Significant interlayer coupling in bilayer graphene and double-walled carbon nanotubes: A refinement of obtaining strain in low-dimensional materials

This paper solves a longstanding debate: Raman measurements on double-walled carbon nanotubes appear to show that significantly more pressure than expected can be transmitted to the inner tube. We reinterpret those Raman spectra consistently reported in the literature, by assigning the Raman peaks to coupled vibrational modes of both walls, instead of individual contributions from the inner and outer tubes. These coupled vibrational modes are important for the correct interpretation of the Raman shift from strained layered 2D materials (we demonstrate it on bilayer graphene as an example), for researching the mechanical properties, thermal expansion, and strain engineering of two-dimensional materials.