Influence of thermal annealing on the properties of monolayer graphene
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Graphene has attracted great attention because of its potential in many areas, including terahertz applications. However, it is difficult to precisely control the electronic properties of graphene in practice because graphene is immediately affected by exposure to ambient atmospheric conditions. This results in unintended performance degradation of graphene-based devices. Thermal treatment is one of the methods to restore graphene toward its intrinsic properties. In this thesis, I investigate the influence of thermal annealing at several temperatures in vacuum on graphene properties using non-destructive methods. With investigating the variation of Raman peaks in graphene, I identified a decrease in defects and an increase in hole doping of graphene. Atomic force microscopy (AFM) and optical microscopy also allows us to intuitively identify the effect of thermal annealing on the graphene surface with respect to the reduction of surface residues and roughness. Lastly, terahertz spectroscopy reveals the variations in graphene, corresponding to those characterized by Raman and AFM, through reflectance measurements. This qualitative analysis may offer the possibility of an efficient, non-destructive, and complementary characterization approach to graphene characterization as well as the understanding of thermal annealing effects on graphene.