Unravelling oxygen driven α to β phase transformation in tungsten

Thin films of beta -W are the most interesting for manipulating magnetic moments using spin-orbit torques, and a clear understanding of alpha to beta phase transition in W by doping impurity, especially oxygen, is needed. Here we present a combined experimental and theoretical study using grazing incidence X-ray diffraction, photoelectron spectroscopy, electron microscopy, and ab initio calculations to explore atomic structure, bonding, and oxygen content for understanding the formation of beta -W. It is found that the W films on SiO2/Si have 13-22 at.% oxygen in A15 beta structure. Ab initio calculations show higher solution energy of oxygen in beta -W, and a tendency to transform locally from alpha to beta phase with increasing oxygen concentration. X-ray absorption spectroscopy also revealed local geometry of oxygen in beta -W, in agreement with the simulated one. These results offer an opportunity for a fundamental understanding of the structural transition in alpha -W and further development of beta -W phase for device applications.