Photoluminescence and Raman investigations of structural transformation of fullerenes into carbon nanotubes in vacuum annealed C60/C70+Ni films Original Research Article

In this paper the luminescence and Raman investigations of structural changes undergoing in C60/C70+Ni films annealed at vacuum are presented. Because of the annealing process of these films, multishell carbon nanotubes were obtained. The structural changes occurring in the films in various thermal conditions were observed by photoluminescence (PL) and Raman spectra. In room temperature Raman spectrum of air exposed “as grown” C60/C70+Ni films only C60 and C70 vibrational bands were found. The bands connected to graphite (∼1340, 1580 and 1620 cm−1) and nanotubes (1565 cm−1) vibrations were observed in Raman spectra of annealed films. In the PL spectrum of “as grown” C60/C70+Ni films three PL peaks were observed. In PL spectra of annealed layers (at 620 and 770 K containing nanotubes) an additional PL peak at 11,940 cm−1 was found. This peak could be attributed to a transition between vibronic states of carbon. In the PL spectra of annealed films, no shift of PL peaks was observed with increasing measurementʹs temperature (from 6 to 300 K).