As already discussed in Section 3.1, we observe the formation of TDMAH-derived surface species. The absence of acidic protons on CoO(100) at 400 K and the fact that nucleation still takes place implies that TDMAH must react with CoO(100) via a different mechanism, i.e. not by splitting off -NMe2 ligands as volatile HNMe2. In fact, the data suggests formation of two very similar but distinguishable ligand species. We propose that TDMAH reacts with CoO(100) in a Lewis acid-base reaction. As a result, -Hf(NMe2)x adsorbents are formed on surface oxygen (electron pair donor) and (4-x) -NMe2 adsorbents are formed on surface cobalt ions (electron pair acceptor) for each reacting TDMAH molecule. We base this hypothesis on two distinct observations. Firstly, we observe that the amount of TDMAH-derived surface species reacting in the first ALD cycle is larger than in later cycles (see Section 3.1). This is consistent with the idea that the -NMe2 ligands are not converted into volatile by-products but also bind to the surface in the first half cycle. Secondly, the described signals contain two overlapping bands, suggesting two very similar surface species. We tentatively assign the lower wavenumber components to -NMe 2 ligands interacting with surface cobalt. As mentioned above, the -Hf(NMe2)x signals at around 1250 and 950 cm -1 contain contributions from ν(Hf-N) stretching modes. As a result, we expect a slight shift for -NMe2 signals containing contributions from ν(Co-N) stretching modes. Interestingly, the two components of each signal change their ratio until saturation. At low exposures, the cobalt-bound -NMe2 signals dominate the spectrum. At the highest exposure, the -Hf(NMe2)x signals dominate the spectrum. This indicates a change in stoichiometry over the course of the nucleation. Similar to the nucleation of TDMAH on pristine Co3O4(111) and Co3O4(111) covered with 4′-hydroxy-4biphenylcarboxylic acid , we suggest that TDMAH loses more ligands at the beginning of the nucleation than at later stages. Accordingly, the number x of Hf bound ligands increases over the course of the experiment. Finally, we note that the slight decrease in peak area observed for the signal at around 950 cm -1 indicates a reorientation of the surface species near saturation.