The investigated adsorption pathway for GaN (Fig. in the supplementary material ) and InN (Fig. ) follow a very similar path, starting from the methyl terminated surface previously found as the final product after a self-limited adsorption cycle of TMG/TMI. This surface has a methyl group on top of each surface metal atom, with a bond length of 1.97 Å for GaN and 2.18 Å for InN, pointing almost perpendicular to the surface. 1c and S1c), physiosorbed CH4 above the NH2 substituted surface (D) (Figs. and), and the NH2 substituted surface with CH4(g) (E) (Figs. and). The energies of the adsorption paths on GaN and InN are given in Tables I and II, respectively, and graphically in Fig. . Table . Energy (in kJ mol -1 ) for NH3 chemisorption pathway on GaN. All energies are relative to the methyl terminated surface and gaseous NH3 (A). When NH3 is introduced to the surface, it is sterically blocked from forming a bond to the Ga/In surface atoms by the methyl groups. This causes the NH3 molecule to form a very week physisorption, with the surface at a large distance (2.9 Å above the methyl groups). The distance is much larger than the expected distance for a covalent bond and the low adsorption energy indicates only non-covalent interactions between NH3 and the surface. NH3 is therefore expected to be able to quickly diffuse over the surface as well as easily desorb.