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Two complementary modeling approaches (1D and 2D) are developed to explain the temperature-dependent growth kinetics of PECVD graphene formation on cobalt substrate. The gas temperature and the species concentrations are predicted for different process conditions by involving gas-phase and surface reaction mechanisms which consist of 15 gas species, 43 gas reactions, 10 surface species and 34 surface reactions. The influence of the growth temperature, the microwave power and the methane flow rate, affecting the gas species mole fractions in the reactor and the surface coverage is evaluated. The numerical results clearly indicate that the hydrogen atoms play an important role in the graphene growth in microwave plasma systems. A global sensitivity analysis is then performed in order to understand the basic mechanisms that lead to the transport of reactants by gas diffusion from the main gas stream through the boundary layer providing insight regarding the growth of graphene on the cobalt substrate.

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.

International audience; 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 (PECVD). The graphene is grown by plasma decomposition of a methane and hydrogen mixture (CH 4 /H 2) 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 (700-1000°C), methane flow rate (1-10 sccm) and catalyst nature (Co-Cu) were experimentally analyzed using the in situ optical emission spectroscopy (OES) 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.

This article describes the significant roles of process parameters in the deposition of boron and nitrogen co-doped multi-walled carbon nanotubes via the arc-discharge process. The fabrication process is based on the vaporization of solid hexagonal boron nitride embedded in graphite cylinders in a nitrogen atmosphere with pressure varying from 350 mbar to 700 mbar and controlled current density between 150 and 420 A/cm2. Our results show the presence of significant amount of doped boron carbon nitride nanotubes in the cathodic deposit. These nanotubes have a narrow diameter distribution (20–30 nm) and a length up to 1 μm as analyzed by scanning electron microscopy and transmission electron microscopy. In addition to the experimental study, numerical simulations were performed to determine the temperature and chemical species distributions in the arc plasma under specific boron carbon nitride nanotubes synthesis conditions, thereby providing valuable insight into nanotubes growth and doping mechanisms in the arc.

Zinc oxide nanoparticles with different sizes and shapes have been synthesized in polyol using a bottom-up approach. We have studied the scale-up of the process to massively produce high quality nanoparticles of controlled size and shape. The scale-up strategy required the effective mixing of reagents using either axial or radial mixing configurations and was experimentally validated by comparing structural properties of particles obtained in a small and a large size reactor. In addition, the flow patterns in these reactors have been calculated using three-dimensional turbulent computational fluid dynamics (CFD) simulations. Our results indicate a strong connection between the flow patterns, as obtained by CFD simulations, and the size and shape of the particles. Actually, our pilot scale reactor allowed producing sample aliquots of ~50 grams with nanoparticle sizes ranging from 8 nm to 600 nm and aspect ratio varying from 1 (nanospheres) to 20 (nanorods). After their synthesis, these two nanoparticle classes have been tested as building blocks in D149-dye-sensitized solar cell (DSSC). The measured power conversion efficiency (PCE) was 4.66% for nanorods shaped particles and 4.21% for nanospheres. These values were significantly higher than the 3.90% PCE obtained with commercial Degussa VP20 ZnO nanoparticles.