Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 47: Metal Substrates I

O 47.5: Talk

Wednesday, March 20, 2024, 11:45–12:00, MA 043

Cluster formation and ordering at high CO coverages on Ru(0001): A combined DFT and STM study — •Hannah Illner¹, Sung Sakong², Axel Gross², and Joost Wintterlin¹ — ¹Ludwig-Maximilians-Universität München, Germany — ²Universität Ulm, Germany

Dense coverages of adsorbates on metal surfaces provide insight into the relation between metal-adsorbate and adsorbate-adsorbate interactions. Depending on the variation of the adsorption energy with binding site, different types of structures can be formed in dense layers, namely moiré structures, structures formed by domain boundaries, and cluster structures. On Ru(0001), CO at 0.58 monolayers (ML) forms a closed ring cluster structure consisting of seven molecules in (2√3 × 2√3)R 30^∘ symmetry. Here we present a study in which CO at higher coverages than 0.58 ML is investigated by low-temperature STM and DFT simulations. We identify six compact cluster structures, which are separated by CO-free Ru rows and a triangular arrangement of CO molecules at the junctions. We discuss how the local configurations stabilize the cluster configuration. By analyzing the Fourier transform of the STM image we provide a new explanation of the LEED pattern of the CO adlayer, that previously has been interpreted as resulting from a moiré structure. The newly identified structures clarify the long-standing conflict between the assumed structure and the vibrational spectroscopy data.

Keywords: High adsorbate coverage; CO adsorption; Ordering; Cluster formation; Local configurations