Abstract : To understand and control friction and wear in both macroscopic and microscopic technologies requires a detailed understanding of material properties, chemical reactivity and intermolecular interactions on the nanometer length scale. The role of nanoscale defects on friction has been elucidated through scanning tunneling microscopy and atomic force microscopy studies of molybdenum disulfide. These investigations have shown that friction increases systematically with increasing defect density, and have demonstrated a novel load-independent friction regime due to sliding on constant area nanocrystals. The mechanical properties of finite size materials, which are important to micro and nanomechanical systems, have also been probed through studies of the bending of different thickness molybdenum oxide nanocrystals. Significantly, this work has shown that there is a substantial and systematic decrease in the modulus with decreasing thickness. This large drop in stiffness shows that materials will exhibit greater flexibility as their dimensions are reduced. Lastly, a new generation of molecular resolution tools has been developed. Carbon nanotubes were attached to conventional force microscopy tips and shown to provide large improvements in image resolution. Methods to localize molecules at the nanotube ends were also developed, and these modified probes were used to measure intermolecular forces and image with chemical sensitivity.
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