Quantitative AFM Measurements
For many years mechanical and optical surface profilers could be used for analyzing paper surface texture. However, such profilers are limited in their horizontal resolution to approximately one micron. Thus, they can readily measure at a length scale of a few millimeters. Traditional quantitative surface roughness parameters such as Sa, Sq, Sr and Sm can be directly calculated from AFM images.  Figure 5: Equations for surface texture that are readily used with the AFM images. As an example, it has been shown that the AFM could be used to explain anomalies in paper gloss. In a study, sheet A had a higher TAPPI (Trade Association of Paper and Pulp Institute) gloss at 75 degrees and sheet B had a higher TAPPI gloss at 20 degrees. By directly measuring the surface texture with an AFM, it was established that although the two sheets of paper had similar surface roughness, the skew and kurtosis were very different. Sheet A was significantly non-Gaussian and Sheet B was approximately Gaussian.
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