Magneto-Raman Microscopy for Probing Local Material Properties of Graphene
The combination of confocal Raman microscopy and magnetic fields at 4 K yields the opportunity to investigate and tune the electron-phonon interaction in graphene and few-layer graphene. In particular, excitations between Landau levels can resonantly couple to the Raman active long wavelength optical phonon (G-phonon), when their energies are matched, resulting in magneto-phonon resonances (MPRs). Such resonances at ±3.7 T are presented in the figure and highlighted by arrows. The details of the coupling depend on various material properties of the investigated graphene layer. From the MPRs, device parameters such as the electron-phonon coupling constant or the Fermi velocity of the charge carriers can be extracted. Interestingly for low charge carrier doping, the Fermi velocity shows signatures of many-body interaction effects.
This measurement was realized with the attoRAMAN.
C Neumann, et al., Nature Communications volume 6, 8429 (2015)
Addressing Strain and Doping by Cryogenic Raman Mapping
T. Verhagen in the Czech Academy of Sciences in Prague conducted a comprehensive study on the effects of temperature induced strain on two-layer Graphene sheets using an attoRAMANxs confocal Raman microscope. Using isotopical labelling, they can differentiate the influences of the surface on the lower and on the upper layer. A correlation analysis allows to separate strain and doping contributions to the observed Raman shifts. This detailed analysis allows to estimate temperature induced strain and doping contributions that are important when analyzing transport measurements on graphene mono- and bilayers.
T. G. A. Verhagen, et al., Phys. Rev. B 92 125437 (2015)