Enhancement Effect of Low-Frequency Raman Modes in Graphene Nanoscrolls

Graphene nanoscrolls (GNSs) are unique structures with interlayer coupling modes distinct from those in graphene and carbon nanotubes, exhibiting potential physical properties yet to be explored. Here we investigated the low-frequency Raman modes in GNSs formed from 1 to 3 layer graphene (1-3LG). The results of the Raman spectroscopy show that both shear (C) and layer breathing (LB) modes have appeared in monolayer graphene nanoscrolls (1L-GNSs), although these modes never exist in the flat 1LG. Remarkably, both 2L- and 3L-GNSs exhibited multiple low-frequency modes linked to other layer numbers, revealing the emergence of additional interlayer coupling. Annealing significantly enhanced low-frequency Raman signals and introduced additional modes, with the C₂₁ mode intensity increasing nearly 3-fold and LBM₆₁ intensity rising 16-fold. Transmission electron microscopy (TEM) imaging showed reduced ∼0.3 Å interlayer spacing after annealing, indicating stronger interlayer coupling. This work provides important scientific evidence for understanding the interlayer coupling in GNSs.