Browsing by Author "Alimi W."

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    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.
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    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.