The contrast mechanism for true atomic resolution by AFM in non-contact mode: Quasi-non-contact mode?

Recent studies in which single point-like defects have been detected by AFM in non-contact mode, i.e., true atomic resolution, have been investigated using numerical simulations. The use of realistic interatomic interaction parameters allows us to do numerical simulations that are in very good agreement with experimental data. As a result, we are able to ''separate'' the different forces acting between the AFM tip and the sample surface. Calculations indicate that the force responsible for image contrast in the experimental studies is the repulsive contact force, and not the attractive contact force. This result remains the same for any reasonable set of interatomic interaction parameters. (C) 1997 Elsevier Science B.V.