Showing papers by "Rodney S. Ruoff published in 2020"
300 citations
TL;DR: It is shown that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene grown by chemical vapour deposition on a single-crystal CuNi(111) surface triggers the formation of interlayer carbon–carbon bonds, resulting in a fluorinated diamond monolayer (‘F-diamane’).
Abstract: Notwithstanding the numerous density functional studies on the chemically induced transformation of multilayer graphene into a diamond-like film carried out to date, a comprehensive convincing experimental proof of such a conversion is still lacking. We show that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene grown by chemical vapour deposition on a single-crystal CuNi(111) surface triggers the formation of interlayer carbon-carbon bonds, resulting in a fluorinated diamond monolayer ('F-diamane'). Induced by fluorine chemisorption, the phase transition from (AB)-stacked bilayer graphene to single-layer diamond was studied and verified by X-ray photoelectron, UV photoelectron, Raman, UV-Vis and electron energy loss spectroscopies, transmission electron microscopy and density functional theory calculations.
169 citations
TL;DR: Large-area, high-quality AB-stacked bilayer and ABA-stacking trilayer graphene films have been achieved, with fine control of Ni content, on single-crystal Cu/Ni(111) alloy foils.
Abstract: High-quality AB-stacked bilayer or multilayer graphene larger than a centimetre has not been reported. Here, we report the fabrication and use of single-crystal Cu/Ni(111) alloy foils with controllable concentrations of Ni for the growth of large-area, high-quality AB-stacked bilayer and ABA-stacked trilayer graphene films by chemical vapour deposition. The stacking order, coverage and uniformity of the graphene films were evaluated by Raman spectroscopy and transmission electron microscopy including selected area electron diffraction and atomic resolution imaging. Electrical transport (carrier mobility and band-gap tunability) and thermal conductivity (the bilayer graphene has a thermal conductivity value of about 2,300 W m−1 K−1) measurements indicated the superior quality of the films. The tensile loading response of centimetre-scale bilayer graphene films supported by a 260-nm thick polycarbonate film was measured and the average values of the Young’s modulus (478 GPa) and fracture strength (3.31 GPa) were obtained. Large-area, high-quality AB-stacked bilayer and ABA-stacked trilayer graphene films have been achieved, with fine control of Ni content, on single-crystal Cu/Ni(111) alloy foils.
119 citations
78 citations
61 citations
06 May 2020
TL;DR: In this article, a new approach was proposed to make highly dense, oriented, and crystalline graphite films from heat-treated and pressed graphene oxide (G-O) flakes.
Abstract: Summary We report a new approach to making highly dense, oriented, and crystalline graphite films from heat-treated and pressed graphene oxide (G-O). By introducing small-diameter reduced graphene oxide (rG-O) flakes into the graphene oxide starting material, we found that after heat treatment at 3,000°C, the sample density and atomic order substantially improved over a film composed, at the outset, only of pure G-O flakes. A subsequent mechanical press increased the density but reduced the atomic order. A second 3,000°C heat treatment restored the graphitic structure with graphitization metrics exceeding even those of the first heat treatment. The optimized graphitic film with an original concentration of 15 wt % reduced G-O in G-O gave well-oriented graphitic films with a density of 2.1 g cm−3, cross-plane thermal conductivity of 5.65 W m−1 K−1, and in-plane thermal conductivity of 2,025 ± 25 W m−1 K−1.
51 citations
TL;DR: It is shown that liquid metals render room-temperature synthesis of 2D graphitic materials possible as they offer catalytic activity and an ultrasmooth templating interface that promotes Frank-van der Merwe regime growth, while allowing facile exfoliation due to the absence of interfacial forces as a nonpolar liquid.
Abstract: Room-temperature synthesis of 2D graphitic materials (2D-GMs) remains an elusive aim, especially with electrochemical means. Here, it is shown that liquid metals render this possible as they offer catalytic activity and an ultrasmooth templating interface that promotes Frank-van der Merwe regime growth, while allowing facile exfoliation due to the absence of interfacial forces as a nonpolar liquid. The 2D-GMs are formed at low onset potential and can be in situ doped depending on the choice of organic precursors and the electrochemical set-up. The materials are tuned to exhibit porous or pinhole-free morphologies and are engineered for their degree of oxidation and number of layers. The proposed liquid-metal-based room-temperature electrochemical route can be expanded to many other 2D materials.
49 citations
TL;DR: Current progress and development in the CVD growth of graphene is reviewed and the important challenges that need to be addressed are highlighted, for example, how to achieve large single crystal graphene films with a controlled number of layers.
Abstract: ConspectusGraphene, 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.
46 citations
05 Aug 2020
TL;DR: In this article, the walls in the graphene foam were found to be two to five graphene layers thick, interconnected to form a low-density porous network with a wide distribution of pore sizes and a high electrical conductivity.
Abstract: Summary Porous Cu/Ni foils were made by electroplating Ni on Cu foils and used as templates for chemical vapor deposition growth of porous graphene foam. The walls in the graphene foam were found to be two to five graphene layers thick, interconnected to form a low-density porous network with a wide distribution of pore sizes and a high electrical conductivity. A comprehensive comparison with previously studied materials for electromagnetic interference (EMI) shielding showed that this graphene foam is among the best EMI shielding materials; its specific EMI shielding effectiveness (>720 dB cm3 g−1) and absolute effectiveness (>45,000 dB cm2 g−1) are superior to those of most other materials. This graphene foam has a large absorption capacity for various organic solvents and oils and adsorbs them within seconds. The synthesis strategy should provide a general approach for generating other 3D porous structures, including those based on a variety of known 2D materials, for various applications.
45 citations
TL;DR: The synthesis and characterization of a two-dimensional (2D) MX2Y2-type copper 1,3,5-triamino-2,4,6-benzenetriol metal-organic framework is reported, which expands the family of 2D redox-active ligand-based electrically conductive MOFs, and offers more opportunities in sensing, photocatalytic, electronic, and energy-related applications.
Abstract: We report the synthesis and characterization of a two-dimensional (2D) MX2Y2-type (M = metal, X, Y = N, S, O, and X ≠ Y) copper 1,3,5-triamino-2,4,6-benzenetriol metal-organic framework (Cu3(TABTO)2-MOF). The role of oxygen in the synthesis of this MOF was investigated. Copper metal is formed along with the MOF when the synthesis is done in argon as suggested by XRD. When the reaction was exposed to air with vigorous stirring, copper metal was not observed by XRD. However, if there is no stirring, then copper metal is formed, and we learned that this is because oxygen was not allowed to enter the solvent due to the formation of a MOF film at the air/water interface. For the sample synthesized in argon (Cu3(TABTO)2-Ar), an insulating Cu3(TABTO)2-Ar pellet (σ < 10-10 S cm-1) became a metallic conductor with an electrical conductivity of 0.78 S cm-1 at 300 K after exposure to iodine vapor. This work provides further insights into the role of oxygen in the synthesis of redox-active ligand-based MOFs, expands the family of 2D redox-active ligand-based electrically conductive MOFs, and offers more opportunities in sensing, photocatalytic, electronic, and energy-related applications.
40 citations
TL;DR: In this article, a method to obtain networks of wrinkles in multilayer graphene flakes (and other layered materials) by thermal contraction of the underlying PDMS substrate they are deposited on is described.
20 Mar 2020
TL;DR: In this article, the authors demonstrate terahertz time-domain spectroscopy (THz-TDS) to probe the interaction-induced Fermi velocity renormalization.
Abstract: We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization nu F*10(12) cm(-2), Fermi le ...
TL;DR: It is demonstrated that the frequency-dependent AC conductivity of graphene can be acquired by comparing the directly transmitted THz pulse with a transient internal reflection within the substrate which avoids the need for a standard reference scan.
Abstract: We present a reference-free method to determine electrical parameters of thin conducting films by steady state transmission-mode terahertz time-domain spectroscopy (THz-TDS). We demonstrate that the frequency-dependent AC conductivity of graphene can be acquired by comparing the directly transmitted THz pulse with a transient internal reflection within the substrate which avoids the need for a standard reference scan. The DC sheet conductivity, scattering time, carrier density, mobility, and Fermi velocity of graphene are retrieved subsequently by fitting the AC conductivity with the Drude model. This reference-free method was investigated with two complementary THz setups: one commercial fibre-coupled THz spectrometer with fast scanning rate (0.2-1.5 THz) and one air-plasma based ultra-broadband THz spectrometer for greatly extended frequency range (2-10 THz). Certain propagation correction terms for more accurate retrieval of electrical parameters are discussed.
TL;DR: A film formed of densely packed amorphous carbon nanofibers is synthesized by chemical vapor deposition using acetylene and hydrogen gases as precursors and copper nanoparticles (<25 nm in diameter) as the catalyst at low temperatures (220-300 °C).
Abstract: A film formed of densely packed amorphous carbon nanofibers is synthesized by chemical vapor deposition using acetylene and hydrogen gases as precursors and copper nanoparticles (<25 nm in diameter) as the catalyst at low temperatures (220-300 °C). This film has a high concentration of sp3 carbon (sp3/sp2 carbon ratio of ∼1-1.9) with a hydrogen concentration of 25-44 atom %, which qualifies it as hydrogenated diamond-like carbon. This hydrogenated diamond-like carbon nanofiber film has properties akin to those of diamond-like carbon films. It has a high electrical resistivity (1.2 ± 0.1 × 106 Ω cm), a density of 2.5 ± 0.2 g cm-3, and is chemically inert. Because of its morphology, different from diamond-like carbon films on the nanometer scale, it has a higher surface area of 28 ± 0.7 m2 g-1 and has differences in mechanical properties, such as Young's modulus, hardness, and coefficient of friction. The hydrophobicity of this film is comparable to the best diamond-like carbon films, and it is wettable by oil and organic solvents. The nanofibers can also be separated from the substrate and each other and be used in a powder form.
TL;DR: A sodium-ethylenediamine graphite intercalation compound made from graphite flakes was used to study the microwave absorption performance of a GIC for the first time and it was found that due to the electrical conductivity of this GIC, only half of the loading content is needed to achieve an outstanding absorption.
Abstract: A sodium-ethylenediamine graphite intercalation compound (Na(ethylenediamine)C15: "GIC") made from graphite flakes was used to study the microwave absorption performance of a GIC for the first time. Compared with the pristine graphite flakes, the neighboring layers in this GIC are pillared by Na(ethylenediamine)+ and possess a larger layer distance and improved electrical conductivity. Owing to the electrical conductivity of this GIC, only half of the loading content, compared to graphite flakes, is needed to achieve an outstanding absorption of -75.6 dB at 9.25 GHz (10.0 wt % GIC in paraffin in a 4.0 mm thick sample), but for graphite, 20.0 wt % is required for an absorption of -37.6 dB.
TL;DR: The oriented van der Waals epitaxy can be generalized to any hexagonal 2D crystals and will serve as a unique growth process to form crystals with orientations along the zigzag directions by epitaxy.
Abstract: The atomic or molecular assembly on 2D materials through the relatively weak van der Waals interaction is quite different from the conventional heteroepitaxy and may result in unique growth behaviors. Here, it is shown that straight 1D cyanide chains display universal epitaxy on hexagonal 2D materials. A universal oriented assembly of cyanide crystals (AgCN, AuCN, and Cu0.5Au0.5CN) is observed, where the chains are aligned along the three zigzag lattice directions of various 2D hexagonal crystals (graphene, h-BN, WS2, MoS2, WSe2, MoSe2, and MoTe2). The potential energy landscape of the hexagonal lattice induces this preferred alignment of 1D chains along the zigzag lattice directions, regardless of the lattice parameter and surface elements as demonstrated by first-principles calculations and parameterized surface potential calculations. Furthermore, the oriented microwires can serve as crystal orientation markers, and stacking-angle-controlled vertical 2D heterostructures are successfully fabricated by using them as markers. The oriented van der Waals epitaxy can be generalized to any hexagonal 2D crystals and will serve as a unique growth process to form crystals with orientations along the zigzag directions by epitaxy.
TL;DR: In this paper, the in-plane stiffness of polycrystalline graphene obtained by chemi cation was analyzed and shown to be strongly affected by their crystal structures and defect configurations.
Abstract: The mechanical properties of nanomaterials can be strongly affected by their crystal structures and defect configurations. Here, the in-plane stiffness of polycrystalline graphene obtained by chemi...
TL;DR: In graphite films, grain boundaries and wrinkles have been found to have detrimental effects on properties such as thermal and electrical conductivities as mentioned in this paper, and these defects are known to have a negative effect on graphite properties.
Abstract: Principal defects found in graphite films include grain boundaries and wrinkles. These defects are well known to have detrimental effects on properties such as thermal and electrical conductivities...
TL;DR: In this paper, the authors demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization of charge carriers in graphene.
Abstract: We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization {
u}F^* of charge carriers in graphene. This allows the quantitative extraction of all electrical parameters (DC conductivity {\sigma}DC, carrier density n, and carrier mobility {\mu}) of large-scale graphene films placed on arbitrary substrates via THz-TDS. Particularly relevant are substrates with low relative permittivity ( 10^12 cm-2, Fermi level > 0.1 eV). From an application point of view, the ability to rapidly and non-destructively quantify and map the electrical ({\sigma}DC, n, {\mu}) and electronic ({
u}F^* ) properties of large-scale graphene on generic substrates is key to utilize this material in applications such as metrology, flexible electronics as well as to monitor graphene transfers using polymers as handling layers.
TL;DR: A chemical route to synthesize centimeter-scale stoichiometric 'graphenol (C6OH)', 2D crystalline alcohol via vapor phase hydroxylation of epitaxial graphene on Cu(111) is reported, demonstrating the feasibility of the same superstructure being achieved at the centimeter length scale.
Abstract: We report a chemical route to synthesize centimeter-scale stoichiometric "graphenol (C6OH1)", a 2D crystalline alcohol, via vapor phase hydroxylation of epitaxial graphene on Cu(111). Atomic resolution scanning tunneling microscopy revealed this highly-ordered configuration of graphenol and low energy electron diffraction studies on a large-area single crystal graphene film demonstrated the feasibility of the same superstructure being achieved at the centimeter length scale. Periodic density functional theory (DFT) calculations about the formation of C6(OH)1 and its electronic structure are also reported.
TL;DR: In this article, a simple process to connect graphene sheets forming graphene hollow microtubes (GHMs) was reported, where the tube diameter can be adjusted in the 100-500nm range by changing reaction conditions.
TL;DR: In this paper, the lattice orientation of graphene grains larger than a centimeter was mapped by measuring the orientation of cracks in a WS2 film grown on graphene that had been previously grown by chemica.
Abstract: We map the lattice orientation of graphene grains (domains) larger than a centimeter by measuring the orientation of cracks in a WS2 film grown on graphene that had been previously grown by chemica...