Accurate measurement of thickness of large-area graphene layers by neutron reflectometry

Neutron reflectometry was used to determine the thickness of large-area graphene layers on SiO2/Si substrates. Preliminary simulations showed that the optimum thickness of the SiO2 layer for neutron reflection is about a few hundred angstroms. The thicknesses of the graphene and the SiO2 layers were obtained by fitting the experimental reflectivity spectra. Transmission electron microscopy and Raman experiments were performed on the same samples, and verified that the neutron reflection results are reliable and accurate at the subangstrom level. This neutron reflectometry is nondestructive and applicable to wafer-size layers to yield the mean thickness. This accurate determination of the thickness will be helpful for managing quality of large-area graphene films.