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Electronic Structure and Band Alignment of LaMnO 3 /SrTiO 3 Polar/Nonpolar Heterojunctions
Author(s) -
Kaspar Tiffany C.,
Sushko Peter V.,
Spurgeon Steven R.,
Bowden Mark E.,
Keavney David J.,
Comes Ryan B.,
Saremi Sahar,
Martin Lane,
Chambers Scott A.
Publication year - 2019
Publication title -
advanced materials interfaces
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.671
H-Index - 65
ISSN - 2196-7350
DOI - 10.1002/admi.201801428
Subject(s) - heterojunction , materials science , x ray photoelectron spectroscopy , epitaxy , polar , transmission electron microscopy , spectroscopy , density functional theory , scanning transmission electron microscopy , valence (chemistry) , electric field , spectral line , condensed matter physics , electronic band structure , electron energy loss spectroscopy , analytical chemistry (journal) , chemical physics , optoelectronics , nanotechnology , computational chemistry , nuclear magnetic resonance , layer (electronics) , chemistry , physics , organic chemistry , astronomy , quantum mechanics , chromatography
Abstract The behavior of polar LaMnO 3 (LMO) thin films deposited epitaxially on nonpolar SrTiO 3 (001) (STO) is dictated by both the LMO/STO band alignment and the chemistry of the Mn cation. Using in situ X‐ray photoelectron spectroscopy, the valence band offset (VBO) of LMO/STO heterojunctions is directly measured as a function of thickness, and found that the VBO is 2.5 eV for thicker (≥3 u.c.) films. No evidence of a built‐in electric field in LMO films of any thickness is found. Measurements of the Mn valence by Mn L ‐edge X‐ray absorption spectroscopy and by spatially resolved electron energy loss spectra in scanning transmission electron microscopy images reveal that Mn 2+ is present at the LMO surface, but not at the LMO/STO interface. These results are corroborated by density functional theory simulations that confirm a VBO of ≈2.5 eV for both ideal and intermixed interfaces. A model is proposed for the behavior of polar/nonpolar LMO/STO heterojunctions in which the polar catastrophe is alleviated by the formation of oxygen vacancies at the LMO surface.