AFM is of the useful methods for scanning of rough surface which was not tool before 1989. It is applicable for reservoir rock study.

you can refer to Hilner et al. (2015) The effect of ionic strength on oil adhesion in sandstone – the search for the low salinity mechanism, Scientific Reports,

link: http://www.nature.com/srep/2015/150422/srep09933/full/srep09933.htm

Kareem (2015) Towards a Nanoscopic Understanding of Oil-sandstone Wettability - Implications for Enhanced Oil Recovery, Proceeding of 18th European Symposium on Improved Oil Recovery

link of abstract: http://earthdoc.org/publication/publicationdetails/?publication=79976

Regards

Massih

Are there any limitations for roughness calculation? - yes, because of Z scale, which is usually no higher than 20um on one scan. It means, if you will scan 25x25um square, differences in Z cant be larger than 20um. Think, better for porous materials is nano/micro topography and 3d reconstruction. If material is reflective, maybe light profilometry should be better than AFM. AFM is for small structure elements. Better than microscope name it nanoscope.

Thank you very much. 

Dear Masih, I checked the references you suggested. They have used AFM for roughness estimation, nevertheless for smooth and less rough materials such as quartz. While the roughness scale in nonpolished sandstone or carbonate rocks could sometimes exceed 400 microns.

Dear Dr. Rebis

Thank you so much for your reply.

It appears that you have had quite a good experience working with AFM technology. I was wondering if there could be a way to modify the setup configuration for large roughnesses?

What You mean 'large roughness'? Z scale enlarge? If so, I did not worked on any AFM/SPM device with higher Z than 20um. In most cases piezoelectric ceramics are used as 'engine' moving sample in all directions. That is why Z scale is (in most cases) not so high. I believe there is some AFM system with z aprox 50um, but I do not believe if such scanner can may work with angstrem resolution. Maybe if You could take into consideration making 50 times 5x5um measurements instead of one 250x250um, statistics taken from roughness of many 3D diagrams may answer your question?

It depends on how your AFM operates to scan the surface. There are some piezo stages available that have long z-ranges (npoint is one such company to look into). Combining one of those stages with an AFM that can move the tip in x-y may allow you to achieve a z-range closer to what you are looking for.

I think AFM could not give you the roughness measurement of your sample, since the height is far larger than 1micrometer, which greatly exceed the Z scanning range of AFM. The RMS, raw roughness or averaged roughness of relatively flat surface could be measured using AFM.

Thank you all for taking your time and helping me out.

I appreciate all your answers.

In general yes, but you need to take into account all mentioned above, especially about z range of the scanner.

There also nice presentation about problems of rougheness estimation:

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

Dr. Safari,

As I know about the AFM topography analysis the limitation of height measurement is about 20 micron and if voids are larger than that it will readjust as given in the diagram. So if some one say yes the Z axis height more than the limitation can be measured than I said yes but only surface topography not the depth analysis. I may be wrong and if so, than I also required some journal papers from the AFM experts.

 With regards.

Dr Safari,

If you believe your samples will have a Z range of ~400microns, AFM will most certainly not be able to obtain effective roughness measurements. Conventional laser profilometry would be more suitable for this application. If your samples could be previously prepared by polishing, you may be able to obtain some data (intermittent contact imaging would be the best approach) on the polished porous rock surface. Approaches like these have been employed previously in other fields when dealing with increased-roughness surfaces, but it depends on whether or not polishing would affect your research question.

Another method could be trying to obtain reduced scan sizes (5x5 microns or smaller) to get an idea of the surface topography at that scale length. Even if your Z range is big, if there are relatively conserved areas it may be possible to image such areas with the AFM.

Best of luck!

Sebastian