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

Abstract

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)].

Structural investigations of hydrogenated epitaxial graphene grown on 4H-SiC (0001)

“…The process of thermal dehydrogenation reported in Ref. 34 also agrees well with our results, as far as the d-spacing is concerned. On the other hand, the presence of negatively charged hydrogen ions in the graphene layers should be treated (among other mechanisms like spontaneous polarization of the substrate 35 ) as a possible additional origin of the p-doping of the hydrogenated graphene.…”

“…Indeed, the "C" model structure proposed in Ref. 34 predicts a situation, where negatively charged hydrogen atoms get loosely trapped between the graphene layers, leading to an increase of the interlayer distance to 3.66 Å , which is in agreement with our observations. The process of thermal dehydrogenation reported in Ref.…”

Structural consequences of hydrogen intercalation of epitaxial graphene on SiC(0001)

“…We emphasize that while XRR is not directly sensitive to the presence of hydrogen between the graphene sheets, H interlayer species are predicted to cause large average graphene interlayer expansion even for nanoscale graphene flakes (EG(0002) $3.7-3.9 Å ) 32 or very low H/C concentrations (EG(0002) $4.4 Å ). 33 Such EG interlayer expansion is not observed in this work despite the $0.1 Å confidence of the XRR model fits to the average graphene interlayer separation spacing. This suggests that if, indeed, the H intercalation process produces trapped interplanar H species, they do not modify the interplanar graphene spacing averaged over large ($lm) lateral length scales.…”

Carrier type inversion in quasi-free standing graphene: studies of local electronic and structural properties

“…With the annealing of the sample in hydrogen environment at temperatures around 1100 °C, the H 2 molecule will enter the graphene stack from the terrace edges and defect sites, where it’s position is more energetically favorable 24 . The intercalated hydrogen molecule will then dissociate into H atoms to form Si-H bonds, which will decouple and lift the IFL from the SiC substrate 8 24 25 and convert it to 1LG ( Fig. 3e ).…”