Multi-Wavelength Raman Characterization of Back-Gated Monolayer and Bilayer Graphene

In this work, we investigate the Raman spectrum of gated monolayer and bilayer graphene devices. We used Raman spectroscopy with three different excitation wavelengths: (488nm, 514nm and 633nm). After producing graphene sheets by scotch tape technique, Raman spectrometry used to distinguish between bilayer, mono layer and other few layer of graphene. We contact the wires on the flakes using micro-soldering method then we applied gate voltage on monolayer and bilayer graphene and investigate the changes in peak of the Raman spectra in different wavelengths in different voltages. Raman spectroscopy probes phonons as well as electronic states. If the electronic dispersion changes, the Raman spectrum will also changes. The shifts of the Raman spectra peaks of the monolayer and bilayer are explained in the current work. Charge carrier concentration as a function of gate voltage in gated graphene is shown as well as the position of the G peak and 2D peak graphene versus gate voltage. For monolayer devices we observed the expected behavior for doped devices. For bilayer devices, we present a comparison between the theoretical model and our experimental results.