To save this undefined to your undefined account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your undefined account.
Find out more about saving content to .
To save this article to your Kindle, first ensure firstname.lastname@example.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for the controlled and large-scale production of graphene nanoribbons (GNR). These structures are considered of great importance for the development of nanoelectronics because of its dimensions and intrinsic nonzero band gap value. Despite many years of investigations some details on the dynamics of the CNT fracture/unzipping processes remain unclear. In this work we have investigated some of these process through molecular dynamics simulations using reactive force fields (ReaxFF), as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. We considered multi-walled CNTs of different dimensions and chiralities and under induced mechanical stretching. Our preliminary results show that the unzipping mechanisms are highly dependent on CNT chirality. Well-defined and distinct fracture patterns were observed for the different chiralities. Armchair CNTs favor the creation of GNRs with well-defined armchair edges, while zigzag and chiral ones produce GNRs with less defined and defective edges.
We revisit the polymorphism of carbon along two directions. First, we discover novel polymorphs in the vicinity of graphite, with outstanding optical and mechanical properties. Using numerical methods and graph-theoretical tools, we find as many as 4 novel superhard and transparent polymorphs, with great technological potential. Second, scaling up a model of rod packing to carbon nanotube (CNT) scaffoldings, we discover that such complex assemblies of CNTs are outstanding adsorbers of hydrogen, capable of reaching the DOE target (~6.0 wt% at ambient conditions). Along this line, we highlight novel paradigms for revisiting carbon, in view of remarkable qualities and superior properties.
Recently, classical elasticity theory for thin sheets was used to demonstrate the existence of a universal structural behavior describing the confinement of sheets inside cylindrical tubes. However, this kind of formalism was derived to describe macroscopic systems. A natural question is whether this behavior still holds at nanoscale. In this work, we have investigated through molecular dynamics simulations the structural behavior of graphene and boron nitride single layers confined into nanotubes. Our results show that the class of universality observed at macroscale is no longer observed at nanoscale. The origin of this discrepancy is addressed in terms of the relative importance of forces and energies at macro and nano scales.
In order to find an efficient method to etch nano-carbon materials by hydrogenation in a controlled manner, we have studied hydrogen-atom adsorption on various deformed nanotubes using computer simulations based on the density-functional theory. The nanotube with an atomic lack is compared to a deformed tube with the Stone-Wales defect and a twisted tube wall. Similar to the known experimental etching condition for graphene, an atomic lack is effective to accumulate hydrogen atoms around the defect. Compared to the flat graphene, however, nanotube walls with curvature allow on-top adsorption of a hydrogen atom and selectivity in the hydrogenated site becomes worse. To achieve a controlled etching process, usage of a tungsten tip which realizes focused hydrogenation is proposed for natotubes and curved graphene.
We have investigated the fabrication of graphene by chemical vapor deposition using a conventional rapid thermal processing system with infrared heating. Graphene films were grown on the pretreated copper foil in RTP at 935-960°C at pressure of 6~7 mbar. The grown films were characterized by scanning electron microscope and Raman spectroscopy to investigate morphology of graphene. The growth of graphene was initiated by small flakes that spread rapidly covering the whole copper surface as a single-layer film in ~20 seconds. Room temperature mobility and sheet resistance extracted by transfer-length method (TLM) for the graphene film transferred onto the SiO2/Si substrate were around 1,800 cm2/Vs and 260 Ω/ð with the gate voltage, respectively.
Understanding of nickel (Ni) grain size, distribution, and structure are critical parameters in a sputter-deposited Ni catalyst for achieving the desired number of graphene layers  grown by atmospheric pressure chemical vapor deposition (APCVD). The size and distribution of grains can be controlled by variations in sputtering parameters, but the final crystal structure and defects are not apparent until after the high temperature annealing. We analyzed the x-ray diffraction patterns in the Ni catalyst to determine effect of thermal annealing on the Ni grain size, orientation, and structural defects. Experiments have shown that in-situ sputter-deposited Ni films at 250 °C are highly oriented in the direction  that produced the high yield of graphene films with desired number of layers. Low defect density in a sputtered nickel (Ni) catalyst is a necessary ingredient for achieving precision number of graphene layers. These sputtering parameters can accelerate or postpone the final preferred orientation of the Ni film. A sputter temperature of 250 °C achieved complete transformation from polycrystalline film to the preferred  orientated film.
Graphene oxide holds great promise for future applications in nano-technology. The chemistry of this material is not well understood. This understanding is crucial to enable future applications of graphene oxide. In this study, experiments and density functional theory calculations are combined to elucidate the chemical properties of multilayer graphene oxide obtained by oxidizing epitaxial graphene grown on silicon carbide via the Hummers method. This study shows that at room temperature as prepared graphene oxide films exhibit a uniform and homogeneous structure, include a minimal amount of edges and holes, and have an oxidation ratio of about 0.44. The comparison with density-functional calculations shows that graphene oxide includes a minimal amount of intercalated water molecules and well-defined fractions of epoxide and hydroxyl groups.
Fluorescence Quenching Microscopy has been shown to be an effective means of characterizing graphene on the macroscale. Centimeter-scale CVD-grown pristine and doped graphene were manufactured in a high temperature (1000°C) furnace on pristine copper substrates. The copper was then etched away in a FeCl3solution and the graphene was coated with DCM-based fluorescent dye before being imaged in a fluorescence microscope. The fluorescence image was then image-processed using modified Matlab software. The resulting image showed clear contrast between the pristine graphene sheet and defects on the graphene surface, which revealed that fluorescence microscopy could determine the quality of a large region of graphene. Also, significant contrast was identified between single-layer and multi-layer regions, showing that this technique is also effective at determining the degree of uniformity within a graphene sample. Lastly, the fluorescence images showed contrast between doped and undoped regions of graphene.
The unique structure and properties of graphene initiated broad fundamental and technological research, and highlighted graphene as a new candidate for various applications such as energy storage, solar cells and electronic devices. Chemical vapor deposition (CVD) has been utilized for industrial large-scale synthesis of graphene. Regardless of the synthesis process, graphene should be transferred to arbitrary substrates for different applications. The transfer processes, introduce defects such as wrinkles and cracks in graphene which compromise the properties and applications. In recent years, fundamental research has been focused on characterization of graphene to develop new techniques for large-scale, high-resolution graphene metrology. Herein, a complementary high throughput metrology technique using fluorescent quenching is further investigated for different fluorescent dyes to characterize CVD synthesized graphene.
Graphene, with unique electrical, optical and mechanical properties is a promising material in industrial applications, such as batteries, supercapacitors, transistors and semiconductor devices. These potential applications of graphene have motivated the development of large-scale synthesis of graphene on copper substrates by chemical vapor deposition (CVD). To enable practical applications of large-area, high quality graphene layers at the centimeter and wafer scales, process control needs to be implemented for optimizing the morphology and electrical properties and enable repeatable growth-cycle of graphene layers for process-line implementation. Here we investigate the effects of process quartz-tube position on the structural properties of graphene. Furthermore, we describe a procedure for process optimization of the growth parameters. Graphene is grown on copper foils by CVD, and transferred to the SiO2/Si and glass substrates. The detailed characterization of the graphene layers are conducted using Raman spectroscopy, optical microscopy (OM), scanning electron microscopy (SEM) and UV-vis spectroscopy. The experimental results show that the position of copper foil into the quartz tube plays a significant role in the Raman features of the graphene, and influences the optical, morphology and surface properties of graphene layers. We believe that these results will be useful for determining the optimum processing conditions of high quality graphene layers at the centimeter and wafer scales.
Supercapacitors are promising candidates for alternative energy storage applications since they can store and deliver energy at relatively high rates. In this work, we integrated large area chemical vapor deposition (CVD) grown three dimensional graphene heterostructures with high capacitance metal oxides (MnO2) to fabricate highly conductive, large surface-area composite thin films. Uniform, large area 3D graphene heterostructures layers were produced by a one-step CVD on nickel foams. MnO2 nanowires were deposited on the as-obtained 3D graphene heterostructures film by a simple chemical bath depostion process. The oxide loading of the 3D graphene/MWNTs/MnO2 nanowires (GMM) composite films can be simply controlled by deposition time and nanowire solution concentration. The surface morphology was investigated by scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM), and Energy-dispersive X-ray spectroscopy (EDS) was performed to characterize the MnO2on the surface of the film. By introducing the fast surface redox reactions into the graphene heterostructures film via integrating pseudocapacitive material like MnO2, the capacitive ability of the system enhanced dramatically. Supercapacitor was fabricated based on the 3D graphene heterostructures /MnO2 hybrid film electrodes; the measurements of cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) are conducted to determine its performance for the electrodes of supercapacitors.
Density functional theory and molecular dynamics were used to study the generation of hydrogen peroxide around a nickel atom anchored on a pyridine-like nitrogen-doped graphene (PNG) layer. First, we found that two hydrogen molecules are adsorbed around the nickel atom, with adsorption energy 0.95 eV/molecule. Then we studied the interaction of oxygen molecules with this system at atmospheric pressure and 300 K. It is found that two hydrogen peroxide molecules are formed. However, at 700 K, one hydrogen peroxide molecule, and one water molecule are desorbed. One oxygen atom stays bound to the nickel atom.
The potential of chemically derived graphene as a solution-processable transparent conductive film has been explored. Synthesis of amine-functionalized graphene oxide was intended for its utilization in layer-by-layer assembly. Layer-by-layer assembly of graphene oxide was utilized to fabricate graphene based thin film in a scalable and highly reproducible way. It was found that optical transmittance and sheet resistance of the film decreases with an increase in number of LBL cycles in a reproducible way. The sheet resistance of LBL-assembled GO film improves by an order of magnitude at the same optical transparency due to more homogeneous coverage and better stacking of graphene flakes. Furthermore, we demonstrated the potential for a large-scale deposition of chemically derived graphene.
In this work, we demonstrated the growth of three dimensional graphene/carbon nanotubes hybrid carbon nanostructures on metal foam through a one-step chemical vapor deposition (CVD). The as-grown three dimensional carbon nanostructure foams can be potentially used as the electrodes of energy storage devices such as supercapacitors and batteries. During the CVD process, the carbon nanostructures are grown on highly porous nickel foam to form a high surface area 3-D carbon nanostructure by introducing a mixture precursor gases (H2, C2H2). The surface morphology was investigated by scanning electron microscopy (SEM) and the results demonstrated relatively homogeneous and densely packed 3-D carbon nanostructure. The quality was characterized by Raman spectroscopy. To further increase the capacitive capability the supercapacitors were fabricated based on the electrodes of carbon nanostructure foam and cyclic voltammetry, charge-discharge, and electrochemical impedance spectroscopy (EIS) were conducted to determine their performance.
We investigate the role of precursor thermal rearrangement and surface catalytic reactions in the synthesis of vertically aligned carbon nanotubes (VA-CNTs) by acetylene-based, chemical vapor deposition (CVD) and demonstrate a millimeter-long growth of single-walled CNT (SWNT) without water assistance. A substrate heater was used to create an ascending temperature gradient from gas injection to catalyst substrate. Whereas temperature of catalyst substrates primarily determines their catalytic activity, it is a thermal condition of a gaseous mixture in the CVD chamber that also influence growth yield and structural features of as-grown CNTs. Employing Egloff’s characterization,  we discuss the importance of various gas thermal zones in producing high-quality nanotubes with augmented growth efficiency. We continue to report production of millimeter-long, VA-SWNT having a mean diameter of 1.7 ± 0.7 nm, catalyzed by iron on an alumina support. Important finding is that a million of aspect ratio of SWNT arrays can be produced, without water assistance, via combined action of an ascending temperature gradient toward catalyst substrate and low partial pressures of acetylene carbon feedstock. Our results do not only emphasize the role of precursor thermal rearrangement in CNT synthesis, but also offer a practical route to the modulation of such complex phenomena for an ultrahigh-yield growth of narrow VA-SWNT.
Ceramic barriers avoid catalyst diffusion to produce better multiwall carbon nanotubes (CNT) on carbon fiber fabrics (CF). We developed a simple method to produce efficiently a silica layer from TEOS pyrolysis at similar conditions of CNT growth from camphor and ferrocene mixtures. This protective layer prevents iron diffusion and allows the vertical alignment of CNTs.
The functionalization of single wall carbon nanotubes (SWCNT) with arenediazonium salts, formed in situ from anilines as dimethyl-5-aminoisophthalate, sulfanilamide and p-anisidine, using the environmentally solvent urea. The functionalized SWNTs were then characterized using spectroscopic and microscopic methods along with thermogravimetric analysis (TGA). According to enhance solubility in solvents after that introduce them into the industrial processes. The molecules added appear on the nanotubes like chemical anchors.
The present work reports the covalent functionalization of few-wall CNTs (FWCNTs) by ferrocene derivatives to i) improve their dispersion efficiency in water and ii) to graft electroactive chemical groups on their side-walls in order to promote electron transfer to biomolecules. The functionalized CNTs (f-CNTs) are used to modify a glassy carbon electrode and this modified electrode is used for oxidizing the cofactor NADH (dihydronicotinamide adenine dinucleotide).
We report on the material characterization of carbon nanofibers (CNFs) which are assembled into a three-dimensional (3D) configuration for making new nanoelectromechanical systems (NEMS). High-resolution scanning electron microscopy (SEM) and x-ray electron dispersive spectroscopy (XEDS) are employed to decipher the morphology and chemical compositions of the CNFs at various locations along individual CNFs grown on silicon (Si) and refractory nitride (NbTiN) substrates, respectively. The measured characteristics suggest interesting properties of the CNF bodies and their capping catalyst nanoparticles, and growth mechanisms on the two substrates. Laser irradiation on the CNFs seems to cause thermal oxidation and melting of catalyst nanoparticles. The structural morphology and chemical compositions of the CNFs revealed in this study should aid in the applications of the CNFs to nanoelectronics and NEMS.
The use of super acids such as chlorosulfonic acid (CSA) has proven to be extremely effective at exfoliating different forms of graphite in high concentrations without covalently functionalizing the surface of the graphene. Once quenched, the acid solutions can then be vacuum filtered through acid resistant polypropylene filter paper with an average pore size of 0.2 μm to collect the exfoliated carbon into a free standing retentate film. These films can then be easily washed, removed, and redispersed into solution by sonicating the films in a surfactant solution. Films were deposited onto various substrates using a range of spin coating parameters. This study has found that exfoliated CNTs provide the best conductivity out of the four types of chemically exfoliated carbon structures studied. CNTs have also proven to be the easiest type of exfoliated carbon to disperse and are able to stay in solution with less than 1%wt surfactant. The findings have shown that the electrical conductivity of the spin coated films actually increases with RPM and is inversely proportional to the film thickness. It is possible to achieve electrical conductivities as high as 10,507 ± 3728.64 [S/m] while still maintaining the transparency of the thin films. The initial spin coating step is more efficient at low ramp rates around 100 rpm/s and results in very smooth films. High spin speeds of 1800 rpm during the casting stage are found to play a large role in improving the conductivity of the films. Lastly, drying the samples on a hot plate for 5 min. on high has significantly improved the films electrical properties and virtually eliminated the need for tedious and expensive plasma cleaning treatments.