Second-order Overtone and Combinational Raman Modes of Graphene Layers in the Range of 1690 cm-1 to 2150 cm-1

TL;DR

This study investigates second-order overtone and combinational Raman modes in graphene within 1690-2150 cm-1, revealing how interlayer interactions and stacking order influence these modes, thus expanding Raman spectroscopy's application in graphene analysis.

Contribution

It identifies new Raman modes in graphene related to stacking order and interlayer interactions, providing insights into phonon dispersion and electronic properties.

Findings

M band disappears in single-layer graphene

Interlayer interaction is crucial for M band presence

M band can serve as a fingerprint for AB-stacked bilayer graphene

Abstract

Though graphene has been intensively studied by Raman spectroscopy, in this letter, we report a study of second-order overtone and combinational Raman modes in an unexplored range of 1690-2150 cm-1 in nonsuspended commensurate (AB-stacked), incommensurate (folded) and suspended graphene layers. Based on the double resonance theory, four dominant modes in this range have been assigned as 2oTO (M band), iTA+LO, iTO+LA and LO+LA. Differing to AB-stacked bilayer graphene or few layer graphene, the M band disappears in single layer graphene. Systematic analysis reveals that interlayer interaction is essential for the presence (or absence) of M band whereas the substrate has no effect on this. Dispersive behaviors of these "new" Raman modes in graphene have been probed by the excitation energy dependent Raman spectroscopy. It is found that the appearance of the M band strictly relies on the AB stacking, which could be a fingerprint of AB-stacked bilayer graphene. This work expands the unique and powerful abilities of Raman spectroscopy on study of graphene and provides another effective way to probe phonon dispersion, electron-phonon coupling, and to exploit electronic band structure of graphene layers.