|The Science and Applications in Making Diamond Slippery, Non-Sticking, and Wear-Resistant |
Laboratory for Surface Modification
|Robert W. Carpick, University of Pennsylvania, Philadelphia Nanotechnology Institute |
12:00 Noon, Chem. 260
Friction, adhesion, and wear are crucial in applications from the macro to the nanoscale, but these effects are yet to be well-understood or controlled. Carbon-based films, including nanocrystalline diamond, are of interest because of their high strength, low friction, and stable surfaces. We use atomic force microscopy (AFM) and a range of surface science tools to determine nanoscale adhesion, friction, and wear as a function of surface atomic structure and environment. We present studies of diamond, where the final atomic layer is tailored. The surface atomic bonding configuration (including the carbon hybridization state) is determined by synchrotron-based X-ray absorption spectroscopy. Nanoscale adhesion and friction are directly affected by the nature of these bonds. Exposure to atomic hydrogen terminates the surface with a hydrogen monolayer, maximizes the pure diamond bonding character, and reduces friction and adhesion to the van der Waals limit (1,2). Photoemission electron microscopy (PEEM) is used to observe localized chemical changes in worn regions of samples, allowing us to show that passivation by adsorbates, not graphitization, is responsible for low friction and wear of diamond (3). Furthermore, we find that nanoscale AFM tips made out of diamond are far more wear-resistant than their conventional Si-based counterparts. This demonstrates the first practical implementation of diamond in a commercial microfabricated mechanical device.
(1) A. V. Sumant et al., Adv. Mater. 17, 1039 (2005)
(2) A. V. Sumant et al., Phys. Rev. B 76, 235429 (2007)
(3) A.R. Konicek et al., Phys. Rev. Lett., 100, 235502 (2008)