Fractal patterns in Au–Ta multilayer films upon ion beam mixing

Abstract

Metallic glass has been formed in Au50Ta50 multilayer films upon 200 keV xenon ion mixing at an irradiation dose of 1 × 1015 Xe+/cm2. Electron diffraction and high-resolution transmission electron microscopy analysis confirm that the metallic glass consists of two amorphous phases, evolved from Au and Ta lattices, respectively, and also reveal the formation of a fractal morphology with a fractal dimension of 1.73 ± 0.05 in the dual-phase glass features. In similar Au65Ta35 multilayer films, a fractal pattern is also observed at a dose of 1 × 1015 Xe+/cm2, while the pattern, with a fractal dimension of 1.74 ± 0.05, is composed in this case of a crystalline Au-based solid solution and a Ta-based amorphous phase. Interestingly, the fractal dimensions of the two irradiation-induced fractal patterns match quite well with that expected on a cluster diffusion-limited aggregation model.