Temperature dependent oxygen depletion in tungsten: a quantitative analysis ofβtoαphase transition

Thin films ofβ-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 ofβ-W films, which irreversibly transform into theαphase upon heating above 200 °C. XPS measurements indicate the presence of approximately 12 at.% oxygen in theβphase, 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 ourab initiodensity functional theory calculations and molecular dynamics simulations. Theoretical studies reveal that theαphase is energetically more stable at low oxygen concentrations of at least up to ∼10 at.%, corroborating experimentally observedβtoαphase transformation by oxygen desorption.