a, HS-AFM images of the monolayer PNR shown in Extended Data Fig. 5f, taken immediately (top) and after six days of air exposure (bottom). Scale bars, 50 nm. b, Normalized histograms showing the width (left) and height (right) of the PNR in a, taken immediately (blue) and after six days in air (yellow). Each histogram has been fitted with a Gaussian function (red). c, Width (left) and height (right) of the PNR during six days in air, taken from fits to the histograms as shown in b. Data are means ± s.d. from the fit. For the histograms in b, the numbers of individual measurements are: 2,086 (day 0 width); 16,565 (day 6 width); 45,850 (day 0 height), and 281,980 (day 6 height). d, HS-AFM images of the bilayer PNR shown in in Extended Data Fig. 5e. Scale bars, 50 nm. e, f, As for b, c, but taken for the bilayer ribbon in d. For the histograms in e, numbers of individual measurements are: 8,343 (day 0 width); 4,169 (day 6 width); 65,614 (day 0 height), and 40,520 (day 6 height). g, Evolution of the Raman A g 1/A g 2 integrated intensity ratio, the A g 2/background intensity ratio, A g 2 position and A g 2 width (FWHM, full width at half-maximum), extracted by analysing maps of 90–100 independent spectra taken over the same location from a sample of PNRs drop-cast onto graphite (data points are means ± s.d. taken from fits; see Methods). h, Evolution of XPS spectra (black dots, data; red curves, fits to P peaks; blue curves, fits to P–O peaks) taken from a sample of PNRs drop-cast onto graphite as a function of increasing air exposure. i, Normalized absorbance at 465 nm (black dots) as a function of time for the same solution of PNRs in NMP over 50 days without exposure to air. A photograph of the solution is in the inset. The red curve is an exponential function fit to the data (see Methods).