Selective reduction of layers at low temperature in artificial superlattice thin films

Reduction and oxidation in transition-metal oxides are keys to develop technologies related to energy and the environment. Here we report the selective topochemical reduction observed when artificial superlattices with transition-metal oxides are treated at a temperature below 300 °C with CaH2. [CaFeO2]m/[SrTiO3]n infinite-layer/perovskite artificial superlattice thin films were obtained by low-temperature reduction of [CaFeO2.5]m/[SrTiO3]n brownmillerite/perovskite artificial superlattice thin films. By the reduction only the CaFeO2.5 layers in the artificial superlattices were reduced to the CaFeO2 infinite layers whereas the SrTiO3 layers were unchanged. The observed low-temperature reduction behaviors strongly suggest that the oxygen ion diffusion in the artificial superlattices is confined within the two-dimensional brownmillerite layers. The reduced artificial superlattice could be reoxidized, and thus, the selective reduction and oxidation of the constituent layers in the perovskite-structure framework occur reversibly

Chemisorbed Oxygen at Pt(111): a DFT Study of Structural and Electronic Surface Properties

Simulations based on density functional theory are used to study the electronic and electrostatic properties of a Pt(111) surface covered by a layer of chemisorbed atomic oxygen. The impact of the oxygen surface coverage and orientationally ordered interfacial water layers is explored. The oxygen adsorption energy decreases as a function of oxygen coverage due to the lateral adsorbate repulsion. The surficial dipole moment density induced by the layer of chemisorbed oxygen causes a positive shift of the work function. In simulations with interfacial water layers, ordering and orientation of water molecules strongly affect the work function. It is found that the surficial dipole moment density and charge density are roughly linearly dependent on the oxygen surface coverage. Moreover, we found that water layers exert only a small impact on the surface charging behavior of the surface