PNNL

Abstract

LaAlO3 epitaxial films with La:Al cation ratios ranging from 0.9 to 1.2 were grown on TiO2-terminated SrTiO3 (001) substrates by off-axis pulsed laser deposition. Although all films are epitaxial, rocking curve and Kiessig fringe oscillation measurements show that the crystallographic quality degrades with increasing La:Al ratio. Films with La:Al ratios of 0.9, 1.0, and 1.1 were coherently strained to the substrate. However, the out-of-plane lattice parameter increases over this range, revealing a decrease in film tetragonality. Although all film surfaces exhibit hydroxylation, the extent of hydroxylation is greater for the La-rich films. Rutherford backscattering spectrometry reveals that La from the film diffuses deeply into the SrTiO3 substrate and secondary ion mass spectroscopy shows unambiguous Sr outdiffusion into the films. Intermixing, which is generally not investigated in studies of the LaAlO3/SrTiO3 interface, may have important implications for the mechanism of electrical conductivity.