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Atomic-scale imaging of nanoengineered oxygen vacancy profiles in SrTiO3

Abstract

At the heart of modern oxide chemistry lies the recognition that beneficial (as well as deleterious) materials properties can be obtained by deliberate deviations of oxygen atom occupancy from the ideal stoichiometry1,2. Conversely, the capability to control and confine oxygen vacancies will be important to realize the full potential of perovskite ferroelectric materials, varistors and field-effect devices3,4. In transition metal oxides, oxygen vacancies are generally electron donors, and in strontium titanate (SrTiO3) thin films, oxygen vacancies (unlike impurity dopants) are particularly important because they tend to retain high carrier mobilities, even at high carrier densities5. Here we report the successful fabrication, using a pulsed laser deposition technique, of SrTiO3 superlattice films with oxygen doping profiles that exhibit subnanometre abruptness. We profile the vacancy concentrations on an atomic scale using annular-dark-field electron microscopy and core-level spectroscopy, and demonstrate absolute detection sensitivities of one to four oxygen vacancies. Our findings open a pathway to the microscopic study of individual vacancies and their clustering, not only in oxides, but in crystalline materials more generally.

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Figure 1: Electron energy-loss spectra (EELS) for oxygen-deficient SrTiO3-δ, for δ ≈ 0, 0.13 and 0.25.
Figure 2: 25 unit cells of oxygen-deficient SrTiO3-δ (δ ≈ 0.13) are grown on bulk SrTiO3 (left of white arrow) and capped with a two-layer-thick LaTiO3 marker layer (right) and more SrTiO3-δ.
Figure 3: Quantitative line profiles through the oxygen-deficient layer.
Figure 4: A LAADF image of an oxygen-modulated superlattice grown on SrTiO3.

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Acknowledgements

We acknowledge partial support from NEDO's International Joint Research Program. N.N. acknowledges partial support from QPEC, Graduate School of Engineering, University of Tokyo. D.A.M. and J.L.G. received partial support from the Cornell Center for Materials Research, a NSF materials research science and engineering centre.

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Correspondence to David A. Muller.

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Supplementary Figures

Supplementary Fig 1. Oxygen-deficient SrTiO3-δ, (δ ≈ 0.25) are grown on bulk SrTiO3 ( 700 ºC, PO2=2x 10-8 torr). Supplementary Fig 2. A LAADF image of an oxygen-modulated superlattice grown on SrTiO3. (PDF 1143 kb)

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Muller, D., Nakagawa, N., Ohtomo, A. et al. Atomic-scale imaging of nanoengineered oxygen vacancy profiles in SrTiO3. Nature 430, 657–661 (2004). https://doi.org/10.1038/nature02756

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