Extended Data Figure 5: TOF-SIMS spectra and mapping of the contact region.

See Supplementary Methods for experimental details. a, Spectrum of material from inside the contact spot (denoted with a circle). b, Spectrum of material from outside the contact spot (denoted with a circle). c, Spectrum after subtraction of the spectra in a and b, verifying the presence of carbon and other hydrocarbon fractions on the contact spot (subtraction has been done after normalization of each spectrum according to total ion counts). d, Two-dimensional TOF-SIMS images from the contact spot and surrounding regions, confirming the presence of carbon and hydrocarbon fractions in the contact spot. The strong carbonaceous signals in the far outside section of the perimeter are due to the carbon-rich debris layers shown in Figs 2b and 4a.