1,721,425 research outputs found
Delivering C, B, and N Atoms into Liquid Metals in Which They Are Normally Insoluble
No full text[No abstract available]11Nsciescopu
Fluorination of Single-Wall Carbon Nanotubes: Toward “Diamond Nanoribbons”
No full textWe report density functional theory calculations that show that adsorption of fluorine on the outer surface of several types of single-walled carbon nanotubes leads to their collapse and to C-C bonding in the neighboring walls, yielding a sp3-bonded “diamond-like nanoribbon”. The calculated ribbons have weak dependence of the band gap on the width (except for special cases of ribbons containing 8-member ring defects in the structure) as well as a mechanical stiffness exceeding that of bulk diamond but comparable with graphene and carbon nanotubes. © 2023 American Chemical Society11Nsciescopu
Synthesis and characterization of chemically modified graphenes
No full textThis review documents our contributions to the synthesis of chemically-modified graphene (CMG) materials. We focus on methods for the preparation of homogenous colloidal suspensions of CMGs and procedures for the chemical reduction of graphene oxide, along with techniques for the structural elucidation of graphene oxide and reduced graphene oxide materials. We conclude with an outline of the persisting chemical challenges and current limitations of practical applications.close
Breaking of Symmetry in Graphene Growth on Metal Substrates
Full text linkIn graphene growth, island symmetry can become lower than the intrinsic symmetries of both graphene and the substrate. First-principles calculations and Monte Carlo modeling explain the shapes observed in our experiments and earlier studies for various metal surface symmetries. For equilibrium shape, edge energy variations delta E manifest in distorted hexagons with different ground-state edge structures. In growth or nucleation, energy variation enters exponentially as similar to e(delta E/kBT), strongly amplifying the symmetry breaking, up to completely changing the shapes to triangular, ribbonlike, or rhombic132351sciescopu
Growth of Single-Layer and Multilayer Graphene on Cu/Ni Alloy Substrates
No full textGraphene, a one-atom-thick layer of carbon with a honeycomb lattice, has drawn great attention due to its outstanding properties and its various applications in electronic and photonic devices. Mechanical exfoliation has been used for preparing graphene flakes (from monolayer to multilayer with thick pieces also typically present), but with sizes limited typically to less than millimeters, its usefulness is limited. Chemical vapor deposition (CVD) has been shown to be the most effective technique for the scalable preparation of graphene films with high quality and uniformity. To date, CVD growth of graphene on the most commonly used substrates (Cu and Ni foils) has been demonstrated and intensively studied. However, a survey of the existing literature and earlier work using Cu or Ni substrates for CVD growth indicates that the bilayer and multilayer graphene over a large area, particularly single crystals, have not been obtained. In this Account, we review current progress and development in the CVD growth of graphene and highlight the important challenges that need to be addressed, for example, how to achieve large single crystal graphene films with a controlled number of layers. A single-layer graphene film grown on polycrystalline Cu foil was first reported by our group, and since then various techniques have been devoted to achieving the fast growth of large-area graphene films with high quality. Commercially available Cu/Ni foils, sputtered Cu/Ni thin films, and polycrystalline Cu/Ni foils have been used for the CVD synthesis of bilayer, trilayer, and multilayer graphene. Cu/Ni alloy substrates are particularly interesting due to their greater carbon solubility than pure Cu substrates and this solubility can be finely controlled by changing the alloy composition. These substrates with controlled compositions have shown the potential for the growth of layer-tunable graphene films in addition to providing a much higher growth rate due to their stronger catalytic activity. However, the well-controlled preparation of single crystal graphene with a defined number of layers on Cu/Ni substrates is still challenging. Due to its small lattice mismatch with graphene, a single crystal Cu(111) foil has been shown to be an ideal substrate for the epitaxial growth of graphene. Our group has reported the synthesis of large-size single crystal Cu(111) foils by the contact-free annealing of commercial Cu foils, and single crystal Cu/Ni(111) alloy foils have also been obtained after the heat-treatment of Ni-coated Cu(111) foils. The use of these single crystal foils (especially the Cu/Ni alloy foils) as growth substrates has enabled the fast growth of single crystal single-layer graphene films. By increase of the Ni content, single crystal bilayer, trilayer, and even multilayer graphene films have been synthesized. In addition, we also discuss the wafer-scale growth of single-layer graphene on the single crystalline Cu/Ni(111) thin films. Recent research results on the large-scale preparation of single crystal graphene films with different numbers of layers on various types of Cu/Ni alloy substrates with different compositions are reviewed and discussed in detail. Despite the remarkable progress in this field, further challenges, such as the wafer-scale synthesis of single crystal graphene with a controlled number of layers and a deeper understanding of the growth mechanism of bilayer and multilayer graphene growth on Cu/Ni substrates, still need to be addressed
Mass production and industrial applications of graphene materials
No full textGraphene is considered a promising material for industrial application based on the intensive laboratory-scale research in the fields of physics, chemistry, materials science and engineering, and biology over the last decade. Many companies have thus started to pursue graphene materials on a scale of tons (for the flake material) or hundreds of thousands of square meters (for the film material) for industrial applications. Though the graphene industry is still in its early stages, very significant progress in mass production and certain industrial applications has become obvious. In this report, we aim to give a brief review of the mass production of graphene materials for some industrial applications and summarize some features or challenges for graphene in the marketplace
Synthesis of Graphene Films on Copper Foils by Chemical Vapor Deposition
No full textOver the past decade, graphene has advanced rapidly as one of the most promising materials changing human life. Development of production-worthy synthetic methodologies for the preparation of various types of graphene forms the basis for its investigation and applications. Graphene can be used in the forms of either microflake powders or large-area thin films. Graphene powders are prepared by the exfoliation of graphite or the reduction of graphene oxide, while graphene films are prepared predominantly by chemical vapor deposition (CVD) on a variety of substrates. Both metal and dielectric substrates have been explored; while dielectric substrates are preferred over any other substrate, much higher quality graphene large-area films have been grown on metal substrates such as Cu. The focus here is on the progress of graphene synthesis on Cu foils by CVD, including various CVD techniques, graphene growth mechanisms and kinetics, strategies for synthesizing large-area graphene single crystals, graphene transfer techniques, and, finally, challenges and prospects are discussed.clos
Low-cost synthesis route for high-performance S/C composite with 90% S content
No full textLithium-sulfur (Li-S) batteries offer a high theoretical energy density of 2567 W?h?kg???1 by the multi-electron-transfer cathode reaction between elemental sulfur and lithium ions, and are a focus of post lithium-ion batteries technology1. Yet, there are challenging obstacles standing in the way of the large-scale application of the Li-S technology in the market, which include the potential safety risky of Li- dendrite formation, low electrical conductivity of sulfur (5*10???30 S?cm???1 at 25 ??C), the dissolution of the charge/discharge intermediates, polysulfides (Li2Sx, 4 ??? x ??? 8) in the electrolyte, and the volume change of the sulfur during lithiation/delithiation (~80%)2. Carbon materials are commonly used as the host to accommodate sulfur to address the issues relevant to the sulfur-cathode owning to their diversity, conductivity, robust stability and chemistry, and their ready abundance and cost3. A carbon host with sulfur nanoparticles adhered can conduct electrons generated by sulfur lithiation/delithiation, limit the dissolution of polysulfides, and withstand the volume change of the sulfur; it therefore can provide an improved specific capacity, rate capability, and cyclic life. However, these improvements are closely connected to both the mass ratio of sulfur in such a sulfur/carbon composite and the areal loading density of sulfur in the cathode. Higher mass ratio and areal loading density of sulfur are favored for practical Li- S battery application, but are usually accompanied by lower???sulfur utility???that yields reduced specific capacity, rate capability, and cycle life.clos
Two-Dimensional Materials for Beyond-Lithium-Ion Batteries
No full textLithium-ion batteries (LIBs) have dominated the portable electronics industry and solid-state electrochemical research and development for the past two decades. In light of possible concerns over the cost and future availability of lithium, sodium-ion batteries (SIBs) and other new technologies have emerged as candidates for large-scale stationary energy storage. Research in these technologies has increased dramatically with a focus on the development of new materials for both the positive and negative electrodes that can enhance the cycling stability, rate capability, and energy density. Two-dimensional (2D) materials are showing promise for many energy-related applications and particularly for energy storage, because of the efficient ion transport between the layers and the large surface areas available for improved ion adsorption and faster surface redox reactions. Recent research highlights on the use of 2D materials in these future 'beyond-lithium-ion' battery systems are reviewed, and strategies to address challenges are discussed as well as their prospects. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim11401501sciescopu
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