Pulsed force mode technique

SFM also enables us to measure specific interaction forces between a small silicon tip and the surface. The pull-off forces between the tip and the surface estimated from Force vs Distance Curves (FDC) can be correlated to the adhesive interactions between tip and surface [9]. Recording of FDCs line-by-line allows us to image surface topography and adhesive surface properties simultaneously [10]. This technique has some disadvantages, like the requirement for a large amount of data acquisition and analysis, which have been alleviated by the invention of the Pulsed Force Mode (PFM). The PFM simplifies and accelerates the measurements of adhesive properties with high lateral resolution [11, 12]. 

In the so-called pulsed force mode AFM technique developed by Marti and coworkers [124], the data acquisition rates are increased. In this mode, as outlined in Sect. 3.2, the sample is modulated sinusoidally ( 1 kHz) during a conventional contact mode AFM scan to cause that the tip contacts, indents, and breaks free from the surface with a frequency of 1 kHz during scanning. Instead of recording the complete f-d curve, pull-off forces and stiffness are acquired parallel to sample topography at useful scan rates that become possible (Fig. 3.54). 

For most quantities measured by scanning probe microscopes a comparison of bulk material properties and SFM-measured properties is lacking. We believe that the Pulsed Force Mode measurement technique together with an accurate characterization and control of the tip size and surface composition will enable a correlation. The technique also lends itself to comparisons with measurements of surface tension. The variation in contact time may lead to new insights in the dynamics of nanoscale wetting. 

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