Extraordinary oxidation behavior of W–Zr thin-film metallic glasses: A route for tailoring functional properties of W–Zr–O films

Abstract

The oxidation behavior of W–Zr thin-film metallic glasses (TFMGs) with 32, 48 and 61 at.% Zr, prepared by dc magnetron co-sputtering, was comprehensively studied after annealing in synthetic air. The study focuses on the effect of the annealing temperature (up to 600 °C) on the oxidation process, oxygen saturation, structure evolution, and their subsequent impact on electrical, optical and mechanical properties. The findings reveal that controlled oxidation transforms W–Zr TFMGs into amorphous ceramic W–Zr–O films with substoichiometric compositions. This is a consequence of an oxidation process that does not proceed through the formation of a stoichiometric oxide layer on the surface of W–Zr TFMGs, acting as a diffusion barrier against fast oxidation, but leads to a gradual incorporation of oxygen across the film volume due to thermodynamics factors. Higher Zr content accelerates the oxygen incorporation and its depth uniformity in the films. As a result, the mechanical properties are significantly enhanced achieving hardness values of up to 17.5 GPa at approximately 50 % oxygen saturation. Simultaneously, the electrical and optical properties are finely tuned with the resistivity and the extinction coefficient (measured at 550 nm) ranging from 1.7 to 95.7 × 10⁻⁴ Ω·cm and 0.28 to 1.06, respectively.