Dielectric screening in polyynes encapsulated inside double-wall carbon nanotubes

A resonance Raman study of the polyyne molecule ${\mathrm{C}}_{10}$H${}_{2}$ encapsulated inside double-wall carbon nanotubes (C${}_{10}$H${}_{2}$@DWNT), excited with many different laser energies between 1.92 and 2.71 eV, is presented. A resonant enhancement of the Raman peaks of the polyynes was observed and the intensity versus laser energy profile was fitted by two Voigt curves associated with resonances with the incident and scattered photons. The charge transfer between the molecule and the nanotubes was evidenced by the shift in the nanotube Raman $G$ band. The comparison of the optical energies of the polyynes encapsulated inside single- and double-wall carbon nanotubes reveals that the screening effect on the polyynes is mainly due to the inner tube of the double-wall carbon nanotubes.