Pulsed force mode (PFM) is based on a standard AFM set-up with a sinusoidal modulation of the z-axis piezo. The tip starts above the surface of the sample, approaches, makes contact, indents then is pulled away from the surface. This makes possible a force-distance curve measurements as illustrated below:

This diagram should be viewed after reading the "introduction to force-distance curves" page. This PFM information is processed in the following manner illustrated below; first the operator picks points to identify the maximum force (3) and the point below the maximum (2) such that the difference between these points is taken as a measure of the stiffness of the sample. The pull-off force is taken as the difference between the maximum negative force (4) and the baseline (5).

In this way images of topography, ‘stiffness’ from the indentation measurement and ‘adhesion’ from the pull off measurement are obtained as shown below.

In reality, the bending of the cantilever means that the tip movement is not normal to the surface during indentation thus this measurement is influences by friction and adhesion as well as stiffness. Also it must be recognised that the viscoelastic properties of the sample as well as the simple work of adhesion between the sample and the tip influence the pull off force. Consequently the terms stiffness and adhesion must be treated with caution when used in this context. However, the fact that, in particular, the pull off force is influenced by viscoelastic properties is an advantage as can be seen from application of this technique used with a temperature stage.

PFM was developed by Marti and co-workers at the university of Ulm in Germany.