Formation of surface oxide in oxygen adsorption with molecular and atomic fluxes on W(100)

Adsorption-desorption processes on the W(100) surface involving oxygen and formation of surface oxide are studied. It is shown that oxygen adsorption in the form of O$_2$ molecules at 1300–1400 K leads to formation of oxygen-deficient surface oxide with stoichiometry WO$_{0.9}$, while oxygen dissolution in the bulk of tungsten is not observed. In the case of mixed adsorption, including both O$_2$ molecules and O atoms, a surface oxide with stoichiometry WO is formed, after the formation of which oxygen atoms dissolve in the bulk of the metal to form a solid solution. Oxygen dissolved in the bulk increases the thermal stability of the surface oxide due to supply of oxygen coming to the surface. The estimates show that the activation energy of oxygen desorption from W(100) varies from $E_d\approx$ 4.7 eV for $\theta_\mathrm{O}\approx$ 1; up to $E_d$ = 6.0 eV for $\theta_\mathrm{O}\ll$ 1.