Fig. 4.

²⁷Al ssNMR spectra of AlNC oxide following various annealing protocols. (A) AlNC illustration showing the most common Al-O coordination states present in the oxide shell. ²⁷Al ssNMR spectra of the oxide region of (B) unannealed AlNCs, (C) He-annealed AlNCs, (D) O₂-annealed AlNCs, and (E) vacuum-annealed AlNCs, with accompanying bar plot showing relative quantities of 4-coordinate (green), 5-coordinate (blue), and 6-coordinate (red) alumina sites. The solid gray line represents experimental data, and the dashed black line represents the numerical fit to the data.