Formation of two dimensional conductive interface by real-time atomic scale crystallization in STEM

Abstract

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 [1]. However, the origin of the interfacial conductivity still have not been fully understood, and any single scenario cannot account the various interfacial phenomena solely. In this study, we observed the atomic as well as electronic reconstruction at the a-LaAlO3/SrTiO3 heterointerface during crystallization of the a-LAO overlayer. The accelerated electron beam (e-beam) in scanning transmission electron microscope (STEM) can epitaxially crystallize the various amorphous oxide materials [2]. This enables a real-time observation on the atomic/electronic structural changes simultaneously. During the crystallization of the a-LAO from the interface, atomic/electronic structural changes near the interface depend on the interfacial conductivity. Also, the origin of the different atomic and electronic reconstructions such as the lattice expansion and Ti valence change near the heterointerface. In addition, we directly measured the electrical property in TEM using Protochips holder and show that the e-beam induced crystallization of LAO above the critical thickness of 4 u.c. in TEM also make the interface conductive. This direct observation gives an account of how the interfacial structure correlated with the interfacial property. In further, we suggest that conducting lines can be patterned into an insulating a-LAO matrix by crystallizing the LAO using e-beam lithography method.