Interfacial Titanium Diffusion Self-adapting Layer in Ultrathin Epitaxial MnO2/TiO2 Heterostructures.

The electrochemical performance of supercapacitors is suppressed by a large number of defects in the interface of heterostructure due to lattice mismatch. In this paper, (001) oriented rutile MnO2 thin films with different thicknesses were grown on rutileTiO2 substrates. The lattice mismatch between film and substrate was minimized through a Ti diffusion self-adapting layer. The energy disperse spectroscopy mappings were used to measure the diffusion range of Ti. The results of high resolution X-ray diffraction confirmed that the dependence of out-of-plane lattice parameter on the thickness was consistent with the self-adapting interface model, indicating that Ti diffusion can indeed alleviate the lattice mismatch. In addition, the results of synchrotron soft X-ray absorption spectrum indicated that the capacitance of the thin films with a large proportion of Ti diffusion increased with the increase of electrons involved in the reaction. Although the decrease of carrier density and conductivity of the thinner films depressed the electrochemical activity, it is worth to mention that the film we designed still has considerable specific capacitance even when it is very thin, which can provide a new idea for the development of thinner and larger capacity potential micro-supercapacitors.