Raman spectroscopy was carried out in a Renishaw inVia Raman Spectrometer using a laser excitation wavelength of 514 nm at 100x magnification, operating at approx. 1 mW. The spectra were acquired through a spectrum window of 250-3500 cm -1 . In all experiments, the 52100 substrate does not contribute to any signals within the observed Raman spectral window.