Observation Of Low-Frequency Combination And Overtone Raman Modes In Misoriented Graphene

Stacking disorder will significantly modify the optical properties and interlayer coupling stretch of few-layer graphene. Here, we report the observation of the Raman breathing modes in the low-frequency range of 100-200 cm(-1) in misoriented few-layer graphene on a SiO2/Si substrate. Two dominant Raman modes are identified. The one at similar to 120 cm(-1) is assigned as the E-g + ZO' combination mode of the in-plane shear and the out-of-plane interlayer optical phonon breathing modes. Another peak at similar to 182 cm(-1) is identified as the overtone mode 2ZO'. The appearance of these Raman modes for different twist angles indicates that stacking disorder in few-layer graphene significantly alters the Raman feature, especially for those combination modes containing the interlayer breathing mode. Further investigation shows that the two Raman vibrational modes (similar to 120 and similar to 182 cm(-1)) are strongly coupled to the excitation laser energy, but their frequencies are independent of the number of graphene layers before folding. The present work provides a sensitive way to study the phonon dispersion, electron-phonon interaction, and electronic band structure of misoriented graphene layers.