Showing papers on "Graphene oxide paper published in 2012"
TL;DR: In this paper, the state-of-the-art status of the reduction of GO on both techniques and mechanisms is reviewed, where the reduction process can partially restore the structure and properties of graphene.
4,187 citations
2,750 citations
TL;DR: In this paper, a high-voltage asymmetric supercapacitor is successfully fabricated using Ni(OH)2/graphene and porous graphene as the positive and negative electrodes, respectively.
Abstract: Hierarchical flowerlike nickel hydroxide decorated on graphene sheets has been prepared by a facile and cost-effective microwave-assisted method. In order to achieve high energy and power densities, a high-voltage asymmetric supercapacitor is successfully fabricated using Ni(OH)2/graphene and porous graphene as the positive and negative electrodes, respectively. Because of their unique structure, both of these materials exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high-voltage region of 0–1.6 V and displays intriguing performances with a maximum specific capacitance of 218.4 F g−1 and high energy density of 77.8 Wh kg−1. Furthermore, the Ni(OH)2/graphene//porous graphene supercapacitor device exhibits an excellent long cycle life along with 94.3% specific capacitance retained after 3000 cycles. These fascinating performances can be attributed to the high capacitance and the positive synergistic effects of the two electrodes. The impressive results presented here may pave the way for promising applications in high energy density storage systems.
1,808 citations
TL;DR: In this article, the importance of synergistic effects between graphene and metal oxides and the beneficial role of graphene in composites for lithium ion batteries (LIBs) and electrochemical capacitors (ECs) is discussed.
1,636 citations
TL;DR: A detailed review on the advances of chemical functionalization of graphene is presented in this article, where the surface modification of graphene oxide followed by reduction has been carried out to obtain functionalized graphene.
1,517 citations
TL;DR: The 3D graphene/Co(3)O(4) composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose and it is demonstrated that it is capable of delivering high specific capacitance and detecting glucose with a ultrahigh sensitivity.
Abstract: Using a simple hydrothermal procedure, cobalt oxide (Co3O4) nanowires were in situ synthesized on three-dimensional (3D) graphene foam grown by chemical vapor deposition. The structure and morphology of the resulting 3D graphene/Co3O4 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The 3D graphene/Co3O4 composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose. We demonstrate that it is capable of delivering high specific capacitance of ∼1100 F g–1 at a current density of 10 A g–1 with excellent cycling stability, and it can detect glucose with a ultrahigh sensitivity of 3.39 mA mM–1 cm–2 and a remarkable lower detection limit of <25 nM (S/N = 8.5).
1,467 citations
TL;DR: In this article, a chemical approach to immobilize sulfur and lithium polysulfides via the reactive functional groups on graphene oxide was proposed, which obtains a uniform and thin (˜tens of nanometers) sulfur coating.
Abstract: The loss of sulfur cathode material as a result of polysulfide dissolution causes significant capacity fading in rechargeable lithium/sulfur cells. Embodiments of the invention use a chemical approach to immobilize sulfur and lithium polysulfides via the reactive functional groups on graphene oxide. This approach obtains a uniform and thin (˜tens of nanometers) sulfur coating on graphene oxide sheets by a chemical reaction-deposition strategy and a subsequent low temperature thermal treatment process. Strong interaction between graphene oxide and sulfur or polysulfides demonstrate lithium/sulfur cells with a high reversible capacity of 950-1400 mAh g −1 , and stable cycling for more than 50 deep cycles at 0.1 C.
1,350 citations
TL;DR: The 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.
Abstract: We found that the 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 the relatively high concentration of the single-layer and bilayer graphene flakes (∼10–15%) present simultaneously with the thicker multilayers of large lateral size (∼1 μm) were essential for the observed unusual K enhancement. The thermal conductivity of the 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 nanotub...
1,272 citations
TL;DR: In this paper, the authors synthesize heteroatom (N or S)-doped graphene with high surface area via thermal reaction between graphene oxide and guest gases (NH3 or H2S) on the basis of ultrathin graphene oxide-porous silica sheets at high temperatures.
Abstract: Heteroatom (N or S)-doped graphene with high surface area is successfully synthesized via thermal reaction between graphene oxide and guest gases (NH3 or H2S) on the basis of ultrathin graphene oxide-porous silica sheets at high temperatures. It is found that both N and S-doping can occur at annealing temperatures from 500 to 1000 °C to form the different binding configurations at the edges or on the planes of the graphene, such as pyridinic-N, pyrrolic-N, and graphitic-N for N-doped graphene, thiophene-like S, and oxidized S for S-doped graphene. Moreover, the resulting N and S-doped graphene sheets exhibit good electrocatalytic activity, long durability, and high selectivity when they are employed as metal-free catalysts for oxygen reduction reactions. This approach may provide an efficient platform for the synthesis of a series of heteroatom-doped graphenes for different applications.
1,161 citations
TL;DR: In this paper, the preparation and characterisation of different forms of graphene are reviewed and different techniques that have been employed to prepare graphene such as mechanical and solution exfoliation, and chemical vapour deposition are discussed briefly.
1,101 citations
TL;DR: A bubbling method is reported to transfer single graphene grains and graphene films joined from such grains on Pt by ambient-pressure chemical vapour deposition to arbitrary substrate, which is nondestructive not only to graphene, but also to the Pt substrates.
Abstract: Large single-crystal graphene is highly desired and important for the applications of graphene in electronics, as grain boundaries between graphene grains markedly degrade its quality and properties. Here we report the growth of millimetre-sized hexagonal single-crystal graphene and graphene films joined from such grains on Pt by ambient-pressure chemical vapour deposition. We report a bubbling method to transfer these single graphene grains and graphene films to arbitrary substrate, which is nondestructive not only to graphene, but also to the Pt substrates. The Pt substrates can be repeatedly used for graphene growth. The graphene shows high crystal quality with the reported lowest wrinkle height of 0.8 nm and a carrier mobility of greater than 7,100 cm 2 V − 1 s − 1 under ambient conditions. The repeatable growth of graphene with large single-crystal grains on Pt and its nondestructive transfer may enable various applications.
TL;DR: Graphene is established as the thinnest known corrosion-protecting coating because it suppresses metal oxidation and oxygen reduction and prevents corrosion of underlying metals.
Abstract: We report the use of atomically thin layers of graphene as a protective coating that inhibits corrosion of underlying metals. Here, we employ electrochemical methods to study the corrosion inhibition of copper and nickel by either growing graphene on these metals, or by mechanically transferring multilayer graphene onto them. Cyclic voltammetry measurements reveal that the graphene coating effectively suppresses metal oxidation and oxygen reduction. Electrochemical impedance spectroscopy measurements suggest that while graphene itself is not damaged, the metal under it is corroded at cracks in the graphene film. Finally, we use Tafel analysis to quantify the corrosion rates of samples with and without graphene coatings. These results indicate that copper films coated with graphene grown via chemical vapor deposition are corroded 7 times slower in an aerated Na2SO4 solution as compared to the corrosion rate of bare copper. Tafel analysis reveals that nickel with a multilayer graphene film grown on it corro...
TL;DR: The method presented here is proved to be versatile to induce macroscopic assembly of reduced graphene sheets with other functional metal oxides and thus to access a variety of graphene-based multifunctional nanocomposites in the form of macroscopy hydrogels or aerogels.
Abstract: We report a one-step fabrication of macroscopic multifunctional graphene-based hydrogels with robust interconnected networks under the synergistic effects of the reduction of graphene oxide sheets by ferrous ions and in situ simultaneous deposition of nanoparticles on graphene sheets. The functional components, such as α-FeOOH nanorods and magnetic Fe3O4 nanoparticles, can be easily incorporated with graphene sheets to assemble macroscopic graphene monoliths just by control of pH value under mild conditions. Such functional graphene-based hydrogels exhibit excellent capability for removal of pollutants and, thus, could be used as promising adsorbents for water purification. The method presented here is proved to be versatile to induce macroscopic assembly of reduced graphene sheets with other functional metal oxides and thus to access a variety of graphene-based multifunctional nanocomposites in the form of macroscopic hydrogels or aerogels.
TL;DR: It is reported that graphene coatings do not significantly disrupt the intrinsic wetting behaviour of surfaces for which surface-water interactions are dominated by van der Waals forces, and contact angle measurements indicate that a graphene monolayer is wetting-transparent to copper, gold or silicon, but not glass, for which the wettability is dominated by short-range chemical bonding.
Abstract: It is demonstrated that graphene coatings do not alter the wetting behaviour of copper, gold or silicon surfaces Such wetting transparency—shown to occur only for surfaces where surface–water interactions are dominated by van der Waals forces—and graphene’s ability to suppress copper oxidation result in a 30–40% increase in condensation heat transfer on copper The findings have implications for graphene-based coatings with independently tunable electronic and wetting properties
TL;DR: It is found that NiO nanosheets (NiO NSs) are bonded strongly to graphene through oxygen bridges, which allows a high reversible capacity and excellent rate performance.
Abstract: Graphene has been widely used to dramatically improve the capacity, rate capability, and cycling performance of nearly any electrode material for batteries. However, the binding between graphene and these electrode materials has not been clearly elucidated. Here we report oxygen bridges between graphene with oxygen functional groups and NiO from analysis by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy and confirm the conformation of oxygen bridges by the first-principles calculations. We found that NiO nanosheets (NiO NSs) are bonded strongly to graphene through oxygen bridges. The oxygen bridges mainly originate from the pinning of hydroxyl/epoxy groups from graphene on the Ni atoms of NiO NSs. The calculated adsorption energies (1.37 and 1.84 eV for graphene with hydroxyl and epoxy) of a Ni adatom on oxygenated graphene by binding with oxygen are comparable with that on graphene (1.26 eV). However, the calculated diffusion barriers of the Ni adatom on...
TL;DR: This simple chemical vapor deposition method provides a unique approach for the synthesis of graphene heterostructures and surface functionalization of graphene and possesses great potential toward the development of new optical and electronic devices as well as a wide variety of newly synthesizable compounds for catalysts.
Abstract: We present a method for synthesizing MoS2/Graphene hybrid heterostructures with a growth template of graphene-covered Cu foil. Compared to other recent reports,(1, 2) a much lower growth temperature of 400 °C is required for this procedure. The chemical vapor deposition of MoS2 on the graphene surface gives rise to single crystalline hexagonal flakes with a typical lateral size ranging from several hundred nanometers to several micrometers. The precursor (ammonium thiomolybdate) together with solvent was transported to graphene surface by a carrier gas at room temperature, which was then followed by post annealing. At an elevated temperature, the precursor self-assembles to form MoS2 flakes epitaxially on the graphene surface via thermal decomposition. With higher amount of precursor delivered onto the graphene surface, a continuous MoS2 film on graphene can be obtained. This simple chemical vapor deposition method provides a unique approach for the synthesis of graphene heterostructures and surface funct...
TL;DR: A systematic study of PMMA decomposition on graphene and of its impact on graphene's intrinsic properties using transmission electron microscopy (TEM) in combination with Raman spectroscopy is reported.
Abstract: Surface contamination by polymer residues has long been a critical problem in probing graphene’s intrinsic properties and in using graphene for unique applications in surface chemistry, biotechnology, and ultrahigh speed electronics. Poly(methyl methacrylate) (PMMA) is a macromolecule commonly used for graphene transfer and device processing, leaving a thin layer of residue to be empirically cleaned by annealing. Here we report on a systematic study of PMMA decomposition on graphene and of its impact on graphene’s intrinsic properties using transmission electron microscopy (TEM) in combination with Raman spectroscopy. TEM images revealed that the physisorbed PMMA proceeds in two steps of weight loss in annealing and cannot be removed entirely at a graphene susceptible temperature before breaking. Raman analysis shows a remarkable blue-shift of the 2D mode after annealing, implying an anneal-induced band structure modulation in graphene with defects. Calculations using density functional theory show that l...
TL;DR: These free-standing thin films provide a route to simplify the electrode-manufacturing process by eliminating conducting additives and binders and are the highest values achieved while simultaneously maintaining excellent specific capacitances and energy densities for graphene materials.
Abstract: We present a novel method to prepare highly conductive, free-standing, and flexible porous carbon thin films by chemical activation of reduced graphene oxide paper. These flexible carbon thin films possess a very high specific surface area of 2400 m2 g–1 with a high in-plane electrical conductivity of 5880 S m–1. This is the highest specific surface area for a free-standing carbon film reported to date. A two-electrode supercapacitor using these carbon films as electrodes demonstrated an excellent high-frequency response, an extremely low equivalent series resistance on the order of 0.1 ohm, and a high-power delivery of about 500 kW kg–1. While higher frequency and power values for graphene materials have been reported, these are the highest values achieved while simultaneously maintaining excellent specific capacitances and energy densities of 120 F g–1 and 26 W h kg–1, respectively. In addition, these free-standing thin films provide a route to simplify the electrode-manufacturing process by eliminating...
TL;DR: In this article, it was shown that nitrogen-doped graphene (NG) has high catalytic activity toward the oxygen-reduction reaction (ORR), which often limits the performance of the cathode in a fuel cell or a metalair battery.
Abstract: excellent thermal conductivity, [ 2 ] and a high optical transparency. [ 3 ] These properties lead to very promising applications of graphene in electronic devices, [ 4 ] transparent electrodes, [ 5 ] and energy-storage devices. [ 6 , 7 ] Recently, it was found that graphene has an extraordinary catalytic activity. [ 8–14 ] For example, N-doped graphene has a high catalytic activity toward the oxygen-reduction reaction (ORR). [ 8 ] Furthermore, graphene oxide (GO), an important derivative of graphene, is an effi cient catalyst for oxidation and hydration reactions of various alcohols, [ 9 ] whereas reduced GO can be used for catalyzing the hydrogenation of nitrobenzene. [ 10 ] Studies have shown that the heteroatoms in graphene derivatives, such as N and O, play a critical role in their catalytic activities. [ 10 , 15 , 16 ] Thus, the introduction of dopants into the graphene lattice has been the focus of much research in order to achieve a high catalytic activity toward target reactions. Among various doped graphenes, nitrogen-doped graphene (NG) has attracted much attention because of its high catalytic activity toward the ORR – the electrode reaction that often limits the performance of the cathode in a fuel cell or a metalair battery. Conventional Pt-based catalysts have a high intrinsic catalytic activity toward the ORR, but suffer from the drawbacks of high cost, poor long-term stability, and susceptibility to the crossover effect, which hinder the commercial viability of Ptloaded fuel cells. [ 17 ] Thus the search for an alternative catalyst, such as NG, is of great importance in replacing these expensive Pt-based catalysts. To prepare NG, chemical-vapor deposition in the presence of N-containing precursors is the most-common method; [ 18 ] arc discharge of graphite electrodes in a H 2 /pyridine or H 2 /NH 3 atmosphere can also produce NG. [ 19 ] However, the extremely low yield and high cost of these methods limit their application only to fundamental studies. Later, it was found that GO can be
TL;DR: Electron microscopic studies demonstrated that the resultant composite has fibrillar morphology with a room-temperature electrical conductivity as high as 8.66 S/cm and capacitance of 250 F/g with good cycling stability.
Abstract: An alternative and effective route to prepare conducting polyaniline-grafted reduced graphene oxide (PANi-g-rGO) composite with highly enhanced properties is reported. In order to prepare PANi-g-rGO, amine-protected 4-aminophenol was initially grafted to graphite oxide (GO) via acyl chemistry where a concomitant partial reduction of GO occurred due to the refluxing and exposure of GO to thionyl chloride vapors and heating. Following the deprotection of amine groups, an in situ chemical oxidative grafting of aniline in the presence of an oxidizing agent was carried out to yield highly conducting PANi-g-rGO. Electron microscopic studies demonstrated that the resultant composite has fibrillar morphology with a room-temperature electrical conductivity as high as 8.66 S/cm and capacitance of 250 F/g with good cycling stability.
TL;DR: In this Review, the importance of graphene-based electrodes, their fabrication techniques, and application areas are discussed.
Abstract: Graphene, the thinnest two dimensional carbon material, has become the subject of intensive investigation in various research fields because of its remarkable electronic, mechanical, optical and thermal properties. Graphene-based electrodes, fabricated from mechanically cleaved graphene, chemical vapor deposition (CVD) grown graphene, or massively produced graphene derivatives from bulk graphite, have been applied in a broad range of applications, such as in light emitting diodes, touch screens, field-effect transistors, solar cells, supercapacitors, batteries, and sensors. In this Review, after a short introduction to the properties and synthetic methods of graphene and its derivatives, we will discuss the importance of graphene-based electrodes, their fabrication techniques, and application areas.
TL;DR: Graphene, a single atomic layer of sp2 hybridized carbon, exhibits a zero-band gap with linear band dispersion at the Fermi-level, forming a Dirac-cone at the K -points of its Brillouin zone as mentioned in this paper.
TL;DR: In this paper, the use of liquid-phase-exfoliated graphene and multilayer graphene as fillers in the thermal interface materials has been discussed, and it has been demonstrated that the addition of an optimized mixture of graphene and multi-layer graphene to the composites with different matrix materials produces the record-high enhancement of the effective thermal conductivity at the small filler loading fraction (f≤10vol%).
TL;DR: Graphene/Mn3O4 composites were prepared by a simple hydrothermal process from KMnO4 using ethylene glycol as a reducing agent in this paper.
Abstract: Graphene/Mn3O4 composites were prepared by a simple hydrothermal process from KMnO4 using ethylene glycol as a reducing agent. Mn3O4 nanorods of 100 nm to 1 μm length were observed to be well-dispersed on graphene sheets. To assess the properties of these materials for use in supercapacitors, cyclic voltammetry and galvanostatic charging–discharging measurements were performed. Graphene/Mn3O4 composites could be charged and discharged faster and had higher capacitance than free Mn3O4 nanorods. The capacitance of the composites was 100% retained after 10 000 cycles at a charging rate of 5 A/g.
TL;DR: This Minireview highlights the recent progress that has led to the successful chemical synthesis of graphene with a range of different sizes and chemical compositions based on both top-down and bottom-up strategies.
Abstract: Graphene, an individual two-dimensional, atomically thick sheet of graphite composed of a hexagonal network of sp2 carbon atoms, has been intensively investigated since its first isolation in 2004, which was based on repeated peeling of highly oriented pyrolyzed graphite (HOPG). The extraordinary electronic, thermal, and mechanical properties of graphene make it a promising candidate for practical applications in electronics, sensing, catalysis, energy storage, conversion, etc. Both the theoretical and experimental studies proved that the properties of graphene are mainly dependent on their geometric structures. Precise control over graphene synthesis is therefore crucial for probing their fundamental physical properties and introduction in promising applications. In this Minireview, we highlight the recent progress that has led to the successful chemical synthesis of graphene with a range of different sizes and chemical compositions based on both top-down and bottom-up strategies.
TL;DR: The unique graphene paper obtained here is promising to act as a new kind of flexible electrode for wearable or rolling-up devices.
Abstract: A novel method to fabricate graphene paper with folded structured graphene sheets is described. When used as an electrode for LIBs and supercapacitors, the as-prepared graphene paper can show much higher performances compared to conventional graphene paper fabricated by a flow-directed assembly method. The unique graphene paper obtained here is promising to act as a new kind of flexible electrode for wearable or rolling-up devices.
TL;DR: Graphene, a monolayer of graphite sheet consisting of sp2 hybridized carbon atoms covalently bonded to three other atoms (discovered in 2004), has recently attracted the attention of chemical sensor researchers owing to its unprecedented structural, mechanical and electrical properties.
Abstract: Graphene, a monolayer of graphite sheet consisting of sp2 hybridized carbon atoms covalently bonded to three other atoms (discovered in 2004), has recently attracted the attention of chemical sensor researchers owing to its unprecedented structural, mechanical and electrical properties. Excellent mechanical strength (Young modulus ∼0.05 TPa), potentiality of ultrafast electron transport (highest mobility ∼200,000 cm 2 /V s) along with the best surface to volume ratio has opened up the opportunity to use the material for future gas and vapor sensors with ultra fast speed and long-term durability. Since it is a two dimensional material, every atom of graphene may be considered a surface atom and as a result every atom site may be involved in the gas interactions. This feature of graphene can eventually be responsible for its ultra sensitive sensor response with the lowest detection capability approaching even a single molecule. Further, the ease of functionalization of the material either by chemical means (absorption of many molecules like oxygen or hydrogen) or by application of voltage or pressure, facilitates bandgap-engineering which in turn may lead to a possible solution to the selectivity issues, the perennial problems of chemical sensors. In this review, the latest advancement and new perspectives of graphene based gas and vapor sensors have been discussed critically.
TL;DR: The interlayer shear mode of FLGs, ranging from bilayer graphene (BLG) to bulk graphite, is uncovered, and it is suggested that the corresponding Raman peak measures the interlayer coupling.
Abstract: The quest for materials capable of realizing the next generation of electronic and photonic devices continues to fuel research on the electronic, optical and vibrational properties of graphene. Few-layer graphene (FLG) flakes with less than ten layers each show a distinctive band structure. Thus, there is an increasing interest in the physics and applications of FLGs. Raman spectroscopy is one of the most useful and versatile tools to probe graphene samples. Here, we uncover the interlayer shear mode of FLGs, ranging from bilayer graphene (BLG) to bulk graphite, and suggest that the corresponding Raman peak measures the interlayer coupling. This peak scales from 43 cm 1 in bulk graphite to 31 cm 1 in BLG. Its low energy makes it sensitive to near-Dirac point quasiparticles. Similar shear modes are expected in all layered materials, providing a direct probe of interlayer interactions.
TL;DR: The systematic evolution of the electronic structure and comprehensive analysis of steady-state and transient PL along with photoluminescence excitation (PLE) spectroscopy measurements indicate that two different types of electronically excited states are responsible for the observed emission characteristics.
Abstract: Graphene oxide (GO) is a graphene sheet modified with oxygen functional groups in the form of epoxy and hydroxy groups on the basal plane and various other types at the edges. It exhibits interesting steady-state photoluminescence (PL) properties. For example, low-energy fluorescence in red to near infrared (NIR) wavelengths (from 600– 1100 nm) has been detected for suspensions and solid thin films of as-synthesized GO. 3] In addition, broad luminescence from 400 to 800 nm from oxygen plasma-treated, mechanically exfoliated, single-layer graphene sheet has been reported. Blue fluorescence with a relatively narrow bandwidth when excited with UV irradiation has also been detected from chemically reduced GO (rGO) and graphene quantum dots. 6] Recently, chemically modified GO or rGO with n-butylamine or Mn has also demonstrated PL emission at a range of energies. 10] A detailed explanation of the origin of such variable energy PL in GO has yet to be elucidated. This is partly because the sample preparation and reduction methods varied, making it difficult to compare the results. Herein, we have prepared GO suspensions that exhibit virtually all of the PL features observed by different groups, through careful and gradual reduction of the GO. The systematic evolution of the electronic structure and comprehensive analysis of steady-state and transient PL along with photoluminescence excitation (PLE) spectroscopy measurements indicate that two different types of electronically excited states are responsible for the observed emission characteristics. GO was synthesized using the modified Hummers method, the details of which have been reported. GO usually contains a large fraction of sp hybridized carbon atoms bound to oxygen functional groups, which makes it an insulator. Reduction can be achieved chemically (e.g. hydrazine exposure) or by thermal annealing in inert environments. Photothermal reduction of GO can be achieved by exposing GO samples to a Xenon flash in ambient conditions. In this study, we prepared aqueous GO solutions and subjected them to steady-state Xe lamp irradiation (500 W) with different exposure times of up to three hours. In contrast to reduction by an instantaneous flash, this method provides a controllable, gradual transformation from GO to rGO, allowing exploration of the PL evolution and emission mechanisms from as-synthesized GO to rGO. The deoxygenation of GO after reduction was confirmed by X-ray photoelectron spectroscopy (XPS), as shown in Figure 1. The C 1s signals of the original GO can be deconvoluted into signals for the C=C bond in aromatic rings (284.6 eV), C O bond (286.1 eV), C=O bond (287.5 eV), and C(=O) OH bond (289.2 eV), in agreement with previous assignments. Increased sp carbon bonding with increased reduction time can be clearly measured, which
TL;DR: This work should provide clear guidelines for the large-scale synthesis of wafer-scale single-crystal graphene, which is essential for the optimized graphene device fabrication.
Abstract: In this research, we constructed a controlled chamber pressure CVD (CP-CVD) system to manipulate graphene’s domain sizes and shapes. Using this system, we synthesized large (∼4.5 mm2) single-crystal hexagonal monolayer graphene domains on commercial polycrystalline Cu foils (99.8% purity), indicating its potential feasibility on a large scale at low cost. The as-synthesized graphene had a mobility of positive charge carriers of ∼11 000 cm2 V–1 s–1 on a SiO2/Si substrate at room temperature, suggesting its comparable quality to that of exfoliated graphene. The growth mechanism of Cu-based graphene was explored by studying the influence of varied growth parameters on graphene domain sizes. Cu pretreatments, electrochemical polishing, and high-pressure annealing are shown to be critical for suppressing graphene nucleation site density. A pressure of 108 Torr was the optimal chamber pressure for the synthesis of large single-crystal monolayer graphene. The synthesis of one graphene seed was achieved on centim...