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

Thin films of<i>β</i>-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, x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and thermal desorption spectroscopy (TDS). Our results reveal the formation of<i>β</i>-W films, which irreversibly transform into the<i>α</i>phase upon heating above 200 °C. XPS measurements indicate the presence of approximately 12 at.% oxygen in the<i>β</i>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<i>ab initio</i>density functional theory calculations and molecular dynamics simulations. Theoretical studies reveal that the<i>α</i>phase is energetically more stable at low oxygen concentrations of at least up to ∼10 at.%, corroborating experimentally observed<i>β</i>to<i>α</i>phase transformation by oxygen desorption.