Thermally Triggered Dedeuteration of Cesium-doped Deuterofullerene Films

Abstract

We have probed the electronic structure and thermal stability of Cs-doped deuterofullerene thin films, Csx(C60Dn), as generated under ultrahigh vacuum conditions, using ultraviolet photoionization (UP) spectroscopy and thermal desorption spectroscopy. Mass spectra taken during sublimation indicate that deuterofullerene (C60Dn) and cesium fulleride regions (CsxC60) can coexist at elevated temperatures. The yield of Cs fulleride phases obtained by heating increases with the amount of Cs atoms initially deposited/intercalated into the deuterofullerene thin films. At highest initial Cs doses, a CsxC60 phase with doping degree of 4 ≤ x ≤ 6 is eventually generated. UP spectra of the as-prepared films taken before heating suggest that C60−D−d−Cs+d complexes are initially formed. Thermally activated conversion of these complexes into Cs fullerides can be followed by recording UP features characteristic for (increasing) C60-LUMO state occupation. The transition from cesium intercalated C60Dn into CsxC60 sets in at a temperature of 610 K and is completed by 670 K. This narrow transition temperature range is also characterized by synchronous desorption of Cs and D2. We conclude that Cs intercalation can significantly weaken >C−D bond strengths relative to C60Dn, thus facilitating thermally activated dedeuteration.