Journal Article Electronic structure of Li+@C60: Photoelectron spectroscopies of the Li+@C60[PF6-] salt and STM of the single Li+@C60 molecules on Cu(111)

Yamada, Y.  ,  V. Kuklin, A.  ,  Sato, S.  ,  Esaka, F.  ,  Sumi, N.  ,  Zhang, C.  ,  Sasaki, M.  ,  Kwon, E.  ,  Kasama, Y.  ,  V. Avramov, P.  ,  Sakai, S.

133pp.23 - 30 , 2018-03
Description
We report the scanning tunneling microscope (STM) observation of the Li+ ion endohedral C60 on Cu(111), prepared by means of evaporation of a high-purity Li+@C60[PF6−] salt. The electronic state of Li+@C60 in the Li+@C60[PF6−] salt was also determined using photoemission and X-ray absorption spectroscopy, along with the density functional theory (DFT) calculations. In the salt, Li and PF6 had nearly single positive and negative charge, respectively; thus the C60 cage was practically neutral. The salt decomposed under ultra-high vacuum while heating at 400 °C. This allowed the selective deposition of Li+@C60 on Cu(111). Although secondary-ion mass spectroscopy of the deposited Li+@C60 film showed a decrease in the Li-content during evaporation, Li+@C60 was successfully identified using STM. The DFT calculations of Li+@C60 on Cu(111) suggested that the Li+ ion was singly charged and the location of the Li+ ion was displaced in an upward direction, which altered the local density of states in an upper section of C60, especially for LUMO+2. The calculated results were mostly in agreement with the bias-dependent STM and dI/dV images. However, an inconsistency was observed between the calculation and experiments in case of empty state imaging where tip-induced displacement of the Li+ ion may occur.

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