Sequential Ta(1 0 0) carbonisation: from adsorption of single carbon atoms to bulk carbide production

Sequential stages of Ta carbonisation from the initial atomic adsorption to bulk carbide (BC) production throughout the sample have been studied by high temperature high resolution Auger spectroscopy in ultra-high vacuum. Two compounds – surface carbide (SC) Ta5C2 and BC TaC – were found. The energy barrier heights for atomic carbon transport from the surface to the bulk were estimated to be Esl=2.1–2.3 eV and back Els=Esl−ΔE≈(1.2–1.6) eV and the activation energy of carbon bulk diffusion in Ta Edif∼1.3 eV was refound. It is shown that SC can be treated as a thermodynamically ‘legal’ phase and should find its place in the equilibrium phase diagram.