Hydrogen trapping state associated with the low temperature thermal desorption spectroscopy peak in hydrogenated nanostructured graphite

Hydrogenated nanostructured graphite has been reported to exhibit a characteristic peak at around 600-800 K in thermal desorption spectroscopy (TDS). The origin of this peak is still controversial. We have reexamined it based on a combination Fourier transform infrared (FT-IR), electron diffraction, and electron energy-loss spectroscopy (EELS) Study. The FT-IR spectrum of HNG exhibited an unknown broad absorption band at very low frequencies around 660 cm(-1), which almost disappeared by annealing up to 800 K. Electron diffraction as well as plasmon peaks in EELS detected unusual shrinkage and subsequent expansion of the graphene interlayer distance by hydrogen incorporation and desorption with annealing, which were well correlated with the change in intensity of the 660 cm(-1) IR band. An energetically stable configuration was found by theoretical model calculations based on GAUSSIAN03. All the present results are consistent with our previous studies, which suggested that hydrogen is loosely trapped between graphene layers [S. Muto et al., Jpn. J. Appl. Phys. 44, 2061 (2005); T. Kimura et al., J. Alloys Compd. 413, 150 (2006)]. (C) 2008 American Institute of Physics.