Confocal Raman imaging is an ideal method for studying 2D materials because it reveals their molecular characteristics through a nondestructive and fast procedure. It is used to describe the orientation of layers and to investigate defects, strain, and functionalization of these materials as their Raman properties are determined by molecular bonds, relative orientation, and number of layers. Their morphological details can be visualized with scanning electron microscopy (SEM). By correlating the information of both approaches with RISE™ (Raman Imaging and Scanning Electron) microscopy, the sample can be more thoroughly analyzed at high resolution.
Here the stacking, folding, and twisting of bilayer graphene was investigated. These factors strongly influence its phononic and electronic properties.
Correlative Raman-SEM (RISE™) imaging was performed with a combined WITec/ZEISS microscope for the analysis of bilayer graphene that was obtained by chemical vapor deposition and placed on a Si/SiO2 substrate.
The SEM image shows that the sample consists of monolayer and multi-layered graphene areas (Figure 1). Whether and how the multi-layers are twisted was established by analyzing the position of the G and 2D peaks of graphene, the peaks' intensities, and their full widths at half maximum (FWHM) (Figure 2).
Additional 2D' and R bands allowed for the determination of the twist angles. Figure 3 shows the color-coded RISE® image derived from the spectra.
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