Plasma–Solution Junction for the Formation of Carbon Material (original) (raw)
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Effect of the Plasma Gas Composition on the Properties of Graphene
High Energy Chemistry, 2020
Theoretical and experimental studies of the synthesis of graphene with the introduction of nitrogen into a jet of helium plasma generated by a direct-current plasma torch with a power of to 40 kW at a pressure of 350 Torr have been performed. A propane-butane mixture was used as a source of carbon. As found by scanning microscopy, Raman scattering, and synchronous thermal analysis, the morphology of the synthesis products changed from graphene flakes to carbon nanotubes upon the addition of nitrogen in a ratio of 1 : 1.22 to the jet of helium plasma. The numerical modeling of the process showed that cyanopolyyne molecules, HC 9 N and HC 11 N, containing many carbon atoms appeared instead of C60 and C80 in the jets of helium upon the addition of nitrogen.
Plasma engineering of graphene
Applied physics reviews, 2016
Recently, there have been enormous efforts to tailor the properties of graphene. These improved properties extend the prospect of graphene for a broad range of applications. Plasmas find applications in various fields including materials science and have been emerging in the field of nanotechnology. This review focuses on different plasma functionalization processes of graphene and its oxide counterpart. The review aims at the advantages of plasma functionalization over the conventional doping techniques. Selectivity and controllability of the plasma techniques opens up future pathways for large scale, rapid functionalization of graphene for advanced applications. We also emphasize on atmospheric pressure plasma jet as the future prospect of plasma based functionalization processes.
Influence of plasma process on the nitrogen configuration in graphene
Diamond and Related Materials, 2016
We investigated nitrogen doping into graphene on copper substrates by plasma treatment and by plasma immersion ion implantation (PIII). Two nitrogen bonding configurations were discovered to be dominant for distinct plasma processes. Pyridinic-N (P1) was the preferential N-bonding for doping with PIII while it was pyrrolic-N (P2) for plasma treatment. The ratio of pyrrolic-N and pyridinic-N bonding (P2/P1) in N-doped graphene obtained from our experiments was associated with the simulated ratio of divacancy and monovacancy defect. Vacancy defect species induced by plasma in graphene play a key role to determine preferential N-bonding. Energetic nitrogen ions can stimulate the conversion of pyrrolic-N to pyridinic-N bonding via thermal spike, which leads to the decrease of the P2/P1 ratios when exposing graphene to nitrogen ions by either prolonging implantation or increasing implantation energy.
Distinctive Features of Graphene Synthesized in a Plasma Jet Created by a DC Plasma Torch
Materials
Synthesis of graphene materials in a plasma stream from an up to 40 kW direct current (DC) plasma torch is investigated. These materials are created by means of the conversion of hydrocarbons under the pressure 350–710 Torr without using catalysts, without additional processes of inter-substrate transfer and the elimination of impurities. Helium and argon are used as plasma-forming gas, propane, butane, methane, and acetylene are used as carbon precursors. Electron microscopy and Raman imaging show that synthesis products represent an assembly of flakes varying in the thickness and the level of deformity. An occurrence of hydrogen in the graphene flakes is discovered by X-ray photoelectron spectroscopy, thermal analysis, and express-gravimetry. Its quantity depends on the type of carrier gas. Quasi-one-dimensional approach under the local thermodynamic equilibrium was used to investigate the evolution of the composition of helium and argon plasma jets with hydrocarbon addition. Hydr...
Journal of vacuum science & technology, 2016
Recent research suggests plasma-induced hydrogenation is an efficient method for inducing a band-gap in graphene. To date, the characterization of plasma treatmentinduced chemical changes is performed almost exclusively by Raman spectroscopy with the extent of hydrogenation presented as the evolution defect structures in the sp 2 lattice of graphene. Alarmingly, almost no attention given to the concurrent electronic modification. Here, X-ray induced Auger emission spectroscopy (XAES) is utilized to better understand the effect of plasma treatment on the electronic properties of graphene beyond the formation of defects as determined by Raman spectroscopy. The results indicate the fine structure of the C KLL emission offers a suitable complement to Raman spectroscopy in assessing the extent of chemical and electronic changes induced by H 2 plasma treatments. Significant changes to the D-value, defined as the distance between local maxima and minima in the C KLL Auger emission, are observed after only 30s of treatment (p < 0.001), while the I D /I G ratio remains statistically equivalent (p = 0.441). The results indicate significant differences in the electronic properties of plasma-treated graphene are observed concomitant to sp 2 defect structures normally attributed to hydrogenation.
Efficient nitrogen doping of graphene by plasma treatment
Carbon, 2016
Doping of pristine materials can change their chemical and electrical properties. Namely nitrogen doping of graphene results in modulation of electronic properties of graphene. In this work we present experimental results on nitrogen doped graphene fabricated in two steps. At first, the graphene samples were synthesized by a chemical vapor deposition method on copper foils. Then they were treated with ammonia radio frequency discharge plasma. The prepared samples were investigated by atomic-force microscopy (AFM), scanning electron microscopy (SEM), Raman spectroscopy, optical absorption spectroscopy including Fourier transform infrared spectroscopy (FTIR), X-ray and ultraviolet photoelectron spectroscopy. In doped graphene a dependence of N-atom concentration on the treatment parameters has been revealed. A maximum doping level of 3 atomic % has been obtained and the shift of valence band maximum of 0.2 eV was observed at this concentration of nitrogen.
Process-specific mechanisms of vertically oriented graphene growth in plasmas
Beilstein Journal of Nanotechnology, 2017
Applications of plasma-produced vertically oriented graphene nanosheets (VGNs) rely on their unique structure and morphology, which can be tuned by the process parameters to understand the growth mechanism. Here, we report on the effect of the key process parameters such as deposition temperature, discharge power and distance from plasma source to substrate on the catalyst-free growth of VGNs in microwave plasmas. A direct evidence for the initiation of vertical growth through nanoscale graphitic islands is obtained from the temperature-dependent growth rates where the activation energy is found to be as low as 0.57 eV. It is shown that the growth rate and the structural quality of the films could be enhanced by (a) increasing the substrate temperature, (b) decreasing the distance between the microwave plasma source and the substrate, and (c) increasing the discharge power. The correlation between the wetting characteristics, morphology and structural quality is established. It is a...
On the plasma-based growth of ‘flowing’ graphene sheets at atmospheric pressure conditions
Plasma Sources Science and Technology, 2015
A theoretical and experimental study on atmospheric pressure microwave plasma-based assembly of free standing graphene sheets is presented. The synthesis method is based on introducing a carbon-containing precursor (C 2 H 5 OH) through a microwave (2.45 GHz) argon plasma environment, where decomposition of ethanol molecules takes place and carbon atoms and molecules are created and then converted into solid carbon nuclei in the 'colder' nucleation zones. A theoretical model previously developed has been further updated and refined to map the particle and thermal fluxes in the plasma reactor. Considering the nucleation process as a delicate interplay between thermodynamic and kinetic factors, the model is based on a set of non-linear differential equations describing plasma thermodynamics and chemical kinetics. The model predictions were validated by experimental results. Optical emission spectroscopy was applied to detect the plasma emission related to carbon species from the 'hot' plasma zone. Raman spectroscopy, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS) techniques have been applied to analyze the synthesized nanostructures. The microstructural features of the solid carbon nuclei collected from the colder zones of plasma reactor vary according to their location. A part of the solid carbon was deposited on the discharge tube wall. The solid assembled from the main stream, which was gradually withdrawn from the hot plasma region in the outlet plasma stream directed to a filter, was composed by 'flowing' graphene sheets. The influence of additional hydrogen, Ar flow rate and microwave power on the concentration of obtained stable species and carbon−dicarbon was evaluated. The ratio of sp 3 /sp 2 carbons in graphene sheets is presented. A correlation between changes in C 2 and C number densities and sp 3 /sp 2 ratio was found.
Nanomaterials, 2020
To develop a synthesis technique providing enhanced control of graphene film quality and uniformity, a systematic characterization and manipulation of hydrocarbon precursors generated during plasma enhanced chemical vapor deposition of graphene is presented. Remote ionization of acetylene is observed to generate a variety of neutral and ionized hydrocarbon precursors, while in situ manipulation of the size and reactivity of carbon species permitted to interact with the growth catalyst enables control of the resultant graphene morphology. Selective screening of high energy hydrocarbon ions coupled with a multistage bias growth regime results in the production of 90% few-to-monolayer graphene on 50 nm Ni/Cu alloy catalysts at 500 • C. Additionally, synthesis with low power secondary ionization processes is performed and reveals further control during the growth, enabling a 50% reduction in average defect densities throughout the film. Mass spectrometry and UV-Vis spectroscopy monitoring of the reaction environment in conjunction with Raman characterization of the synthesized graphene films facilitates correlation of the carbon species permitted to reach the catalyst surface to the ultimate quality, layer number, and uniformity of the graphene film. These findings reveal a robust technique to control graphene synthesis pathways during plasma enhanced chemical vapor deposition.
Large-scale synthesis of free-standing N-doped graphene using microwave plasma
Scientific Reports
Direct assembling of N-graphene, i.e. nitrogen doped graphene, in a controllable manner was achieved using microwave plasmas at atmospheric pressure conditions. The synthesis is accomplished via a single step using ethanol and ammonia as carbon and nitrogen precursors. Tailoring of the high-energy density plasma environment results in a selective synthesis of N-graphene (~0.4% doping level) in a narrow range of externally controlled operational conditions, i.e. precursor and background gas fluxes, plasma reactor design and microwave power. Applying infrared (IR) and ultraviolet (UV) irradiation to the flow of free-standing sheets in the post-plasma zone carries out changes in the percentage of sp 2 , the N doping type and the oxygen functionalities. X-ray photoelectron spectroscopy (XPS) revealed the relative extension of the graphene sheets π-system and the type of nitrogen chemical functions present in the lattice structure. Scanning Electron microscopy (SEM), Transmission Electron microscopy (TEM) and Raman spectroscopy were applied to determine morphological and structural characteristics of the sheets. Optical emission and FT-IR spectroscopy were applied for characterization of the highenergy density plasma environment and outlet gas stream. Electrochemical measurements were also performed to elucidate the electrochemical behavior of NG for supercapacitor applications. Beyond its unique set of physico-chemical properties, graphene can be considered as a robust, atomic scale scaffold from which other 2D materials can be derived through the attachment of foreign atoms and functional groups 1-4. Among the possible doping agents, nitrogen has drawn a considerable amount of attention because its atomic radius is comparable to that of carbon and contains five valence electrons available to form strong covalent bonds. The conjugation between the nitrogen lone-pair electrons and the graphene π-system modifies graphene physical and chemical properties. The substitution of carbon atoms by nitrogen ones influences the atomic charge distribution on the graphene scaffold and creates "active sites" thus significantly increasing the electrochemical activity of nitrogen-doped graphene, known as N-graphene (NG) 4. The theoretical studies 4,5 predicted modified electronic and chemical properties of nitrogen-doped graphene, which is being supported by numerous experimental investigations. Indeed, there is significant experimental evidence of the advanced properties of the NG-based materials in respect to already practically implemented ones 4,5. For instance, NG has been tested in fuel cells either as the catalyst or carbon supports. The "active sites" can be engaged in catalytic reactions, such as oxygen reduction reaction (ORR), or can be used as a scaffold for other catalysts 3-8. NG demonstrates better chemical reactivity and sheet-to-sheet separation than the pristine graphene 9. To this end, N-doping is a very promising approach for the development of metal-free carbon-based catalysts with even better performance than commercially available Pt-based electrodes, with prospective impact on fuel cells' commercialisation. However, the lack of an appropriate synthesis route providing both high quality and quantity of NG hinders its practical implementation.