AVS 51st International Symposium
    Nanometer-scale Science and Technology Wednesday Sessions
       Session NS-WeA

Paper NS-WeA9
Novel Tribological Properties of Quasicrystals in Ultra-High Vacuum

Wednesday, November 17, 2004, 4:40 pm, Room 213D

Session: Nanotribology and Nanomechanics
Presenter: J.Y. Park, Lawrence Berkeley National Laboratory
Authors: J.Y. Park, Lawrence Berkeley National Laboratory
D.F. Ogletree, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
C.J. Jenks, Ames Laboratory, Iowa State University
P.A. Thiel, Ames Laboratory, Iowa State University
Correspondent: Click to Email
The structural and tribological properties of the interface between decagonal Al-Ni-Co quasicrystals and conductive TiN-coated cantilevers have been investigated. This was accomplished using a combined atomic force and scanning tunneling microscopy apparatus in ultrahigh vacuum. Atomically resolved STM images of the 2-fold Al-Ni-Co surface were obtained showing a clear periodicity along 10-fold direction, and a quasi-periodicity (following Fibonacci sequences) along the 2-fold direction. To decrease the high adhesion between the atomically clean quasicrystal surface and the metallic AFM tip (with has high adhesion force as large as 1000 nN), the tip or the surface were passivated by hydrocarbon molecules (ethylene and alkylthiol), which made possible the formation of stable contacts. This allowed us to observe an elastic to plastic transition occurring at a threshold load. With alkylthiol passivated tips the friction properties of the highly anisotropic 2-fold surface could be studied. We found a strong dependence of the friction force on the scanning direction, with low friction occurring along the aperiodic direction and high friction in the periodic direction. This result will be discussed in light of friction models of the interface based on existence or not of commensurability between the two contacting surfaces.