Hydrogen adsorption on single-walled carbon nanotubes studied by core-level photoelectron spectroscopy and Raman spectroscopy

We have investigated the adsorption of atomic hydrogen on vertically aligned carbon nanotube (CNT) films using in situ synchrotron-radiation-based core-level (CL) photoelectron spectroscopy and Raman spectroscopy. From C 1s CL spectra, we identified a CL peak component due to C–H bonds of carbon atoms in single-walled carbon nanotubes (SWCNTs). We also found the suppression of π-plasmon excitation, indicating that the hydrogen adsorption deforms the bonding structure. Raman spectra of the SWCNT film indicated that the radial-breathing-mode intensities of SWCNTs decreased due to the adsorption-induced bonding-structure deformation. Moreover, the decrease for small-diameter SWCNTs was more severe than that for large-diameter SWCNTs. Our results strongly suggest that the hydrogen adsorption, which induces the structure deformation from sp2 to sp3-like bonding, depends on the diameter of SWCNTs.