Research Paper On Raman Line Scan Mapping

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5.3.2. Raman line scan mapping
Spatial line scans of the graphene Raman G and 2D modes were made across the middle of the micro-ring resonators for both 10μm and 20μm radius devices. The spectra were taken using 100X objective lens, and the spatial measurements were obtained with a step size of 0.1μm long a horizontal.
Typical Raman spectra at ON, and OFF of the waveguide are shown in Fig. 5.3 for G peak and Fig 5.4 for 2D peak position, respectively. These clearly reveal the up-shift in peak frequency where the graphene sits on the underlying silicon waveguide structure. The 2D-peak is well described by a by a symmetric Lorentzian function, a signature of single layer graphene [8]. Rather we found that the fit to the 2D peak was
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The second underlying scattering mode (G-), responsible for the asymmetry, also exhibits a much more significant decrease in width of ~35% G-G (G) from ~20cm-1 to~13cm-1 as we go from the suspended graphene to where the graphene sits on the cavity waveguide structure. Asymmetry in the graphene Raman G-peak has previously been attributed to highly localised charge inhomogeneity within the laser probe area [26], i.e. on the sub-micron scale and it has also already been observed when comparing Raman spectra of suspended graphene with that supported by a substrate [22]. Recent studies of graphene supported by nanostructured surfaces [27] have also revealed a multi-peak fine-structure in the G-band, which was interpreted as being the result of extreme curvature or ‘wrinkling’, similar to what is observed in single wall carbon nanotubes. In this case, the doubly degenerate in-plane E2g optical mode can be split between phonons along the nanotube axis, and those that are perpendicular to it, with the degree of splitting, being a strong function of the nanotube size (i.e. degree of curvature), even in the absence of any externally applied strain [28]. G-peak splitting has also been observed in graphene under uniaxial strain [5] and in isolated Carbon nanotube’s under hydrostatic pressure [29] where the curvature-sensitive lower

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