A study on thermal stability of nanocrystalline pillars

Using nanocrystalline pillars as models of surface quantum dots, and Al nanocrystalline pillar as example, the relaxation processes of the pillars with different sizes at different temperatures have been simulated by molecular dynamics. An EAM potential developed by Ercolessi was used to calculate the inter-atomic forces. The results show that, for nanocrystalline pillars with near-square cross section and with {110} and {211} planes as side surfaces, there exists a critical size for stability transition. The nano-pillars with thickness lower than the critical size melted quickly and then recrystallized, while those with thickness larger than the critical size will be slowly reconstructed by surface migration of atoms. The reconstructed stable structures, through either the melt-recrystallization or surface migration, are polyhedrons consisting of {111} and {100} surfaces with different ratios of the areas. The critical size increases linearly with raising temperature. The simulations also show that the stability of the nanocrystalline pillars is insensitive to their height.