Konicek, Andrew R.

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2008 - 20102
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  • Publication
    Thermal Stability and Rehybridization of Carbon Bonding in Tetrahedral Amorphous Carbon
    (2010-02-11) Grierson, David S; Konicek, Andrew; Sumant, A V; Friedmann, T A; Carpick, Robert W; Sullivan, J P
    We preform a quantitative investigation of the energetics of thermally induced sp3 → sp2 conversion of carbon-carbon bonds in tetrahedral amorphous carbon (ta-C) films by using near edge x-ray absorption fine structure (NEXAFS) and Raman spectroscopy. We investigate the evolution of the bonding configuration in ta-C thin films subjected to high temperature annealing in flowing Argon gas using a rapid thermal annealing furnace over the range of 200-1000 ºC. We observe no substantial change in bonding structure below 600 ºC, and by 1000 ºC a significant increase in the sp2 bonding in the film is observed. No oxygen bonding is detected in the NEXAFS spectra, but we do observe an isosbestic point, demonstrating that the thermally driven sp3 → sp2 conversion reaction occurs without passing through an intermediate transition state. This allows us to use NEAFS spectra of thermally annealed ta-C films to quantitatively determine that the activation energy for directly converting the sp3-bonded carbon to the sp
  • Publication
    Origin of Ultralow Friction and Wear in Ultrananocrystalline Diamond
    (2008-06-11) Konicek, Andrew R.; Grierson, D. S.; Gilbert, P.U.P.A.; Sawyer, W. G.; Carpick, Robert W; Sumant, A. V.
    The 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.