Carbon nanoballs belong to the fullerenes family, but they are a little different in structure. Other fullerenes as C60 are single walled, but nanoballs are multi walled. It is void in the center of carbon nanoballs but, in the wall of nanoballs, there is no hollow structure or channel as in the case of MWCNTs. Because their structures are similar to the onions, scientists call them bucky onions. Nanoballs in Fig. 11.16 have diameters of between 500 nm and 1|im (Liu 2002). Recently, our group produced hollow carbon nanoballs by chemical reduction of carbon dioxide with metallic Li (Fig. 11.17). By studying the defect of bucky onions it is found that the self-interstitial concentration remains low and is only slightly enriched near the onion centre. The loss of atoms from the outer surface of the bucky onions by sputtering acts as a vacancy source for the whole onion (Sigle et al. 1997).
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