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

Yoichi Yamada, Artem V. Kuklin, Sho Sato, Fumitaka Esaka, Naoto Sumi, Chunyang Zhang, Masahiro Sasaki, Eunsung Kwon, Yukihiko Kasama, Pavel V. Avramov, Seiji Sakai

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Abstract

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.

Original languageEnglish
Pages (from-to)23-30
Number of pages8
JournalCarbon
Volume133
DOIs
Publication statusPublished - 2018 Jul

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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    Yamada, Y., Kuklin, A. V., Sato, S., Esaka, F., Sumi, N., Zhang, C., Sasaki, M., Kwon, E., Kasama, Y., Avramov, P. V., & Sakai, S. (2018). Electronic structure of Li+@C60: Photoelectron spectroscopy of the Li+@C60[PF6] salt and STM of the single Li+@C60 molecules on Cu(111). Carbon, 133, 23-30. https://doi.org/10.1016/j.carbon.2018.02.106