Amorphous hydrogen-free carbon films (sp2-dominated a-C) were deposited under ultrahigh vacuum conditions between room temperature and 800°C. These films served as matrices for the in-situ incorporation of alkali-metal atoms (Li, Na). In-situ sample characterization was performed by photoelectron spectroscopy with both x-ray and ultraviolet excitation (XPS, UPS). While the clean metal-containing samples were prepared with metal contents of about 10 at%, a strong oxidation driven accumulation of metal atoms on the film surface exceeding 50 at% was observed upon exposure to molecular oxygen. Work-function measurements by UPS reflected the changes within the electronic structure of the material. Metal incorporation considerably decreased the work-function, but only after oxidation we observed work-functions below the values given for pure alkali metals.
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Töwe, M., Reinke, P. & Oelhafen, P. Alkali-Metal Containing Amorphous Carbon: Reactivity and Electronic Structure. MRS Online Proceedings Library 593, 167–172 (1999). https://doi.org/10.1557/PROC-593-167