The present work has demonstrated the large-capacity oxygen storage of various isomorphous lanthanide
oxysulfates, Ln2O2SO4 (Ln = La, Pr, Nd and Sm), which utilize the nonmetallic element (S) as a redox
site instead of metallic cations. The reduction by H2 or hydrocarbons and subsequent reoxidation by O2
between Ln2O2SO4(S6+) and Ln2O2S(S2-) achieved an oxygen storage of 2 (mol of O2)·mol-1, which is
8 times larger than that of the conventional CeO2−ZrO2 material. Although the reversible redox cycle of
thermostable Ln2O2SO4 with Ln = La, Sm, and Nd was possible only at high temperatures above 700
°C, the Pr system could work at an exceptionally low temperature of ca. 600 °C. Furthermore, the redox
of the Pr system could be accelerated in the presence of impregnated noble metals (1 wt % Pd), which
supply activated hydrogen as well as oxygen by spillover. Because the elimination of a large amount of
sulfate species as SO2/O2 from the bulk crystallites of sulfate precursors yields the macroporous texture
of Ln2O2SO4 and Ln2O2S with a high specific surface area, the resultant rapid gas diffusion as well as
solid−gas reactions would facilitate the oxygen storage and release processes.
In order to study a formation mechanism of thin Ti-rich layers formed on the surfaces of Cu(Ti) wires after annealing at elevated temperatures, the 300-nm-thick Cu(Ti) alloy films with Ti concentration of 1.3 at.% or 2.9 at.% were prepared on the SiO 2 /Si substrates by a co-sputter deposition technique. The electrical resistivity and microstructural analysis of these alloy films were carried out before and after annealing at 400°C. The Ti-rich layers with thickness of ϳ15 nm were observed to form uniformly both at the film surface and the substrate interfaces in the Cu(2.9at.%Ti) films after annealing (which we call the self-formation of the layers) using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Both the resistivities and the microstructures of these Cu(Ti) films were found to depend strongly on the Ti concentrations. The resistivities of the films decreased upon annealing due to segregation of the supersaturated Ti solutes in the alloy films to both the top and bottom of the films. These Ti layers had excellent thermal stability and would be applicable to the self-formed diffusion barrier in Cu interconnects of highly integrated devices. The selection rules of the alloy elements for the barrier self-formation were proposed based on the present results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.