Effect of a sulfur monolayer on graphite precipitation on cobalt

Carbon segregation followed by graphite formation was studied on a fcc cobalt single crystal, both starting from a clean and a sulfur covered surface. The presence of one monolayer of sulfur atoms was found to affect greatly the graphite formation. In isothermal conditions at high temperatures, the graphite film covers completely the cobalt surface, in any case. However, the time necessary depends on the sulfur coverage and on the surface region. In the most perfect areas of the surface the decrease in the rate of graphite precipitation was found to reach two orders of magnitude.