On the Atomic Scale Origins of Static and Kinetic Friction J. Krim Physics Department North Carolina State University Raleigh, North Carolina Studies of the fundamental origins of friction have undergone rapid progress in recent years with the development of new experimental and computational techniques for measuring and simulating friction at atomic length and time scales. [1] The increased interest has sparked a variety of discussions and debates concerning the nature of the atomic-scale mechanisms which dominate the dissipative process by which mechanical energy is transformed into heat. Measurements of the sliding friction of physisorbed monolayers and bilayers can provide information on the relative contributions of electronic to phononic dissipative mechanisms, since phonon dissipation is present at all film coverages, while electronic dissipation primarily impacts the monolayer. We will be reporting our measurements for physisorbed layers adsorbed on lead, iron and copper surfaces in open geometries and also in confined geometries obtained by bringing a STM tip into tunneling contact with the QCM electrode. Lead is of particular interest on account the occurrence of superconductivity-dependent sliding friction on this metal. The system Xe/Cu is interesting because the interaction potential of Xe/Cu is known to a high degree of accuracy, allowing highly reliable comparisons of theory to experiment. Iron is of interest for a variety of practical applications.[2] [1] Surface Science and the Atomic-Scale Origins of Friction: What Once was Old is new Again, J. Krim, Surface Science, Volume 500 (2002) [2] Bridging the Gap between Macro- and Nanotribology: A Quartz Crystal Microbalance Study of Tricresyphosphate Uptake on Metal and Oxide Surfaces, M. Abdelmaksoud, J.W. Bender and J. Krim, Phys. Rev. Lett. (2004), in press