The chemistry of TEMPO layers was studied with XPS, providing insight into changes in chemical structure and attachment resulting from surface interactions. Overlaid XPS spectra collected in the N 1s region are shown in Figure , h, and i for deposition times of 5s, 300s, and 600s, respectively (see Figure for the fitted spectra). As a guide, we also show dotted lines indicating three common nitrogen environments (N, NO, NH2+) corresponding to the amine groups (primary, secondary and tertiary), the nitroxide group, and protonated monomer at 399, 400, and 401.5 eV, respectively. For samples exposed to 5 seconds of TEMPO plasma, we see that the N 1s environment on SiO2 and HOPG is centred at 399.2 eV due to a dominating N component and exhibit a tail at higher binding energies attributed to the NH2 + environment (Figure ), consistent with previous observations . In comparison, the N 1s spectra on Au(111) is significantly wider, and is centred at 400 eV, which is indicative of multiple chemical environments. The precise origin of this broadening is difficult to determine, and could be attributed to either an increased relative abundance of NO in the TEMPO film, (i.e. reduced molecular damage and higher functional group retention), or potentially the presence of nitrogen interaction with the Au surface .