HREELS study of the intercalation of K atoms in C60 monolayers

Extra- and intramolecular vibrations of K-doped C60 monolayers adsorbed on Ag(111) and Cu(111) have been studied by high-resolution electron energy loss spectroscopy (HREELS) in reflection geometry. Intramolecular modes are used to assess the electronic occupancy of C60, which is increased by intercalating K atoms. Regardless of the charge donated by the substrate, extramolecular modes have characteristic frequencies for K1C60, K2C60, and K4C60 monolayers. When the K concentration exceeds four, the K-doped monolayers exhibit different structures on Ag(111) and Cu(111).