The pressure response of double-wall carbon nanotubes has been investigated by means of Raman spectroscopy up to 10 GPa. The intensity of the radial breathing modes of the outer tubes decreases rapidly but remain observable up to 9 GPa, exhibiting a behavior similar (but less pronounced) to that of single-wall carbon nanotubes, which undergo a shape distortion at higher pressures. In addition, the tangential band of the external tubes broadens and decreases in amplitude. The corresponding Raman features of the internal tubes appear to be considerably less sensitive to pressure. All findings lead to the conclusion that the outer tubes act as a protection shield for the inner tubes whereas the latter increase the structural stability of the outer tubes upon pressure application.Comment: PDF with 15 pages, 3 figures, 1 table; submitted to Physical Review

The pressure evolution of the Raman spectrum of graphene grown by chemical vapor deposition on polycrystalline copper is investigated with the use of polar and nonpolar pressure transmitting media (PTM). The $G$ and 2$D$ Raman bands exhibit similar pressure slopes for both PTM irrespective of any unintentional initial doping and/or strain of the samples. Our analysis suggests that any pressure-induced charge transfer effects are too small to influence the pressure response of graphene; rather, it is determined by the compressibility of the substrate and the graphene interaction with the substrate and the PTM. For the nonpolar PTM, a peculiar pressure behavior of graphene is observed in the PTM solidification regime, which resembles that of freestanding graphene.