Phase imaging and stiffness in tapping-mode atomic force microscopy

The dependence of phase angles in tapping-mode atomic force microscopy on the magnitude of tip-sample repulsive interactions was investigated, and phase images of several hard and soft samples were recorded as a function of the free amplitude A(0) and the set-point tapping amplitude A(sp). The phase angle of probe oscillation increases with decreasing the set-point amplitude ratio A(sp)/A(0). Phase imaging at moderate tapping (A(sp)/A(0)=similar to 0.5) allows one to distinguish different surface features of both multi component materials and one-component systems with different density distributions. Phase images recorded at moderate tapping are related to surface stiffness variations associated with Young's modulus change. (C) 1997 Elsevier Science B.V.