  Atomic Force Microscopy (AFM) in the tapping (intermittent contact) mode is a
commonly used tool to measure the thickness of graphene and few layer graphene
(FLG) flakes on silicon oxide surfaces. It is a convenient tool to quickly
determine the thickness of individual FLG films. However, reports from
literature show a large variation of the measured thickness of graphene layers.
This paper is focused on the imaging mechanism of tapping mode AFM (TAFM) when
measuring graphene and FLG thickness and we show that at certain measurement
parameters significant deviations can be introduced in the measured thickness
of FLG flakes. An increase of as much as 1 nm can be observed in the measured
height of FLG crystallites, when using an improperly chosen range of free
amplitude values of the tapping cantilever. We present comparative Raman
spectroscopy and TAFM measurements on selected single and multilayer graphene
films, based on which we suggest ways to correctly measure graphene and FLG
thickness using TAFM.
