Experimental Study of Few‐Layer Graphene: Optical Anisotropy and Pseudo‐Brewster Angle Shift in Vacuum Ultraviolet Spectral Range

Abstract

The optical properties of mono‐ and trilayer graphene on SiO2/Si substrate are studied at hydrogen Lyman‐alpha (121.6 nm) spectral line for the first time. The optical anisotropy of graphene at this wavelength is experimentally demonstrated by retrieving the anisotropic “effective” optical constants. The results confirm that the axis of symmetry is nearly perpendicular to the surface and coherently related to the π‐orbitals’ structural orientation. Furthermore, it is observed that graphene strongly affects the performances of the substrate by inducing a pseudo‐Brewster angle downshift, which depends on the number of graphene layers. This finding is in contrast with what occurs in the visible spectral range, where the upshift of the pseudo‐Brewster angle is experienced in similar samples.

Measurement of the Ellipsometric Parameters of Thin Graphene Layers in the Extreme Ultraviolet

“…Since the only difference between the two systems is the presence of graphene, it is clear that the difference in contrast is due to this material. This results confirm that the equipment and the measurement procedure allow to detect even the presence of extremely thin thickness film [5], the error associated to the measurements is ±0.011. (Right) reflectance ratio for the same two assemblies.…”

“…The polarimeter device has been tested as a tool for performing ellipsometric measurements of 2D materials [5,6] by applying the procedure described hereafter. The CiPo beamline allows the selection of the polarization state of the light.…”

“…one sample of three-layer graphene deposited onto SiO2 substrate; 2. one bare SiO2 substrate. Both samples have been measured in order to retrieve the effects of three-layer graphene on the contrast and reflectance ratio of the SiO2 substrate [5]. The measured contrast in the two analysed cases is shown in figure 4a); the typical error associated to the experimental data is ±0.014 @ 17.5 eV and ±0.005 @ 30 eV.…”