Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices

We have conducted a detailed microscopic investigation of [LaNiO3(1 u.c.)/LaAlO3(1 u.c.)](N) superlattices grown on (001) SrTiO3 and LaAlO3 to explore the influence of polar mismatch on the resulting electronic and structural properties. Our data demonstrate that the initial growth on the nonpolar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of Ni in the initial LaNiO3 layer, which is not observed after growth on the polar surface of LaAlO3. A devised model suggests that the polar mismatch can be resolved if the perovskite layers grow with an excess of LaO, which also accounts for the observed electronic, chemical, and structural effects.