed and analyzed. The conductivity and mobility of charge carriers in graphene are examined in the presence of impurities trapped in the substrate near graphene. The
impurities encompass a wide range of possible structures and parameters, including different types of impurities, their distance from graphene, and the spatial correlation between them. Furthermore, we extend our models to analyze the influence of impurities on the fluctuations of the electrostatic
potential and the charge carrier density in the plane of graphene. The results of our mathematical
models are compared with current experimental results in the literature.
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Yen-ChangChiu and 邱彥彰. "Microstructure, electrical conductivity and crystalline properties of syndiotactic polystyrene/graphene nanocomposites." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/86068756341379821604.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
100
Syndiotactic polystyrene (sPS) possesses some unique properties, including high crystallization rate, high melting temperature and good mechanical strength. It is a noticeable engineering plastic. Graphene is a single layer material with sp2 2D structure, making graphene as a material with great mechanical ,electrical and thermal conductivity properties. In this research, we blend sPS and grapehene whith thickness of about 1 nm (G1) or 10 nm (G10) by a coagulation method to prepare nanocomposites. The microstructure, crystallization behavior and electrical properties of the as-prepared nanocomposites are studied.. SEM, TEM and AFM results show that G1 is a wrinkled flake and its real thickness is less than 2 nm. G10 is a sheet with a smoother surfacre and its real thickness is less than 50 nm. The lateral sizes of these two kinds of graphene are reduced after sonication in o-DCB solution. Raman spectra reveal that G1 powders have more defects and sp3 structure than G10 powders. WAXD results show that melt-quenched nanocomposites produce the-form crystal of sPS. TEM results of the microtomed sample reveal that some striped lamella are developed in these melt-quenched nanocomposites and G1 fillers disperse more well in the sPS matrix. Dynamic heating and cooling of DSC results show that the addition of graphene decreases the cold crystallization temperature and increases the melt crystallization temperature of melt-quenched samples. Addition of graphene declines the Avrami exponent and increases the overall crystallization rate of sPS. The cold crystallization peak of sPS coagulation powders is lower than that of the original sPS pellets. From the electrical conductivity measurement, the percolation threshold of sPG/G1 composite is 0.46 vol%, and sPS/G10 is 3.84 vol%. Compared to the G10 fillers, lower G1 content is to form a conductivity network.
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Lin, Tsung-Ju, and 林宗儒. "Electrical Properties and Analysis of ICP-CVD Graphene on Copper Interconnects." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/472qet.
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Jen, Shuo-Fang, and 鄭碩方. "Cu-catalyst graphene synthesis by chemical vapor deposition and its electrical properties of ammonia-doped graphene nanoribbons." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/79276794432165103595.
Full text