Room temperature redox reaction by oxide ion migration at carbon/Gd-doped CeO2 heterointerface probed by an in situ hard x-ray photoemission and soft x-ray absorption spectroscopies

Takashi Tsuchiya; Shogo Miyoshi; Yoshiyuki Yamashita; Hideki Yoshikawa; Kazuya Terabe; Keisuke Kobayashi; Shu Yamaguchi

doi:10.1088/1468-6996/14/4/045001

Room temperature redox reaction by oxide ion migration at carbon/Gd-doped CeO₂ heterointerface probed by an in situ hard x-ray photoemission and soft x-ray absorption spectroscopies

Sci Technol Adv Mater. 2013 Jul 8;14(4):045001. doi: 10.1088/1468-6996/14/4/045001. eCollection 2013 Aug.

Authors

Takashi Tsuchiya¹, Shogo Miyoshi², Yoshiyuki Yamashita³, Hideki Yoshikawa³, Kazuya Terabe⁴, Keisuke Kobayashi³, Shu Yamaguchi²

Affiliations

¹ Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan; WPI Center for Materials Nanoarchitechtectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
² Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656, Japan.
³ NIMS Beamline Station at SPring-8, National Institute for Materials Science, Kouto 1-1-1, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
⁴ WPI Center for Materials Nanoarchitechtectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.

Abstract

In situ hard x-ray photoemission spectroscopy (HX-PES) and soft x-ray absorption spectroscopy (SX-XAS) have been employed to investigate a local redox reaction at the carbon/Gd-doped CeO₂ (GDC) thin film heterointerface under applied dc bias. In HX-PES, Ce3d and O1s core levels show a parallel chemical shift as large as 3.2 eV, corresponding to the redox window where ionic conductivity is predominant. The window width is equal to the energy gap between donor and acceptor levels of the GDC electrolyte. The Ce M-edge SX-XAS spectra also show a considerable increase of Ce³⁺ satellite peak intensity, corresponding to electrochemical reduction by oxide ion migration. In addition to the reversible redox reaction, two distinct phenomena by the electrochemical transport of oxide ions are observed as an irreversible reduction of the entire oxide film by O₂ evolution from the GDC film to the gas phase, as well as a vigorous precipitation of oxygen gas at the bottom electrode to lift off the GDC film. These in situ spectroscopic observations describe well the electrochemical polarization behavior of a metal/GDC/metal capacitor-like two-electrode cell at room temperature.

Keywords: 10.06; 30.07; 30.09; ReRAM; atom transistor; atomic switch; hard x-ray photoemission spectroscopy; ionics; redox reaction.