SURFACE PRECIPITATION OF GRAPHITE LAYERS ON CARBON-DOPED NICKEL AND THEIR STABILIZATION EFFECT AGAINST CHEMISORPTION AND INITIAL OXIDATION

A new method for coating the inner surface of ultrahigh-vacuum (UHV) vessels with an inert material is proposed, namely coating with highly oriented graphite layers which precipitate on the surface of a carbon-doped nickel substrate. By using various surface analytical methods, characterization of the precipitated graphite has been performed. AES measurements at elevated temperatures clarified the surface precipitation process on polycrystalline Ni-C. Low-energy electron diffraction studies on Ni(111) showed that the surface-precipitated graphite grew epitaxially with the substrate and its structure was found to agree with that of highly oriented pyrolytic graphite. Reflection high-energy electron diffraction studies revealed that the basal planes (0001) of precipitated graphite preferentially cover the surface even in the caw of polycrystalline Ni-C. AES measurements in an O2 atmosphere showed that the graphite-covered surface was hardly oxidized by prolonged oxygen exposure. Thermal desorption spectroscopy measurements suggested that the desorption of CO after O2 dosing was much smaller from the graphite-precipitated surface than from a stainless steel surface. From the standpoint of applications to problems in engineering, graphite precipitation on metals is found to be a promising method for making an inert and low-outgassing surface for UHV use.