Raman study of the high-pressure hydrogenated single-wall carbon nanotubes: In search of chemically bonded and adsorbed molecular hydrogen

Single-wall carbon nanotubes (SWNT) hydrogenated at P ≈ 5.0 GPa and T ≈ 500 °C (SWNT-H) were investigated by micro-Raman spectroscopy. The main feature of the Raman spectrum of the as-prepared SWNT-H is a giant structureless hot luminescence background that screens all vibrational modes. This disorder-induced background, attributed to random binding of the hydrogen atoms, vanishes after annealing of the SWNT-H in vacuum or in air. The changes in the Raman spectra of the partially annealed samples reflect the gradual decrease of structural disorder, related to removal of randomly bonded hydrogen. Complete outgassing restores the characteristic Raman spectrum of the pristine SWNT.