Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 10: Oxides I: Growth and Characterization
O 10.2: Talk
Monday, March 16, 2020, 10:45–11:00, WIL B321
Epitaxial growth of wurtzite CoO(0001) on Au(111) and conversion into rocksalt CoO(001) — •Maximilian Ammon1, Lutz Hammer1, Sara Baumann1, Andreas Raabgrund1, Tilman Kisslinger1, Josef Redinger2, and M. Alexander Schneider1 — 1Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg — 2Institut für Angewandte Physik & CMS, TU Wien
Wurtzite (w-)CoO is a semiconducting [1] and antiferromagnetic [2] material. We establish the preparation parameters for the epitaxial growth of closed w-CoO films on Au(111) of several nanometer thickness. A LEED-IV analysis (Rp = 0.112) proves the structure to be w-CoO (a = 3.26 Å, c=5.22 Å) with small relaxations in the 1. surface layer only. DFT calculations based on hybrid functionals or LDAU schemes reproduce all measured geometrical parameters very well.
We used STS and DFT to study the electronic properties of these w-CoO films. Films with a thickness of 15 bilayers (BL) ≈ 4 nm exhibit a bandgap of 1.8± 0.2 eV around EF as measured by STS that is comparable to the optical bandgap quoted in literature [1]. We observe a reduction of the bandgap with decreased film thickness.
Annealing of w-CoO(0001) films to 600 ∘C induces a phase transition to closed rocksalt (rs-)CoO(001) films. Experiments with ultra-thin films (≤ 4 BL) show that this conversion results in films of homogeneous thickness corresponding to three cubic lattice constants of rs-CoO (≈ 1.2 nm).
[1] Wang et al., Chem. Commun. 54, 13949 (2018)
[2] Roca et al., Small 14, 1703963 (2018)