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 Ao and the set-point tapping amplitude Asp. The phase angle of probe oscillation increases with decreasing the set-point amplitude ratio Asp/Ao. Phase imaging at moderate tapping (Asp/Ao= ~0.5) allows one to distinguish different surface features of both multicomponent 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. © 1997 Elsevier Science B.V. All rights reserved.