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 flexibleand stretchable electronics applications. The Lorentz models proposed for the optical response of bilayer and trilayer graphene samples fitvery well the experimental data. Some interesting properties have been observed. A never-before-reported absorption peak at e3 eV on bilayer and trilayer graphene on SiO2/Si is discussed. The absorption peak due to resonant excitons has been found at e4.4 eV on bilayer graphene on SiO2/Si and its value is red-shifted from e4.6 eV in monolayer graphene toe4.4 eV in bilayer graphene. This peak shift has not been observed on bilayer graphene on PET substrates.