Crucial role of oxygen on the bulk and surface electronic properties of stable β phase of tungsten.

The A15 β phase of tungsten has recently attracted great interest for spintronic applications due to the finding of giant spin-Hall effect. As β phase is stabilized by oxygen, we have studied the electronic structure of O-doped β-W from first principles calculations. It is found that 20 at.% O-doping makes β phase lower in energy than α-W. These results are in good agreement with energy dispersive X-ray spectroscopy which also shows ~ 16.84 at.% O in 60 nm thick W films. The latter has predominantly β phase as confirmed by grazing incidence X-ray diffraction (XRD). The simulated XRD of bulk β having 15.79 at.% O also agrees with XRD results. Oxygen binds strongly on the surface and affects the Dirac fermion behavior in pure β-W. There is structural disorder, O-inhomogeneity, and higher density-of-states in O-doped β-W at E compared with pure α. These results are promising to understand the properties of β-W.