Surface chemistry of Fe2O3 nanoparticles on ultrathin oxide layers on Si and Ge

In this paper, we report on a comparative study of the effect of Fe₂O₃ nanoparticles (NP), introduced onto a thin oxide layer formed on silicon and germanium surfaces, on the thermal decomposition pathway of the individual oxide layers. On both the surfaces, NP of Fe₂O₃ undergo a reduction reaction through a bonding partner change reaction, where the oxygen atoms change from Fe to Si or Ge. On both the surfaces, annealing results in the conversion of the suboxide-like species to dioxide-like species (SiO_x to SiO₂ and GeO_x to GeO₂ respectively for Si and Ge surfaces), until the oxide layer decomposes following the desorption of the respective monoxide species (SiO and GeO). Both the Si and Ge corelevels show a larger chemical shift (4.1 and 3.51 eV in Si 2p and Ge 3d corelevels, respectively) for the as-prepared oxide samples with the NP, at room temperature compared to that without the NP (3.7 and 3.4 eV), indicating a catalytic enhancement of the dioxide formation. Selective formation of silicon oxides leads to encapsulation of the nanoparticles and acts like a protective layer, preventing the oxidation of Fe.