The electronic structure and chemical bonding in reactively magnetron sputtered ZrH x (x = 0.15, 0.30, 1.16) thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level, and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significant reduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H 1s–Zr 4d hybridization region at ∼6 eV below the Fermi level. For low hydrogen content (x = 0.15, 0.30), the films consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ-ZrH x (CaF 2 -type structure) phases, while for x = 1.16, the films form single-phase ZrH x that largely resembles that of stoichiometric δ-ZrH 2 phase. We show that the cubic δ-ZrH x phase is metastable as thin film up to x = 1.16, while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated ZrH 1.16 film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4p 3/2 and 3d 5/2 peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifies a charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemical shifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affects the conductivity by charge redistribution in the valence band.
Magnuson, M., Schmidt, S., Hultman, L., & Högberg, H. (2017). Electronic properties and bonding in Zr Hx thin films investigated by valence-band x-ray photoelectron spectroscopy. Physical Review B, 96(19). https://doi.org/10.1103/PhysRevB.96.195103