Raman spectroscopy was performed using a Renishaw inVia microscope with a 514 nm excitation laser with a power of 1 mW and a 100 x objective and a grating 2400 l/mm. For AFM imaging, a JPK NanoWizard atomic force microscope was operated in non-contact mode. SEM was carried out with an accelerating voltage of 10 kV. XPS was conducted using an ESCA2SR spectrometer (ScientaOmicron GmbH) equipped with a monochromated Al Kα radiation (1486.6 eV, 20 mA emission at 300 W, 1 mm spot size) with a base vacuum pressure of ~1 × 10 -9 mbar. A low energy electron flood source (FS40A, PreVac) was used to achieve charge neutralisation. C-C in the C1s photoelectron peak at 285 eV was used to perform binding energy scale calibration.