TRIBOLOGICAL PROPERTIES OF 1-ALKENES ON COPPER FOILS: EFFECT OF LOW COORDINATION SURFACE SITES

BRENDAN PAUL MILLER; OCTAVIO JAVIER FURLONG; WILFRED T. TYSOE

TRIBOLOGY LETTERS

SPRINGER/PLENUM PUBLISHERS

Lugar: New York; Año: 2013 vol. 51 p. 357 - 363

1023-8883

It has been suggested from molecular dynamics simulations that low-coordination-number sites are produced at a sliding metal-metal interface, but, because of their instability, they may rapidly relax to increase their coordination number. The possible presence of such low-coordination sites on the surface is tested by exploiting the observation that the desorption temperatures of 1-alkenes on copper increase with both the number of carbons atoms in the 1-alkenes and the surface roughness. Thus, 1-alkenes desorb from a Cu(111) single crystal, with relatively few low-coordination sites, at temperatures between 60 and 100 K lower than from a polycrystalline copper foil. The decrease in friction after impinging a flux of various 1-alkenes on a copper foil, while rubbing in an ultrahigh vacuum tribometer, correlates very well with the corresponding 1-alkene coverages on a copper foil, estimated using the desorption kinetics. This suggests either that rubbing does not result in the formation of lower-coordination sites or that they relax sufficiently rapidly that they do not influence the surface chemistry of 1-alkenes. Surface analyses indicate that shear at the interface causes carbon to diffuse into the subsurface region to form a tribofilm.