Variable angle spectroscopic ellipsometry characterization of turbostratic CVD-grown bilayer and trilayer graphene

We report a Variable Angle Spectroscopic Ellipsometry (VASE) characterization of the surface of CVD-grown bilayer and trilayer graphene produced by multiple transfer on SiO2/Si and polyethylene terephthalate (PET) substrates. The graphene layers are randomly stacked. The study of the optical properties of single- and few-layer graphene on PET by means of VASE, which has not been published yet, could be useful in the light of novel graphene-based flexible and stretchable electronics applications. The Lorentz models proposed for the optical response of bilayer and trilayer graphene samples fit very well the experimental data. Some interesting properties have been observed. A never-before-reported absorption peak at ~3 eV on bilayer and trilayer graphene on SiO2/Si is discussed. The absorption peak due to resonant excitons has been found at ~ 4.4 eV on bilayer graphene on SiO2/Si and its value is red-shifted from ~4.6 eV in monolayer graphene to~ 4.4 eV in bilayer graphene. This peak shift has not been observed on bilayer graphene on PET substrates.