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(a) The original Raman spectra measured on a 6H-SiC substrate as a function of e-beam irradiation time and (b) the corresponding Raman spectra with the Raman signals coming from the 6H-SiC substrate subtracted.
(a) The relative Raman intensities of the D and 2D peaks compared to the G peak as e-beam irradiation time increases and (b) the zoom-in of the 2D peak measured on the 6H-SiC substrate irradiated by e-beam for 2 h with the curve fitted to the measured data by a single Lorentzian function.
Schematic diagram showing the formation of epitaxial graphene on the 6H-SiC substrate by directly irradiating e-beam on the sample surface: (a) 6H-SiC substrate before e-beam irradiation, (b) the early stage of e-beam irradiation with many small graphene islands distributed randomly on the sample surface, (c) the lateral growth of the formed graphene islands as e-beam irradiation time increases, and (d) the 6H-SiC substrate after e-beam irradiation is completed where epitaxial graphene layers cover most of the e-beam irradiated area.
(a) Cross-sectional HR-TEM image of the 6H-SiC substrate irradiated by e-beam for 2 h where 7∼8 layers brighter than the others can be seen on the surface. The spacing between adjacent brighter layers, measured to be ∼0.32 nm in (b) the profile of HR-TEM signal intensity, confirms that the brighter layers are actually graphene layers, in conjunction with the AES spectra of (c) C KLL and (d) Si KLL electrons before and after e-beam irradiation.
The measured resistances (open squares) between the inner and outer circular contacts in the CTLM structure with varying contact pad spacing and the curve (red line) fitted to the measured data by using the known equation between resistance and contact pad spacing for the CTLM structure.
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