Desorption of C60 upon thermal decomposition of cesium C58 fullerides

A monodispersed fullerene material comprising exclusively C-58 cages was doped with Cs to generate CsxC58 films of various compositions. The resulting modified properties have been studied using a variety of surface analysis methods with emphasis on thermal desorption and ultraviolet photoelectron spectroscopies. Cs doping raises the thermal stability of C-58 films which are characterized by quasi-covalent cage-cage bonds between annelated pentagon sites. Desorption mass spectra show emission of significant amounts of C-60 at elevated temperatures implying that Cs doping can activate C-58 -> C-60 conversion in the condensed phase. In the case of saturated CsxC58 films, up to 4.5% of the initially deposited C-58 can be desorbed as C-60. From the spectroscopic data, we infer that Cs insertion and transport into the interstitial sites of the C-58 solid is accompanied by spontaneous electron transfer to the electronegative fullerene framework-leading to a weakening of intercage carbon-carbon bonds. At the same time, the overall cohesion of the solid film is enhanced by the formation of multiple ionic Cs+beta C58-delta interactions. Near 800 K, Cs+ activates/catalyzes concerted disproportionation reactions resulting in the transfer of C-2 from C-58(-delta) to neighbouring cages to yield C-60 (and C-56). Heating CsxC58 films to beyond this temperature range yields a (high temperature) stable reaction product with a significantly modified UP spectrum and a finite density of states at the Fermi level. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694831]