Artificial Dielectric Superlattices with Broken Inversion Symmetry

Warusawithana, Maitri; Colla, Eugene V.; Eckstein, J. N.; Weissman, M. B.

doi:10.1103/physrevlett.90.036802

Cited by 129 publications

(112 citation statements)

References 7 publications

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“…3,4 Reactive molecular-beam epitaxy (MBE) and pulsed-laser deposition (PLD) are the two most successful growth techniques for epitaxial heterostructures of complex oxides. PLD possesses experimental simplicity, low cost, and versatility in the materials to be deposited.…”

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confidence: 99%

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

et al. 2017

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Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive molecular-beam epitaxy and pulsed-laser deposition, we show here, with examples of Sr 1+x Ti 1-x O 3+δ , Ruddlesden-Popper phase La n+1 Ni n O 3n+1 (n = 4), and LaAl 1+y O 3(1+0.5y) /SrTiO 3 interfaces, that atomic layer-by-layer laser molecular-beam epitaxy significantly advances the state of the art in constructing oxide materials with atomic layer precision and control over stoichiometry. With atomic layer-by-layer laser molecular-beam epitaxy we have produced conducting LaAlO 3 /SrTiO 3 interfaces at high oxygen pressures that show no evidence of oxygen vacancies, a capability not accessible by existing techniques. The carrier density of the interfacial two-dimensional electron gas thus obtained agrees quantitatively with the electronic reconstruction mechanism.npj Quantum Materials (2017) 2:10 ; doi:10.1038/s41535-017-0015-x INTRODUCTION Technological advances in atomic-layer control during oxide film growth have enabled the discoveries of new phenomena and new functional materials, such as the two-dimensional (2D) electron gas at the LaAlO 3 /SrTiO 3 interface, 1, 2 and asymmetric three-component ferroelectric superlattices. 3,4 Reactive molecular-beam epitaxy (MBE) and pulsed-laser deposition (PLD) are the two most successful growth techniques for epitaxial heterostructures of complex oxides. PLD possesses experimental simplicity, low cost, and versatility in the materials to be deposited. 5 Reactive MBE employing alternately-shuttered elemental sources (atomic layerby-layer MBE, or ALL-MBE) can control the cation stoichiometry precisely, thus producing oxide thin films of exceptional quality. [6][7][8] There are, however, limitations in both techniques. Reactive MBE can use only source elements whose vapor pressure is sufficiently high, excluding a large fraction of 4d and 5d metals. In addition, ozone is needed to create a highly oxidizing environment while maintaining low-pressure MBE conditions, which increases the system complexity. On the other hand, conventional PLD using a compound target often results in cation off-stoichiometry in the films. 9, 10 In this paper we present an approach that combines the strengths of reactive MBE and PLD: atomic layer-by-layer laser MBE (ALL-Laser MBE) using separate oxide targets. Ablating alternately the targets of constituent oxides, for example SrO and TiO 2 , a SrTiO 3 film can be grown one atomic layer at a time. Stoichiometry for both the cations and oxygen in the oxide films can be controlled. Although the idea of depositing atomic layers by PLD has been explored since the early days of laser MBE, 11,12 we show that levels of stoichiometry control and crystalline perfection rivaling those of

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Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

et al. 2017

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“…1,2,6,8 Such enhancement of ferroelectric polarization is known to originate from the strong strain coupling of ferroelectric polarization in BaTiO 3 -based ferroelectrics. 9,10 Recently, by including PE CaTiO 3 (CTO) layers, three-component SLs have been designed and raised an intriguing issue of artificially broken compositional inversion symmetry, 11,12 resulting enhanced ferroelectric properties. 7,13 Along with these experimental developments, recent progress in computational methods [14][15][16] have provided us with opportunities to systematically investigate these FE oxide SLs as well.…”

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Strain-coupled ferroelectric polarization in BaTiO3–CaTiO3 superlattices

Seo

Lee

2009

Applied Physics Letters

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We report on growth and ferroelectric (FE) properties of superlattices (SLs) composed of the FE BaTiO 3 and the paraelectric (PE) CaTiO 3 . Previous theories have predicted that the polarization in (BaTiO 3 )n/(CaTiO 3 )n SLs increases as the sublayer thickness (n) increases when the same strain state is maintained. However, our BaTiO 3 /CaTiO 3 SLs show a varying lattice-strain state and systematic reduction in polarization with increasing n while coherently-strained SLs with n=1, 2 show a FE polarization of ca. 8.5 µC/cm 2 . We suggest that the strain coupling plays more important role in FE properties than the electrostatic interlayer coupling based on constant dielectric permittivities. *

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“…the periodic structure containing alternating layers of different materials. Several 2,19 The properties of such structures are not just simple combination of those known for constituent bulk materials. In particular, it was described theoretically [20][21][22] and observed experimentally, 2,11 that remanent polarization in SLs can be enhanced above the value of that in bulk constituents.…”

Section: Introductionmentioning

confidence: 99%

“…The resulting asymmetry of the ferroelectric double-well potential in such a structure suggests a possible appearance of effective permanent bias fields, predicted theoretically 36 and observed experimentally. 19 Use of CaTiO 3 (bulk pseudocubic lattice constant a = 3.83Å) and BaTiO 3 (a = 3.992Å)) in combination with SrTiO 3 can result in a superlattice growing commensurately on SrTiO 3 substrate (a = 3.905Å). In such a superlattice, the constituent BaTiO 3 and CaTiO 3 layers are subject to significant epitaxial strain of opposite signs.…”

Section: Introductionmentioning

confidence: 99%

Ferroelectric phase transitions in three-component short-period superlattices studied by ultraviolet Raman spectroscopy

Ténné

Lee

Katiyar

et al. 2009

Journal of Applied Physics

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Vibrational spectra of three-component BaTiO 3 /SrTiO 3 /CaTiO 3 short-period superlattices grown by pulsed laser deposition with atomic-layer control have been investigated by ultraviolet Raman spectroscopy. Monitoring the intensity of the first-order phonon peaks in Raman spectra as a function of temperature allowed determination of the ferroelectric phase transition temperature, T c . Raman spectra indicate that all superlattices remain in the tetragonal ferroelectric phase with out-of-plane polarization in the entire temperature range below T c . The dependence of T c on the relative thicknesses of ferroelectric (BaTiO 3 ) to non-ferroelectric materials (SrTiO 3 and CaTiO 3 ) has been studied. The highest T c was found in superlattices having the largest relative amount of BaTiO 3 , provided that the superlattice maintains its coherency with the substrate. Strain relaxation leads to a significant decrease in the ferroelectric phase transition temperature.

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Artificial Dielectric Superlattices with Broken Inversion Symmetry

Cited by 129 publications

References 7 publications

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

Strain-coupled ferroelectric polarization in BaTiO3–CaTiO3 superlattices

Ferroelectric phase transitions in three-component short-period superlattices studied by ultraviolet Raman spectroscopy

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