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 lowcoordination 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.