LiOx-modification of Ni and Co3O4 surfaces: An XPS, LEIS and LEED study

LiOx was deposited at room temperature by physical vapor deposition (PVD) on polycrystalline Ni foil and Co3O4(111) thin film, creating uniform model systems well-suited for surface-sensitive characterization by X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS) or low energy electron diffraction (LEED). In the case of Ni, about 15 layers of LiOx film were grown under the current conditions either stepwise or continuously, with XPS analysis indicating a deposition rate of 0.16 and 0.24 ML/min, respectively. Li 1s and O 1s spectra revealed that Li2O and to a lesser extent LiOH were preferentially formed. The stability of the LiOx films was examined in UHV, upon annealing at 573 K and upon hydrogen reduction at 723 K. On the more reactive Co3O4(111) film grown on Ir(100), the Li accommodation rate was about twice as high, at least within the first minutes of deposition. Post-deposition LEED showed an obscured cobalt oxide diffraction pattern, not unexpected in light of the LiOx deposited. On both substrates, LEIS characterization of Li (≈ 103 eV) was prevented by the high background in this kinetic energy region, due to surface roughness and unspecific scattering. Still, LiOx deposition was evident from the vanished LEIS signals of Ni or Co. The prepared LiOx-modified surfaces may serve as starting point for the future growth of epitaxial LixCoO2 model systems.