Konicek, Andrew R.Grierson, D. S.Gilbert, P.U.P.A.Sawyer, W. G.Carpick, Robert WSumant, A. V.2023-05-222023-05-222008-06-112011-01-19https://repository.upenn.edu/handle/20.500.14332/39986The impressively low friction and wear of diamond in humid environments is debated to originate from either the stability of the passivated diamond surface or sliding-induced graphitization/rehybridization of carbon. We find ultralow friction and wear for ultrananocrystalline diamond surfaces even in dry environments, and observe negligible rehybridization except for a modest, submonolayer amount under the most severe conditions (high load, low humidity). This supports the passivation hypothesis, and establishes a new regime of exceptionally low friction and wear for diamond.EngineeringMechanical EngineeringArticle