Effects of annealing on the compositional heterogeneity and structure in zirconium-based bulk metallic glass thin films

• Zr51Cu32Al9Ni8 thin films were studied with in-situ heating electron microscopy.
• Annealing at 400 °C increases the Zr and Cu compositional fluctuations.
• Short-range order in Zr51Cu32Al9Ni8 becomes less homogeneous above 350 °C.
• Medium-range order changes in degree and types at 400 °C, well below Tg.
• Annealing increases composition and structure heterogeneities until crystallization.

In-situ heating fluctuation electron microscopy and scanning transmission electron microscopy have been utilized to study compositional and structural heterogeneities in Zr51Cu32Al9Ni8 thin films upon annealing. Composition fluctuations are present in the as-deposited thin films. Well below the glass transition temperature, the composition fluctuations increase with annealing time. Short- and medium-range order also change with annealing temperature. The observed heterogeneities in the glass structure persist until annealing causes crystallization. The 20 nm thick Zr51Cu32Al9Ni8 films contain oxide layers both at the surface and the film/substrate interface with the total thickness of 7–8 nm. In-situ annealing increased the oxygen content of the whole films to about 24 wt.% after 2 h at 400 °C.