The Relationship Between AFM Force-Distance Curves and Indentation Load-Penetration Curves
Mark R. VanLandingham
The atomic force microscope (AFM) is used to generate images based on the interaction forces between the probe tip and the sample surface. These interaction forces can be monitored directly using the AFM in force mode. During force mode, the probe tip moves vertically with respect to the sample surface, and the probe tip deflection is measured as a function of the vertical displacement of the scanner. The corresponding plot that is generated is termed a force curve or force-distance curve. Tip deflection can be measured as the tip is pushed against the sample, and if tip penetration occurs, the force curve can be converted to an indentation load-penetration curve. This conversion requires the removal of the compliance of the probe. However, for most combinations of AFM probes and sample materials, the probe tip will not penetrate into the sample significantly, in which case the slope of the force curve during tip-sample contact will not contain any information regarding the sample stiffness. In any case, analysis of a force-distance curve using equations from the indentation literature is incorrect.
atomic force microscope, detector sensitivity, force curve, force mode, indentation, spring constant