An Electronic and Structural Study of Growth Iridium Oxide on Ir(100)

Lu-Hsin Lee^1*, Chia-Hsin Wang², Yaw-Wen Yang², Meng-Fan Luo¹

¹Department of Physics, National Center University, Tuoyuan, Taiwan
²National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Lu-Hsin Lee, email:luca10234@gmail.com

We study the growth of iridium (Ir) oxides on Ir(100) substrate, with varied surface probe techniques including reflection high energy electron diffraction (RHEED), ambient pressure X-ray photoelectron spectroscopy (APXPS), and scanning tunneling microscopy (STM). A recent study shows that the oxidation of Ir(100) surface under ambient oxygen pressure conditions produces reactive iridium oxides, disparate from those grown under high or ultrahigh vacuum conditions [1]. However, how the iridium oxides evolve structurally with the oxygen pressure remains unknown. The present study aims to shed light on the structural evolution. The structure evolution of iridium oxide depends not only on the oxygen dosage(D) but pressure, especially in the near-ambient pressure range. As the oxygen dosage increase and the oxygen pressure is under medium vacuum range, the RHEED patterns evolve from 2×1 line (D <2×10⁸L), dot (2×10⁸L< D <6×10⁹L), to line and dot coexist state (6×10⁹L < D). The intensity of Ir 4f(IV) oxide state in Ir 4f spectrums do not increase a lot in the XPS experiment. If we increase the oxygen pressure to 1torr, surprisingly, it shows totally different RHEED pattern, consisting of line, square, and dot in the pattern, compared with the one grown in a medium vacuum. The Ir 4f(III) and Ir 4f(IV) dominate the spectrum and the Ir 4f bulk state disappear in the XPS result. The structure grown under 1torr oxygen can’t be accumulated by increasing the time of exposing the sample to 0.1torr oxygen. The unintuitive result indicates that different oxygen pressure during iridium oxide growth plays an important role in determining the surface structure and valance electron properties.

[1] Z. Liang, T. Li, M. Kim, A. Asthagiri and J. F. Weaver, Low-temperature activation of methane on the IrO₂ (110) surface, Science 356, 299 (2017)

Keywords: Iridium, Oxide, XPS, RHEED