A computational study of hcp Ti and Zr stepped surfaces

The structure and energetics of ledge pairs (atomic steps) in surfaces ð0001Þ; ð10 10Þ; ð1 210Þ of hcp Zr and Ti are studied by computer simulation using embedded-atom-type interatomic potentials. The configurations considered are the face-to-face, back-to-back, sequential, and double, according to their cross-sectional view. Ledge and kink formation and interaction energies are obtained. Vacancies and adatoms are introduced to study their formation and migration energies in interaction with the ledges. But for one case (surface ð10 10Þ) it is found that ledges are preferred sites for vacancy and adatom formation; also, their overall effect on diffusion is predicted to be small. The results indicate that the effect of ledges can be neglected beyond a few atomic distances.