When Surface Dynamics Fakes Symmetry -- Oxygen on Rh(100) Revisited

TL;DR

This study reveals that surface fluctuations can create false symmetry signals in surface phases, affecting interpretation of surface structure and reactivity, demonstrated on oxygen-covered Rh(100) using LEED, STM, and DFT.

Contribution

It uncovers how surface fluctuations can mislead symmetry analysis, emphasizing the importance of local symmetry in surface chemistry, with combined experimental and theoretical approaches.

Findings

Fluctuating ordered domains can mimic different symmetries in surface analysis.

Local symmetry influences CO binding energy and reactivity.

Surface fluctuations can lead to misinterpretation of surface periodicity.

Abstract

Heating a long-range ordered adsorbate phase beyond its stability temperature does not necessarily result in a disordered phase, it can also break up into heavily fluctuating ordered domains. Temporal and/or spatial averaging over these fluctuations may give the impression of both a wrong periodicity and a false local symmetry. This can happen even below liquid-nitrogen temperature, so that the true nature of the phase might remain undetected. We demonstrate this scenario at the catalytically active Rh(100) surface covered by 1/2 monolayer of oxygen, using quantitative low energy electron diffraction (LEED), variable-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). Using the example of CO adsorption, we show that local symmetry can have a decisive influence on the binding energy and thus the chemical reactivity.