Juli 2020

Graphene fine structures visualized by high-resolution confocal Raman imaging

Raman imaging is a non-destructive tool for evaluating the quality of 2D materials as strain, doping, defects and layer number can be assessed. These two large-area Raman images visualize defect density (top) and strain fields (bottom) in a CVD-grown graphene flake at high spatial resolution (100 nm per pixel). They were acquired using the fully automated Raman microscope alpha300 apyron equipped with a 532 nm laser for excitation and TrueSurface for focus stabilization.

The upper Raman image is color-coded according to the intensity of the D-band in the recorded Raman spectra. It visualizes crystal defects, as the D-band intensity depends on the defect density in the carbon lattice. The observed width of the fine structures is very close to the diffraction limited lateral resolution achievable with 532 nm excitation, demonstrating the microscope’s high performance.

The lower Raman image is color-coded according to the peak position of the 2D-band, which was quantified by a Pseudo-Voigt fit. The image visualizes local strain/doping effects, as the frequency of the 2D-band is influenced by local strain and, to a lesser extent, by doping.

These examples offer conclusive proof that with an advanced and highly sensitive system, Raman imaging alone can provide access to the finest details of graphene crystal properties.

High-resolution Raman imaging of CVD-grown graphene (100 nm per pixel). Top: Raman image representing the intensity of the D-band, visualizing crystal defects. Bottom: Raman image representing the frequency of the 2D-band, visualizing local strain/doping effects.