Highly aligned multi-wall carbon nanotubes were investigated with scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after bombardment performed using noble gas ions of different masses (argon, neon and helium), in an ultra-high-vacuum (UHV) environment. Ion irradiation leads to change in morphology, deformation of the carbon (C) honeycomb lattice and different structural defects in multi-wall carbon nanotubes. One of the major effects is the production of bond distortions, as determined by micro-Raman and micro-X-ray photoelectron spectroscopy. We observe an increase in sp${}^3$ distorted bonds at higher binding energy with respect to the expected sp${}^2$ associated signal of the carbon 1s core level, and increase in dangling bonds. Furthermore, the surface damage as determined by the X-ray photoelectron spectroscopy carbon 1s core level is equivalent upon bombarding with ions of different masses, while the impact and density of defects in the lattice of the MWCNTs as determined by micro-Raman are dependent on the bombarding ion mass; heavier for helium ions, lighter for argon ions. These results on the controlled increase in sp${}^3$ distorted bonds, as created on the multi-wall carbon nanotubes, open new functionalization prospects to improve and increase atomic hydrogen uptake on ion-bombarded multi-wall carbon nanotubes.

Atomic deuterium adsorption on multi-walled carbon nanotubes (MWCNTs) has been achieved with a high deuteration level (≃70% of deuterated carbon atoms), and studied using complementary spectroscopic techniques, namely, photoelectron spectroscopy and Raman spectroscopy. As a consequence of the deuterium (D) adsorption on the MWCNTs, the sp2 bonds of the C atoms are distorted toward an sp3 configuration, and the π plasmon excitation of the metallic MWCNTs is quenched, suggesting the transition to a semiconducting phase. Such a controlled deuteration in ultra-high vacuum conditions induces the opening of an energy gap in the metallic MWCNTs, with the valence band maximum at about ∼3.1 eV below the Fermi level. The bond distortion and the strain induced by the D uptake is evidenced by the modification of the Raman response. This work shows that the molecular cracking of D2 in ultra-high vacuum is an efficient way to obtain stable, homogeneous, and high uptake of deuterium atoms with minimal presence of defects.