Diffusion and formation energies of adatoms and vacancies on magnesium surfaces

This paper reports classical molecular statics calculations of magnesium {0 0 0 1}, , , and surfaces, specifically formation energies of defects (adatoms and surface vacancies) and flat surfaces and diffusion energy barriers of the defects. The formation energies show that the surface is thermodynamically more favorable than , and surfaces; in contrast, literature reports have often ignored the surface. The diffusion energy barriers of both adatoms and surface vacancies show strong diffusion anisotropy on , , and surfaces. Based on this anisotropy, the ratio of diffusion distances (of either adatoms or surface vacancies) along two orthogonal directions on is 37–55 at room temperature. Using the results of formation energies and diffusion energy barriers we develop a more complete understanding of surface orientations in Mg nanoblades synthesized by physical vapor deposition F. Tang, T. Parker, H.-F. Li, G.-C. Wang, T.-M. Lu, J. Nanosci. Nanotechnol. 7 (2007) 3239]. In contrast to previous reports, we postulate that the side surfaces of Mg nanoblades are because (a) they have the second lowest surface formation energy and (b) the ratio of diffusion distances on them agrees with the experimental value of approximately 50.