ALD precursors for group 13 elements are Lewis acids and thus have the tendency to form bonds with Lewis bases. This includes the heteroatoms of the ligands or even the alkyl groups and leads to dimerization of the precursor (Fig. .). Fig. . Dimerization reaction of Al precursors shown at the example of TMA with the equilibrium constant Kdiss for the dissociation defined via the partial pressures pmonomer and pdimer and standard pressure p0. Reprint with permission from reference .