Growth and structures of C 60 shells
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Growth and structures of C60 shells H. Sakuma Graduate School of Integrated Science, Yokohoma City University, 22-2 Seto, Kanazawa-ku, Yokohama 236, Japan
M. Tachibana,a) H. Sugiura, and K. Kojima Department of Physics, Faculty of Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236, Japan
S. Ito and T. Sekiguchi Research Institute for Materials, Tohoku University, 2-1 Katahira-machi, Aoba-ku, Sendai 980, Japan
Y. Achiba Department of Chemistry, Faculty of Science, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo 192-03, Japan (Received 13 September 1996; accepted 17 October 1996)
The growth of the shells of C60 crystals was carried out under various conditions. The detailed structures of the grown shells were investigated by transmission electron microscopy and Raman spectroscopy. The shells were formed during thermal sublimation of the C60 crystals, which were irradiated with white light in air. The shells were mainly composed of a kind of amorphous carbon. From these results, it is suggested that the oxygen-induced disintegration of C60 cages is responsible for the shell formation.
I. INTRODUCTION
Several investigations on the crystal growth of the large size of C60 single crystals have shown that the shells of C60 crystals are left in the source region when the larger crystals are grown by sublimation method where not powder but crystals are used as the source materials.1–3 These shells were composed of the surface layer of the original source crystals and kept the shapes of the original crystals. Recently much attention has been paid on the shells as new formation of C60 . Some characteristics of shells have been reported as follows: the shells are stable for thermal sublimation, light irradiation, and organic solvents.1–3 The structures of the shells were investigated by Li et al.3 Raman spectra of the shell showed two peaks at 1469 and 1459 cm–1 , which are due to the pristine C60 crystal and the photopolymerization of C60 , respectively. Moreover, electron diffraction patterns of the shell indicated that it consists of crystalline region with face-centered-cubic (fcc) structure and porous amorphous region. X-ray powder diffraction of the shell also showed that it is fcc crystalline matter whose lattice constant is slightly smaller than that of pristine C60 crystals. From these results, it is predicted that the shells are mainly composed of the photopolymerized C60 crystalline matter which is produced by the photoillumination on the surface of the pristine C60 crystal. However, it has been reported that a)
Address all correspondence to this author. J. Mater. Res., Vol. 12, No. 6, Jun 1997
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the photopolymerized C60 is unstable and decomposed above ,100 ±C.4,5 This result is inconsistent with those that the shells are composed of the photopolymerized C60 and stable for the thermal sublimation. Thus, the characteristics of the shells have been controversial so far. In parti
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