We demonstrate that energy losses during friction of alkylsilane self-assembled monolayers with sharp atomic force microscope tips can be correlated to molecular events occurring at specific threshold loads. Under these loads, discrete molecular tilts occur, which are dictated by the geometrical requirements of the close packing of molecules. The barriers overcome during these tilt events give rise to discrete changes in the frictional forces.
- Received 17 November 1998
©1999 American Physical Society