While performing RMS roughness analysis, some researchers prefer bow/tilt correction and plane fitting etc. But most of the reports do not seem to follow a standard procedure. What is the meaning of plane fitting? What order should be chosen?
On analyzing my polymer thin film samples, I came across very large RMS roughness of 500-1000 nm which is not supposed to be that high. How do I choose the AFM image correction methods before I go for RMS roughness calculation?
thanks in advance
This is the method itself . It is written in Russian . I hope it will help you .
Dear Akhil,
First of all, you have to be aware of the fact that whatever correction (fitting) you use, you affect the original data. This means that if you use too much correction, you would be processing something that is not your accurate data any more.
In most cases your sample mount and scanner would introduce 1st and 2nd order plane errors. The 1st order ones (tilt) would result from the fact that you can hardly put your sample perfectly flat (relative to the scanner movement). The 2nd order (bow) will be related to piezotube scanners, which work based on bending. The other thing is that the error introduced would depend – in a sense – on the scanning area. I mean that in very small scan areas (let’s say, 500 nm × 500 nm) you would hardly notice the 2nd order error.
The best way to use the proper correction would be to have a flat sample (e.g. a piece of silicon) and see, what are the errors your set-up introduces in the scanning area you use.
You also need to know if you really expect flat sample surface. I mean, if your thin film is made of a completely novel material which has never been investigated, you should try methods other than AFM as well.
And the last but not least, if what you are investigating is a soft polymer, make sure if you are using an AFM measurement mode which affects the surface as little as possible. In general and if available, I would suggest some non-contact mode. Some short-contact-time and low-force tapping mode should be fine as well. But – in general – I would avoid contact-mode imaging with these samples.
As you can see, it could have been better for us to provide you with a good answer, if you gave us some more details on your investigation. If possible, of course.
Have fun with your measurements,
Grzegorz Wielgoszewski
Dear Magomed
Thank you for sharing the instructions. In session 10 it is mentioned that before processing the topography images, average values of the height should be subtracted. Did I understand correctly?
Dear Grzegorz
Your comments were quite informative. Many thanks. I performed AFM measurements on soft polymer thin films of thickness 100-750 nm coated on both microporous polymer support and Si wafer. I used non-contact mode, with moderate tapping. The samples coated on microporous polymer support produced very high roughness (~1 um) and that on Si wafer produced lower (~400nm) without any correction/treatment.
Gwyddion documentation has a nice description of correct rougness evaluation:
http://gwyddion.net/presentations/talk-roughness-David-Necas-2012.pdf
http://gwyddion.net/documentation/user-guide-en/roughness-iso.html
http://gwyddion.net/documentation/user-guide-en/leveling-and-background.html
Dear Akhil,
Thanks for the details.
You probably know that: the best would be to have a piece of non-covered substrate area within the scan. But I can understand this is not always available or can cause interpretation errors related to non-homogeneous thickness of the layer.
Anyway, you should probably go through the Gwyddion documentation (thanks, Daniil, fo posting that!) and decide, if you really need any whole-area corrections.
The other thing to consider would be the repeatability of these roughness values. Are they similar in different scan positions? Does the area look homogeneously rough, or are there pits or hills that affect the averaging (see David Nečas’ presentation)?
And again, try to have a look with a different imaging technique. If these are values like 1 µm of roughness, you should easily see it in SEM.
Enjoy your research!
Best regards,
Grzegorz Wielgoszewski
Gwyddion user guide gives a nice presentation of post analysis techniques. Though I had installed Gwyddion back sometime, I wasn't aware of its functions. Thanks Daniil.
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