High-Temperature CsxC58 Fullerides

Cs doped non-IPR fullerides (IPR: isolated pentagon rule) have been grown by co-depositing C-58 cations and Cs atoms on highly oriented pyrolytic graphite (HOPG). The C-58 cages, as building blocks of the material, form a predominantly covalently stabilized scaffold, C-58-C-58, which is doped by Cs atoms thermally diffusing across the bulk. The heating of the solid CsxC58 sample is accompanied by sublimation of Cs, C-58, and C-60 species from the topmost layers of the sample. However, the major part (>94%) of the material survives the heating procedure and constitutes a doped high-temperature carbon solid, HT-CsxC58. The new non-IPR material exhibits surprisingly high thermal stability. It survives a heating flash up to 1100 K at which the classic IPR-CsxC60 phase does not exist anymore. However, the thermally treated HT-CsxC58 phase exhibits a considerably depleted Cs content (x < 2) and a significantly modified carbon scaffold. The apparent stability of the scaffold results from covalent C-C bonds interlinking adjacent carbon cages. Cs atoms in the HT-CsxC58 phase contribute to this stability only as minority species, forming comparably weak ionic bonds with C-58-C-58 oligomers. However, this interaction facilitates the formation of structural defects (new non-IPR sites) in carbon cages. The surface topography of the HT-CsxC58 as monitored by scanning photoemission microscopy, atomic force microscopy, and scanning electron microscopy is governed by islands standing out by their elevated Cs/C ratio.