Identification of inner and outer shells of double-wall carbon nanotubes using high-pressure Raman spectroscopy

The high-pressure Raman response of double-wall carbon nanotubes (DWCNTs) in the radial breathing mode (RBM) frequency region can be used for the identification of both the inner and their respective outer tubes. A simple anharmonic model of this system demonstrates that the pressure response of the inner tube in a DWCNT is uniquely defined by the inner-outer tube spacing. Consequently, a plot of the normalized pressure coefficients of the inner tube RBM frequencies as a function of their ambient pressure frequency serves as a map which allows the identification of unknown DWCNTs. The present experimental results form the basis of such a plot.