Direct Cross-Linking of C70 in Ar Plasma

C 70 polymer films were prepared by rf plasma irradiation in Ar atmosphere. Laser desorption ionization time-of-flight mass spectra (LDITOF-MS) for the polymer films showed that C 2 loss occurred in the course of direct cross-linking of C 70 molecules. The polymer structure is discussed based on molecular orbital (MO) calculations of C 70 dimers at semiempirical levels, and the lower probability of direct cross-linking of C 70 molecules than that of C 60 molecules is suggested. The electric dark current of the plasma-polymerized C 70 was 10 -13 S/cm, compared to 10 -8 S/cm in the C 60 polymer prepared at the same plasma power. The almost-insulating electric conductivity of the C 70 polymer is attributable to the lower probability of conductive cross-linking of C 70 molecules originating from the electronic structure of C 70 . The experimental and theoretical results suggest that the C 70 molecule is the smallest carbon nanotube with polyhedral caps and that the chemical properties of the caps closely resemble the C 60 molecule.