On the Existence of Transition-Metal Fullerides:  Deposition and Characterization of Ti<i>_x</i>C₆₀

Abstract

Titanium fulleride films (Ti x C 60 ) were prepared by coevaporating Ti and C 60 onto moderately heated substrates (∼100 °C) in an ultrahigh vacuum system. The Ti x C 60 films were all amorphous according to X-ray diffraction and exhibited a gray, metallic luster different from the brown color of pristine C 60 . The compound also appeared to be metallic or semiconducting as no charging was observed in X-ray photoelectron spectroscopy (XPS) in contrast to analyses of pure C 60 . XPS of the films showed a maximum titanium content of about 5.3−5.5 at. % (Ti ∼ 3.5 C 60 ). For higher titanium contents, carbide formation was observed. The XPS analyses also showed binding energy shifts and line broadening effects consistent with the formation of chemical bonds between Ti and C 60 . Raman spectroscopy showed a softening of the A g (2) mode upon Ti incorporation (−4 cm - 1 /Ti atom) which is consistent with a partial charge transfer from Ti to C 60 . The Ti x C 60 films oxidized immediately upon air exposure. However, XPS and Raman spectroscopy show persistent differences from pristine C 60 which might indicate that another phase, Ti x O y C 60, is formed upon oxidation.