Electron-energy-loss spectroscopy of K xC 60 and K-halides: comparison in the K 3p excitation region

Abstract

We have investigated the electronic structure of K x C 60 ( x=0–6) using low-energy electron energy loss spectroscopy (LEELS), especially focusing on the K 3p core-electron excitation spectra. It is found that the structure of the K 3p-excitation spectrum of K x C 60 quite differs from that of KCl. Furthermore, the K 3p-excitation LEELS of K 3C 60 has been revealed to be different from that of K 6C 60. K 3p electrons are excited into K 4s- and K 3d-derived empty states in both K x C 60 and KCl, but in the case of K x C 60 the K 3d-derived empty states have a rather complicated structure where several levels are not well separated. Consequently, K 3p-excitation LEEL spectra of K x C 60 show wide-spread plateau-like structures. The difference in the K 3p-excitation spectra of K 3C 60 and K 6C 60 is considered to originate from the different crystal field around K + cations in the C 60 molecular crystal.