Página 1 dos resultados de 1200 itens digitais encontrados em 0.018 segundos

Graphene-based materials in catalytic wet peroxide oxidation

Gomes, Helder; Ribeiro, Rui; Pastrana-Martínez, Luisa; Figueiredo, José; Faria, Joaquim; Silva, Adrián
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
67.72724%
In catalytic wet peroxide oxidation (CWPO),an advanced oxidation process, hydrogen peroxide (H2O2) is decomposed catalytically giving rise to hydroxyl radicals (HO•).These radicals, exhibiting high oxidizing potential, serve as effective and non selective species for the degradation of several organic pollutants in liquid phase. Since the report of Lücking et al. [1], carbon materials have been explored as catalysts for CWPO[2]. Recent reports address process intensification issues, broadening the window of industrial applications for this wastewater treatment technology [3]. In this work, graphene-based materials were tested for the first time as catalysts for CWPO.

Graphene-based materials for the catalytic wet peroxide oxidation of highly concentrated 4-nitrophenol solutions

Ribeiro, Rui; Silva, Adrián; Pastrana-Martínez, Luisa; Figueiredo, José; Faria, Joaquim; Gomes, Helder
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
98.22799%
Reduced graphene oxide (rGO) samples were prepared from graphene oxide (GO) using different reducing agents (i.e., glucose, hydrazine and vitamin C, resulting in rGOG, rGOH and rGOV, respectively). These samples were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol(4-NP) solutions (5 g L−1) at mild operating conditions (i.e., atmospheric pressure, T = 323 K, pH = 3,[catalyst] = 2.5 g L−1and [H2O2]0= 17.8 g L−1). The highest catalytic activity was found for the rGOV sample, reaching a 4-NP removal of 1294 mg g−1and a TOC removal of 241 mg g−1after 24 h runs (corresponding to 4-NP and TOC removals of 65% and 23%, respectively). The TOC removal per unit of H2O2decomposed decreases with the increase of the surface oxygen content of the samples, as well as with the increase of their amounts of structural defects. This was ascribed, respectively, to the electron withdrawal capacity of oxygen-containing functionalities and to reduced adsorption of 4-NP in the samples with higher amounts of defects, which diminish the efficiency of the reaction between hydroxyl radicals resulting from the decomposition of H2O2and the organic compounds.In a series of three consecutive CWPO runs, rGOH was the most stable material (4-NP removal slightly decreasing from 980 mg g−1...

Biocompatibility of poly(lactic acid) with incorporated graphene-based materials

Pinto, Artur Moreira; Moreira, Susana Margarida Gomes; Gonçalves, Inês; Gama, F. M.; Mendes, Adélio; Magalhães, Fernão D.
Fonte: Elsevier; Elsevier BV Publicador: Elsevier; Elsevier BV
Tipo: Artigo de Revista Científica
Publicado em //2013 ENG
Relevância na Pesquisa
68.172314%
The incorporation of graphene-based materials has been shown to improve mechanical properties of poly(lactic acid) (PLA). In this work, PLA films and composite PLA films incorporating two graphene-based materials – graphene oxide (GO) and graphene nanoplatelets (GNP) – were prepared and characterized regarding not only biocompatibility, but also surface topography, chemistry and wettability. The presence of both fillers changed the films surface topography, increasing the roughness, and modified the wettability – the polar component of surface free energy increased 59% with GO and decreased 56% with GNP. Mouse embryo fibroblasts incubated with both fillers exceeded the IC50 in both cases with a concentration of 10 μg mL−1. No variations in cell proliferation at the surface of the composite films were observed, except for those containing GO after 24 h incubation, which presented higher cell proliferation than pristine PLA films. Platelet adhesion to PLA and PLA/GNP films was lower in the presence of plasma proteins than when no proteins were present. Furthermore, incorporation of GNP into PLA reduced platelet activation in the presence of plasma proteins. The results indicated that low concentrations of GO and GNP may be incorporated safely in PLA to improve aspects relevant for biomedical applications...

Toxicology of chemically modified graphene-based materials for medical application

Nezakati, Toktam; Cousins, Brian G.; Seifalian, Alexander M.
Fonte: Springer Berlin Heidelberg Publicador: Springer Berlin Heidelberg
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
58.00095%
This review article aims to provide an overview of chemically modified graphene, and graphene oxide (GO), and their impact on toxicology when present in biological systems. Graphene is one of the most promising nanomaterials due to unique physicochemical properties including enhanced optical, thermal, and electrically conductive behavior in addition to mechanical strength and high surface-to-volume ratio. Graphene-based nanomaterials have received much attention over the last 5 years in the biomedical field ranging from their use as polymeric conduits for nerve regeneration, carriers for targeted drug delivery and in the treatment of cancer via photo-thermal therapy. Both in vitro and in vivo biological studies of graphene-based nanomaterials help understand their relative toxicity and biocompatibility when used for biomedical applications. Several studies investigating important material properties such as surface charge, concentration, shape, size, structural defects, and chemical functional groups relate to their safety profile and influence cyto- and geno-toxicology. In this review, we highlight the most recent studies of graphene-based nanomaterials and outline their unique properties, which determine their interactions under a range of environmental conditions. The advent of graphene technology has led to many promising new opportunities for future applications in the field of electronics...

Hybrid hydrogels of porous graphene and nickel hydroxide as advanced supercapacitor materials

Chen, S.; Duan, J.; Tang, Y.; Qiao, S.
Fonte: Wiley-V C H Verlag GMBH Publicador: Wiley-V C H Verlag GMBH
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
68.23163%
Graphene-based hydrogels can be used as supercapacitor electrodes because of their excellent conductivity, their large surface area and their high compatibility with electrolytes. Nevertheless, the large aspect ratio of graphene sheets limits the kinetics of processes occurring in the electrode of supercapacitors. In this study, we have introduced in-plane and out-of-plane pores into a graphene–nickel hydroxide (Ni(OH)₂) hybrid hydrogel, which facilitates charge and ion transport in the electrode. Due to its optimised chemistry and architecture, the hybrid electrode demonstrates excellent electrochemical properties with a combination of high charge storage capacitance, fast rate capability and stable cycling performance. Remarkably, the Ni(OH)₂ in the hybrid contributes a capacitance as high as 3138.5 F g⁻¹, which is comparable to its theoretical capacitance, suggesting that such structure facilitates effectively charge-transfer reactions in electrodes. This work provides a facile pathway for tailoring the porosity of graphene-based materials for improved performances. Moreover, this work has also furthered our understanding in the effect of pore and hydrogel structures on the electrochemical properties of materials.; Sheng Chen...

Surface Functionalization of Graphene-based Materials

Mathkar, Akshay
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
78.24523%
Graphene-based materials have generated tremendous interest in the past decade. Manipulating their characteristics using wet-chemistry methods holds distinctive value, as it provides a means towards scaling up, while not being limited by yield. The majority of this thesis focuses on the surface functionalization of graphene oxide (GO), which has drawn tremendous attention as a tunable precursor due to its readily chemically manipulable surface and richly functionalized basal plane. Firstly, a room-temperature based method is presented to reduce GO stepwise, with each organic moiety being removed sequentially. Characterization confirms the carbonyl group to be reduced first, while the tertiary alcohol is reduced last, as the optical gap decrease from 3.5 eV down to 1 eV. This provides greater control over GO, which is an inhomogeneous system, and is the first study to elucidate the order of removal of each functional group. In addition to organically manipulating GO, this thesis also reports a chemical methodology to inorganically functionalize GO and tune its wetting characteristics. A chemical method to covalently attach fluorine atoms in the form of tertiary alkyl fluorides is reported, and confirmed by MAS 13C NMR, as two forms of fluorinated graphene oxide (FGO) with varying C/F and C/O ratios are synthesized. Introducing C-F bonds decreases the overall surface free energy...

Nanostructured Few-Layer Graphene with Superior Optical Limiting Properties Fabricated by a Catalytic Steam Etching Process

Sun, Zhenyu; Dong, Ningning; Xie, Kunpen; Xia, Wei; König, Dennis; Tharamani, Chikka Nagaiah; Sanchez, Miguel Dario; Ebbinghaus, Petra; Erbe, Andreas; Zhang, Xiaoyan; Ludwig, Alfred; Schuhmann, Wolfgang; Wang, Jun; Muhler, Martin
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
Relevância na Pesquisa
58.286465%
Tailoring the morphology and structure of graphene can result in novel properties for advanced applications. Here, we demonstrate the fabrication of nanostructured few-layer graphene through a mild etching process via catalytic steam gasification of carbon by Fe nanoparticles (NPs). Controlling the reaction temperature, steam concentration, and the loading density of the NPs enables the finetuning of the etching level of graphene. Well-defined nanotrenches with a width of less than 25 nm were formed by channeling of the catalytic NPs. Etching caves and  quasisemicircular etched edges were observed as well. The nonlinear optical properties of the resulting nanostructured graphene were studied under a 532 nm nanosecond pulse laser through an open-aperture apparatus. At the same level of the linear extinction coefficient, it exhibits superior optical limiting performance in comparison with pristine graphene and C60, showing a large potential in nanophotonic devices. This enhancement is ascribed to the defects formed by etching resulting in a finite band gap in nanostructured graphene.; Fil: Sun, Zhenyu. Ruhr-University Bochum. Laboratory of Industrial Chemistry; Alemania;; Fil: Dong, Ningning. Chinese Academy of Sciences. Shanghai Institute of Optics and Fine Mechanics. Key Laboratory of Materials for High-Power Laser; China;; Fil: Xie...

Emergence of local magnetic moments in doped graphene-related materials

Venezuela, P.; Muniz, R. B.; Costa, A. T.; Edwards, D. M.; Power, S. R.; Ferreira, M. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 31/08/2009
Relevância na Pesquisa
68.300903%
Motivated by recent studies reporting the formation of localized magnetic moments in doped graphene, we investigate the energetic cost for spin polarizing isolated impurities embedded in this material. When a well-known criterion for the formation of local magnetic moments in metals is applied to graphene we are able to predict the existence of magnetic moments in cases that are in clear contrast to previously reported Density Functional Theory (DFT) results. When generalized to periodically repeated impurities, a geometry so commonly used in most DFT-calculations, this criterion shows that the energy balance involved in such calculations contains unavoidable contributions from the long-ranged pairwise magnetic interactions between all impurities. This proves the fundamental inadequacy of the DFT-assumption of independent unit cells in the case of magnetically doped low-dimensional graphene-based materials. We show that this can be circumvented if more than one impurity per unit cell is considered, in which case the DFT results agree perfectly well with the criterion-based predictions for the onset of localized magnetic moments in graphene. Furthermore, the existence of such a criterion determining whether or not a magnetic moment is likely to arise within graphene will be instrumental for predicting the ideal materials for future carbon-based spintronic applications.; Comment: Submitted to PRL

Graphene based spin field effect transistor

Semenov, Y. G.; Kim, K. W.; Zavada, J. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/07/2007
Relevância na Pesquisa
57.976733%
A spin field effect transistor (FET) is proposed by utilizing a graphene nanoribbon as the channel. Similar to the conventional spin FETs, the device involves ferromagnetic metals as a source and drain; they, in turn, are connected to the graphene channel. Due to the negligible spin-orbital coupling in the carbon based materials, the bias can accomplishes spin manipulation by means of electrical control of electron exchange interaction with a ferromagnetic dielectric attached to the nanoribbon between source and drain. The numerical estimations show the feasibility of graphene-based spin FET if a bias varies exchange interaction on the amount around 5 meV. It was shown that the device stability to the thermal dispersion can provide the armchair nanoribbons of specific width that keeps the Dirac point in electron dispersion law.; Comment: 7 pages, 2 figures

Visualizing Graphene Based Sheets by Fluorescence Quenching Microscopy

Kim, Jaemyung; Cote, Laura J.; Kim, Franklin; Huang, Jiaxing
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/12/2009
Relevância na Pesquisa
68.25604%
Graphene based sheets have stimulated great interest due to their superior mechanical, electrical and thermal properties. A general visualization method that allows quick observation of these single atomic layers would be highly desirable as it can greatly facilitate sample evaluation and manipulation, and provide immediate feedback to improve synthesis and processing strategies. Here we report that graphene based sheets can be made highly visible under a fluorescence microscope by quenching the emission from a dye coating, which can be conveniently removed afterwards by rinsing without disrupting the sheets. Current imaging techniques for graphene based sheets rely on the use of special substrates. In contrast, the fluorescence quenching mechanism is no longer limited by the types of substrates. Graphene, reduced graphene oxide, or even graphene oxide sheets deposited on arbitrary substrates can now be readily visualized by eye with good contrast for layer counting. Direct observation of suspended sheets in solution was also demonstrated. The fluorescence quenching microscopy offers unprecedented imaging flexibility and could become a general tool for characterizing graphene based materials.; Comment: J. Am. Chem. Soc., Article ASAP

Ultrafast Liquid Water Transport Through Graphene-Based Nanochannels Measured by Isotope Labelling

Sun, Pengzhan; Liu, He; Wang, Kunlin; Zhong, Minlin; Wu, Dehai; Zhu, Hongwei
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
57.97565%
Graphene-based laminates, with ultralong and tortuous nanocapillaries formed by simply stacking graphene flakes together, have great promises in filtration and separation. However, the information on liquid water trans-membrane permeation is lacking, which is the most fundamental problem and of crucial importance in solution-based mass transport. Here, based on isotope labelling, we investigate the liquid water transportation through graphene-based nanocapillaries under no external hydrostatic pressures. Liquid water can afford an unimpeded permeation through graphene-based nanochannels with a diffusion coefficient 4~5 orders of magnitude larger than through sub-micrometer-sized polymeric channels. When dissolving ions in sources, the diffusion coefficient of ions through graphene channels lies in the same order of magnitude as water, while the ion diffusion is faster than water, indicating that the ions are mainly transported by fast water flows and the delicate interactions between ions and nanocapillary walls also take effect in the accelerated ion transportation.

Conversion of self-assembled monolayers into nanocrystalline graphene: Structure and electric transport

Turchanin, Andrey; Weber, Dirk; Buenfeld, Matthias; Kisielowski, Christian; Fistul, Mikhail V.; Efetov, Konstantin B.; Weimann, Thomas; Stosch, Rainer; Mayer, Joachim; Golzhauser, Armin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/05/2011
Relevância na Pesquisa
58.23163%
Graphene-based materials have been suggested for applications ranging from nanoelectronics to nanobiotechnology. However, the realization of graphene-based technologies will require large quantities of free-standing two-dimensional (2D) carbon materials with tuneable physical and chemical properties. Bottom-up approaches via molecular self-assembly have great potential to fulfil this demand. Here, we report on the fabrication and characterization of graphene made by electron-radiation induced cross-linking of aromatic self-assembled monolayers (SAMs) and their subsequent annealing. In this process, the SAM is converted into a nanocrystalline graphene sheet with well defined thickness and arbitrary dimensions. Electric transport data demonstrate that this transformation is accompanied by an insulator to metal transition that can be utilized to control electrical properties such as conductivity, electron mobility and ambipolar electric field effect of the fabricated graphene sheets. The suggested route opens broad prospects towards the engineering of free-standing 2D carbon materials with tuneable properties on various solid substrates and on holey substrates as suspended membranes.; Comment: 30 pages, 5 figures

Advanced Asymmetrical Supercapacitors Based on Graphene Hybrid Materials

Wang, Hailiang; Liang, Yongye; Mirfakhrai, Tissaphern; Chen, Zhuo; Casalongue, Hernan Sanchez; Dai, Hongjie
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/04/2011
Relevância na Pesquisa
58.30667%
Supercapacitors operating in aqueous solutions are low cost energy storage devices with high cycling stability and fast charging and discharging capabilities, but have suffered from low energy densities. Here, we grow Ni(OH)2 nanoplates and RuO2 nanoparticles on high quality graphene sheets to maximize the specific capacitances of these materials. We then pair up a Ni(OH)2/graphene electrode with a RuO2/graphene electrode to afford a high performance asymmetrical supercapacitor with high energy and power densities operating in aqueous solutions at a voltage of ~1.5V. The asymmetrical supercapacitor exhibits significantly higher energy densities than symmetrical RuO2-RuO2 supercapacitors and asymmetrical supercapacitors based on either RuO2-carbon or Ni(OH)2-carbon electrode pairs. A high energy density of ~48Wh/kg at a power density of ~0.23kW/kg, and a high power density of ~21kW/kg at an energy density of ~14Wh/kg have been achieved with our Ni(OH)2/graphene and RuO2/graphene asymmetrical supercapacitor. Thus, pairing up metal-oxide/graphene and metal-hydroxide/graphene hybrid materials for asymmetrical supercapacitors represents a new approach to high performance energy storage.; Comment: Nano Research in press

Optical Separation of Mechanical Strain from Charge Doping in Graphene

Lee, Ji Eun; Ahn, Gwanghyun; Shim, Jihye; Lee, Young Sik; Ryu, Sunmin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/09/2012
Relevância na Pesquisa
57.97079%
Graphene, due to its superior stretchability, exhibits rich structural deformation behaviors and its strain-engineering has proven useful in modifying its electronic and magnetic properties. Despite the strain-sensitivity of the Raman G and 2D modes, the optical characterization of the native strain in graphene on silica substrates has been hampered by excess charges interfering with both modes. Here we show that the effects of strain and charges can be optically separated from each other by correlation analysis of the two modes, enabling simple quantification of both. Graphene with in-plane strain randomly occurring between -0.2% and 0.4% undergoes modest compression (-0.3%) and significant hole doping upon thermal treatments. This study suggests that substrate-mediated mechanical strain is a ubiquitous phenomenon in two-dimensional materials. The proposed analysis will be of great use in characterizing graphene-based materials and devices.; Comment: 22 pages, 5 figures

Study of Thermal Properties of Graphene-Based Structures Using the Force Constant Method

Karamitaheri, Hossein; Neophytou, Neophytos; Pourfath, Mahdi; Kosina, Hans
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/02/2012
Relevância na Pesquisa
68.10949%
The thermal properties of graphene-based materials are theoretically investigated. The fourth-nearest neighbor force constant method for phonon properties is used in conjunction with both the Landauer ballistic and the non-equilibrium Green's function techniques for transport. Ballistic phonon transport is investigated for different structures including graphene, graphene antidot lattices, and graphene nanoribbons. We demonstrate that this particular methodology is suitable for robust and efficient investigation of phonon transport in graphene-based devices. This methodology is especially useful for investigations of thermoelectric and heat transport applications.; Comment: 23 pages, 9 figures, 1 table

Simple approach for high-contrast optical imaging and characterization of graphene-based sheets

Jung, Inhwa; Pelton, Matthew; Piner, Richard; Dikin, Dmitriy A.; Stankovich, Sasha; Watcharotone, Supinda; Hausner, Martina; Ruoff, Rodney S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
68.270615%
A simple optical method is presented for identifying and measuring the effective optical properties of nanometer-thick, graphene-based materials, based on the use of substrates consisting of a thin dielectric layer on silicon. High contrast between the graphene-based materials and the substrate is obtained by choosing appropriate optical properties and thickness of the dielectric layer. The effective refractive index and optical absorption coefficient of graphene oxide, thermally reduced graphene oxide, and graphene are obtained by comparing the predicted and measured contrasts.; Comment: New measurements, calculations modified, discussion revised

Graphene -- Based Nanocomposites as Highly Efficient Thermal Interface Materials

Shahil, Khan M. F.; Balandin, Alexander A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/01/2012
Relevância na Pesquisa
58.11526%
We found that an optimized mixture of graphene and multilayer graphene - produced by the high-yield inexpensive liquid-phase-exfoliation technique - can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300 % in the graphene-based polymer at the filler loading fraction f =10 vol. %. It was determined that a relatively high concentration of single-layer and bilayer graphene flakes (~10-15%) present simultaneously with thicker multilayers of large lateral size (~ 1 micrometer) were essential for the observed unusual K enhancement. The thermal conductivity of a commercial thermal grease was increased from an initial value of ~5.8 W/mK to K=14 W/mK at the small loading f=2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene - multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and lower Kapitza resistance at the graphene - matrix interface.; Comment: 4 figures

Opening Band Gap without Breaking Lattice Symmetry: A New Route toward Robust Graphene-Based Nanoelectronics

Kou, Liangzhi; Hu, Feiming; Yan, Binghai; Frauenheim, Thomas; Chen, Changfeng
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/02/2014
Relevância na Pesquisa
58.141743%
Developing graphene-based nanoelectronics hinges on opening a band gap in the electronic structure of graphene, which is commonly achieved by breaking the inversion symmetry of the graphene lattice via an electric field (gate bias) or asymmetric doping of graphene layers. Here we introduce a new design strategy that places a bilayer graphene sheet sandwiched between two cladding layers of materials that possess strong spin-orbit coupling (e.g., Bi2Te3). Our ab initio and tight-binding calculations show that proximity enhanced spin-orbit coupling effect opens a large (44 meV) band gap in bilayer graphene without breaking its lattice symmetry, and the band gap can be effectively tuned by interlayer stacking pattern and significantly enhanced by interlayer compression. The feasibility of this quantum-well structure is demonstrated by recent experimental realization of high-quality heterojunctions between graphene and Bi2Te3, and this design also conforms to existing fabrication techniques in the semiconductor industry. The proposed quantum-well structure is expected to be especially robust since it does not require an external power supply to open and maintain a band gap, and the cladding layers provide protection against environmental degradation of the graphene layer in its device applications.

Strain-Tunable Spin Moment in Ni-Doped Graphene

Santos, Elton J. G.; Ayuela, Andrés; Sánchez-Portal, Daniel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/12/2011
Relevância na Pesquisa
57.98455%
Graphene, due to its exceptional properties, is a promising material for nanotechnology applications. In this context, the ability to tune the properties of graphene-based materials and devices with the incorporation of defects and impurities can be of extraordinary importance. Here we investigate the effect of uniaxial tensile strain on the electronic and magnetic properties of graphene doped with substitutional Ni impurities (Ni_sub). We have found that, although Ni_sub defects are non-magnetic in the relaxed layer, uniaxial strain induces a spin moment in the system. The spin moment increases with the applied strain up to values of 0.3-0.4 \mu_B per Ni_sub, until a critical strain of ~6.5% is reached. At this point, a sharp transition to a high-spin state (~1.9 \mu_B) is observed. This magnetoelastic effect could be utilized to design strain-tunable spin devices based on Ni-doped graphene.; Comment: To appear in Journal of Physical Chemistry C

Charge and Spin Transport in Disordered Graphene-Based Materials

Van Tuan, Dinh; Pascual, Jordi
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
68.18453%
Esta tesis está enfocada en la modelización y simulación del transporte de carga y spin en materiales bidimensionales basados en Grafeno, así como en el impacto de la policristalinidad en el rendimiento de transistores de efecto campo diseñados con este tipo de materiales. Para este estudio se ha utilizado la metodología de transporte Kubo-Greenwood, la cual presenta grandes ventajas a la hora de realizar cálculos numéricos en sistemas microscópicos con el fin de obtener las propiedades de transporte de carga. Este trabajo cubre todos los tipos de desorden que pueden tener lugar en Grafeno, desde vacantes a la posible adsorción de especies químicas a lo largo de las fronteras de grano en el caso de Grafeno policristalino. Además tiene en cuenta importantes efectos cuánticos, como las interferencias cuánticas y los efectos debidos al acoplamiento spin-órbita intrínseco y extrínseco. Para el transporte de spin, se ha desarrollado un nuevo método basado en el formalismo de transporte en espacio real de orden O(N). Este nuevo método permite explorar y entender los mecanismos de relajación de spin en Grafeno y sus derivados. A partir de esta nueva metodología ha sido posible descubrir un nuevo mecanismo de relajación de spin basado en el acoplamiento entre spin y pseudospin (en presencia de un acoplamiento spin-órbita extrínseco o Rashba) que podría ser el mecanismo principal que gobierna la rápida relajación de spin observada experimentalmente en muestras de grafeno de alta calidad.; This thesis is focused on modeling and simulation of charge and spin transport in two dimensional graphene-based materials as well as the impact of graphene polycrystallinity on the performance of graphene field-effect transistors. The Kubo-Greenwood transport approach has been used as the key method to carry out numerical calculations for charge transport properties. The study covers all kinds of disorder in graphene from vacancies to chemical adsorbates on grain boundaries of polycrystalline graphene and takes into account important quantum effects such as the quantum interferences and spin-orbit coupling effects. For spin transport...