High‐Temperature Cs_xC₅₈ Fullerides

Abstract

Cs doped non‐IPR fullerides (IPR: isolated pentagon rule) have been grown by co‐depositing C58 cations and Cs atoms on highly oriented pyrolytic graphite (HOPG). The C58 cages, as building blocks of the material, form a predominantly covalently stabilized scaffold, C58–C58, which is doped by Cs atoms thermally diffusing across the bulk. The heating of the solid CsxC58 sample is accompanied by sublimation of Cs, C58, and C60 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 C58–C58 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.

Desorption of Fullerene Dimers upon Heating Non-IPR Fullerene Films on HOPG

“…Instead, we have used preparative mass spectrometry to generate a range of pure non-IPR fullerene materials for the first time and have described their cage-size-dependent properties in a series of previous publications. − Our approach starts with sublimed IPR cages and uses electron impact to both ionize and fragment them to smaller non-IPR fullerene cations in the gas phase . These are then mass-selected and deposited onto a clean surface under low energy impact conditions (thus precluding further fragmentation or backscattering).…”

“…The associated solid-state reaction processes have also been found to strongly affect the mechanical properties: tempering μm thick films of C 58 at 1100 K significantly increases their hardness from 1.2 to 3.9 GPa . At the same time, the electronic structure of the material changes significantly as measured by UPS/XPS. , In contrast, Raman spectra of thick films still show residual fullerene-like signatures even after annealing up to 1100 K …”