Precursor size is typically discussed in terms of van-der-Waals volumes, leading to the assumption that small precursors like TMA show high risks of penetration. This has been shown recently by computational analysis, confirming the experimentally observed inability to achieve AS-ALD processes of Al2O3 using TMA. It was shown that TMA cannot only penetrate the inhibitor layer more effectively, but it is also more likely to react with reactive surface groups at the investigated SiO2 surface (Fig. .). The larger triethylaluminum (TEA) shows the same thermodynamic driving force for penetration and adsorbing to the surface. However, the reaction with the surface OH-groups at medium coverages is governed by the reactivity-reduction mechanism (Fig. .