  Ostwald ripening is a well-known physicochemical phenomenon in which smaller
particles, characterized by high surface energy, dissolve and feed the bigger
ones that are thermodynamically more stable. The effect is commonly observed in
solid and liquid solutions, as well as in systems consisting of supported metal
clusters or liquid droplets. Here, we provide the first evidence for the
occurrence of Ostwald ripening in an oxide-on-metal system which, in our case,
consists of ultrathin iron monoxide (FeO) islands grown on Ru(0001)
single-crystal support. The results reveal that the thermally-driven sintering
of islands allows altering their fine structural characteristics, including
size, perimeter length, defect density and stoichiometry, which are crucial,
e.g., from the point of view of heterogeneous catalysis.
