Graphene characterization and device fabrication: doping analysis, strains engineering towards terahertz radiation
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As one of the most promising two-dimensional materials, graphene’s outstanding electrical, mechanical and optical properties have made many new devices possible. Its ultra-thin thickness makes both the fabrication and characterization of graphene-based device challenging. In my thesis, I will discuss different approaches to fabricate and characterize graphene devices for the use in transport and THz radiation devices, as well as strain engineering. These approaches could be potentially used to produce next generation electrical devices, photonics devices and generate ultra-high pseudomagnetic fields. To analyze graphene’s quality, I use multi-variable Raman spectroscopy for identifying graphene’s defect density, strain and doping. A case study of strain redistribution on a silicon dioxide grating with sub-diffraction limit resolution of the strain variation is presented, where atomic force microscopy and Raman spectroscopy are applied for characterization. The strain redistribution is used to determine the strain dependent friction between graphene and the substrate. This work has also lead to more precise determination of the strain and shear response using the 2D phonon band. Improvements of the electrical property of graphene is achieved by using graphene encapsulated between atomically flat hBN layers as well as tuning surface hydrophobicity via substrate salinization. This also provides an improved method to optically determine charge density in graphene with order of magnitude enhancement in sensitivity.