Página 1 dos resultados de 11190 itens digitais encontrados em 0.007 segundos

Efeito Casimir e as propriedades óticas do grapheno; Casimir effect and optical properties of graphene

Fialkovskiy, Ignat
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/11/2012 PT
Relevância na Pesquisa
36.896038%
Este trabalho é dedicado à investigação de diferentes aspectos da física de monocamadas de grafeno suspenso e epitaxial. A descrição do grafeno é baseada no modelo quase-relativístico de Dirac. Isso permite a aplicação dos métodos da Teoria Quântica de Campos (TQC) na investigação dos efeitos de interação entre o grafeno e o campo eletromagnético (EM). Usando o formalismo de integral de trajetória, nós formulamos uma teoria efetiva do campo EM na presença de monocamadas de grafeno. Esta teoria é governada pelo operador de polarização das quase-partículas de Dirac. Dois fenômenos importantes são investigados: as propriedades óticas do grafeno (o efeito Faraday em particular) e a interação de Casimir entre uma camada de grafeno e um metal paralelo. Em primeiro lugar, estudamos a propagação de ondas eletromagnéticas na presença de camadas de grafeno. A dinâmica de ondas é governada pelas equações modificadas de Maxwell obtidas a partir da teoria efetiva para o campo EM. Nós calculamos os coeficientes de reflexão e transmissão de luz polarizada linearmente e investigamos detalhadamente o efeito quântico de Faraday no campo magnético externo. Em particular, mostramos que as previsões do modelo de Dirac estão em boa concordância com os recentes resultados experimentais sobre a transmissão de luz e rotação de Faraday gigante em regime de ressonância cíclotron. Novos regimes também são previstos. Em segundo lugar...

A nonzero gap two-dimensional carbon allotrope from porous graphene

Brunetto, Gustavo; Santos, Bruno I.; Autreto, Pedro A. S.; Machado, Leonadro D.; Dos Santos, Ricardo P. B.; Galvao, Douglas S.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 79-84
ENG
Relevância na Pesquisa
36.849155%
Graphene has been one of the hottest topics in materials science in the last years. Because of its special electronic properties graphene is considered one of the most promising materials for future electronics. However, in its pristine form graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Many approaches have been tried to create, in a controlled way, a gap in graphene. These approaches have obtained limited successes. Recently, hydrogenated graphene-like structures, the so-called porous graphene, have been synthesized. In this work we show, based on ab initio quantum molecular dynamics calculations, that porous graphene dehydrogenation can lead to a spontaneous formation of a nonzero gap two-dimensional carbon allotrope, called biphenylene carbon (BC). Besides exhibiting an intrinsic nonzero gap value, BC also presents well delocalized frontier orbitals, suggestive of a structure with high electronic mobility. Possible synthetic routes to obtain BC from porous graphene are addressed. © 2012 Materials Research Society.

Determinação estrutural de grafeno sobre Irídio (111) por difração de fotoelétrons; Structural determination of graphene on iridium (111) by photoelectron diffraction

Caio César Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/08/2014 PT
Relevância na Pesquisa
36.917644%
O material bidimensional grafeno possui um conjunto fascinante de propriedades que não são vistas juntas em qualquer outro material. Grafeno pode substituir outros materiais em diversas aplicações existentes, além de abrir uma janela para uma série de novas aplicações. As propriedades do grafeno foram mostradas em amostras sintetizadas através do método de esfoliação, no entanto, este método requer vários passos de litografia durante a preparação da amostra. Por outro lado, grafeno tem sido sintetizado pelo método de CVD (Chemical Vapor Deposition) por grandes áreas e com grande qualidade. O processo de CVD envolve um substrato metálico que interage com o grafeno, assim, um sistema alternativo que permite o estudo das propriedades do grafeno é o chamado grafeno quasi-free-standing, ou seja, grafeno que preserva suas propriedades mesmo quando _e suportado por um substrato. Estudos recentes demonstram que Ir(111) permite a preparação de grafeno com alta qualidade estrutural e com estrutura de banda praticamente idêntica à do grafeno puro. Determinar a topografia da superfície em nível atômico é fundamental para compreender a relação entre a estrutura eletrônica e a estrutura geométrica. O objetivo deste trabalho é determinar a estrutura do grafeno sobre Ir(111) através da técnica experimental de difração de fotoelétrons (XPD). A determinação da estrutura da superfície...

Simulações de sistemas em nanoescala : membranas de grafeno e espectroscopia fora do equilíbrio; Simulations of nanoscale systems : from graphene membranes to non equilibrium spectroscopy

Gustavo Brunetto
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 26/02/2014 PT
Relevância na Pesquisa
36.907551%
Nas últimas décadas, sucessivas descobertas em materiais baseados em carbono abriram uma nova era na ciência dos materiais. Exemplos destas descobertas são os fulerenos, nanotubos de carbono e, mais recentemente, o grafeno. O grafeno é uma rede bi-dimensional de unidades hexagonais de carbono com ligações do tipo sp2. Grafeno apresenta propriedades mecânicas e eletrônicas não usuais e muito interessantes e devido a estas propriedades é um dos materiais mais promissores para aplicações em diversas áreas da tecnologia tais como eletrônica, militar, aeroespa- cial, dispositivos e outras. Entretanto, há algumas barreiras que devem ser superadas a fim de utilizar o grafeno em aplicações práticas. O grafeno, em sua forma pura, é um semicondutor com gap zero. Esta característica impõe sérias limitações em algumas aplicações em eletrônica, tal como, transistores. Além do mais, é muito difícil a síntese de grandes porções de grafeno que possuam poucos ou nenhum defeito estrutural. Através de simulações de primeiros princípios, propomos uma rota de síntese a partir da de-hidrogenação completa do grafeno poroso para a obtenção de um alótropo de carbono conhecido como BPC. Cálculos de estrutura eletrônica mostraram que o BPC possui um gap da ordem de 0...

Formation of graphene nanoribbons in solution

Paiva, M. C.; Cunha, Eunice Paula Freitas; Proença, M. Fernanda R. P.; Araújo, Rui Filipe; Costa, Florinda; Fernandes, António J.; Ferro, Marta A.
Fonte: Graphene 2012 Publicador: Graphene 2012
Tipo: Conferência ou Objeto de Conferência
Publicado em //2012 ENG
Relevância na Pesquisa
46.72588%
Recently, the formation of graphene by exfoliation of carbon nanotubes (CNT) has shown increasing interest. This process originates graphene nanoribbons (GNR) that are expected to present excellent electrical properties, depending on their width and on their edge shape [1]. Several methods for the unzipping of graphene from CNT were proposed along the past few years [2-6]. These methods often present some limitation, such as low yield of GNR, or extensively oxidized GNR without electrical conductivity. Recently, the formation of GNR was observed “in situ” by unzipping of carbon nanotubes under ultra-high vacuum scanning tunneling microscopy (UHV STM) [7]. The CNT under observation were functionalized by the 1,3-dipolar cycloaddition reaction [8]. This particular functionalization route seems to be responsible for the unzipping of the CNT under STM imaging conditions. The present work demonstrates the formation of GNR in solution by unzipping of functionalized CNT, in different solvents. The GNR thus formed were analyzed by UV-vis and Raman spectroscopy, and by transmission electron spectroscopy. GNR bundles were deposited from an ethanol solution and observed by TEM.; Institute for Nanostructures, Nanomodelling and Nanofabrication (I3N)

Unusual reflection of electromagnetic radiation from a stack of graphene layers at oblique incidence

Bludov, Yuliy V.; Peres, N. M. R.; Vasilevskiy, Mikhail
Fonte: IOPScience Publicador: IOPScience
Tipo: Artigo de Revista Científica
Publicado em 28/10/2013 ENG
Relevância na Pesquisa
36.867344%
We study the interaction of electromagnetic (EM) radiation with single-layer graphene and a stack of parallel graphene sheets at arbitrary angles of incidence. It is found that the behavior is qualitatively different for transverse magnetic (or p-polarized) and transverse electric (or s-polarized) waves. In particular, the absorbance of single-layer graphene attains a minimum (maximum) for the p (s)-polarization at the angle of total internal reflection when the light comes from a medium with a higher dielectric constant. In the case of equal dielectric constants of the media above and beneath graphene, for grazing incidence graphene is almost 100% transparent to p-polarized waves and acts as a tunable mirror for the s-polarization. These effects are enhanced for a stack of graphene sheets, so the system can work as a broad band polarizer. It is shown further that a periodic stack of graphene layers has the properties of a one-dimensional photonic crystal, with gaps (or stop bands) at certain frequencies. When an incident EM wave is reflected from this photonic crystal, the tunability of the graphene conductivity renders the possibility of controlling the gaps, and the structure can operate as a tunable spectral-selective mirror.; Fundação para a Ciência e a Tecnologia (FCT); EC under Graphene Flagship

Surface modification of graphene nanosheets with gold nanoparticles: the role of oxygen moieties at graphene surface on gold nucleation and growth

Gonçalves, Gil; Marques, Paula A. A. P.; Granadeiro, Carlos M.; Nogueira, Helena I. S.; Singh, M. K.; Grácio, J.
Fonte: ACS Publicador: ACS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.867344%
Graphene sheets, which possess unique nanostructure and a variety of fascinating properties, are considered as promising nanoscale building blocks of new nanocomposites, namely as a support material for the dispersion of metal nanoparticles. One of the methodologies used to prepare graphene sheets is the chemical exfoliation of graphite in aqueous medium, which produces oxygen functionalized graphene sheets. Here, we show that the presence of oxygen functionalities at the graphene surface provides reactive sites for the nucleation and growth of gold nanoparticles. Gold nanoparticles are effectively grown at functionalized graphene surfaces using a simple chemical method in aqueous medium. The nucleation and growth mechanism depends on the degree of oxygen functionalization at the graphene surface sheets, no gold nanoparticles are obtained at totally reduced graphene surfaces. Additionally, our studies indicate that the graphene/gold nanocomposites are potential substrates for SERS (surface enhanced Raman scattering) in particular for single gold nanoparticle SERS studies.

Direct Graphene Growth on Insulator

Lippert, Gunther; Dabrowski, Jarek; Lemme, Max; Marcus, Charles Masamed; Seifarth, Olaf; Lupina, Grzegorz
Fonte: Wiley Publicador: Wiley
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
36.867344%
Fabrication of graphene devices is often hindered by incompatibility between the silicon technology and the methods of graphene growth. Exfoliation from graphite yields excellent films but is good mainly for research. Graphene grown on metal has a technological potential but requires mechanical transfer. Growth by SiC decomposition requires a temperature budget exceeding the technological limits. These issues could be circumvented by growing graphene directly on insulator, implying Van der Waals growth. During growth, the insulator acts as a support defining the growth plane. In the device, it insulates graphene from the Si substrate. We demonstrate planar growth of graphene on mica surface. This was achieved by molecular beam deposition above 600 °C. High resolution Raman scans illustrate the effect of growth parameters and substrate topography on the film perfection. Ab initio calculations suggest a growth model. Data analysis highlights the competition between nucleation at surface steps and flat surface. As a proof of concept, we show the evidence of electric field effect in a transistor with a directly grown channel. Energetic carbon atoms impinge onto the mica. Few-layer graphene nucleates at step edges and at chemisorbed carbon atoms (black circles). At temperatures above 600 °C...

Growth Morphology, Electronic Properties and Interaction of Organo-Metallic Molecules Adsorbed on Graphene

SCARDAMAGLIA, MATTIA
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
37.004248%
Since the isolation of a single graphene flake in 2004, the extraordinary electronic, optical and mechanical properties of this one-atom-thick material emerged, attracting a continuous rising interest both from fundamental and technological perspectives. Within this research field, a key challenge is to move from model structures to more complex configurations: being graphene a surface without bulk, its properties are very sensitive to local perturbations, but the countless possibilities of modifying graphene properties by suitable functionalization procedures with atoms or molecules are still largely unexplored. The possibility to control and tailor the electronic, morphological and transport properties of graphene, by influencing its band parameters and interaction strength, is a requirement in the perspective of nano-devices fabrication. Furthermore, the effect that graphene itself could have on the molecular or metal nanostructure deposited onto it is an intriguing ambivalence of the graphene functionalization. However, reproducibility and reliability is still an issue. An important help in the formation of ordered and reproducible nano-architectures on graphene comes from the epitaxial growth of graphene on hexagonally close-packed surfaces of transition metals: the similar...

Raman Spectroscopy Study of Graphene Under High Pressure

Hadjikhani, Ali
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
36.849155%
Due to its exceptional mechanical and electrical properties, graphene (one layer sheet of carbon atoms) has attracted a lot of attention since its discovery in 2004. The purpose of this research is to compare the Raman spectra of graphene with plasma treated graphene sheets which have been treated by changing the different parameters affecting the plasma treatment like gas flow, power and pressure and treatment time. The graphene we used for our high pressure studies are 4-5 layer CVD deposited graphene samples prepared by our collaborators in Dr. W. B. Choi’s group. First we report a Raman spectroscopy study of graphene on copper substrate at high pressures. Diamond anvil cell (DAC) was used to generate pressure. In situ Raman spectra were collected at pressures up to 10 GPa. The results indicate that the G band of graphene shifts with pressure significantly (about 5 cm-1/GPa) whereas the 2D band changes very little. The plasma treated samples were loaded into DAC. Raman spectrum was captured. Parts of the spectrum which were not related to the grapheme peak position were eliminated. The background was reduced. Peaks were found and fitted using FITYK software and the shift of each peak compared to its last position was observed when the pressure was increased. Next we studied plasma treated graphene samples treated with different partial pressure treatments under high pressure and compared them to each other using zirconia anvil cell with the same method.

Modelling interaction of atoms and ions with graphene

Chan, Y.; Hill, J.
Fonte: The Institution of Engineering and Technology Publicador: The Institution of Engineering and Technology
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
36.867344%
In this Letter, the authors invéstigate the interaction of various atoms/ions with a graphene sheet and two parallel graphene sheets using the continuous approximation and the 6–12 Lennard-Jones potential. The authors assume that the carbon atoms are smeared across the surface of the graphene sheet so that the total interaction between the single atom/ion and the graphene sheet can be approximated by a surface integration over the graphene sheet. They determine the equilibrium position for the atom/ion on the surface of the graphene sheet and the minimum intermolecular spacing between two graphene sheets. This minimum spacing is by symmetry twice the value for the equilibrium positions for a single graphene sheet and is such that the atom/ion undergoes no net force. The same methodology together with basic statistical mechanics are also employed to investigate the diffusion of the atom/ion from a central location to the edge of the graphene sheet at different temperatures. The results presented in this Letter are consistent with a similar study adopting a molecular dynamics simulation approach. Possible applications of the present study might include the development of future drug delivery systems and future high-performance alkali battery design using nanomaterials as components.; Y. Chan and J.M. Hill

Implementation of Hot Electrons in Hybrid Antenna-Graphene Structures

Wang, Yumin
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
36.849155%
Graphene, a one-atom-thick sheet of hexagonally packed carbon atoms, is a novel material with high electron mobility due to its unique linear and gapless electronic band structure. Its broadband absorption and unusual doping properties, along with superb mechanical flexibility make graphene of promising application in optoeletronic devices such as solar cell, ultrafast photodetectors, and terahertz modulators. How- ever, the current performance of graphene-based devices is quite unacceptable owning to serious limitations by its inherently small absorption cross section and low quan- tum efficiency. Fortunately, nanoscale optical antennas, consisting of closely spaced, coupled metallic nanoparticles, have fascinating optical response since the collective oscillation of electrons in them, namely surface plasmons, can concentrate light into a subwavelength regime close to the antennas and enhance the corresponding field considerably. Given that optical antenna have been applied in various areas such as subwavelength optics, surface enhanced spectroscopies, and sensing, they are also able to assist graphene to harvest visible and near-infrared light with high efficiency. Moreover, the efficient production of hot electrons due to the decay of the surface plasmons can be further implemented to modulate the properties of graphene. Here we choose plasmonic oligomers to serve as optical antenna since they pos- sess tunable Fano resonances...

Optical Studies on Functionalized Graphene Systems

Galande, Charudatta
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
36.917644%
Graphene, the ‘wonder material’, has received a lot of attention for its excellent electronic properties. However, the lack of a band gap severely limits its use, especially in optoelectronic applications. Therefore, opening a band gap in Graphene and controllably modifying its band structure has long been the holy grail in the physics of Graphene. Of these methods, chemical functionalization offers the most degrees of freedom in controllably modifying the band structure of Graphene. Graphene Oxide (GO), the most widely studied chemical derivative of Graphene exhibits a host of optical phenomena such as broadband tunable fluorescence, multiphoton-induced absorption and emission etc. and presents an excellent platform for studying the effects of chemical functionalization on the optical properties of Graphene. In the present work, we first deal with the issue of origin of fluorescence in GO. It is argued that the broadband emission arises due to localized states created on the Graphene surface due to presence of functional groups, and not due to quantum confinement. Next, we attempt to find which of the many functional groups in GO contribute the most to the emission intensity. We find that the carbonyl and epoxide functional groups contribute the most to fluorescence. Further...

Graphene Photonic Devices for Terahertz and Mid-Infrared

Gao, Weilu
Fonte: Universidade Rice Publicador: Universidade Rice
Relevância na Pesquisa
36.982925%
Graphene and other strictly two-dimensional materials are the rising stars on the horizon of material science, condensed matter physics and engineering. The richness of optical and electronic properties of graphene attract much interest due to the exceptional high crystal and electronic quality resulting in large carrier mobility at room temperature and easily electrical control of carrier density, which find its true potential in photonics and optoelectronics. Novel graphene based broadband modulators, polarizer, active plasmonic resonators, ultra-fast lasers and etc are proposed and implemented in many literatures. Despite ample demonstrations of the true potential of graphene in optoelectronic devices, there is still unexplored region. In this thesis, we investigate the graphene photonic properties and optoelectronic devices in different regions ranging from longer wavelength terahertz frequency (THz) to shorter wavelength telecommunication frequency to reveal the whole picture of graphene. The Drude-like intraband absorptoion (i.e. free carrier effect) in graphene plays an important role in THz region. However, the extinction ratio that can be obtained when THz waves passing through a single layer graphene is limited due to its one-atomic-layer thickness and the non-resonant nature of the intraband absorption. By incorporating resonate structures with graphene...

Chemical and Physical Graphene Modifications

Pembroke, Elvira
Fonte: Universidade Rice Publicador: Universidade Rice
Relevância na Pesquisa
36.953826%
This dissertation is inspired by recent progress in the chemistry, physics, and nanotechnology of graphene, a single layer of carbon atoms. Studying and controllably modifying the electrical properties of graphene while minimizing damage to the lattice continues to be a challenge to the scientific community. Chapter 1 focuses on the covalent attachment of molecules with different functional groups to graphene and how functionalization modifies the electrical transport properties of graphene field effect transistors (FET) devices. Functionalization is shown to predominantly induce p-­type doping, undiminished mobility, and increased conductivity at the neutrality point. Physisorbed molecules desorb easily and do not have a significant effect. Statistical analysis enables us to extract trends even though identically fabricated graphene devices can exhibit a wide range of electrical behaviors, emphasizing that conclusions should not be drawn based on singular extremes. In Chapter 2 we present the fabrication and characterization of graphene antidot lattices produced by placing graphene on pre-patterned substrates. While the graphene remains intact atop a periodic well pattern we observe a surface potential differential inside vs. outside the wells. Chapter 3 investigates graphene FETs with multiple neutrality points. We used Raman mapping to determine if multiple local gating fields can be spatially resolved. While we were able to show doping inhomogeneity in graphene devices...

Propriétés optiques dans l'infrarouge des nanotubes de carbone et du graphène

Lapointe, François
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
Relevância na Pesquisa
36.849155%
Les nanotubes de carbone et le graphène sont des nanostructures de carbone hybridé en sp2 dont les propriétés électriques et optiques soulèvent un intérêt considérable pour la conception d’une nouvelle génération de dispositifs électroniques et de matériaux actifs optiquement. Or, de nombreux défis demeurent avant leur mise en œuvre dans des procédés industriels à grande échelle. La chimie des matériaux, et spécialement la fonctionnalisation covalente, est une avenue privilégiée afin de résoudre les difficultés reliées à la mise en œuvre de ces nanostructures. La fonctionnalisation covalente a néanmoins pour effet de perturber la structure cristalline des nanostructures de carbone sp2 et, par conséquent, d’affecter non seulement lesdites propriétés électriques, mais aussi les propriétés optiques en émanant. Il est donc primordial de caractériser les effets des défauts et du désordre dans le but d’en comprendre les conséquences, mais aussi potentiellement d’en exploiter les retombées. Cette thèse traite des propriétés optiques dans l’infrarouge des nanotubes de carbone et du graphène, avec pour but de comprendre et d’expliquer les mécanismes fondamentaux à l’origine de la réponse optique dans l’infrarouge des nanostructures de carbone sp2. Soumise à des règles de sélection strictes...

Mecanismos de alargamento de níveis de Landau em grafeno : um estudo por espalhamento Raman = Landau level broadening mechanisms in graphene: a Raman scattering study; Landau level broadening mechanisms in graphene : a Raman scattering study

Fábio Machado Ardito
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 31/07/2015 PT
Relevância na Pesquisa
36.896038%
O célebre efeito Hall quântico semi-inteiro no grafeno é uma consequência direta dos níveis de Landau característicos previstos pela equação de Dirac. Apesar de se saber que os níveis de Landau devam ser tão estreitos quanto possível para que os efeitos de mecânica quântica relativística sejam realçados, pouca informação sobre os mecanismos mais relevantes que levam ao alargamento destes níveis em grafeno está disponível atualmente. Nesta tese, experimentos de micro-Raman a baixas temperaturas e campos magnéticos de até 15~T foram feitos em tipos diferentes de amostras de grafeno: monocamadas e bicamadas depositadas sobre um substrato de Si/SiO$_2$; e multicamadas produzidas sobre SiC. As larguras das transições interbanda entre níveis de Landau são obtidas pela análise do amortecimento das ressonâncias magneto-fônon que ocorrem quando transições opticamente ativas entre níveis de Landau cruzam a energia do fônon E$_{2g}$. A partir de uma análise quantitativa das larguras dependentes do índice de cada transição, encontramos que amostras produzidas por meios distintos mostram mecanismos de alargamento de níveis de Landau amplamente diferentes. O alargamento na amostra com multicamadas é causado por uma distribuição nas velocidades de Fermi ($delta v_F sim 8.7times10^4$~m/s) possivelmente devida a flutuações residuais nas interações entre camadas...

Electronic spin transport and thermoelectric effects in graphene

Neumann, Ingmar
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2014 ENG
Relevância na Pesquisa
36.896038%
La espintrónica y la espín caloritronica en grafeno son campos de investigación muy activos, y esta tesis es una contribución a ambos campos. El tema principal es el estudio de la corriente de espín a través de métodos de inyección y detección eléctrica en válvulas de espín no locales de grafeno. Preliminarmente, estudiamos analíticamente el efecto túnel de electrones de conducción entre materiales ferromagnéticos y no magnéticos. En la parte experimental, se investiga la precesión de espín en las válvulas de espín de grafeno en suspensión. En este contexto, hemos desarrollado un nuevo método para la fabricación de dispositivos de grafeno suspendido que, además, proporciona una inyección y detección de espín más eficiente. Con el fin de investigar estas corrientes de espín más eficientes, hemos realizado medidas en función de la corriente inyectada. Estos experimentos han dado lugar a la demonstración experimental de un termopar de espín en grafeno. La predicción teórica de distancias de relajación de espín de varias decenas de micrómetros en grafeno nos ha motivado a estudiar las propiedades intrínsecas de grafeno. Para ello el grafeno es suspendido libremente, eliminando así las influencia de substrato y permitiendo a posteriori emplear métodos de limpieza. Con el fin de lograr este objetivo...

GRAPHENE BASED FLEXIBLE GAS SENSORS

Yi, Congwen
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2013
Relevância na Pesquisa
36.917644%

Graphene is a novel carbon material with great promise for a range of applications due to its electronic and mechanical properties. Its two-dimensional nature translates to a high sensitivity to surface chemical interactions thereby making it an ideal platform for sensors. Graphene's electronic properties are not degraded due to mechanical flexing or strain (Kim, K. S., et al. nature 07719, 2009) offering another advantage for flexible sensors integrated into numerous systems including fabrics, etc.

We have demonstrated a graphene NO2 sensor on a solid substrate (100nm SiO2/heavily doped silicon). Three different methods were used to synthesize graphene and the sensor fabrication process was optimized accordingly. Water is used as a controllable p-type dopant in graphene to study the relationship between doping and graphene's response to NO2. Experimental results show that interface water between graphene and the supporting SiO2 substrate induces higher p-doping in graphene, leading to a higher sensitivity to NO2, consistent with theoretical predications (Zhang, Y. et al., Nanotechnology 20(2009) 185504).

We have also demonstrated a flexible and stretchable graphene-based sensor. Few layer graphene, grown on a Ni substrate...

PVDF-graphene conductive composite membrane and PVA-graphene conductive composite membrane preparation and application

Shi, Lu
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
36.867344%
Huang, Chin-Pao; Graphene has a great potential to revolutionize many fields because of its perfect electrical conductivity. Therefore, it is considered a possible material for the preparation of conductive membrane. In this research, polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) were used together with graphene to create graphene based polymer composite conductive membrane. First, Boehm titration was used to determine the linkage of carboxyl groups on the surface of graphene sheet. Then pure PVDF membrane was trail-produced to investigate the best ratio of PVDF, plasticizer, and solvent. Results showed that PVDF amount should not be higher than 15% by weight. In addition, the breaking stain and the contact angle increased with increasing plasticizer concentration; whereas the ultimate force decreased. The resistance of PVDF-graphene membrane was measured. Results showed that although the whole membrane became conductive, the resistance was not less than 8000 ohm. PVA-graphene membrane was prepared. This membrane had much lower resistance than the PVDF-graphene membrane. However, PVA-graphene had a bad performance in perchlorate adsorption due to lack of inside area. Besides, it could not prevent membrane blocking in dead-end electrical filtration. Based on calculation...