AVS 49th International Symposium
    Surface Science Thursday Sessions
       Session SS-ThA

Paper SS-ThA5
Nanopormorphism of C60 and Hydrocarbons on Metal Surfaces

Thursday, November 7, 2002, 3:20 pm, Room C-110

Session: Tribology at Surfaces
Presenter: T.S. Coffey, North Carolina State University
Authors: T.S. Coffey, North Carolina State University
M. Abdelmaksoud, North Carolina State University
J. Krim, North Carolina State University
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We report investigations of the validity of beliefs that nanoscale objects might have the same properties as macroscale objects, termed nanopormorphism. Since C60 molecules to rapidly rotate within their lattice position, tribologists envisioned nano-sized ball bearings. C60 is not an effective lubricant.@footnote 1@ But differences in interfacial friction between rigid vs. rotating C60 remains an interesting topic. C60 forms close packed hexagonal films on both Ag(111) and Cu(111). However, on Ag(111), C60 spins in its lattice position, while it is rigid on Cu(111).@footnote 2@ To determine if the spinning of C60 affects interfacial friction, we are employing QCM and AFM to compare the friction of methanol on C60/Ag(111) vs. methanol on C60/Cu(111). We examine whether the rolling nature of the C60 layer impacts the sliding friction as probed by QCM and AFM. Adsorbates at a surface can cause changes in the phonon dispersion curves, creating new modes that can be related to the sliding friction of the adsorbate. Among these new vibrational modes are three Frustrated Translational (FT) modes which probe the curvature of the molecule/surface potential along different spatial directions. For hydrocarbons adsorbed on many metals, the FT modes parallel to the surface (FTx, FTy) have energies much smaller than that perpendicular to the surface (FTz).@footnote 3@ The stiffness or high "spring constant" of the FTz mode compared to the low "spring constant" of the FTx and FTy modes brings to mind molecular scale shock absorbers. We are using QCM to study octane and acetylene sliding on Cu(111) and Pb(111) to determine how energy and damping of the FTz mode affects sliding friction. @FootnoteText@ @footnote 1@ T. Coffey et al., J. Phys. Condensed Matter, 13 (2001) 4991-4999.@footnote 2@ T. Sakurai et al., App. Surf. Sci., 87/88 (1995) 405.@footnote 3@ B.N.J. Persson and E. Tosatti, Eds, Physics of Sliding Friction, Ch. Woll, Kluwer Academic Publishers, Dorcdrecht, 1996.