A scanning force microscope study of a tribochemical system: stress-enhanced dissolution

Scanning force microscopy (SFM) is employed to study a model tribochemical system: single-crystal calcite in saturated (>= 60 mu M) CaCO3 solution. The tribological stimulus is provided by the SFM tip itself. Local dissolution along monolayer steps is readily increased by an order of magnitude by scanning at high contact forces (e.g., 270 nN). Indentations near pre-existing steps also locally enhance the step velocity. At very high contact forces and point-like scans (10 x 10 nm(2)), etch pits can be nucleated in flat terraces. The wear produced by drawing the SFM tip back and forth in a linear fashion across monolayer steps can be quantitatively described in terms of the volume-activated nucleation of double kinks. The resulting activation volumes (4 x 10(-29) m(3) and 6 x 10(-29) m(3) for the two crystallographically distinct steps in this study) are similar to the average volume per ion in the calcite lattice. This technique is readily adapted to more corrosive environments, and may allow for a more fundamental understanding of tribochemical effects.