Browsing by Author "Farhat S."
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Item Erratum: Computer-aided design of graphene and 2D materials synthesis via magnetic inductive heating of 11 transition metals (J. Phys. D: Appl. Phys. (2021) 55 (105302) DOI: 10.1088/1361-6463/ac357d)(2022-04-14) Dhaouadi E.; Hinkov I.; Pashova K.; Challab N.; Roussigné Y.; Abderrabba M.; Farhat S.There was a typo during the production of our paper. The alpha factor has been omitted from equation (3). The equation should appear as follows: ρ = ρ0 (1 + αT).Item Graphene synthesis by electromagnetic induction heating of oxygen-rich copper foils(2023-02-01) Dhaouadi E.; Alimi W.; Konstantakopoulou M.; Hinkov I.; Abderrabba M.; Farhat S.We report in this article an optimized synthesis of high-quality monolayer graphene by chemical vapor deposition (CVD) using methane as carbon source. The synthesis occurs on a centimeter-sized copper substrate previously oxidized in air at 180 °C then heated by electromagnetic induction in a controlled atmosphere of argon and hydrogen in which the steady-state temperature of ∼1050 °C is reached after only ∼2 min heating from room temperature. The rapidity of the heating and cooling process highlights the advantage of using the electromagnetic induction heating method in order to achieve the synthesis of graphene. When applied to CVD, electromagnetic inductive heating only heats the metallic substrate avoiding energy losses in the reaction medium. Therefore, inductive heating has great potential for large-scale and rapid manufacturing of graphene and 2D materials. This work includes an experimental study that consists in comparing the quality of the synthesized graphene over different substrates ranging from oxygen-free copper foil to oxidized copper with the aim to reduce the defects in the graphene and also to increase the domain size. We find that copper with an oxidized surface can drastically reduce graphene nucleation density thereby increasing the graphene domain sizes. In addition, we demonstrated experimentally and by numerical simulations that the presence of a thin layer of copper oxide does not disturb the mechanism of induction heating allowing the growth of high-quality graphene films by inductive heating of copper oxides. Graphene quality was studied by Raman spectroscopy, and scanning electron microscopy (SEM) which respectively showed very little defective monolayer graphene (ID / IG < 0.2) and non-defective graphene subdomains of average size ranging from ∼5 μm to∼10 μm which is comparable, if not better, to traditional thermal CVD method. These results provide directions for effective control of the defects and layers of graphene.Item Graphene synthesis by electromagnetic induction heating: Domain size and morphology control(2024-04-01) Dhaouadi E.; Alimi W.; Hinkov I.; Abderrabba M.; Farhat S.In this paper we discuss the effect of hydrogen and methane content during low-pressure chemical vapor deposition (LPCVD) of graphene on inductively heated copper foils. By increasing the H2/CH4 ratio by a factor of 5 from 25 to 125, different graphene morphologies ranging from dendritic fractals to compact hexagonal islands are obtained. In addition, increasing the hydrogen concentration allows the nucleation rate to be slowed down by a factor of ∼10 thereby high-quality regular hexagonal graphene single crystals of significant size of 0.1 mm are found. From these measurements, we estimate the activation energy for graphene nucleation in low-pressure CVD (2 eV) and propose a phenomenological law for graphene nucleation. As compared to conventional CVD methods, considerable advantages of inductive heating are outlined, and some fundamental aspects of this approach are discussed.Item Graphene synthesis by inductively heated copper foils: Reactor design and operation(2020-04-01) Pashova K.; Dhaouadi E.; Hinkov I.; Brinza O.; Roussigné Y.; Abderrabba M.; Farhat S.We report on the design of a reactor to grow graphene via inductively heating of copper foils by radio frequency (RF) magnetic fields. A nearly uniform magnetic field induced by Helmholtz-like coils penetrates the copper foil generating eddy currents. While the frequency of the current is being rapidly varied, the substrate temperature increases from room temperature to ~1050 °C in 60 s. This temperature is maintained under Ar/H2 flow to reduce the copper, and under Ar/H2/CH4 to nucleate and grow the graphene over the entire copper foil. After the power cut-off, the temperature decreases rapidly to room temperature, stopping graphene secondary nucleation. Good quality graphene was obtained and transferred onto silicon, and coated with a 300 nm layer of SiO2 by chemical etching of the copper foil. After synthesis, samples were characterized by Raman spectroscopy. The design of the coils and the total power requirements for the graphene induction heating system were first estimated. Then, the effect of the process parameters on the temperature distribution in the copper foil was performed by solving the transient and steady-state coupled electromagnetic and thermal problem in the 2D domain. The quantitative effects of these process parameters were investigated, and the optimization analysis results are reported providing a root toward a scalable process for large-sized graphene.Item Graphene synthesis by microwave plasma chemical vapor deposition: Analysis of the emission spectra and modeling(2019-04-03) Pashova K.; Hinkov I.; Aubert X.; Prasanna S.; Bénédic F.; Farhat S.In this article, we report on some of the fundamental chemical and physical processes responsible for the deposition of graphene by microwave plasma-enhanced chemical vapor deposition. The graphene is grown by plasma decomposition of a methane and hydrogen mixture (CH4/H2) at moderate pressures over polycrystalline metal catalysts. Different conditions obtained by varying the plasma power (300-400 W), total pressure (10-25 mbar), substrate temperature (700 °C-1000 °C), methane flow rate (1-10 sccm) and catalyst nature (Co-Cu) were experimentally analyzed using the in situ optical emission spectroscopy technique to assess the species rotational temperature of the plasma and the H-atom relative concentration. Then, two modeling approaches were developed to analyze the plasma environment during graphene growth. As a first approximation, the plasma is described by spatially averaged bulk properties, and the species compositions are determined using kinetic rates in the transient zero-dimensional (0D) configuration. The advantage of this approach lies in its small computational demands, which enable rapid evaluation of the effects of reactor conditions and permit the identification of dominant reactions and key species during graphene growth. This approach is useful for identifying the relevant set of species and reactions to consider in a higher-dimensional model. The reduced chemical scheme was then used within the self-consistent two-dimensional model (2D) to determine auto-coherently the electromagnetic field, gas and electron temperatures, heavy species, and electron and ion density distributions in the reactor. The 0D and 2D models are validated by comparison with experimental data obtained from atomic and molecular emission spectra.Item One-step synthesis of graphene, copper and zinc oxide graphene hybrids via arc discharge: Experiments and modeling(2020-04-01) Kane A.; Hinkov I.; Brinza O.; Hosni M.; Barry A.H.; Cherif S.M.; Farhat S.In this paper, we report on a modified arc process to synthetize graphene, copper and zinc oxide graphene hybrids. The anode was made of pure graphite or graphite mixed with metals or metal oxides. After applying a controlled direct current, plasma is created in the interelectrode region and the anode is consumed by eroding. Continuous and abundant flux of small carbon, zinc or copper species, issued from the anode at a relatively high temperature, flows through the plasma and condenses in the vicinity of a water-cooled cathode leading to few-layered graphene sheets and highly ordered carbon structures. When the graphite rod is filled with copper or zinc oxide nanoparticles, few layers of curved graphene films were anchored with spherical Cu and ZnO nanoparticles leading to a one-step process synthesis of graphene hybrids, which combine the synergetic properties of graphene along with nanostructured metals or semiconducting materials. The as-prepared samples were characterized by Raman spectroscopy, X-ray diffraction (XRD), spatially resolved electron energy loss spectroscopy (EELS), energy filtered elemental mapping and transmission electron microscopy (TEM). In addition to the experimental study, numerical simulations were performed to determine the velocity, temperature and chemical species distributions in the arc plasma under specific graphene synthesis conditions, thereby providing valuable insight into growth mechanisms.