Transformation of Active Carbon to Onion-like Fullerenes Under Electron Beam Irradiation
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Transformation of Active Carbon to Onion-like Fullerenes Under Electron Beam Irradiation Bingshe Xu1 Husheng Jia1 Hefeng Zhou1 Hideki Ichinose2 Chihiro Iwamoto2 1 College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi, China, 030024 2 Department of Materials Science, School of Engineering, The University of Tokyo, Tokyo, Japan, 113-0033 ABSTRACT The transformation of an active carbon film with Pt nanoparticles to onion-like fullerenes has been in-situ investigated by a high-resolution transmission electron microscope. It was found that the onion-like fullerenes/metals polycrystalline film was formed under electron irradiation. The formation process was consisted of three steps: first, the flakes of onion-like fullerenes were induced by Pt nanoparticles; second, the flakes grew into a few ellipsoidal graphite shell; and third, a gradual reorganization of the formation of quasi-spheroid graphite shells and the bond of Pt particles was took place. It was a composite film of onion-like fullerenes and metal particles. It is suggested that the transformation mechanism involves an irradiation of electron and a catalytic effect of Pt nanoparticles, while any temperature rise due to electron irradiation seems to be negligibly small. INTRODUCTION Since the discovery of fullerenes, their synthesis and characterization have attracted a great deal of interest in the scientific community. The fullerenes with different structure such as buckminsterfullerene[1,2], nanotubes[3], onion-like fullerenes[4], and metal-fullerenes[5] have been produced by laser vaporization, resistive heating, and arc discharge. For onion-like fullerenes (OLF), Iijima synthesized the onion structure carbon by arc discharge[4], Ugarte obtained OLF from polyhedral graphite and nanotubes by intense electron bombardment. Such OLF were usually formed from ordered structure carbons. Xu reported the transformation of an amorphous carbon film with metallic nanoparticles of Al, Au and Pt into giant onion-like fullerenes induced by electron beam irradiation in a high resolution transmission electron microscope [6-8]. They were the first experiments in which OLF were formed from an amorphous carbon film using an electron irradiation technique and metallic nanoparticle catalysts. Four kinds of onion-like fullerenes have been produced, such as signal-nuclei OLF, multiple-nuclei OLF, intercalation OLF with metal atoms inside its shells, and metallofullerene with metal atoms in its center. Here, an experimental study is reported in which onion-like fullerenes/metals film was produced from active carbon by electron beam irradiation and Pt nanoparticle catalysts. The kinetics and mechanism of their formation were also discussed. EXPERIMENTAL
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Pt nanoparticls were prepared on amorphous carbon films by Ar+ beam sputtering. The ion acceleration voltage was 2-4kV, with a beam current of 0.2-0.3 mA. The process was done under vacuum of 10-4 Pa. The size of Pt nanoparticles ranges from 1 to 6 nm in diameter. The thickness of amo
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