Atomic-resolution spectroscopic imaging of oxide interfaces

Kourkoutis, Lena F.; Xin, Huolin L.; Higuchi, Tohru; Hotta, Yoshiki; Lee, J.H.; Hikita, Y.; Schlom, Darrell G.; Hwang, Harold Y.; Muller, David A.

doi:10.1080/14786435.2010.518983

Cited by 61 publications

(55 citation statements)

References 72 publications

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“…The most pronounced one is the large shift observed in the position of the second peak (marked with an asterisk). This peak has been attributed to the hybridization of the O 2p with Sr 4d and with Pb 6sp states for STO and PTO, respectively, [22][23][24] making it possible to distinguish between Sr and Pb containing cells by identifying the position of this peak. The analysis of the Ti L 2,3 and O K edges therefore offers an excellent method for determining both structural and chemical variations within the PTO/STO superlattices.…”

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confidence: 99%

Spectroscopic mapping of local structural distortions in ferroelectric PbTiO3/SrTiO3superlattices at the unit-cell scale

et al. 2011

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The local structural distortions in polydomain ferroelectric PbTiO 3 /SrTiO 3 superlattices are investigated by means of high spatial and energy resolution electron-energy-loss spectroscopy combined with high-angle annular dark field imaging. Local structural variations across the interfaces have been identified with unit-cell resolution through the analysis of the energy-loss near-edge structure of the Ti L 2,3 and O K edges. Ab initio and multiplet calculations of the Ti L 2,3 edges provide unambiguous evidence for an inhomogeneous polarization profile associated with the observed structural distortions across the superlattice. Complex oxide heterostructures offer a vast playground for exploring and combining the many functional properties of these interesting materials arising from the subtle interplay between their charge, spin, orbital, and lattice degrees of freedom. Bilayers, multilayers, and superlattices composed of ultrathin oxide layers not only shed light on our fundamental understanding of the constituent materials, but frequently reveal unexpected phases at their interfaces.1 Superlattices composed of ferroelectric and paraelectric oxides have been the subject of numerous studies, motivated by fundamental questions about ferroelectric size effects, by the possibilities these artificially layered materials offer for tailoring their functional properties, and by the interesting interface physics they display. Ultrafine period superlattices, composed of ferroelectric PbTiO 3 (PTO) and paraelectric SrTiO 3 (STO), for example, have been shown to exhibit improper ferroelectricity driven by the coupling of the polar and nonpolar distortions at the interface.2 More recently, regular ferroelectric nanodomains have been observed in PTO/STO superlattices with larger periodicities and were shown to be responsible for large enhancements in the effective dielectric constant.3 Such domains are expected to give rise to complex inhomogeneous structural distortions and polarization profiles, 4,5 departing from uniform polarization models, frequently used to describe the properties of ferroelectric/paraelectric superlattices in the absence of domains. 6 Thus a microscopic insight into the local structure is key to understanding the behavior of these artificially layered materials, and here transmission electron microscopy (TEM), with recent advances in spatial resolution, provides an invaluable tool. Individual ionic displacements within a single perovskite unit cell can now be identified from phase contrast images. The spatial resolution is high enough to determine the direction and even the magnitude of the local dipole moments in ferroelectric materials, 7-9 and has recently enabled the direct verification of the existence of polarization rotation at domain walls in Pb(Zr,Ti)O 3 ferroelectric thin films. 10In this Rapid Communication, we focus on an alternative spectroscopic technique to study local ferroelectric distortions at the single unit-cell scale. Atomically resolved electronenergy-loss spectra (EELS) and ...

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confidence: 99%

Spectroscopic mapping of local structural distortions in ferroelectric PbTiO3/SrTiO3superlattices at the unit-cell scale

et al. 2011

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“…23 Analysis of the EELS line shape can thus produce atomic-resolution information about the oxidation state and bonding information of the constituent species present. [24][25][26][27] While other techniques including X-ray absorption spectroscopy 4,12,28 and hard X-ray photoemission spectroscopy 29 have detected the presence of multiple europium valence states in EuO 1±δ films, electron microscopy is uniquely poised to investigate variations in the interface structure at the atomic scale, which are not discernable by bulk characterization. Transmission electron microscopy on EuO is challenging due to its reactivity with air and we are aware of only one report of its use, 4 though no images were shown in that report.…”

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Hetero-epitaxial EuO interfaces studied by analytic electron microscopy

Mundy

Hodash

Melville

et al. 2014

Applied Physics Letters

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With nearly complete spin polarization, the ferromagnetic semiconductor europium monoxide could enable next-generation spintronic devices by providing efficient ohmic spin injection into silicon. Spin injection is greatly affected by the quality of the interface between the injector and silicon. Here, we use atomic-resolution scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy to directly image and chemically characterize a series of EuO|Si and EuO|YAlO 3 interfaces fabricated using different growth conditions. We identify the presence of europium silicides and regions of disorder at the EuO|Si interfaces, imperfections that could significantly reduce spin injection efficiencies via spin-flip scattering. a These authors contributed equally to this work.

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“…Over the last decade, atomic-resolution core-level spectroscopy has developed to become an extremely powerful tool for probing nanomaterials. [1][2][3][4][5][6][7][8] Performed in a scanning transmission electron microscope (STEM), the technique uses an atomic-sized electron probe to excite core-level electrons in the sample, while detectors monitor the spectra of energy-loss electrons and/or the flux of characteristic x-rays. A wealth of atomic-scale information is provided, 3,4,[9][10][11] including the locations and species of atoms, i.e., elemental maps, and, in the case of electron energy-loss spectroscopy (EELS), information on electronic bonding.…”

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Towards artifact-free atomic-resolution elemental mapping with electron energy-loss spectroscopy

Zhu

Soukiassian

Schlom

et al. 2013

Applied Physics Letters

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Atomic-resolution elemental maps of materials obtained using energy-loss spectroscopy in the scanning transmission electron microscope (STEM) can contain artifacts associated with strong elastic scattering of the STEM probe. We demonstrate how recent advances in instrumentation enable a simple and robust approach to reduce such artifacts and produce atomic-resolution elemental maps amenable to direct visual interpretation. The concept is demonstrated experimentally for a (BaTiO3)8/(SrTiO3)4 heterostructure, and simulations are used for quantitative analysis. We also demonstrate that the approach can be used to eliminate the atomic-resolution elastic contrast in maps obtained from lower-energy excitations, such as plasmon excitations.

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Atomic-resolution spectroscopic imaging of oxide interfaces

Cited by 61 publications

References 72 publications

Spectroscopic mapping of local structural distortions in ferroelectric PbTiO3/SrTiO3superlattices at the unit-cell scale

Spectroscopic mapping of local structural distortions in ferroelectric PbTiO3/SrTiO3superlattices at the unit-cell scale

Hetero-epitaxial EuO interfaces studied by analytic electron microscopy

Towards artifact-free atomic-resolution elemental mapping with electron energy-loss spectroscopy

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