Adhesion Measurements of Physisorbed Layers on Metal Surfaces

At this writing, the ONR grant has been in effect for three years. During the recent year, two graduate students have been partially supported David Solina and Chris Daly. Solina completed an investigation of relationship between Van der Waals interaction strength at a film-substrate interface and the observed interfacial friction. Friction levels were monitored for variations in the Van der Waals attraction energy due to both film thickness and interface chemistry. We observed systematic increases in interfacial friction levels with Van der Waals attraction energy and also with film thickness. We are now studying these results within the context of available theory and computer simulation. Daly completed the construction of controlled environment scanning tunneling microscope which operates in conjunction with a quartz crystal microbalance. With this setup we are able to record the drag of the STM tip on the oscillator as a function of adsorbed film thickness in addition to being able to image the surface as it shakes back and forth.