Effect of Surface Adsorbates on Graphene Probed by Hall-Effect and Raman Spectroscopy

The impact of adsorbed gases on graphene layers grown by SiC sublimation is investigated by temperature-dependent Hall-effect and Raman spectroscopy. For samples stored in ambient laboratory conditions, irreversible changes are seen in sheet resistance (Ush), mobility, and carrier concentration after heating to 400 K in vacuum. Subsequent heating to 400 K produces no additional changes in Ush, mobility or carrier concentration. Re-exposure of this ‘clean ’ surface to air produces only minor changes in the electrical characteristics of the film. These kinetics suggest chemisorbed species produce a larger impact on electrical transport in graphene layers than do physisorbed species. The graphene Raman 2D peak is shifted ~15 cm-1 at 500 °C in vacuum, while the room temperature Raman 2D frequency is unchanged after heating