  Raman spectroscopy is the prime non-destructive characterization tool for
graphene and related layered materials. The shear (C) and layer breathing modes
(LBMs) are due to relative motions of the planes, either perpendicular or
parallel to their normal. This allows one to directly probe the interlayer
interactions in multilayer samples. Graphene and other two-dimensional (2d)
crystals can be combined to form various hybrids and heterostructures, creating
materials on demand with properties determined by the interlayer interaction.
This is the case even for a single material, where multilayer stacks with
different relative orientation have different optical and electronic
properties. In twisted multilayer graphene samples there is a significant
enhancement of the C modes due to resonance with new optically allowed
electronic transitions, determined by the relative orientation of the layers.
Here we show that this applies also to the LBMs, that can be now directly
measured at room temperature. We find that twisting does not affect LBMs, quite
different from the case of the C modes. This implies that the periodicity
mismatch between two twisted layers mostly affects shear interactions. Our work
shows that Raman spectroscopy is an ideal tool to uncover the interface
coupling of 2d hybrids and heterostructures.
