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Mechanical properties of C58 materials and their dependence on thermal treatment

: Ulas, S.; Bundschuh, S.; Jester, S.-S.; Eberl, C.; Kraft, O.; Hölscher, H.; Böttcher, A.; Kappes, M.M.


Carbon 68 (2014), S.125-137
ISSN: 0008-6223
Fraunhofer IWM ()
fullerenes; mechanical properties; thin film

C58 fullerene cages made by electron-impact induced fragmentation of C60 fullerenes have been assembled into several micron thick solid films by low energy cluster beam deposition onto inert substrates held at room temperature under ultrahigh vacuum. The resulting asprepared material, RT-C58, behaves as an amorphous wide-band semiconductor. Nanoindentation was used to measure ist mechanical properties revealing that RT-C58 has a higher elastic modulus E and hardness H than the reference carbon allotropes solid C60 and Highly Ordered Pyrolytic Graphite (HOPG): E(RT-C58) = 14 Gpa and H(RT-C58) = 1.2 Gpa. This effect can be explained by the unique intrinsic functionalization of C58 cages: they comprise reactive surface sites constituted by annelated pentagon rings which give rise to covalently stabilized oligomers, C58C58C58, under our deposition conditions. Annealing, thick RT-C58 films up to 1100 K in ultrahigh vacuum results in HAT-C58, a new material with considerably modified electronic and vibrat