Strain-Controlled Epitaxial Stabilization in Ultrathin LaNiO 3 Films Grown by Pulsed Laser Deposition E. J. Moon,* ,† B. A. Gray, † A. Pimpinelli, ‡,§ M. Kareev, † D. Meyers, † and J. Chakhalian † † Physics Department, University of Arkansas, Fayetteville, Arkansas 72701, United States ‡ Department of Physics, University of Maryland, College Pk, Maryland 20742, United States § LASMEA, UMR 6602 CNRS, Universite ́ Blaise Pascal-Clermont 2, F-63177 Aubire, France ABSTRACT: We report on the epitaxial stabilization effect of strain on the growth of ultrathin heterostructures of a correlated metal LaNiO 3 (10 unit cells, ∼3.84 nm; u.c. hereafter) grown on a series of perovskite oxide substrates with both tensile and compressive strain. An unusual polynomial dependence of the activation energy for surface relaxation processes in terms of the lattice misfit was observed. Our experimental investigations further demonstrate the influence of strain relaxation on the self-ordering of complex oxide compounds in the perovskite structure during high supersaturation monolayer (interrupted layer-by-layer) deposition. H eteroepitaxial growth, in which lattice-mismatched materials are grown one on top of the other, is the choice technique for building advanced material devices. 1-3 The growth of epitaxial oxide films has especially attracted wide interest for the last two decades because of their important physical properties and applications in many areas such as high T c superconductors, ferroelectrics, colossal magnetoresistance, wide band gap oxide materials, etc. Additionally, in a wide scope of materials, both thermodynamical stability and kinetic processes establish the phase stability in epitaxial growth. Surface diffusion and adatom binding energies in strained systems of (III-V) 1-x IV 2x semiconductors and other com- pounds have been theoretically studied to identify the origin of stabilization in epitaxial structures. For instance, the growth of micrometer-thick epitaxial films using liquid-phase epitaxy providing very fast mass transfer and low supersaturation confirmed the theory of thermodynamic epitaxial stabiliza- tion. 4,5 Several groups have extended the epitaxial stabilization phenomenon to the behavior of oxides leading to a quadratic relationship between the energy barrier and strain, 6,7 utilizing the stabilization model of Little et al. 8 Furthermore, the dependence of surface energy barriers with strain has also been described in another diffusion model. 9 A number of simulation studies including ab initio calculations for III-V semi- conductors show a linear dependence of activation energy vs biaxial strain. 10,11 Indeed, this epitaxial stabilization could also be dependent on the growth technique. In metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), 1-3 the layer-by-layer (LBL) growth mode requires no or a vanishingly small misfit. In addition, modulated flux can drive the growth into different regimes than those achievable by MOCVD or MBE-like techniques. Here we examine the effect of lattice misfit-induced strain on the surface diffusion of adsorbed atoms (adatoms) in the case of high supersaturation for complex oxides by pulsed laser deposition (PLD). These films maintain a two-dimensional epitaxial LBL growth during levels of high supersaturation in a far-from-equilibrium environment and thus offer a unique opportunity for studying epitaxial stabilization in the quasi 2D wetting layer. 13 The growth mode for these films is driven by the energy balance between the elastic energy cost via lattice parameter mismatch and substrate-absorber adhesion. In this paper, we experimentally investigate the epitaxial stabilization of ultrathin oxide films in a PLD system with various in-plane strain mismatches from compressive to tensile. We restrict our analysis to only lattice mismatch: in the cases where a film exhibits coherent growth, with no dislocations. Specular intensity oscillations from high-pressure high-energy electron diffraction (HP-RHEED) were recorded at different temperatures, and activation barriers were extracted. Guided by these experimental observations, we investigated the epitaxial growth stabilization model for ultrathin oxide films, which are thinner than the critical film thickness. 14 The experiments were performed with in situ analysis by growth monitoring via HP-RHEED in PLD. The LaNiO 3 (LNO) ultrathin film were grown on single-crystal perovskite substrates: YAlO 3 (YAO, lattice misfit= -3.95%), SrLaAlO 4 (SLAO, -1.96%), LaAlO 3 (LAO, -0.56%), NdGaO 3 (NGO, +1.27%), LaGaO 3 (LGO, +1.91%), TiO 2 -terminated SrTiO 3 (001) (STO, +1.94%) prepared by the new wet-etch procedure 12 to minimize electronic surface and near-surface defects, DyScO 3 (DSO, +3.02%), and GdScO 3 (GSO, +3.61%). 16 A KrF excimer laser (λ = 248 nm) was used to ablate a stoichiometry LNO target under 100 mTorr oxygen Received: July 10, 2012 Revised: March 23, 2013 Published: April 24, 2013 Article pubs.acs.org/crystal © 2013 American Chemical Society 2256 dx.doi.org/10.1021/cg300958z | Cryst. Growth Des. 2013, 13, 2256-2259