Full coverage of N atoms was also investigated, and similar to the NH terminated surfaces N terminations was also found to form both N monomer and N2 dimers on the surface. The N monomer, Figures 8 and S7 As with the N2H2 dimer, the N2 dimer also has two different configurations in which the dimer is either at the hollow or at the bridging site, Figures and. For AlN the only reconstruction possible is with the dimer in the hollow site. In this configuration one of the N atoms binds to a single metal site with bond length 1.91 Å, while the other N atom binds to the two other metal sites around the hollow site with almost equal bond length (2.10 and 2.25 Å). This causes the adatom to be forced into a bucking configuration with the single bonded nitrogen raised further from the surface than the double bonded. For GaN only the bridging dimer is possible, where the dimer is placed between two surface metal sites, with bonds of 2.18-2.21Å. The N-N bond