Steric effects -the three dimethylamido ligands of TDMAA suggest a planar coordination around a sp 2 -hybridized Al atom. The four ligands of TDMAT suggest a tetrahedral coordination around a sp -hybridized Ti atom. The sp 2 -hybridized Al atom, with a lone p-orbital should be more susceptible to a nucleophilic attack from a surface amine group with a free electron pair on the nitrogen atom. This suggests that Al is more easily incorporated in the films.