Plasma polymerisation. Plasma polymerisation of TEMPO (Alfa Aesar, purity ≥ 98%) was performed with a custom-built glass barrelled plasma reactor. The glass barrel of the reactor was a QVF process pipe (De Dietrich, UK) -dimensions 500 mm length, 100 mm diameter, clamped between two custom-made steel end plates which serve as ground electrodes. The system was evacuated using an Edwards RV3 rotary vane pump (base pressure: c. 2 x 10 -3 mbar). The pressure within the system was monitored by a Thermovac TTR 96N SC Pirani gauge and Display One Controller (Leybold UK Ltd). An in-line liquid nitrogen cold trap was installed to enhance the system base pressure and prevent monomer vapours from reaching the rotary pump. Plasma was ignited using a RFG-C-100-13 power generator and automatic matching network (Coaxial Power System Ltd, Eastbourne, UK), operated at a frequency of 13.56 MHz, connected to a 1 cm thick copper braid (Tranect Ltd, Liverpool, UK) wrapped around the glass barrel three times. Sample wafers include SiO2 (Inseto, UK), HOPG (Mickromasch), and Au(111):mica (Georg Albert PVD) placed 12 cm away from the ground electrode through which the monomer enters the reactor. SiO2 was precleaned using ultrasonication, HOPG was exfoliated with scotch-tape, and Au(111) was cleaned via standard sputter-annealing cycles under UHV conditions. After the chamber was evacuated the monomer valve was opened and the pressure adjusted to reach 10 Pa by partially closing the valve to the pump and keeping the monomer flask in a water bath at 25 °C. The polymerisation was performed at a nominal power of 5 W for 5, 300, and 600 s after the plasma ignition.