Interfacial Reconstruction during E-beam Induced Crystallization at the a-LAO/STO Interface

Abstract

Various intriguing physical properties are observed at the oxide interfaces. A two-dimensional electron gas (2DEG) in LaAlO3/SrTiO3 (LAO/STO) system is one of the most representative materials of the electron correlated novel properties. Many experimental as well as theoretical studies have been conducted to figure out the interfacial properties, and several major mechanisms have been suggested for the interfacial conductivity; polar catastrophe, oxygen vacancies and intermixing. However, the origin of the interfacial conductivity still have not been fully understood, and any single scenario cannot account the various interfacial phenomena solely. Here, we directly investigated the 2DEG formation mechanism in LAO/STO heterostructure. The amorphous(a)-LAO overlayer was grown on the STO substrate and it annealed under oxygen atmosphere to minimize the effect of intermixing as well as oxygen vacancies on 2DEG. The a-LAO overlayer was crystallized layer-by-layer by electron beam (e-beam) in scanning transmission electron microscope (STEM), and the atomic as well as electronic reconstruction at the a-LAO/STO heterointerface was observed during crystallization of the a-LAO overlayer. This enables a real-time observation on the atomic/electronic structural changes simultaneously. Also, the origin of the different atomic as well as electronic reconstructions such as the lattice expansion and Ti valence change near the heterointerface was discussed. This gives an account of how the interfacial structure correlated with the interfacial property. The observation of interatomic distance as well as octahedral distortions at the heterointerface were performed by aberration-corrected STEM (Titan S80-300; FEI) and JEOL JEM-ARM300F. The change of electronic structures were observed by electron energy loss spectroscopy (EELS).