X-ray photoelectron spectroscopy. XPS was performed using a Kratos Analytical AXIS Supra spectrometer with a monochromatic Al Kα 1486.7 eV Xray source, operating at 15 kV, 15 mA, and equipped with an electron gun for charge neutralisation. The binding energies were referenced to the C 1s peak at 285.0 eV. For the 5 s set of samples on HOPG, the C 1s peak was referenced to 284.5 eV due to the pure sp2 hybridisation of the substrate dominating the polymer signal. All the spectra were analysed using CASAXPS (Casa Software Ltd, UK). Atomic force microscopy. AFM images were collected using a Bruker Multimode 8 AFM equipped with a Nanoscope V controller and operated in the PeakForce mode. NuNano Scout 70 probes were used with a nominal resonant frequency of 70 kHz, 2 N/m cantilever stiffness, and less than 10 nm probe radius. To measure the polymer thickness, the coating was first scratched in contact mode in a 2 µm x 2 µm area and then scanned in peak force mode to check that the film was completely removed. The thickness was computed from peaks of height distribution corresponding to the area inside and outside the scratch. The uncertainty associated with the measurement depends on the peaks FWHM. The RMS roughness was computed using Gwyddion by analysing 500 nm x 500 nm scans. Density Functional Theory. Using the density functional code SIESTA the optimum geometries of isolated TEMPO molecules were obtained by relaxing the molecules until all forces on the atoms were less than 0.01 eV / Å. A double-zeta plus polarization orbital basis set, norm-conserving pseudopotentials, and an energy cut-off of 250 Rydbergs defining the real space grid were used. Both GGA and van der Waals functionals were employed to find the most energetically favourable structures.