Effect of grain size on the melting point of confined thin aluminum films

The melting of aluminum thin film was studied by a molecular dynamics (MD) simulation technique. The effect of the grain size and type of confinement was investigated for aluminum film with a constant thickness of 4 nm. The results show that coherent intercrystalline interface suppress the transition of solid aluminum into liquid, while free-surface gives melting point depression. The mechanism of melting of polycrystalline aluminum thin film was investigated. It was found that melting starts at grain boundaries and propagates to grain interiors. The melting point was calculated from the Lindemann index criterion, taking into account only atoms near to grain boundaries. This made it possible to extend melting point calculations to bigger grains, which require a long time (in the MD scale) to be fully molten. The results show that 4 nm thick film of aluminum melts at a temperature lower than the melting point of bulk aluminum (933 K) only when the grain size is reduced to 6 nm.