Contiguous Petal-like Carbon Nanosheet Outgrowths from Graphite Fibers by Plasma CVD (original) (raw)
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Graphene layer is a monolayer of graphite. Graphene single layer has confirmed to have a higher electron and hole mobility than silicon and has high heat conduction and special optical properties. And un-perfect graphene sheets exist in any carbon materials. In our previous result to determine the graphene sheets content in any carbon material can be determined by X-ray spectrum combination with a peak decomposition method. In this study, we have prepared two serious carbon materials from wood wastes, with and without MnO 2 catalytic pyrolysis processes. Results show that all the G band intensity of all synthesized samples including a commercial graphene powder in Raman spectrum has a proportional relation with the graphene sheets content in these carbon materials.
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High-quality, free-standing, and vertically interconnected three-dimensional (3-D) graphitic nanosheets (GNSs) were synthesized over the surface of hemispherical carbon particles/GaN at 700 °C by microwave plasma chemical vapor deposition (CVD) in presence of methane gas, whereas the hemispherical carbon particles have been directly deposited on GaN/sapphire template. The GNSs are ∼1–5 nm in thickness and have a graphitic flake structure on hemispherical carbon particles. The vertically interconnected 3-D GNSs on hemispherical carbon particles have been characterized by scanning electron microscopy, transmission electron microscopy, selective area electron diffraction pattern, X-ray diffraction, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and nitrogen gas adsorption-Brunauer-Emmet-Teller. The present CVD approach is capable of producing large quantities of GNSs with high purity. Moreover, a high-purity free-standing and vertically interconnected 3-D GNSs on hemispherical carbon particles have an enormous potential for applications in electronic devices, biological sensors, gas uptake and storage, fuel cells, lithium ion batteries, and more.
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Vertically aligned carbon nanosheets (CNSs) with bi-and trilayer graphene have been achieved on various metal substrates from solid carbon sources by irradiation with H 2 and Ar plasma. The resulting graphene structures have fewer layers, bigger sizes, and higher graphitization compared to previous reports obtained from gas sources, as confirmed by scanning and transmission electron microscopes, Raman and X-ray photoelectron spectroscopes. The results suggest that the interaction between the plasma (of H 2 and Ar) and carbon sources favors the formation of bigger and thinner nucleation cites in the initial stage and atomic H etching dominates during the whole thinner CNS growth. The vertically aligned graphene film can be directly transferred on as-patterned SiO 2 /Si to form a heterojunction photovoltaic cell with a power conversion efficiency of 0.9%.
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A mechanism for carbon nanosheet formation
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The growth, structure and properties of a two-dimensional carbon nanostructure-carbon nanosheet produced by radio frequency plasma enhanced chemical vapor deposition have been investigated. The effects of deposition parameters on the structure and properties of carbon nanosheets were also investigated. A growth model has been described proposing that atomically thin graphene sheets result from a balance between deposition through surface diffusion and etching by atomic hydrogen, and that the observed vertical orientation of these sheets results from the interaction of the plasma electric field with their anisotropic polarizability.
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Structure changes of MPECVD-grown carbon nanosheets under high-temperature treatment
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Vertically-aligned carbon nanosheets (CNSs), which were fabricated by microwave plasmaenhanced chemical vapor deposition in Ar and CH 4 system, have been annealed at high temperatures in the range of 1200-3000°C. The morphologies and microstructures of the treated CNSs were analyzed by scanning and transmission electron microscopes, and Raman spectroscopy. High temperature treatment process efficiently removed the amorphous carbon and some defects and improved the graphitization of the CNSs. The graphitized grains increase and the interlayer spacing decreases with increasing heat temperatures. Heat treatment of the CNSs at temperatures from 1500 to 2000°C was found to achieve the edges consisting of many single-layer graphene sheets. Annealing at temperatures above 2100°C, the edges of nanosheets consist of 2-5 layer graphene with many zigzag junctions. The mechanism of reconstruction for the edges in the CNSs ascribes possibly to the carbon atom vaporization at high temperatures.
Laser-Assisted Growth of Carbon-Based Materials by Chemical Vapor Deposition
MDPI, 2022
Carbon-based materials (CBMs) such as graphene, carbon nanotubes (CNT), highly ordered pyrolytic graphite (HOPG), and pyrolytic carbon (PyC) have received a great deal of attention in recent years due to their unique electronic, optical, thermal, and mechanical properties. CBMs have been grown using a variety of processes, including mechanical exfoliation, pulsed laser deposition (PLD), and chemical vapor deposition (CVD). Mechanical exfoliation creates materials that are irregularly formed and tiny in size. On the other hand, the practicality of the PLD approach for large-area high-quality CMB deposition is quite difficult. Thus, CVD is considered as the most effective method for growing CBMs. In this paper, a novel pulsed laser-assisted chemical vapor deposition (LCVD) technique was explored to determine ways to reduce the energy requirements to produce high quality CBMs. Different growth parameters, such as gas flow rate, temperature, laser energy, and deposition time were considered and studied thoroughly to analyze the growth pattern. CBMs are grown on Si and Cu substrates, where we find better quality CBM films on Cu as it aids the surface solubility of carbon. Raman spectroscopy confirms the presence of high-quality PyC which is grown at a temperature of 750 ◦C, CH4 gas flow rate of 20 sccm, a laser frequency of 10 Hz, and an energy density of 0.116 J/cm2 per pulse. It is found that the local pulsed-laser bombardment helps in breaking the carbon-hydrogen bonds of CH4 at a much lower substrate temperature than its thermal decomposition temperature. There is no significant change in the 2D peak intensity in the Raman spectrum with the further increase in temperature which is the indicator of the number of the graphene layer. The intertwined graphene flakes of the PyC are observed due to the surface roughness, which is responsible for the quenching in the Raman 2D signal. These results will provide the platform to fabricate a large area single layer of graphene, including the other 2D materials, on different substrates using the LCVD technique.