The measured height of a graphene flake has been shown to vary with applied force from 1.7 nm to 0.4 nm, with a linear correlation. Since the thickness of a single graphene layer is expected to be 0.34 nm (atomic layer spacing in graphite), the error in measured thickness has decreased drastically by simply imaging with a higher applied force.

The key parameter to accurately measuring graphene is found to be the applied pressure. At low applied pressure the measured height is equivalent to the sum of the graphene layer thickness and the buffer layer thickness. As the pressure applied to the graphene by the AFM tip increases, the graphene is pushed into the buffer layer and a more accurate value is measured until finally the graphene is pushed through the buffer layer to the underlying substrate.

More information about this research can be found in the journal Nanotechnology 27 125704.

Further reading

Nanomechanical spectroscopy in tapping mode atomic force microscopy (Apr 2015)