Identifying Ionic and Electronic Charge Transfer at Oxide Heterointerfaces

Abstract

The ability to tailor oxide heterointerfaces has led to novel properties in low‐dimensional oxide systems. A fundamental understanding of these properties is based on the concept of electronic charge transfer. However, the electronic properties of oxide heterointerfaces crucially depend on their ionic constitution and defect structure: ionic charges contribute to charge transfer and screening at oxide interfaces, triggering a thermodynamic balance of ionic and electronic structures. Quantitative understanding of the electronic and ionic roles regarding charge‐transfer phenomena poses a central challenge. Here, the electronic and ionic structure is simultaneously investigated at the prototypical charge‐transfer heterointerface, LaAlO3/SrTiO3. Applying in situ photoemission spectroscopy under oxygen ambient, ionic and electronic charge transfer is deconvoluted in response to the oxygen atmosphere at elevated temperatures. In this way, both the rich and variable chemistry of complex oxides and the associated electronic properties are equally embraced. The interfacial electron gas is depleted through an ionic rearrangement in the strontium cation sublattice when oxygen is applied, resulting in an inverse and reversible balance between cation vacancies and electrons, while the mobility of ionic species is found to be considerably enhanced as compared to the bulk. Triggered by these ionic phenomena, the electronic transport and magnetic signature of the heterointerface are significantly altered.

Reconfiguration of Amorphous Complex Oxides: A Route to a Broad Range of Assembly Phenomena, Hybrid Materials, and Novel Functionalities

“…[20,44,47] Therefore, establishing tunable strains and strain gradients in complex oxides via reconfiguration-driven assembly is a viable approach to tailor ionic and electronic transports in oxide-based devices on conventional semiconductor substrates. [48,49]…”

Nature of the surface space charge layer on undoped SrTiO3(001)

“…12,23 On the other hand, the creation of Sr vacancies (V Sr ) is also known to occur under oxygen rich PLD conditions. 2,24,25 Under the presence of oxygen species on the SrTiO 3 surface, Sr atoms make surface migration to form SrO oxide at a cost of electrons in the subsurface region, i.e., formation of an electron depletion layer near the surface. 2,24,26,27 In the case of V Sr formation, the surface resistance increases, affecting the electrical properties of the interfacial layer.…”

“…2,24,25 Under the presence of oxygen species on the SrTiO 3 surface, Sr atoms make surface migration to form SrO oxide at a cost of electrons in the subsurface region, i.e., formation of an electron depletion layer near the surface. 2,24,26,27 In the case of V Sr formation, the surface resistance increases, affecting the electrical properties of the interfacial layer. In fact, both types of V O or V Sr can occur simultaneously during the PLD process in which an oxygen environment and elevated temperature are required.…”

Harnessing Conductive Oxide Interfaces for Resistive Random-Access Memories

“…Besides the polar catastrophe mechanism, the ionic aspect of the interface plays an important role in its electronic properties [57]. Interdiffusion and intermixing of atoms across the interface [58] and oxygen vacancies [59][60][61] can account for the 2DEG formation via various ionic doping mechanisms.…”