Atomic force microscopy (AFM) is not only suitable for imaging surfaces with nanometer-scale resolution, but also for investigating various mechanical and other physical properties of the sample surface. This is enabled by the AFM measurement principle, in which a cantilever with a fine tip at its end mechanically scans the surface. Scanning can be performed in contact mode or, when the cantilever oscillates, in tapping mode.

In most AFM modes, the distance between the tip and the surface ranges from 0.1 nm to 10 nm. In tapping mode, the cantilever is subject to both long-range attractive forces and short-range repulsive forces, which is why the oscillation amplitude must be optimized to prevent these effects from compromising contrast and resolution.

In addition to simple topography measurement, various other modes can be unambiguously measured, including phase and amplitude. While both of these modes highlight edges, the phase also depends on the sample hardness, the surface elasticity, and the adhesion between the sample surface and the tip, thereby enabling a qualitative distinction between different materials on a surface.

Here, we report on investigations of various polyamide (PA 12) blends with glass fibers, which were examined by AFM phase imaging, and compare the results with those obtained from Raman microscopy. The AFM measurements were performed by a FlexAFM Axiom (Nanosurf) in tapping mode with Tap190Al-G cantilevers; Raman microscopy was performed using a WITec alpha300 apyron microscope.

The results underscore that AFM phase imaging is a versatile tool for distinguishing between different materials on a surface and suggest that further investigations of polymer blends are warranted to gain a better understanding of the quantitative phase differences measured by AFM.