An AFM produces a 3-dimensional representation of the surface that it scans over. Unlike optical or electron microscopes, AFM collects topographic data. That means that you can look at the shape and size of individual features, such as the pits on a DVD, or determine the particle density, such as the number of nanoparticles in a given area.

The line profile provides the height information of the surface along a user-selected line. From the thickness profile, and using statistical tools in Gwyddion, we can determine t the thickness of a coating. AFM can measure thicknesses up to 10 micrometers and down to 10 nm, or less depending on sample and environmental conditions.

Another useful measurement is the distance between features in an AFM image. The lateral distance can be simply measured using Gwyddion. 

Surface roughness is a component of the texture of a surface: a higher value means that the surface is rougher. Surface roughness is also known as surface finish. The arithmetic roughness (Ra) and the root-mean-squared roughness (Rq) are common parameters used to describe roughness. Because AFM collects topographic data in two dimensions, the surface roughness can be calculated from the entire 2-d scan area rather than just 1-d data. The 2-d/area roughness parameters are arithmetic (Sa) and RMS (Sq).

When operating in a mode called Tapping Mode, AFMs generate two different images: the topography image and the phase image. The phase image comes from the phase shift of the signal: the phase shift is the lag between the driving signal and the feedback signal. This lag is caused by the interaction between the probe tip and the surface, which can be affected by adhesive forces, frictional forces and viscoelastic forces.

Regions with different material properties can be distinguished using the contrast of the phase image. Since the topography image and the phase image are generated at the same time, analysis of both images side by side can reveal information that might be hidden from just the topography image alone.

Particle analysis is a very common application of AFM. A line profile can be used to look at individual particles, but for more than a few particles, it’s best to automate the routine somehow. A particle segmentation routine does just that by separating the particles from the flat surface that they are on. Segmentation routines can also be used for particle counting. Software such as ImageJ can be used for segmentation.

It is possible to complement the topography images with the phase images to determine whether the particles are indeed separate and different from the substrate. Phase imaging is described in detail below.