Formation of a surface graphite monolayer and intercalationlike compound in the La/graphite system under thermal annealing

Formation of a graphite monolayer and an intercalationlike compound at the surface of the La/graphite system annealed at temperatures between 180 ^∘{}C and 900 ^∘{}C was studied by C $1s$ photoemission, high-resolution electron energy loss spectroscopy as well as by low energy electron diffraction. After annealing at temperatures above 600 ^∘{}C an accumulation of C at the surface takes place in the form of ``zig-zag'' chains with atomic arrangement similar to that in cis- and trans-polyacetylene molecules. With increasing temperatures, these chains are transformed, first into chains of closed hexagons and then into a complete graphite monolayer on the top of the underlying La carbide. At elevated temperatures above 850--900 ^∘{}C, formation of a thin surface layer of a La-derived intercalationlike compound occurs.