Reactivity of lithium-containing amorphous carbon (a-C) films

The reactivity of lithium-containing amorphous carbon (a-C) films was studied by in situ photoelectron spectroscopy in both the X-ray and ultraviolet excited regimes (XPS, UPS). All preparation and measurement procedures were carried out in ultrahigh vacuum (UHV). Carbon matrices were deposited by evaporation of graphite onto substrates at temperatures from ambient to 800°C. Lithium incorporation was achieved by diffusion after deposition of lithium atoms on top of the carbon films. Changes in the filmsʹ surface composition and in their electronic structure were monitored after exposure to molecular oxygen, to energetic oxygen ions and to air. While gettering oxygen and oxygen containing species, lithium atoms segregate from the films and accumulate in a mainly oxidic layer on top of them. This process is accompanied by a decrease in the electron work-function. Exposure to air effected the formation of an additional carbonate compound.