IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Tribology Wednesday Sessions
       Session TR+SS-WeM

Paper TR+SS-WeM3
Comparative Energy Dissipation in Nanoscale Shear and Tensile Interactions

Wednesday, October 31, 2001, 9:00 am, Room 132

Session: Fundamentals of Tribology & Adhesion
Presenter: G. Haugstad, University of Minnesota
Correspondent: Click to Email
A case study of ultrathin polyvinyl alcohol films is presented, comparing energy dissipation in three modes of scanning force microscopy: friction force, pulsed force mode and "tapping mode". Relative energy dissipation is measured on three distinct film components: a continuous first layer (~1 nm thick) strongly adsorbed to mica; a thicker, discontinuous overlayer, autophobically dewetted from the first layer; ordered overlayer islands (1 nm thick) located within the breaks of component #3. These films are chemically homogeneous but structurally heterogeneous. The components differ in amorphous content (free volume) and confinement, giving rise to differences in energy dissipation. Energy dissipation during sliding is quantified as friction force multiplied by a sliding distance of one contact diameter. Dissipation per cycle during vertical cantilever oscillation is quantified from the cantilever phase lag and the ratio of reduced to free resonance amplitude, via the method proposed by Cleveland et al.@footnote 1@ Dissipation during pull-off in pulsed force mode is quantified with a newly proposed method: by measuring the cantilever deflection with high time resolution (5 MHz) and comparing the (slowly damped) free oscillation amplitude (squared) immediately following pull-off to the quasistatic deflection (squared) immediately prior to pull-off. Corrections arise from (a) the relationship between linear deflection and (measured) angular tilt near the end of the cantilever;@footnote 2@ (b) the excitation of higher cantilever eigenmodes@footnote 2@ upon pull-off. Our results demonstrate that energy dissipation contrast in pulsed force and "tapping" modes is very similar, though the time scales of interaction are very different, whereas contrast in sliding friction is markedly different from either. @FootnoteText@ @footnote 1@J. P. Cleveland, B. Anczykowski, A. E. Schmid and V. B. Elings, Appl. Phys. Lett. 72, 2613-2615 (1998). @footnote 2@H. J. Butt and M. Jaschke, Nanotechnology 6, 1 (1995).