Chemical reactivity of pristine and defected supported graphene.

Carraro G., Vattuone L., Smerieri M., Celasco E., Savio L., Rocca M.

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II - Fisica della materia
GSSI Ex ISEF - Aula C - Venerdì 27 h 09:00 - 12:00
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Due to its exceptional properties graphene (G) is considered as one of the most promising materials for the future. Its possible use includes gas sensoring, but the underlying chemistry is still unclear since clean G was reported to be nearly unreactive for ammonia. The sensitivity towards CO was thereby even lower than for ammonia. We report non-dissociative chemisorption at cold, pristine G on Ni(111). The adlayer remains thereby stable up to 125 K, allowing to estimate an adsorption energy of 0.58 eV/molecule at low coverage, much higher than for unsupported G films (0.014 eV/molecule). Among the different adsorption configurations of G on Ni(111), the top-fcc one resulted to be the most reactive. No adsorption occurs, on the other hand, at G supported on the less interacting polycrystalline Cu substrate. We investigated experimentally also the effect of doping with nitrogen atoms and find further increases the reactivity of the G/Ni(111) system towards CO. The doped layer is obtained by sputtering pristine G/Ni(111) with $N_{2}^{+}$ ions. For an $\sim 11$% dopant concentration, an additional electron energy loss at 238 meV appears in the HREEL spectra besides the loss around 256 meV present also on pristine G/Ni(111). The new feature corresponds to a CO species with a higher desorption temperature and, consequently, a higher adsorption energy than the one forming on pristine G/Ni(111). At low coverage, the adsorption energy is estimated to be $\sim 0.85$ eV/molecule.

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