Gap Opening in Double-Sided Highly Hydrogenated Free-Standing Graphene

Atomic deuterium bonding to multi-walled carbon nano tubes

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.

Spectromicroscopy Study of Induced Defects in Ion-Bombarded Highly Aligned Carbon Nanotubes

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 sp3 distorted bonds at higher binding energy with respect to the expected sp2 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 sp3 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.

Homogeneous Spatial Distribution of Deuterium Chemisorbed on Free-Standing Graphene

Atomic deuterium (D) adsorption on free-standing nanoporous graphene obtained by ultra-high vacuum D2 molecular cracking reveals a homogeneous distribution all over the nanoporous graphene sample, as deduced by ultra-high vacuum Raman spectroscopy combined with core-level photoemission spectroscopy. Raman microscopy unveils the presence of bonding distortion, from the signal associated to the planar sp2 configuration of graphene toward the sp3 tetrahedral structure of graphane. The establishment of D–C sp3 hybrid bonds is also clearly determined by high-resolution X-ray photoelectron spectroscopy and spatially correlated to the Auger spectroscopy signal. This work shows that the low-energy molecular cracking of D2 in an ultra-high vacuum is an efficient strategy for obtaining high-quality semiconducting graphane with homogeneous uptake of deuterium atoms, as confirmed by this combined optical and electronic spectro-microscopy study wholly carried out in ultra-high vacuum conditions.