Microscopic insights into the pathways of mass transport in oxygen-induced reversible morphologic transformation of faceted rhenium surfaces*

The shape (morphology) of supported metal nanoparticles often varies under reaction conditions, which in turn can induce changes in their catalytic activity. Faceted metal surfaces, free of any support materials, can be used as model catalysts or templates for synthesizing new catalysts due to their well-defined facet structures and controlled facet sizes on the nanometer scale. Here we present reversible morphology changes on a faceted Re($11\bar{{2}}1)$ single crystal surface under ultra-high vacuum (UHV) conditions, which are controlled by tuning adsorbed oxygen coverage, using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We find microscopic structural connections between the various morphologies on the faceted Re($11\bar{{2}}1)$ surface, which provide a natural explanation for the mass transport pathways in the structural evolution. Our findings motivate a more detailed future exploration of oxygen-induced morphology transitions on catalytically active metal single crystal surfaces, which is of importance for development of new catalysts operating under oxygen rich conditions.