Atomic Layer Deposition (ALD) has gained increasing attention for the sub-nm growth of high permittivity (k) rare earth oxide films. State of the art device operation heavily depends on the oxide/semiconductor interface properties. In this work, we address mainly through HRTEM-EELS experiments interface issues for ALD-grown Lu2O3/Si and La2O3/Si interfaces. Complementary results from GIXRD and electrical measurements on selective samples are presented. We show that, after exposure to air, Lu2O3 films capped with an Al2O3 layer are essentially free of interfacial layer formation, even if the starting Si surface is chemically oxidized. We also demonstrate that the La2O3 film reactivity with Si can be controlled up to a certain extent by appropriately choosing the ALD precursor combination. In particular, the La (Cp) 3+ O3 scheme favours over the La (Cp3)+ H2O one in terms of a (i) smaller low-k interfacial layer …