Pressure coefficients of Raman modes of carbon nanotubes resolved by chirality: environmental effect on graphene sheet

Abstract

Studies of the mechanical properties of single-walled carbon nanotubes are hindered by their availability only as ensembles of tubes with a range of diameters. However, tunable Raman spectroscopy is capable of identifying individual tubes from such ensembles. Interestingly, both the radial breathing mode and, surprisingly, the G-mode pressure coefficients exhibit strong environmental effects, which are largely independent of the nature of the environment. We show that the G-mode pressure coefficient varies with diameter, consistent with the thick-wall tube model. Reappraisal of literature data for graphene and graphite suggests revision of both the G-mode Gr¨uneisen parameter γ and the shear deformation parameter β toward the value of 1.34.