Mid-IR reflectance spectrum of multilayer graphene: Influence of adsorbate at the graphene – substrate interface

Water adsorbate at the interface between graphene and SiO₂/Si substrate is found to affect the reflectance spectra of (3 – 6)-layer graphene in the mid-IR range (λ = 2 – 16 μm). The sample under study was previously kept in acetone vapour to remove water adsorbate from the graphene – substrate interface. The graphene reflectance in the range of 8–16 μm tends to decrease with recovery of water adsorbate layer at the graphene – substrate interface at room temperature and relative air humidity RH = 40% – 60%. The observed effect is most likely caused by the blue shift of the absorption edge at interband transitions due to the change in the Fermi level position in the graphene valence band under the influence of the charge induced in graphene by the water adsorbate film.