NEXAFS characterization of nanostructured carbon thin-films exposed to hydrogen

Nanostructured carbon films were grown by supersonic cluster beam depositio n using a focusing nozzle for selecting small clusters and increasing the d eposition rate. The films present a pore structure in the mesopore range (m aximum of the pore size distribution at 34 Angstrom) with a specific surfac e area of 665 m(2)/g. Temperature programmed desorption (TPD) analysis show s sorption of hydrogen after hydrogen exposure. In the near edge X-ray abso rption fine structure (NEXAFS) spectra a strong peak at similar to 288.5 eV , related to C-H bonds (hydrogen chemisorbed), is evident. After sample ann ealing at temperature of approximately 500 degreesC, the prominent C-H* pea k is strongly reduced. The samples experienced reiterated exposures to wate r vapor and hydrogen and subsequent annealings. The partial restoration of the C-H* peak after exposures and its decrease after moderate heating indic ate that the sorption and release of hydrogen is a reversible process. (C) 2001 Elsevier Science B.V. All rights reserved.