Concurrent bandgap narrowing and polarization enhancement in epitaxial ferroelectric nanofilms

0448711 - FZÚ 2016 RIV NL eng J - Journal Article
Tyunina, Marina - Yao, L. - Chvostová, Dagmar - Dejneka, Alexandr - Kocourek, Tomáš - Jelínek, Miroslav - Trepakov, Vladimír - van Dijken, S.
Concurrent bandgap narrowing and polarization enhancement in epitaxial ferroelectric nanofilms.
Science and Technology of Advanced Materials. Roč. 16, č. 2 (2015), 026002. ISSN 1468-6996. E-ISSN 1878-5514
R&D Projects: GA ČR GAP108/12/1941
Institutional support: RVO:68378271
Keywords : epitaxial growth * ferroelectric nanofilms
Subject RIV: BM - Solid Matter Physics ; Magnetism
Impact factor: 3.433, year: 2015

Perovskite-type ferroelectric (FE) crystals are wide bandgap materials with technologically valuable optical and photoelectric properties. Here, versatile engineering of electronic transitions is demonstrated in FE nanofilms of KTaO3, KNbO3 (KNO), and NaNbO3 (NNO) with a thickness of 10–30 unit cells. Control of the bandgap is achieved using heteroepitaxial growth of new structural phases on SrTiO3 (001) substrates. Compared to bulk crystals, anomalous bandgap narrowing is obtained in the FE state of KNO and NNO films. This effect opposes polarization-induced bandgap widening, which is typically found for FE materials. Transmission electron microscopy and spectroscopic ellipsometry measurements indicate that the formation of higher-symmetry structural phases of KNO and NNO produces the desirable red shift of the absorption spectrum towards visible light, while simultaneously stabilizing robust FE order.
Permanent Link: http://hdl.handle.net/11104/0250352