Pulsed-laser deposition of superconducting LiTi2O4 ultrathin films

We report epitaxial growth, structural characterizations arid thickness dependent superconducting properties of LiTi2O4 films grown on (111) MgAl2O4 substrates by using pulsed laser deposition. The variations of growth temperature (T-g) and excess Li composition of target materials were found to be crucial for improving the crystallinity, as verified by X-ray diffraction rocking curve and the in-plane domain configuration. The crystallinity of the desired LiTi2O4 phase improved with increasing T-g, whereas the inclusion of Li-deficient phases became more significant due to high sublimation rate of Li species. The use of the excess Li targets allowed us to elevate T-g up to 750 degrees C (Li/Ti=1.0) with keeping high crystallinity and phase purity. For films grown under the best condition, the superconducting transition was observed near 12 K even when thickness was as thin as 9 nm. (C) 2015 Elsevier B.V. All rights reserved.