Premelting of bismuth nanoparticles embedded in aluminum

The melting of Bi nanoparticles embedded in nanometer-thick amorphous Al film was studied by electron diffraction. The Bi nanoparticles were prepared by sputtering an Al-Bi-Al multilayer followed by annealing at 60 K above the Bi bulk melting point, Tm. For heating at a rate of ~ 3 K/min, the onset melting of the Bi nanoparticles was ~ 120 K below the Tm of Bi, as observed by the change of the unit cell volume with temperature. Lattice contraction with an anisotropic thermal expansion coefficient was observed. The large depression of the melting point is mainly attributed to the incoherent Al-Bi interfaces with defects at the interface of the Bi nanoparticles and surrounding Al.