Influence of ion irradiation on the surface electronic structure of epitaxial lanthanum nickelate films

We studied the influence of Ag15+ (200 MeV) ion irradiation on the surface electronic structure of an epitaxial LaNiO3 films on a (100) oriented LaAlO3 substrate, using surface sensitive La (4d to 4f) and Ni (3p to 3d) photoemission transitions in the pristine, highest (1012 ions/cm2), medium (5 x 1011 ions/cm2), and lowest (1011 ions/cm2) ion-doses of irradiation. The Super-Coster Kronig induced slight enhancement in the spectral features around -115-116 eV photon energy for La (4d to 4f) transitions were observed, with absence of such enhancement for Ni (3p to 3d) transitions in the pristine and irradiated samples. Moreover, an alteration in the constant initial state (CIS) spectra for La (4d to 4f) transitions and presence of a surface states close to the Fermi level in the valence band spectra for Ni (3p to 3d) transitions, with a different ion-doses found to be associated with the oxygen vacancies. Interestingly for Ni (3p to 3d) transition spectra, the density of states (DOS) at the Fermi Level was found to increase orderly with the irradiation dose, and a systematic correlation between the DOS at Fermi level and the surface states was found in the pristine and irradiated samples. For the highest dose sample, the surface states lie above the Fermi level has highest DOS at the Fermi level, which is due to upward shift of the surface states towards the Fermi level with an increase in the irradiation dose.