similarly shows a common evolution, but ML (Cu) shows a contrasting trend line. In comparing the peak areas of the G and D bands, we observe trends that show that there is a relationship between the A D /A G ratios on both ML (Ni) and ML (Cu) tracks, to the number of defects generated over longer sliding times previously observed when analyzing the other Raman spectroscopic markers discussed above. A more detailed discussion on the relationship between the evolution of the Raman spectroscopic markers with the evolution of the graphitic tribofilm can be found in the Supporting Information section.