Reconstruction of TiAl intermetallic surfaces: A combined STM and DFT study

The structure of the γ-TiAl(111) alloy surface was studied with combined experimental and theoretical approaches. The experimental scanning tunneling microscopy (STM) images indicate surface reconstruction with a (2 × 2) superstructure as a result of Al depletion of the alloy surface after preparation. The atomic protrusions form a zigzag pattern oriented along the direction of the shorter surface unit vector of the (2 × 2) supercell, that is, the [101̄] direction. The theoretical investigations performed with molecular dynamics in combination with simulated annealing based on the density functional theory (DFT) show that the surface starts to reconstruct at temperatures higher than 950 K, in agreement with the experimental annealing temperature. Geometric analysis and simulated STM images obtained from periodic DFT calculations show that the atomic protrusions forming the zigzag patterns correspond to Al atoms of the reconstructed topmost plane. The persistence of the reconstructed structure up to the simulated melting temperature of 1800 K shows the high stability of Al vacancies injected in the topmost plane of the alloy.