In mixed metal oxides we find, using maps of their composition acquired while growth takes place, that the nucleation of a new phase can trigger a compositional change in the previously present phase.

The growth of mixed cobalt-iron oxides on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy has been monitored in real time and real space by x-ray absorption photoemission microscopy. The initial composition is a mixed Fe-Co (II) oxide wetting layer reflecting the ratio of the deposited materials. However, as subsequent growth of three dimensional spinel islands nucleating on this wetting layer takes place, the composition of the oxide in the wetting layer changes as iron is transferred into the spinel islands. The composition of the islands themselves also changes during growth.

S. Ruiz-Gómez, A. Mandziak, J. E. Prieto, M. Aristu, E. M. Trapero, G. D. Soria, A. Quesada, M. Foerster, L. Aballe, J. de la Figuera, "A Real Time XAS PEEM Study of the Growth of Cobalt Iron Oxide on Ru(0001)", J. Chem. Phys. 152 (2020) 074704 , DOI: 10.1063/1.5140886