Berlin 2018 – scientific programme
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O: Fachverband Oberflächenphysik
O 65: Focus Session: Structure and Chemistry of Metal-Oxide Surfaces III
O 65.5: Talk
Wednesday, March 14, 2018, 16:15–16:30, MA 005
Structural and electronic differences between tetragonal and monoclinic ZrO2 films on Rh(111) — •Peter Lackner, Zhiyu Zou, Sabrina Mayr, Ulrike Diebold, and Michael Schmid — Institute of Applied Physics, TU Wien, Vienna, Austria
The applications of zirconia (ZrO2) are manifold, e.g. as catalyst support or solid electrolyte in fuel cells. Despite the importance of the material, its surface has not yet been studied thoroughly on an atomic level. This has a simple reason: ZrO2 has a band gap of more than 5 eV and is therefore non-conductive, which makes the study of bulk zirconia with methods like x-ray photoelectron spectroscopy (XPS) impracticable, and scanning tunneling microscopy (STM) close to impossible.
To circumvent this issue, we prepared five-monolayer-thick layers of ZrO2(111) [1] on Rh(111) using a home-build UHV-compatible sputter source [2]. By annealing in pO2 = 10−6 mbar at T < 700 ∘C, we prepared tetragonal ZrO2, while above 700 ∘C a phase transformation to monoclinic ZrO2 – the stable bulk structure – was observed. Tetragonal ZrO2 was atomically resolved, showing the expected (2 × 1) structure (w.r.t. cubic ZrO2). The domain size grows with annealing temperature; at 650 ∘C, domains of 40 × 40 nm2 are common. For monoclinic ZrO2, a (2 × 2) structure was resolved. The two phases have distinct binding energies in the Zr3d region, with an unexpectedly high Δ EB of 1.4 eV, pointing towards an unusual structure in one of the two.
[1] Meinel et al., Phys. Rev. B 74, 235444 (2006).
[2] Lackner et al., Rev. Sci. Instrum. 88, 103904 (2017).