• Löffler, Stefan
• Orgiani, Pasquale
• Oberaigner, Michael
• Chaluvadi, Sandeep Kumar
• Kothleitner, Gerald
• Ciancio, Regina
• Ederer, Manuel
• Knez, Daniel

Abstract

In recent years, a lot of research has been performed on transition metal oxides, because of<br/>their fascinating behaviour at heterostructural interfaces. Arising phenomena, like the<br/>formation of two-dimensional electron gas (2DEG) with high charge densities make such<br/>systems interesting for potential technical applications. The physical origins of the 2DEG are<br/>still highly discussed and are often attributed to polar discontinuity at the interface or oxygen<br/>vacancies. However, a fully characterization and understanding of the oxide interfaces is<br/>unavoidable to apply them reliable at electronic devices and be able to tune their electric<br/>properties. A 2DEG with promising electric properties is also present at the interface of<br/>anatase TiO2 and lanthanum aluminate LaAlO3, which we will investigate in this work. The<br/>lattice mismatch of these crystals is only around 0.2 %, enabling the fabrication of atomic<br/>sharp interfaces (Fig. 1 (a)). We utilize scanning transmission electron microscopy (STEM)<br/>and electron energy loss spectroscopy (EELS) to map directly individual electronic states,<br/>which are located at the Fermi-level and responsible for the 2DEG, by using very narrow<br/>integration windows in front of the oxygen core-losses. The experiments are supported by<br/>density functional theory (DFT) calculation and multislice simulation. The good agreement<br/>between experiments and<br/>defect-free simulation<br/>indicates that the 2DEG is<br/>already formed by electronic<br/>reconstruction (Fig. 1 (b)).<br/>Nevertheless, STEM-EELS<br/>reveals further accumulation<br/>of oxygen vacancies (Fig. 1<br/>(c)). The direct mapping of<br/>such an electron gas opens<br/>up entirely new ways of<br/>investigating<br/>heterostructures in<br/>electronics. Combined with<br/>DPC experiments, we are a<br/>step closer to a fully<br/>characterization of complex<br/>oxide heterostructures.

Topics

• density
• impedance spectroscopy
• theory
• experiment
• simulation
• Oxygen
• transmission electron microscopy
• defect
• Lanthanum
• density functional theory
• two-dimensional
• electron energy loss spectroscopy