Electrostatics and Polarity in 2D Oxides

Noguera, Claudine; Goniakowski, Jacek

doi:10.1007/978-3-319-28332-6_7

Oxide Materials at the Two-Dimensional Limit

2016

DOI: 10.1007/978-3-319-28332-6_7

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Electrostatics and Polarity in 2D Oxides

Claudine Noguera

Jacek Goniakowski

Abstract: We review the manifestations of electrostatic interactions, and in particular polarity effects, in oxide ultra-thin films and two-dimensional nano-objects. We discuss the efficiency of various compensation mechanisms such as overall structural transformations, strong lattice relaxations, inhomogeneous charge redistributions, support effects, and/or the formation of 2D or 1D electron/hole gases.

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Cited by 2 publications

References 130 publications

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Formation and Tuning of 2D Electron Gas in Perovskite Heterostructures

Maznichenko

Ostanin

Ernst

et al. 2019

Physica Status Solidi (b)

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Oxide interfaces provide very intriguing phenomena, in particular a 2D electron gas (2DEG) emerging between robustly insulating perovskites. The 2DEG was detected in 2004 beneath polar LaAlO 3 (LAO) epitaxially grown on TiO 2terminated SrTiO 3 (001) (STO). Herein, recent first-principles studies of 2DEGs are reviewed. Using a Green function method, the family of the polar/nonpolar (001) interfaces: LAO/STO, LaFeO 3 /STO, and STO/KTaO 3 is computed. In the context of 2DEG, one of two insulating perovskites, at least, must be polar. The effect of a polar/polar interface is modeled for LAO/KTaO 3 (001) and also for the ( 110) and ( 111) interfaces of LAO/STO. Starting from the defectless superlattice with its two differently terminated interfaces, we demonstrate that the 2DEG and 2D hole gas appear there, respectively, due to the presence of excessive electrons or holes. 2DEG is evaluated by its layer-resolved density profile along [001], as well as the Fermi surface cross sections and effective masses, which are directly related to the transport properties. The effects of intermixed cations, their vacancies, and oxygen vacancies at each interface of LAO/STO are calculated. Finally, we show how to tune reversibly the 2DEG by changing the electronic balance at the LAO surface that mimics the effect of ionic liquid gating.

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Formation and Tuning of 2D Electron Gas in Perovskite Heterostructures

Maznichenko

Ostanin

Ernst

et al. 2019

Physica Status Solidi (b)

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Metallicity at interphase boundaries due to polar catastrophe induced by charge density discontinuity

2018

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The electronic properties of interphase boundaries are of basic importance for most materials, particularly when those properties deviate strongly from the bulk behavior. We introduce a mechanism that can result in metallicity at stoichiometric interphase boundaries between semiconductors based on the idea of polar catastrophe, which is usually considered only in the context of heterostructures. To this end, we perform ab initio calculations within density functional theory to investigate the electronic states at stoichiometric SnO/SnO 2 (110) interphase boundaries. In this system, one would not expect polar catastrophe to have a role according to state-of-the-art theory because the interface lacks formal charge discontinuity. However, we observe the formation of a hole gas between the semiconductors SnO and SnO 2 . To explain these findings, we provide a generalized theory based on the idea that the charge density discontinuity between SnO and SnO 2 , a consequence of lattice mismatch, drives a polar catastrophe scenario. As a result, SnO/SnO 2 (110) interphase boundaries can develop metallicity depending on the grain size. The concept of metallicity due to polar catastrophe induced by charge density discontinuity is of general validity and applies to many interphase boundaries with lattice mismatch.

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Electrostatics and Polarity in 2D Oxides

Cited by 2 publications

References 130 publications

Formation and Tuning of 2D Electron Gas in Perovskite Heterostructures

Formation and Tuning of 2D Electron Gas in Perovskite Heterostructures

Metallicity at interphase boundaries due to polar catastrophe induced by charge density discontinuity

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