Ion irradiation effects on tungsten-oxide films and charge state effect on electronic erosion

We have studied electronic- and atomic-structure modifications of polycrystalline WO₃ films (bandgap of ∼3 eV) by ion irradiation. WO₃ films were prepared by oxidation of W films on MgO substrates and of W sheets. We find disordering or amorphization, the lattice expansion of ∼1.5% and bandgap increase of 0.2 eV after 90 MeV Ni ion irradiation at ∼3 × 10¹² cm⁻². A broad peak of optical absorption appears around 1.6 μm by ion irradiation. We also find that the erosion yield by high-energy ions with the equilibrium charge exceeds 10⁴ and that the erosion yield under ion impact with non-equilibrium charge (90 MeV Ni⁺¹⁰) is ∼1/5 of that with the equilibrium charge (89 MeV Ni⁺¹⁹). Effects of depth dependence of the ion mean charge on the erosion yields are discussed. The erosion yield by low-energy ions is also presented.