AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA2
Friction Anisotropy at Pd(100)/Pd(100) Interfaces

Monday, November 3, 2003, 2:20 pm, Room 327

Session: Tribology, Adhesion, and Friction
Presenter: A.J. Gellman, Carnegie Mellon University
Authors: A.J. Gellman, Carnegie Mellon University
C.M. Mancinelli, Carnegie Mellon University
Correspondent: Click to Email
Friction anisotropy has been studied between two Pd(100) single crystal surfaces in an ultrahigh vacuum environment. Friction measurements were made using Pd(100)/Pd(100) interfaces modified by adsorption of octane at coverages ranging from 4 to 40 molecular layers. The relative crystallographic orientation of the two Pd(100) surfaces was systematically varied and friction measurements were made at each orientation as a function of octane coverage. These measurements have revealed that friction is anisotropic with respect to Pd(100) lattice orientation. When the surfaces were aligned, forming a commensurate interface, and sheared along the <110> direction with 4ML of octane at the interface, the static friction coefficient was µ@sub s@ > 8.0 ± 2.0. A minimum in the static friction coefficient was obtained when the two Pd(100) surfaces with 4ML of octane at the interface were misoriented by @theta@ ~ 45°. Under these conditions the static friction coefficient for sliding along the <110> direction of the stationary surface was µ@sub s@ = 4.0 ± 2.0. Higher coverages of octane decreased the friction, but friction anisotropy persisted for coverages of octane as high as 20 ML at the sliding interface between the two Pd(100) surfaces. Wear scares were observed on both surfaces indicating that plastic deformation had occurred during sliding. The observation of friction anisotropy in the presence of disordered overlayers of octane and during shearing of surfaces that deform plastically suggests that friction anisotropy originates with the properties of the bulk crystal lattices rather than surface lattice commensurability. These results corroborate the findings of a previous study of friction anisotropy between Ni(100) surfaces.@footnote 1@ @FootnoteText@ @footnote 1@ Langmuir, 2000, 16(22), 8343.