Simulations of friction anisotropy on ordered organic monolayer

A method of molecular dynamics is used to investigate friction anisotropy o bserved on a hexagonally packed organic monolayer of straight-chain molecul es, which tilt in a specific direction. A rigid gold slider with a single a tomic protuberance is used as a model of a typical atomic force microscope tip apex. The friction anisotropy is observed at 50 K, which is below the m elting point of rotation around a long axis of the molecule. The anisotropi c frictional behavior is that sliding in directions normal to the direction of the collective tilt of the molecules results in the maximum friction fo rce. The origin of the anisotropy is attributed to anisotropy in lateral co mpliance in the monolayer.