Carbon Adsorption and Absorption in the (111) L12 Fe3Al Surface

Density functional theory is used to investigate the adsorption of carbon on the (111) surface of the L12 Fe3Al structure under various carbon coverages and the absorption in interstitial sites of the subsurface. Surface reconstruction is observed after carbon is adsorbed on the surface, and as carbon coverage increases carbon structures are formed in most cases with enhanced adsorption energies. C structures evolve, becoming sp3-like at intermediate coverage, and at much higher coverage sp2 networks form a graphene sheet that separates from the metal surface. The surface Fe magnetic moments are decreased in the presence of C, and the change is dependent on the position of the adsorbed C atom. At low C coverage, C interacting with Fe has an induced magnetic moment on the order of 0.15 μB that becomes reduced as C−C structures are formed. The interstitial octahedral sites of the first interlayer below the surface are the most stable sites for carbon absorption, where carbon is more stable than when adsorbed on the surface at the same total coverage. Carbon diffusion from the surface to the subsurface at low coverage has a barrier of 0.99 eV, but the barrier is significantly reduced to 0.33 eV at higher C surface coverage. Strong lattice distortions occur due to the incorporation of carbon on the surface and subsurface, giving some insights into possible carburization pathways of the L12 F3Al phase.