D. Díaz-Fernández, J. Méndez, F. Yubero, G. Domínguez-Cañizares, A. Gutiérrez, L. Soriano
Surface and Interface Analysis, 46 (2014) 975-979
doi: 10.1002/sia.5366

The growth of Cobalt oxides by reactive thermal evaporation of metallic Cobalt in an oxygen atmosphere on a series of oxide substrates, namely SiO₂, Al₂O₃ and MgO, has been chemically and morphologically studied by means of XPS and atomic force microscopy (AFM). The XPS results reveal that cobalt oxide grows as CoO (Co²⁺) for coverages up to some tens of equivalent monolayers on all substrates. For larger coverages, the formation of the spinel oxide Co₃O₄ has been observed. AFM and XPS quantification allowed us to determine the way of growth of CoO on all substrates, being of Volmer–Weber (i.e. islands) mode for SiO₂, whereas for Al₂O₃ and MgO, the growth follows the Frank-van der Merwe (i.e. layer-by-layer) mode. The results are discussed in terms of the mismatch of the lattice parameters of the CoO adsorbates with the substrates.