Oscillatory forces in liquid atomic force microscopy

By analysing oscillatory type solvation forces acting at the tip-surface interface in atomic force microscopy (AFM) in liquids it is possible to study interactions arising from purely physical effects. The observation of oscillatory forces with sharp tips indicates a high geometric symmetry of the tip-liquid-surface system. As such, liquid mediated forces may prove general for high resolution non-contact imaging in liquids, The effective viscosity (damping) increases markedly as the tip apex samples the liquid solvation layers closest to the surface and this suggests that strong damping effects (low Q) may always be present in non-contact imaging in liquids. The magnitude of solvation effects (both interfacial stiffness and viscosity) is less than that observed using the surface force apparatus (SFA) and this is probably related to tip roughness (asymmetry) or to the more limited volume over which liquid is confined in AFM.