NEXAFS characterization of nanostructured carbon thin-films exposed to hydrogen

Nanostructured carbon films were grown by supersonic cluster beam deposition using a focusing nozzle for selecting small clusters and increasing the deposition rate. The films present a pore structure in the mesopore range (maximum of the pore size distribution at 34 Å) with a specific surface area of 665 m2/g. Temperature programmed desorption (TPD) analysis shows sorption of hydrogen after hydrogen exposure. In the near edge X-ray absorption fine structure (NEXAFS) spectra a strong peak at ~ 288.5 eV, related to C-H bonds (hydrogen chemisorbed), is evident. After sample annealing at temperature of approximately 500°C, the prominent C-H* peak is strongly reduced. The samples experienced reiterated exposures to water vapor and hydrogen and subsequent annealings. The partial restoration of the C-H* peak after exposures and its decrease after moderate heating indicate that the sorption and release of hydrogen is a reversible process.