Hydrogen Incorporation and Reaction with Graphene on SiO2
Starting samples consisted of monolayer graphene grown by chemical vapor deposition (CVD) on copper and then transferred to SiO2 films (285 nm thick) on Si. Bare SiO2 films of the same thickness on Si were also submitted to the same experiments for the sake of comparison. Samples were loaded in a static pressure and resistively heated quartz tube furnace, which was initially pumped down to 2 x 10-7 mbar. Hereafter, they were annealed at temperatures ranging from 100 up to 1000 ºC, for 1 h, in a 1000 mbar H2 atmosphere enriched in the 2H (D) rare isotope. This rare isotope was chosen in order to distinguish H incorporated during experiment from those incorporated due to air exposure. As references, samples annealed at the same temperatures but in ultra high vacuum (UHV) were also investigated. D quantification was accomplished by nuclear reaction analyses (NRA), using the D(3He,p)4He nuclear reaction at 700 keV (1012 D/cm2 sensitivity and 5% accuracy). In addition, Raman scattering and X-ray photoelectron spectroscopy (XPS) were used for the characterization of the graphene.
Distinct D incorporation behavior was observed for samples with and without graphene overlayer. For annealing temperature above 100ºC, we observed a higher incorporation of species in graphene when compared to bare SiO2 samples. This incorporation reaches saturation for temperature around 400ºC. XPS measurements suggest the formation of C-H on graphene, increasing its relative concentration with temperature until 800ºC. At higher annealing temperatures, the etching of graphene layer takes place introducing bonding configurations related to defective states. Mechanisms of hydrogen reaction and incorporation based on the observed results will be discussed.
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