Rough film surfaces can be characterized by a series of parameters, usually calculated from a two-dimensional scan of the film surface with a diamond needle (standard is EN ISO 4287). The most commonly used measurements are the Ra, the Rz, and the peak count. To achieve results that can be compared, the length of the measured line and the cut off (part of the beginning and end of the measured line, which is not taken into the calculation) are important.
The Ra is the area between the roughness curve and the base line (transformation of the area enclosed between roughness curve and middle line into a rectangle).
The Rz is the average of the maximum height of five parts of the measurement line.
The “peak count” is the number of peaks per cm, which pass both the lower and the upper limit. These limits (d) have to be taken into account when comparing different measurement results.
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