Showing papers by "Rodney S. Ruoff published in 2010"
TL;DR: This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material.
Abstract: The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)
10,126 citations
TL;DR: An overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
Abstract: There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
8,919 citations
TL;DR: A novel reducing agent system (hydriodic acid with acetic acid (HI-AcOH) that allows for an efficient, one-pot reduction of a solution-phased RG-O powder and vapour-phasingRG-O (VRG-O) paper and thin film is reported.
Abstract: Reduced graphene oxides (RG-Os) have attracted considerable interest, given their potential applications in electronic and optoelectronic devices and circuits. However, very little is known regarding the chemically induced reduction method of graphene oxide (G-O) in both solution and gas phases, with the exception of the hydrazine-reducing agent, even though it is essential to use the vapour phase for the patterning of hydrophilic G-Os on prepatterned substrates and in situ reduction to hydrophobic RG-Os. In this paper, we report a novel reducing agent system (hydriodic acid with acetic acid (HI-AcOH)) that allows for an efficient, one-pot reduction of a solution-phased RG-O powder and vapour-phased RG-O (VRG-O) paper and thin film. The reducing agent system provided highly qualified RG-Os by mass production, resulting in highly conducting RG-O(HI-AcOH). Moreover, VRG-O(HI-AcOH) paper and thin films were prepared at low temperatures (40 °C) and were found to be applicable to flexible devices. This one-pot method is expected to advance research on highly conducting graphene platelets.
1,923 citations
TL;DR: In this paper, the authors review and validate best practice test methods that accurately predict a material's performance, yet are flexible and quick enough to accommodate a wide range of material sample types and amounts.
Abstract: Ultracapacitors are rapidly being adopted for a wide range of electrical energy storage applications. While ultracapacitors are able to deliver high rates of charge and discharge, they are limited in the amount of energy stored. The capacity of ultracapacitors is largely determined by the electrode material and as a result research to improve the performance of electrode materials has dramatically increased. While test methods for packaged ultracapacitors are well developed, it is often impractical for the materials scientist to assemble full sized, packaged cells to test electrode materials. Methodology to reliably measure a material's performance for use as an ultracapacitor electrode is not well standardized with various techniques yielding widely varying results. In this manuscript, we review and validate best practice test methods that accurately predict a material's performance, yet are flexible and quick enough to accommodate a wide range of material sample types and amounts.
1,891 citations
TL;DR: It is shown experimentally that κ of monolayer graphene exfoliated on a silicon dioxide support is still as high as about 600 watts per meter per kelvin near room temperature, exceeding those of metals such as copper.
Abstract: The reported thermal conductivity (κ) of suspended graphene, 3000 to 5000 watts per meter per kelvin, exceeds that of diamond and graphite. Thus, graphene can be useful in solving heat dissipation problems such as those in nanoelectronics. However, contact with a substrate could affect the thermal transport properties of graphene. Here, we show experimentally that κ of monolayer graphene exfoliated on a silicon dioxide support is still as high as about 600 watts per meter per kelvin near room temperature, exceeding those of metals such as copper. It is lower than that of suspended graphene because of phonons leaking across the graphene-support interface and strong interface-scattering of flexural modes, which make a large contribution to κ in suspended graphene according to a theoretical calculation.
1,708 citations
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TL;DR: In this paper, the authors review the best practice test methods that accurately predict a materials performance, yet are flexible and quick enough to accommodate a wide range of material sample types and amounts.
Abstract: Ultracapacitors are rapidly being adopted for use for a wide range of electrical energy storage applications. While ultracapacitors are able to deliver high rates of charge and discharge, they are limited in the amount of energy stored. The capacity of ultracapacitors is largely determined by the electrode material and as a result, research to improve the performance of electrode materials has dramatically increased. While test methods for packaged ultracapacitors are well developed, it is often not feasible for the materials scientist to assemble full sized, packaged cells to test electrode materials. Methodology to reliably measure a material's performance for ultracapacitor electrode use is not well standardized with the different techniques currently being used yielding widely varying results. In this manuscript, we review the best practice test methods that accurately predict a materials performance, yet are flexible and quick enough to accommodate a wide range of material sample types and amounts.
1,665 citations
TL;DR: In this paper, the authors measured the laser heating and monitoring the Raman G peak and obtained room-temperature thermal conductivity and interface conductance of (370 + 650/−320) W/m K and (28 + 16/−9.2) MW/m2 K for the supported graphene.
Abstract: Graphene monolayer has been grown by chemical vapor deposition on copper and then suspended over a hole. By measuring the laser heating and monitoring the Raman G peak, we obtain room-temperature thermal conductivity and interface conductance of (370 + 650/−320) W/m K and (28 + 16/−9.2) MW/m2 K for the supported graphene. The thermal conductivity of the suspended graphene exceeds (2500 + 1100/−1050) W/m K near 350 K and becomes (1400 + 500/−480) W/m K at about 500 K.
1,100 citations
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TL;DR: In this paper, the ability of graphene films grown by chemical vapor deposition to protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy from air oxidation was demonstrated.
Abstract: The ability to protect refined metals from reactive environments is vital to many industrial and academic applications. Current solutions, however, typically introduce several negative effects, including increased thickness and changes in the metal physical properties. In this paper, we demonstrate for the first time the ability of graphene films grown by chemical vapor deposition to protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy from air oxidation. SEM, Raman spectroscopy, and XPS studies show that the metal surface is well protected from oxidation even after heating at 200 \degree C in air for up to 4 hours. Our work further shows that graphene provides effective resistance against hydrogen peroxide. This protection method offers significant advantages and can be used on any metal that catalyzes graphene growth.
992 citations
TL;DR: The effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy is reported.
Abstract: The fundamental properties of graphene are making it an attractive material for a wide variety of applications. Various techniques have been developed to produce graphene and recently we discovered the synthesis of large area graphene by chemical vapor deposition (CVD) of methane on Cu foils. We also showed that graphene growth on Cu is a surface-mediated process and the films were polycrystalline with domains having an area of tens of square micrometers. In this paper, we report on the effect of growth parameters such as temperature, and methane flow rate and partial pressure on the growth rate, domain size, and surface coverage of graphene as determined by Raman spectroscopy, and transmission and scanning electron microscopy. On the basis of the results, we developed a two-step CVD process to synthesize graphene films with domains having an area of hundreds of square micrometers. Scanning electron microscopy and Raman spectroscopy clearly show an increase in domain size by changing the growth parameters...
988 citations
TL;DR: The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.
Abstract: Mechanical properties of ultrathin membranes consisting of one layer, two overlapped layers, and three overlapped layers of graphene oxide platelets were investigated by atomic force microscopy (AFM) imaging in contact mode. In order to evaluate both the elastic modulus and prestress of thin membranes, the AFM measurement was combined with the finite element method (FEM) in a new approach for evaluating the mechanics of ultrathin membranes. Monolayer graphene oxide was found to have a lower effective Young’s modulus (207.6 ± 23.4 GPa when a thickness of 0.7 nm is used) as compared to the value reported for “pristine” graphene. The prestress (39.7−76.8 MPa) of the graphene oxide membranes obtained by solution-based deposition was found to be 1 order of magnitude lower than that obtained by others for mechanically cleaved graphene. The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.
975 citations
TL;DR: Flexible and lightweight chemiresistormade of a thin film composed of overlapped and reduced graphene oxide platelets (RGO film) that can reversibly and selectively detect chemicallyaggressive vapors such asNO.
Abstract: Described herein is a flexible and lightweight chemiresistormade of a thin film composed of overlapped and reducedgraphene oxide platelets (RGO film), which were printedonto flexible plastic surfaces by using inkjet techniques. TheRGO films can reversibly and selectively detect chemicallyaggressivevapors suchasNO
TL;DR: In this paper, a simple yet versatile method to simultaneously achieve the exfoliation and reduction of graphite oxide was proposed, which was shown to achieve specific capacitance values as high as 191 F/g with KOH electrolyte.
TL;DR: Using atomistic calculations, graphene sheets with large-angle tilt boundaries that have a high density of defects are as strong as the pristine material and, unexpectedly, are much stronger than those with low-angle boundaries having fewer defects.
Abstract: Graphene in its pristine form is one of the strongest materials tested, but defects influence its strength. Using atomistic calculations, we find that, counter to standard reasoning, graphene sheets with large-angle tilt boundaries that have a high density of defects are as strong as the pristine material and, unexpectedly, are much stronger than those with low-angle boundaries having fewer defects. We show that this trend is not explained by continuum fracture models but can be understood by considering the critical bonds in the strained seven-membered carbon rings that lead to failure; the large-angle boundaries are stronger because they are able to better accommodate these strained rings. Our results provide guidelines for designing growth methods to obtain sheets with strengths close to that of pristine graphene.
TL;DR: This detailed account of the fascinating development of the synthesis and characterization of graphene is hoped to demonstrate that the rich history of graphene chemistry laid the foundation for the exciting research that continues to this day.
Abstract: There has been an intense surge in interest in graphene during recent years. However, graphene-like materials derived from graphite oxide were reported in 1962, and related chemical modifications of graphite were described as early as 1840. In this detailed account of the fascinating development of the synthesis and characterization of graphene, we hope to demonstrate that the rich history of graphene chemistry laid the foundation for the exciting research that continues to this day. Important challenges remain, however; many with great technological relevance.
TL;DR: An overview of the synthesis, properties, and applications of graphene and related materials from a materials science perspective can be found in this article, where the authors present a review of recent work in this area.
Abstract: There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.
TL;DR: These studies suggest the possibility of tuning the properties of GO composites by altering the density of functional groups on individual platelets, the water content, and possibly the functional groups participating in hydrogen bonding with interlayer water molecules.
Abstract: A multilayered composite structure formed by a random stacking of graphene oxide (GO) platelets is an attractive candidate for novel applications in nanoelectromechanical systems and paper-like composites. We employ molecular dynamics simulations with reactive force fields to elucidate the structural and mechanical properties of GO paper-like materials. We find that the large-scale properties of these composites are controlled by hydrogen bond networks that involve functional groups on individual GO platelets and water molecules within the interlayer cavities. Water content controls both the extent and collective strength of these interlayer hydrogen bond networks, thereby affecting the interlayer spacing and elastic moduli of the composite. Additionally, the chemical composition of the individual GO platelets also plays a critical role in establishing the mechanical properties of the composite—a higher density of functional groups leads to increased hydrogen bonding and a corresponding increase in stiffn...
TL;DR: In this article, a 2-cell ultracapacitor with specific capacitance values of about 120 F/g was obtained by adding TEA BF 4 to the reduced graphene oxide/propylene carbonate slurry.
Abstract: Disclosed are compositions and methods wherein graphite oxide was exfoliated and dispersed in propylene carbonate (PC) by bath sonication. Heating the graphene oxide suspensions at 150°C significantly reduced the graphene oxide platelets; paper samples comprised of such reduced graphene oxide platelets had an electrical conductivity of 5230 S/m. By adding TEA BF 4 to the reduced graphene oxide/PC slurry and making a 2-cell ultracapacitor, specific capacitance values of about 120 F/g were obtained.
TL;DR: The microscopic origin of the bipolar resistive switching behavior was elucidated and is attributed to rupture and formation of conducting filaments at the top amorphous interface layer formed between the graphene oxide film and the top Al metal electrode, via high-resolution transmission electron microscopy and in situ X-ray photoemission spectroscopy.
Abstract: There has been strong demand for novel nonvolatile memory technology for low-cost, large-area, and low-power flexible electronics applications. Resistive memories based on metal oxide thin films have been extensively studied for application as next-generation nonvolatile memory devices. However, although the metal oxide based resistive memories have several advantages, such as good scalability, low-power consumption, and fast switching speed, their application to large-area flexible substrates has been limited due to their material characteristics and necessity of a high-temperature fabrication process. As a promising nonvolatile memory technology for large-area flexible applications, we present a graphene oxide based memory that can be easily fabricated using a room temperature spin-casting method on flexible substrates and has reliable memory performance in terms of retention and endurance. The microscopic origin of the bipolar resistive switching behavior was elucidated and is attributed to rupture and...
TL;DR: In this article, the deposition of films composed of overlapped and stacked platelets of graphene oxide (G-O) reduced by an electrophoretic deposition (EPD) process was reported.
Abstract: We report the deposition of films composed of overlapped and stacked platelets of graphene oxide (G-O) reduced by an electrophoretic deposition (EPD) process. The oxygen functional groups of G-O were significantly removed by the EPD process, and the as-deposited G-O film by EPD showed improved electrical conductivity (1.43 × 104 S·m−1) over G-O papers made by the filtration method (0.53 × 10−3 S·m−1). This method for reducing G-O without added reducing agents has the potential for high-yield, large-area, low-cost, and environmentally friendly production of films composed of reduced G-O platelets.
TL;DR: The self-assembly of chemically modified graphene platelets into a complex 3D morphology was achieved by the “breath-figure” method, which is a straightforward procedure for synthesizing large-area porous polymer films.
Abstract: Graphene is an atom-thick, two-dimensional material comprised of a monolayer hexagonal sp-hybridized carbons. It is flexible, has a large specific surface area, and exhibits excellent electrical and thermal conductivities and also good mechanical properties. Moreover, given the low cost of natural graphite, the potential for obtaining large quantities of graphene by a low-cost production process is high. As such, graphene and its chemically modified forms are promising building blocks for accessing highly ordered assemblies that are suitable for nanoelectronics, energy storage/conversion, catalysis, composites, and other applications. Although previous efforts have demonstrated that graphene-based platelets may be assembled into papers, thin films, or other two-dimensional constructs, the ability to control the assembly such platelets into three-dimensional (3D) structures could result in the carbon materials that exhibit very large surface areas, unusual or novel physical and electronic properties, unsurpassed chemical functionality, and other attractive features that are necessary for the aforementioned applications. Herein we demonstrate the self-assembly of graphene oxide (GO) platelets into mechanically flexible, macroporous 3D carbon films with tunable porous morphologies. Selfassembly is the spontaneous bottom-up organization of preexisting components into patterned structures. The intrinsic parallelism and scalability inherent to self-assembly can, in principle, enable low-cost, large-scale syntheses of highly ordered nanostructures. Indeed, as will be described below, the self-assembly of chemically modified graphene platelets into a complex 3D morphology was achieved by the “breath-figure” method, which is a straightforward procedure for synthesizing large-area porous polymer films. The breath-figure method as employed herein is illustrated in Figure 1A. Briefly, polymer-grafted GO platelets were synthesized and dispersed in an organic solvent. The dispersion was then cast onto a suitable substrate and exposed to a stream of humid air. Endothermic evaporation of the volatile organic solvent resulted in the spontaneous conden-
TL;DR: This work presents the production of a free-standing ‘‘paperlike’’ material composed of TWEEN and reduced graphene oxide (RGO) platelets and obtained by simple filtration of a homogeneous aqueous colloidal suspension of TweEN/RGO hybrid, which was highly stable in water without leakage of T WEEN and is compliant and sufficiently robust to be handled by hand without breaking.
Abstract: Nonspecific binding (NSB), a random adsorption of biocomponents such as proteins and bacteria on noncomplementary materials,isoneofthebiggestproblemsinbiological applications including biosensors, protein chips, surgical instruments, drug delivery, and biomedicine. Polyoxyethylene sorbitan laurate (TWEEN), a commercially available chemical with aliphatic ester chains, has shown promise as a medical material and in overcomingproblems associated withNSB. [1‐4] However,stability during solution-based processing and uniformity of the materials that have TWEEN coating on flat substrates or nanomaterials using the selfassembled-monolayer (SAM) method has been an important issue. Further, biocompatible materials with high strength are important for several medical applications including stents, nail implants, and strong invasive instruments. Here, we present the production of a free-standing ‘‘paperlike’’ material composed of TWEEN and reduced graphene oxide (RGO) platelets and obtained by simple filtration of a homogeneous aqueous colloidal suspension of TWEEN/RGO hybrid. The ‘‘TWEEN paper’’ was highly stable in water without leakage of TWEEN and is compliant and sufficiently robust to be handled by hand without breaking. Furthermore, the TWEEN paper was noncytotoxic to three mammalian cell lines and biocompatible, inhibiting nonspecific binding of Gram-positive bacteria. [5] In contrast, RGO paper without TWEEN showed nonspecific bacterial binding. TWEEN is composed ofthree chemical parts (Fig. 1a): aliphatic esterchains that can prevent NSB ofbiomolecules, three-terminal hydroxyl groups that are hydrophilic and can be chemically modified for further applications, and an aliphatic chain that can easily be adsorbed on a hydrophobic surface by noncovalent interaction. Protein microarrays on flat substrates with SAM of TWEEN [4] and highly sensitive biosensors, [1‐3] built using field-effect transistor (FET) behavior of individual carbon nanotube (CNT) strands coated with TWEEN, have demonstrated that TWEEN can be effectively used to overcome NSB.
01 Jan 2010
TL;DR: In this paper, a method of simultaneous reduction and surface funcionalization of graphene oxide by a one-step poly(norepinephrine) funcionalisation was presented, which can be a useful platform for graphene-based ano-composites.
Abstract: his study presents a method of simultaneous reduction and surface funcionalization of graphene oxide by a one-step poly(norepinephrine) funcionalization. The pH-induced aqueous functionalization of graphene oxide y poly(norepinephrine), a catecholamine polymer inspired by the robust dhesion of marine mussels, chemically reduced and functionalized graphene xide. Moreover, the polymerized norepinephrine (pNor) layer provided mulifunctionality on the reduced graphene oxide that includes surface-initiated olymerization and spontaneous metallic nanoparticle formation. This facile urface modifi cation strategy can be a useful platform for graphene-based ano-composites.
TL;DR: A method for growing polymers directly from the surface of graphene oxide using atom transfer radical polymerization (ATRP) is demonstrated and the resulting materials were found to significantly improve the solubility properties of grapheneoxide.
Abstract: A method for growing polymers directly from the surface of graphene oxide is demonstrated. The technique involves the covalent attachment of an initiator followed by the polymerization of styrene, methyl methacrylate, or butyl acrylate using atom transfer radical polymerization (ATRP). The resulting materials were characterized using a range of techniques and were found to significantly improve the solubility properties of graphene oxide. The surface-grown polymers were saponified from the surface and also characterized. Based on these results, the ATRP reactions were determined to proceed in a controlled manner and were found to leave the structure of the graphene oxide largely intact.
TL;DR: This research highlights the need to understand more fully the interaction between materials science and nanofiltration, as well as the types of materials that can be incorporated into electronics and telecommunications systems.
Abstract: [*] Prof. S. O. Kim, D. H. Lee, J. E. Kim, T. H. Han, J. W. Hwang, Prof. S. W. Jeon, Prof. S. H. Hong, Prof. W. J. Lee Department of Materials Science and Engineering, KAIST Daejeon 305-701 (Republic of Korea) E-mail: sangouk.kim@kaist.ac.kr Dr. S. Y. Choi Convergence Components and Materials Laboratory Electronics and Telecommunication Research Institute (ETRI) Daejoen 305-700 (Republic of Korea)
TL;DR: This work presents a novel macroscopic graphene-based actuator that shows actuation that depends on variation of humidity and/or temperature and tries to make mechanical actuators by using graphene oxide platelets.
Abstract: The development of new mechanical actuators that convert external stimuli such as thermal, light, electrical, or chemical energy to mechanical energy depends on the development of new materials. Reversible mechanical actuators based on carbon nanotubes (CNTs) and hydrogel polymers have suggested applications in robotics, sensors, mechanical instruments, microscopy tips, switches, and memory chips. Recently, electromechanical resonators composed of singleand multilayer graphene sheets were reported. We present here a novel macroscopic graphene-based actuator that shows actuation that depends on variation of humidity and/or temperature. The actuator is a free standing ‘‘paper-like’’ material made by sequential filtration of CNT, and then graphene oxide, aqueous colloidal suspensions. ‘‘Paper-like’’ materials composed of stacked graphene oxide platelets produced by simple filtration of an aqueous graphene oxide suspension exhibited good mechanical properties, with a modulus of about 40 GPa and a fracture strength of about 130 MPa. Chemical modification of graphene oxide paper with divalent ions can enhance its mechanical properties. Based on these results that show excellent mechanical properties of individual graphene sheets and of paper-like materials composed of them, we have tried to make mechanical actuators by using graphene oxide platelets. Graphite oxide (GO) is generated by oxidation of graphite and contains a wide range of oxygen functional groups, such as hydroxyl and epoxy groups on the basal plane and carboxylic acid groups at the edges, which make the GO hydrophilic. The oxygen functional groups in the GO, which contains a layered structure of graphene oxide platelets, allow dynamic intercalation of water molecules into the gallery between the layers. The interlayer distance between the graphite oxides reversibly varies from 6 to 12 A depending on the relative humidity, with increased interlayer distance as the relative humidity increases. Graphene oxide paper contains a layered structure similar to, but not identical to, GO (the coherence length in the paperlike material is 6–7 platelets,
TL;DR: A solid-state NMR (SSNMR)-based structural modeling approach is presented on graphite oxide (GO), which is a prominent precursor and interesting benchmark system of modified graphene, and is likely to be applicable to other chemically modified graphenes and graphite-based systems.
Abstract: Chemically modified graphenes and other graphite-based materials have attracted growing interest for their unique potential as lightweight electronic and structural nanomaterials. It is an important challenge to construct structural models of noncrystalline graphite-based materials on the basis of NMR or other spectroscopic data. To address this challenge, a solid-state NMR (SSNMR)-based structural modeling approach is presented on graphite oxide (GO), which is a prominent precursor and interesting benchmark system of modified graphene. An experimental 2D 13C double-quantum/single-quantum correlation SSNMR spectrum of 13C-labeled GO was compared with spectra simulated for different structural models using ab initio geometry optimization and chemical shift calculations. The results show that the spectral features of the GO sample are best reproduced by a geometry-optimized structural model that is based on the Lerf−Klinowski model (Lerf, A. et al. Phys. Chem. B 1998, 102, 4477); this model is composed of i...
TL;DR: In this article, the authors show that the stiffness of amine-modified graphene oxide paper is directly correlated with the length of the intercalated alkyl chain, and that the tensile strength of the modified papers slightly decreases with increasing amine lengths.
Abstract: Graphene oxide paper can be systematically modified with alkylamines in both solution- and vapor-phase, with the latter process being significantly slower. After removal of physisorbed amine, the increases in gallery spacing, physical thickness, and mass of amine-modified papers can be directly correlated to the length of the intercalated alkyl chain. While the tensile strength of the modified papers slightly decreases with increasing amine lengths, their “effective graphene oxide moduli” were essentially unchanged, suggesting that graphene oxide is the sole contributor to the stiffness of amine-modified papers.
TL;DR: In the version of this Review Article originally published, the unit for conductivity in the first line of Table 2 should have been S cm−1, but this error has been corrected in the HTML and PDF versions of the text.
Abstract: Nature Nanotechnology 4, 217–224 (2009); published online: 29 March 2009; corrected after print: 21 March 2010. In the version of this Review Article originally published, the unit for conductivity in the first line of Table 2 should have been S cm−1. This error has been corrected in the HTML and PDF versions of the text.
TL;DR: In this article, the deposition effect of metals on graphene was studied by in situ field effect transistor (FET) measurements in high vacuum, and the induced carrier concentration was estimated at 2-6×1012/cm2.
Abstract: The deposition effect of metals on graphene was studied by in situ field effect transistor (FET) measurements in high vacuum. Metals such as gold (Au), silver (Ag), and copper (Cu) were deposited onto clean graphene surfaces, followed by FET measurements. The results show that Ag and Cu cause a shift in the Fermi level in the graphene from the Dirac point into the conduction band while Au causes a shift into the valence band. The induced carrier concentration was estimated at 2–6×1012/cm2. The shifts in the Fermi level of the graphene are explained by the different work functions of these metals.