Figure 2 shows the IR spectra of the C60 film before and after EB irradiation. Before irradiation ~a! four intensive peaks corresponding to the fundamental IR-active modes of the C60 molecule were observed. After 10 h EB irradiation ~b!, while the four fundamental peaks decreased, an intensive broadband appeared around 1390 cm. Furthermore, after 20 h irradiation ~c!, the broadband became more intensive and shifted to 1360 cm. Besides this broadband, another weak peak appeared at 480 cm. On the other hand, the fundamental peak of C60 at 1430 cm disappeared completely. This IR peak originating only from the in-plane stretching motions of the C60 cage is very sensitive to any change in its cage structure, while the other fundamental peaks originating not only from the motion but also from the radial motion of the cage are not sensitive to any structural change in C60 ~Ref. 6!. The IR fundamental peak appearing at around 1430 cm21 is, therefore, a good indicator for the change in the amount of C60. Accordingly, the disappearance of the peak indicates that all C60 molecules in the film were