Phase contrast and attraction-repulsion transition in tapping mode atomic force microscopy

The origin of phase contrast in tapping mode (TM) atomic force microscopy (AFM) images has been a persistent issue of concern to many TM-AFM users. In the present study, it is revealed experimentally that phase contrast relates principally to large phase differences between regions of attractive and repulsive dominated probe-sample interactions at the attraction-repulsion transition point rather than variations in energy dissipation due to shifting probe-sample interactions. To provide a rational basis for characterizing phase contrast we demonstrate that the length of the attractive-dominated region in amplitude-phase-distance (apd) data can not only help to determine whether a reliable phase image can be obtained on a particular sample surface, but also provide a quantitative fingerprint for a sample surface. We term this quantity the attraction-dominated region length. (C) 2002 Elsevier Science B.V. All rights reserved.