AVS 53rd International Symposium
    Nanometer-scale Science and Technology Wednesday Sessions
       Session NS+SS+TF-WeM

Paper NS+SS+TF-WeM2
Spectromicroscopy of Tribochemistry: X-PEEM Characterization of Wear vs. Humidity for Ultrahard Carbon Films

Wednesday, November 15, 2006, 8:20 am, Room 2016

Session: Nanotribology and Nanomechanics
Presenter: A.R. Konicek, UW-Madison
Authors: A.R. Konicek, UW-Madison
D.S. Grierson, UW-Madison
A.V. Sumant, UW-Madison
N.N. Naguib, Argonne National Lab
O. Auciello, Argonne National Lab
J.A. Carlisle, Argonne National Lab
T.A. Friedmann, Sandia National Labs
J.P. Sullivan, Sandia National Labs
J. Birrell, Advanced Diamond Tech.
P.U.P.A. De Stasio, UW-Madison
R.W. Carpick, UW-Madison
Correspondent: Click to Email
The outstanding tribological performance of carbon-based films can be seriously affected by variations in humidity. To explore the tribochemical origins of this behavior, self-mated interfaces of tetrahedral amorphous carbon (ta-C) and ultrananocrystalline diamond (UNCD) films were subjected to fretting wear in dry N2 with relative humidity values of 0%, 25% and 50%. Relative friction was measured during fretting, and the resulting wear tracks were examined with atomic force microscopy (AFM) and X-PEEM-XANES (X-ray PhotoElectron Emission Microscopy combined with X-ray Absorption Near-Edge Structure) spectromicroscopy. X-PEEM is capable of discerning chemical and bonding contrast at high spatial resolution, readily distinguishing between the wear track and the unworn film. For both films, friction increases as the relative humidity decreases. However, there are opposing trends in the behavior of graphitization and oxidation due to wear. For ta-C, as the relative humidity is decreased there is an increase in both graphitization and oxidation. This implies that the harsher wear environment has more heavily modified the carbon bonds compared to the wear at a higher relative humidity, inducing graphitization and oxidation. In contrast, the self-mated UNCD interface showed a comparative decrease in graphitization and oxidation in the wear track as the relative humidity was decreased. We will discuss changes observed in both friction and the chemical signature of the surface as the amount of relative humidity in the environment is varied. We will also discuss the relation between the amount of relative humidity in the environment and the level of graphitization that occurs in the wear track. @FootnoteText@ This work was partially supported by the US Department of Energy, BES-Materials Sciences, under Contract W-13-109-ENG-38.