Defect Engineering in A₂BO₄ Thin Films via Surface‐Reconstructed LaSrAlO₄ Substrates

Abstract

Ruddlesden–Popper oxides (A2BO4) have attracted significant attention regarding their potential application in novel electronic and energy devices. However, practical uses of A2BO4 thin films have been limited by extended defects such as out‐of‐phase boundaries (OPBs). OPBs disrupt the layered structure of A2BO4, which restricts functionality. OPBs are ubiquitous in A2BO4 thin films but inhomogeneous interfaces make them difficult to suppress. Here, OPBs in A2BO4 thin films are suppressed using a novel method to control the substrate surface termination. To demonstrate the technique, epitaxial thin films of cuprate superconductor La2‐xSrxCuO4 (x = 0.15) are grown on surface‐reconstructed LaSrAlO4 substrates, which are terminated with self‐limited perovskite double layers. To date, La2‐xSrxCuO4 thin films are grown on LaSrAlO4 substrates with mixed‐termination and exhibit multiple interfacial structures resulting in many OPBs. In contrast, La2‐xSrxCuO4 thin films grown on surface‐reconstructed LaSrAlO4 substrates energetically favor only one interfacial structure, thus inhibiting OPB formation. OPB‐suppressed La2‐xSrxCuO4 thin films exhibit significantly enhanced superconducting properties compared with OPB‐containing La2‐xSrxCuO4 thin films. Defect engineering in A2BO4 thin films will allow for the elimination of various types of defects in other complex oxides and facilitate next‐generation quantum device applications.

Significant effects of epitaxial strain on the nonlinear transport properties in Ca2RuO4 thin films with the current-driven transition

“…12,21) Prior to precursor deposition, the YAlO 3 (001) and LaAlO 3 (001) substrates were etched with concentrated HCl solutions, and the other substrates were preannealed at 1300 °C (the same conditions as for the film growth) to form atomically flat step-and-terrace structures on their surfaces. [31][32][33] The crystal structures and surface morphologies of the Ca 2 RuO 4 thin films were analyzed by X-ray diffraction (XRD) and atomic force microscopy using a SmartLab (Rigaku), a D8 Discover (Bruker AXS Inc.) and a NanoCute (Hitachi High-Tech Co.). The resistivity-temperature characteristics of the Ca 2 RuO 4 thin films were measured by the four-probe method using the physical property measurement system (PPMS, Quantum Design).…”

Growth and Electronic Structure of Copper Oxide Monolayer Epitaxial Films

“…Before film growth, LSAO substrates were surface-treated by thermal annealing and water leaching for single-terminated surfaces. The detailed method for LSAO surface treatment is described elsewhere . Stoichiometric LAO, CTO, and LSCO polycrystalline targets with Sr doping of x = 0.15 and 0.20 were used for film growth.…”

“…The detailed method for LSAO surface treatment is described elsewhere. 30 Stoichiometric LAO, CTO, and LSCO polycrystalline targets with Sr doping of x = 0.15 and 0.20 were used for film growth. For LSCO film growth, the substrate temperature, oxygen partial pressure, and laser fluence were kept at 700 °C, 100 mTorr, and 0.7 J/cm 2 , respectively.…”