title: Core-level spectroscopy to probe the oxidation state of single europium atoms.
abstract: The valence of individual europium atoms confined in carbon nanotubes is successfully measured by using core-level electron energy loss spectroscopy. Changes in the oxidation state at the atomic scale have been observed in Eu atomic chains exposed to oxygen. A transitory behavior has been identified where multiple atoms show a signal consistent with a sum of Eu^{2+} and Eu^{3+}. This indicates that single atoms change their valence state multiple times during the reaction, suggesting that oxidation in confined spaces and with extra energy input (from the electron beam) might not be a simple one step electron transfer event.
authors.affiliation: Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan.
authors.forename: Luiz H G
authors.initials: LH
authors.lastname: Tizei
authors.affiliation: Department of Chemistry, Nagoya University, Nagoya 468-8602, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Nakanishi
authors.affiliation: Department of Chemistry, Nagoya University, Nagoya 468-8602, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Kitaura
authors.affiliation: Department of Chemistry, Nagoya University, Nagoya 468-8602, Japan.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Shinohara
authors.affiliation: Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan.
authors.forename: Kazu
authors.initials: K
authors.lastname: Suenaga