Single layers of MoS2 deposited on ITO appear as high as 4-5 nm in AFM. I'm pretty confident this is an overstimation since the Raman and photoluminescence spectra show the single layer nature of the sample.
The AFM scanner is well-calibrated so that is not the problem.
I wonder if the differences in tip-sample interaction, or water or other adlayers can be responsible for this inconsistency in AFM results.
Has anyone observed this issue?
Dear Raul D. Rodriguez,
You're right, the problem is there. I also faced it during thickness measurements of graphene atomic lattice(s)/layers.
Actually, AFM can/should provide height detection up to 0.1 nm. However, it is very difficult in practical to get very precise values for 2D film height, as it can depend upon changing cohesive forces between 2D film and supporting substrate. Sometimes film surface absorbs water vapors and a very thin layer of water is formed on the film, and sometimes different contaminations stay on the surface of film. Hence, it becomes very hard to determine actual thickness of the 2D films.
If this regard, the Raman and photoluminescence spectra would be more reliable.
Please investigate the ultrasonic methods. It maybe you can use it to determine thickness of layers.
There are further method for Film thickness determination:
1. X-Ray Reflectivity (XRR) which is very precise if you have very smooth substrates (Rq
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