Optical anisotropy of 6-A graphene nanoribbons synthesized inside aligned nanotubes

• Thermal heating up to 750°C of 3-AGNR encapsulated inside SWCNT leads to formation of 6-AGNR • Synthesis of GNR inside a host matrix of aligned nanotubes provides the similar alignment of GNR • The Raman signal from aligned GNR@SWCNT film reveals a strong anisotropy 6- atom-wide armchair graphene nanoribbons (6-AGNRs) are synthesized through two-step process inside a matrix of single-walled carbon nanotubes (SWCNTs) pre-aligned by controlled vacuum filtration method. The typical Raman modes of nanoribbons as radial breathing-like mode at 453 cm -1 , edge C-H mode at 1245 cm -1 and middle-range mode at 1270 cm -1 appear in the Raman spectra alongside with the modes of carbon nanotubes. Polarized Raman spectra reveal the strong anisotropy of the signal depending on the orientation of the sample, as the alignment of nanoribbons is provided by the alignment of the nanotube host matrix. This result is in agreement with polarized Raman density functional theory (DFT) calculations carried out for the main vibrational modes of the 6-AGNR. The proposed method ensures the alignment of graphene nanoribbons (GNRs) on a macroscale and preserves the anisotropy of their optical properties.