Incommensurate Moiré overlayer with strong local binding: CoO(111) bilayer on Ir(100)

Abstract

Incommensurate relaxed overlayer Moiré structures are often interpreted as systems with weak lateral variations of the binding potential and thus no structural modulations in the overlayer material. We discuss here the example of a CoO(111) bilayer on Ir(100), which is a relaxed overlayer with strong structural response to the lateral modulation of interface properties but nevertheless is incommensurate. By means of DFT calculations we quantitatively reproduce all the structural parameters of the CoO(111) bilayer on Ir(100) as proposed by a recent LEED analysis [C. Ebensperger et al., Phys. Rev. B 81, 235405 (2010)]. The calculations predict energetic degeneracies with respect to registry shifts of the CoO(111) film along [011]. Large-scale, low-temperature STM topographies reveal that the true structure of the film is incommensurate in this direction, exhibiting a onedimensional Moiré pattern with a period of about 9.4 aIr. From DFT calculations for limiting (periodic) models, we can sample the potential landscape of the cobalt and oxygen atoms in the Moiré structure across the Ir(100) unit cell. We find that despite the non-commensurability of the film, the binding to the substrate is site specific with strong attraction and repulsion points for both cobalt and oxygen atoms, leading to severe local distortions in the film. The lateral modulation of the structural elements within the oxide film can be understood as a combination of the lateral variation in the Co-Ir binding potential and additional O-Ir binding.

Adsorption and Intermolecular Interaction of Cobalt Phthalocyanine on CoO(111) Ultrathin Films: An STM and DFT Study

“…47 All atomic coordinates were relaxed until the residual forces were below 0.01 eV/Å. In order to maintain consistency with our previous studies 36,45 the calculations were performed for a substrate Ir lattice constant of 3.88 Å, corresponding to the bulk value determined for a PBE functional. Typical bond lengths for the CoPc molecule are 1.91 Å for the Co-N bond, 1.09 Å for the C-H bond 1.40 Å and 1.45 Å for the C-C bonds in the benzene and imide ring, respectively.…”

X-ray analysis of wurtzite-type CoO(111) films on Ir(001): Correlation of structure, stress, electronic, and magnetic properties

“…On the other extreme, for a single CoO(111) bilayer, ordered patches of a h-BN type and a RS type CoO phase were proposed [1]. This model was later corroborated by scanning tunneling microscopy and density functional theory (DFT) calculations [5,6].…”

“…We applied the generalized gradient approximation (GGA) for the exchange-correlation functional [37] and the GGA + U approach of Dudarev [38] to describe the localized nature of the Co d states with the effective parameter U * = U − J = 1 eV as was suggested in the previous studies [5,6].…”

“…Ultrathin films of CoO have been intensely studied in recent years because of their intriguing structural and magnetic properties [1][2][3][4][5][6]. This is also due to the intimate relation between structure and magnetic properties and the large variety of structures observed for ultrathin CoO films depending on stoichiometry and film thickness.…”

Thermal evolution of cobalt deposits on Co3O4(111): atomically dispersed cobalt, two-dimensional CoO islands, and metallic Co nanoparticles

“…33,34 Here, various other factors were considered, in particular the presence of oxygen vacancies and surface Co 2+ ions. [38][39][40][41][42][43][44][45][46][47][48] In a unique fashion, these films allow varying the stoichiometry, the surface orientation, the film thickness, and the defect density. 29 The present work aims at the development of new cobaltoxide-based model systems which allow us to study their surface chemistry under well-controlled ultrahigh vacuum (UHV) conditions.…”