| In this work, I have used the Quartz Crystal Microbalance (QCM) to study nanoscale friction of monolayer adsorbates on (111) metals. The friction of these systems is viscous friction, defined as Ff = etanu = ( mt )nu. Here, eta is the viscous coefficient of friction, nu is the velocity of the adsorbate, m is adsorbate mass, and tau is the slip time, which is the time required for the film's speed to fall to 1/e of its original value. The main focus of this dissertation is to determine the factors that control eta, the viscous coefficient of friction. I have examined three different parameters in order to determine their effect on eta.; An equation for predicting the viscous coefficient of friction has been proposed: eta = etasubs + aU2o . Here, etasubs is the damping of adsorbate sliding energy within the substrate, a is a constant depending on mainly temperature and adsorbate film coverage, and Uo is the atomic-scale surface corrugation.; I have examined the sliding friction of n-octane on Cu(111) vs. Pb(11I) surfaces, which have gamma = 0.45 meV and gamma = 0.26 meV, respectively. I have observed that the slip time for a monolayer of n-octane/Cu(111) is 0.94 ns +/- 0.36 ns, and the slip time of noctane/Pb(111) is 0.59 ns +/- 0.13 ns. I therefore observe no direct evidence of a link between the damping of perpendicular FT modes and sliding friction. It is still possible, however, that the damping of the parallel FT phonon mode affects sliding friction.; Finally, I studied the slippage of monolayer methanol films at room temperature on rotating, rigid, and slowly ratcheting C60 substrates, to examine the effect that the molecular rotation of the substrate surface has on the sliding friction of an adsorbate. I found that at all coverages, the slip time for methanol on rigid and slowly ratcheting C60 was longer (hence lower friction) than the slip time for methanol on rotating C 60, defying the ball bearing analogy. (Abstract shortened by UMI.)... |
