Dear G. Rambabu

We normally consider the "image Rq" and the "image Ra" for judging the roughness of the sample.

Rq is the root mean square average of height deviation taken from the mean image data plane.

Ra is the arithmetic average of the absolute values of the surface height deviations measured from the mean plane.

I always took into consideration Ra, Rz, Rmax - just because it is easy to find it in standards (ISO, ASTM, etc). And these values are known for all. There are much more roughness parameters, but usual based on mentioned three.

Dear G. Rambabu

We normally consider the "image Rq" and the "image Ra" for judging the roughness of the sample.

Rq is the root mean square average of height deviation taken from the mean image data plane.

Ra is the arithmetic average of the absolute values of the surface height deviations measured from the mean plane.

I think it depends on your application etc.. Typically, we prefer to use "Image Rq" and "Image Rmax" which is same as Rz I believe and is the sum of Rp (max. height) + Rv (max. valley).  Also, look at the olympus tutorial provided with the the link.

http://www.olympus-ims.com/en/knowledge/metrology/roughness/2d_parameter/

Many parameters can be used in order to calculate roughness. Which ones to use depend on exactly what you are looking for: deviation from mean height, valley quantification, peak quantification, symetry... The clasic roughness parameters are Ra and RMS, though. It should be a good place to start.

I found this document particularly clarifying. It explains the different parameters which can be used to analyze a height image. As for the parameter calculation, I would definitely try Gwyddion. It's a powerful and intuitive software, as well as free! The calculation for most parameters is automatic and instantaneous.

Hello!! I have been reading your comments, they are very useful!! I have another question, if you want to calculate the Ra or Rq of an AFM image, you select an area so how does the software calculate the Ra or Rq? from the average height in every line or from the average heigh of all the selected area. Thank you in advance!

Take look at PDF I attached in this topic: https://www.researchgate.net/post/AFM_Statistics_analysis

I always refer to this book chapter when I need any information about surface roughness and comes well referenced. I hope it comes clear

http://www.intechopen.com/books/atomic-force-microscopy-imaging-measuring-and-manipulating-surfaces-at-the-atomic-scale/measurement-of-the-nanoscale-roughness-by-atomic-force-microscopy-basic-principles-and-applications

We use Rq

I think it is not very important which parameter you compare. Instead, it is important to fully controll of the apex of your tip. We normally calculate tip apex before and after measurement using TGT-1 and TGG callibration grating to be sure that any alterations to the tip apex geometry were done during measurement. Moreover, if you want to compare two samples of different young modulus be carefull to maintain stable loading force. For softer samples we noticed decrease in roughness due to too large loading force.

can any one elaborate me how to calculate roughness from AFM image using "image Ra" and "image  Rq". (using some example)

I found this nice presentation about roughness calculation which you may find helpfull:

http://gwyddion.net/presentations/talk-roughness-David-Necas-2012.pdf

Simply, you can calculate it using Gwyddion free software. Just load an image and click indicated button (attachment)

Can anyone elaborate whether the roughness average parameter 'Ra' value is enough to establish the roughness of a surface or should it be define in conjunction with 'Sa' values?

Thanks

dears, Hizb Ullah Sajid and A. Monamary, I think the most soft wares which related with AFM devices gives the parameters  

Dear Francis, what if a surface is too rough, in scale of microns. AFM and 3d surface profiler do not work on that. In that case, can we use Ra to establish roughness,? Thanks.

Hi brothers

How to calculate surface roughness factor analytically?

Dear all, everyone tried to tell about the roughness but not the roughness factor which is defined as the ratio of the average area of the actually attached interface (Ar) to its projected part (A). This factor is used in Wenzel equation for measuring apparent contact angle. So now my quiestion how to calculate this factor? In one paper they calculated from AFM derivative image and they have shown that the roughness factor is basically rms slope. Ref : A. Metya et al. / Applied Surface Science 293 (2014) 18– 23. Thank you.

to calculate the alpha and beta you have to solve kuramoto sivansky equation or KS equation. then you can estimate from experiment. actually this is calculated from height height correlation function. alpha=(2-d)/2 and beta =(2-d)/4 and Z= alpha /beta

see phys rev b 50(1994) 7635.

experimentally what deepak said is https://en.wikipedia.org/wiki/Wetting

What does the values of peaks shown on AFM images represent? Rz, RMS or Ra?

All answers will be provided by a free downloadable software called gwyddion.

Dear G. Rambabu

If you are looking for some practical information, I suggest you to look for webinars in the internet. Depending on the system you are using, specif Image Analysis softwares have different procedures to give you the results you are looking for.

For Bruker you may find something here: https://www.bruker.com/service/education-training/webinars/afm.html

For Asylum: https://afm.oxinst.com/webinars

NT-MDT: https://www.youtube.com/watch?v=fBHJ2avU0JY

If you have a SPIP license, you can use this method: https://www.youtube.com/watch?v=5_J79rD4iQA

Or you can use a free software like Gwyddion. Some step-by-step information on the image analysis can be found here: https://www.youtube.com/watch?v=OX8q1CYMf8Q

Good luck !

Best regards,

João

Gwyddion provides the root mean square roughness which is quite handy for basic roughness calculations.