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    One-step synthesis of spontaneously graphitized nanocarbon using cobalt-nanoparticles
    (Springer International Publishing Ag, 2020) Elnobi, Sahar; Sharma, Subash; Ohsugi, Tetsuya; Paudel, Balaram; Kalita, Golap; Yusop, Mohd Zamri Mohd; Ayhan, Muhammed Emre
    Amorphous carbon (a-C) films containing metallic Cobalt nanoparticles (Co NPs) were deposited onto microgrids and SiO2/Si substrates by a magnetron sputter-deposition technique at room temperature (RT) using aC target with an attachment of a small Co platelet. Transmission electron microscopy (TEM) with a fast Fourier-transform (FFT) revealed the short-range ordering of the lattice corresponding to graphite (002) between Co NPs in the amorphous C matrix. The 2D peak and graphite (002) peak were clearly observed in Raman spectra and x-ray diffraction (XRD), respectively, for the Co-C films. X-ray photoelectron spectroscopy analyses were used to determine the metallic state of Co NPs and sp(2) graphitization in the film. Thus, the Co NPs exhibited higher catalytic activity in spontaneous graphitization at low-temperature than Ni-NPs prepared under the same conditions. So, the metallic NPs were concluded to be promising as the catalyst for the ultra-low temperature graphitization in the solid-phase reaction.
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    Room-temperature graphitization in a solid-phase reaction
    (Royal Soc Chemistry, 2020) Elnobi, Sahar; Sharma, Subash; Araby, Mona Ibrahim; Paudel, Balaram; Kalita, Golap; Yusop, Mohd Zamri Mohd; Ayhan, Muhammed Emre
    Graphitized carbon including graphene has recently become one of the most investigated advanced materials for future device applications, but a prerequisite for broadening its range of applications is to lower its growth temperature. Here we report a great decrease in graphitization temperature using the well-known catalyst Ni. Amorphous carbon films with Ni nanoparticles (NPs) were deposited, using a simple one-step magnetron sputtering method, onto microgrids and a SiO2/Si substrate for transmission electron microscopy (TEM) and Raman spectroscopy analyses, respectively. The amorphous carbon surroundings and locations between the Ni NPs started to become graphitized during the film deposition even at room temperature (RT) and 50 degrees C. The graphitization was confirmed by both high-resolution TEM (HR-TEM) and Raman 2D peak analyses. The increase in the relative amount of Ni in the amorphous carbon film led to the partial oxidation of the larger Ni NPs, resulting in less graphitization even at an elevated deposition temperature. Based on the detailed HR-TEM analyses, a decreased oxidation of NPs and enhanced solubility of carbon into Ni NPs were believed to be key for achieving low-temperature graphitization.