Temperature dependent oxygen depletion in tungsten: a quantitative analysis of β to α phase transition

Thin films of β-W have attracted much attention due to their fascinating properties for spintronic and magnetic random-access memory but their thermal behavior has still not been well understood. Here we have performed a systematic investigation of their thermal stability and phase transformation behavior using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and thermal desorption spectroscopy (TDS). Our results reveal the formation of β-W films, which irreversibly transform into the α phase upon heating above 200 °C. XPS measurements indicate the presence of approximately 12 at.% oxygen in the β phase, decreasing to a few percent after annealing up to 500 °C. Complementary TDS, XPS, and SIMS analyses provide quantitative insights into compositional and structural changes during heat treatment, while XPS elucidates the electronic structure, consistent with our ab initio density functional theory (DFT) calculations and molecular dynamics simulations. Theoretical studies reveal that the α phase is energetically more stable at low oxygen concentrations of at least up to ~10 at.%, corroborating experimentally observed β to α phase transformation by oxygen desorption.