Energy transfer plays an important role in many surface processes such as surface diffusion, vibrational relaxation and sliding friction in adsorbed molecules. The Quartz Crystal Microbalance (QCM) has in recent years been employed to reveal much fundamental information on the phononic and electronic energy dissipation mechanisms associated with the sliding of atomically thin films along surfaces, a phenomenon closely related to the spreading diffusion of a film on its substrate. While in quantitative agreement with theory and computer simulation, the QCM data have not been cross-referenced to scanning probe measurements of sliding friction and diffusive behavior of atoms along surfaces. We have thus combined a Scanning Tunneling Microscope and a QCM to allow direct imaging of films adsorbed on the QCM electrode under both stationary and oscillating conditions. The results of these studies will be described, along with a discussion of whether our current knowledge of the fundamentals of friction is sufficient to enable control of adsorbates on surfaces through frictional drag forces.
Work supported by AFOSR and NSF
"Spreading Diffusion and its Relation to Sliding Friction in Molecularly Thin Films", A. Widom and J. Krim, Phys. Rev. E, 49, 4154 (1994)
"Scanning Tunneling Microscope Measurements of the Amplitude of a Quartz Crystal Oscillator", B. Borovsky, B.L. Mason and J. Krim, J. Appl. Phys., in press