I am getting different roughness values for same sample surface by Taylor Hobson surface profilometer and AFM. Approximately half the roughness value coming in case of AFM as compared to surface profilometer. Why is this happening, please answer about it, I have to put a specific reason in my journal.
The cutoff length or sampling length was 4 mm in the profilometer but it was 10 µm in the AFM (scan area = 10 µm × 10 µm).
If you are taking a surface (area) roughness by AFM and a profile (line) roughness by profilometer, then they are not directly comparable. You could try extracting a profile from the AFM surface and analysing that for comparison (making sure you account for the difference in tip radius), but I think you will probably find 3 issues;
- Firstly, you should take several measurements and compare the average. >10 samples from each surface would be appropriate.
- Your surface could have directionality - therefore, the direction of your profile sample across the surface is of importance.
- Also, your surface could have features which are not consistent with scale. Your profile scan is 400 times longer than the longest feature you might have seen with the AFM.
Overall, I would say that the most likely reason for the difference is that there are features with a wavelength which cannot be captured by such a small area of investigation under the AFM.
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