The late 20th century marked a renaissance in fundamental areas of tribology, sparked by new experimental and theoretical techniques capable of studying the force of friction in geometries which are well defined at the atomic scale. This project involves the use of one such technique, namely the Quartz Crystal Microbalance, to probe critical topics in this field. A first set of experiments will explore how friction impacts directed transport of polystyrene microspheres, to document control of motion through variations in atomic-scale friction levels. The second involves studies of the impact of sliding on the two-dimensional melting point of monolayer thick Krypton layers, important for fundamental studies of temperature rise and heat transport. The final set of experiments will document the manner in which magnetic fields influence the firmly established, yet still poorly understood phenomenon of superconductivity-dependent friction, for helium and oxygen films. The goal is to deepen our knowledge of electronic contributions to energy dissipation mechanisms in sliding friction. A complimentary educational component includes (1) ongoing participation of undergraduates in the research, and (2) direct dissemination of state-of-the-art information on friction to instructors developing curriculum on the topic, as well as to more general audiences through lectures and written reviews.
Non-Technical By most recent estimates, improved attention to friction and wear would save developed countries up to 1.6% of their gross national product, well over $100 billion annually in the U.S. alone. As the price of energy rises, and the need to conserve both energy and raw materials becomes increasingly urgent, physicists' rush to understand basic tribological processes can only be expected to accelerate. The late 20th century marked a renaissance in fundamental areas of tribology (the study of friction and wear), sparked by a number of new experimental and theoretical techniques capable of studying the force of friction in geometries which were are well-defined at the nanometer scale. This project involves the use of one such technique, namely the Quartz Crystal Microbalance (QCM), (1) to explore the role of friction to control micron scale particles, an important feature in emerging nano-technological areas that include medical, electronic and manufacturing applications, (2) to probe the temperature of a simplified sliding contact, a quantity that has been exceptionally difficult to quantify from theoretical, experimental and computational approaches, and (3) to explore the firmly established, yet still poorly understood phenomenon of superconductivity-dependent friction. The goal is to deepen our fundamental knowledge of how electrons contribute to energy loss. A complimentary educational component includes (1) ongoing participation of undergraduates in the research, and (2) direct dissemination of state-of-the-art information on friction to instructors developing curriculum on the topic, as well as to more general audiences through lectures and written reviews.
Our research program is unique world-wide, exploring the nano-scale origins of friction in well-defined geometries with a Quartz Crystal Microbalance (QCM) technique that the PI pioneered in the early 1990’s. Notable accomplishments of work performed under NSF DMR0805204 program include: Documentation of frictional heating and temperature rise in a molecularly thin lubricant, demonstrating for the first time a fundamental understanding of the balance of frictional heating with evaporative cooling effects. Pioneering of a new method for studying temperature rise at a nanoscale contact, making use of a scanning tunneling microscope (STM) tip in contact with the surface of a quartz crystal microbalance (QCM). The technique resolved challenges in the field associated with distinguishing frictional heating from tip sample heating effects. Publication of the first experimental observation of tribo-induced melting at a nano-asperity contact by monitoring the QCM response to the rubbing action of a scanning tunneling microscope tip. QCM measurements of the sliding of adsorbed films of ethanol and documentation of their "reservoir lubricating effect" on micro-electro-mechanical systems. Establishment of a link between the atomic scale vibrations probed with QCM and sliding friction in macroscopic systems. The experiment also linked atomic scale friction theory with earthquake models. A complimentary educational component of the research program included ongoing participation of undergraduates, direct dissemination of state-of-the-art information on friction to instructors developing curriculum on the topic, as well as more general audiences through lectures and written reviews.
