Self-organization of ultrathin vanadium oxide layers on a Rh(111) surface during a catalytic reaction. Part II: A LEEM and spectromicroscopy study

Upon exposure of ultrathin vanadium oxide layers on Rh(111) (θV ∼ 0.2 MLE) to the H2 + O2 reaction, we observe the reversible formation of stationary macroscopic stripe patterns caused by lateral redistribution of the vanadium oxide. These patterns are investigated in the 10–6 mbar range at around 750 K, employing LEEM (low energy electron microscopy), microprobe-LEED and microprobe-XPS. The stripe patterns evolve via several stages and structures: essentially, vanadium oxide nanoislands with a (√7 × √7)R19.1° structure are reduced from V+5 to V3+ and condense into a macroscopic (2 × 2) oxide phase upon increasing p(H2). The orientation of the stripe patterns is determined by step bunches, which introduce a diffusional anisotropy. The stationary patterns are discussed within the concept of reactive phase separation.