Surface stability of epitaxial LaNiO_3-δthin films

Abstract

Thin LaNiO 3−δ films with pseudocubic (100) preferred orientation were prepared by reactive DC magnetron sputtering and in situ annealed in O2 and vacuum. X-ray photoelectron spectroscopy (XPS) was used to determine the variation in composition of the films under high temperature annealing. The experimental O 1s and La 3d -Ni 2p 3/2 spectra of LaNiO 3−δ films was analysed in terms of O 2− , O − /(OH) − , and weakly adsorbed oxygen species. It was shown that the change in the type of conductivity from metallic to semiconducting one is accompanied by a marked increase in the intensity of the lateral (∼531 eV) peak of oxygen. The quantitative analyses of La 3d -Ni 2p 3/2 spectra show that the Ni/La concentration ratio significantly decreases after heating above the dehydration temperature. These variations in conductivity and surface composition were attributed to the loss of lattice oxygen with subsequent adsorption of O − and (OH) − anions and weakly adsorbed oxygen species from ambient air.

Hydrophobicity of Rare Earth Oxides Grown by Atomic Layer Deposition

“…Other reports have consistently noted large amounts of hydroxyl groups detected in La 2 O 3 films, 53 and the amount of hydroxyl groups has been increased by exposure to hightemperature environments because the interactions between La 2 O 3 and absorbed water are kinetically accelerated by greater temperatures. 54 Therefore, the correlation between hygroscopy and hydrophobicity is one way to explain the observed differences in REO thermal stability. Also, it is believed that there are other effects that change the hydrophobicity, because the contact angle reductions of Dy 2 O 3 and Y 2 O 3 were different even though Dy and Y have the same electronegativity.…”

XPS study of sol–gel produced lanthanum oxide thin films

“…The metal-insulator transition, high-temperature superconductivity, ferroelectricity, and colossal magnetoresistance compounds of perovskites are excellent materials for future technological application [1][2][3][4]. For example, LaNiO 3 is one of a few conductive oxides proper for integration in epitaxial heterostructures with perovskites [5,6]. However, the rare earth oxides have a tendency to absorb water and carbon dioxide from the environment, so that any ex situ exposure of these films to ambient air will result in an uncontrolled reaction and surface stoichiometry variation [7].…”

“…In [5,8,9] La-Ni-O films were deposited onto NdGdO 3 monocrystalline (100)-plane oriented substrate using a DC magnetron sputtering system. Investigations on electronic structure and chemical composition of grown LaNiO 3-δ thin films after heating above dehydration temperatures in air and vacuum were performed.…”

XPS study of sol–gel produced lanthanum oxide thin films

“…The metal-insulator transition, high-temperature superconductivity, ferroelectricity, and colossal magnetoresistance compounds of perovskites are excellent materials for future technological application [1][2][3][4]. For example, LaNiO 3 is one of a few conductive oxides proper for integration in epitaxial heterostructures with perovskites [5,6]. However, the rare earth oxides have a tendency to absorb water and carbon dioxide from the environment, so that any ex situ exposure of these films to ambient air will result in an uncontrolled reaction and surface stoichiometry variation [7].…”

“…In [5,8,9] La-Ni-O films were deposited onto NdGdO 3 monocrystalline (100)-plane oriented substrate using a DC magnetron sputtering system. Investigations on electronic structure and chemical composition of grown LaNiO 3-δ thin films after heating above dehydration temperatures in air and vacuum were performed.…”