Three-Dimensional Imaging of Individual Dopant Atoms in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>SrTiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

Hwang, Jinwoo; Zhang, Jack; D’Alfonso, Adrian J.; Allen, L. J.; Stemmer, Susanne

doi:10.1103/physrevlett.111.266101

Cited by 88 publications

(103 citation statements)

References 38 publications

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“…Another source of I Sm;Sr variations is the Sr doping. The Sr dopants have a lower Z than the host (Sm); thus, Sr-containing columns show lower image intensity, with the column intensity depending on the number of Sr atoms, their depth locations, the total number of atoms in the column, and the STEM parameters [28,[38][39][40]. The white arrows in the I Sm;Sr maps indicate selected columns that show significantly reduced intensities relative to those of nearest-neighbor Ti-O columns, which have similar thicknesses.…”

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Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

et al. 2017

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The lattice response of a prototype Mott insulator, SmTiO 3 , to hole doping is investigated with atomic-scale spatial resolution. SmTiO 3 films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metalinsulator transition (MIT). The GdFeO 3 -type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation. Significant distortions persist into the metallic state. The results present a new picture of the physics of this prototype filling-controlled MIT, which is discussed.

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Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

et al. 2017

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“…Furthermore, most techniques cannot provide direct information about atom relaxations around a point defect even though these are crucial for many properties.Previously, we have shown that HAADF-STEM can provide three-dimensional information of the location of individual dopant atoms in SrTiO3 from a single image [1]. The number of dopant atoms in a column and the depth position information are extracted using quantitative STEM, by comparing the experimental column intensities with calculations for all possible dopant configurations, and determining the most probable dopant position given an experimentally determined noise function.…”

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Imaging Point Defects in Complex Oxides Using Quantitative STEM

2017

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While methods to measure the global concentration of point defects exist, determining their spatial arrangement is significantly more challenging. Furthermore, most techniques cannot provide direct information about atom relaxations around a point defect even though these are crucial for many properties.Previously, we have shown that HAADF-STEM can provide three-dimensional information of the location of individual dopant atoms in SrTiO3 from a single image [1]. The number of dopant atoms in a column and the depth position information are extracted using quantitative STEM, by comparing the experimental column intensities with calculations for all possible dopant configurations, and determining the most probable dopant position given an experimentally determined noise function. This method is limited by inherent experimental noise (detector noise, sample instability under the beam, sample contamination, surface amorphous layers, sample imperfections, etc.), in particular, when intensity differences between different configurations are small. The contrast and interpretability can be improved using variable-angle HAADF-STEM (VA-HAADF).A key feature of VA-HAADF is that it utilizes information provided by the angular dependence of the scattering in HAADF (Fig. 1). This angular dependence depends on the dopant depth position. As the incident probe channels along a column, atoms deeper in the foil see a more focused probe, resulting in scattering to higher angles, relative to a dopant atom nearer to the entrance surface. Thus, by selecting certain angular ranges, different dopant atom configurations may be more easily distinguished. VA-HAADF allows for precise and accurate determination of three-dimensional dopant atom configurations in doped SrTiO3 films [2]. The acquisition of multiple variable angle data and use of compound probabilities significantly improved the accuracy and precision of both the number of dopants as well as the their position(s). Configurations that are ambiguous in one detector regime can be resolved in the other.Detecting vacancies in STEM images is even more challenging than dopant atoms that have a large atomic number difference with the host. We have combined VA-HAADF and rigid registration methods to detect Sr vacancies in SrTiO3 and their associated local atom relaxations [3]. Lattice relaxation around the vacancies are detected with picometer precision (Fig. 2). Rigid registration methods not only improve the precision in measurements of atom column positions but also the quantification of image intensities, which allows for the detection of point defects with low Z-contrast, such as vacancies. The number of vacancies in each column can be quantified. Discrepancies between the measured lattice relaxations and predictions from DFT simulations underscore the need for atomic-scale experimental input in developing a microscopic understanding of how point defects control real materials properties [4].

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“…An important complementary method in STEM is position averaged convergent beam electron diffraction (PACBED), which is highly sensitive to information that cannot easily be obtained from HAADF-STEM images, such as small displacements of atom or tilts of oxygen octahedra in perovskite materials [2,3]. In this presentation, we will discuss our recent [4,5] work in applications of quantitative HAADF-STEM and PACBED to pertinent problems in materials science.Our first example concerns the determination of the three-dimensional location of individual Gd dopant atoms in SrTiO3 [4]. The method is based on using quantitative comparisons of experimental and calculated image intensities.…”

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“…Our first example concerns the determination of the three-dimensional location of individual Gd dopant atoms in SrTiO3 [4]. The method is based on using quantitative comparisons of experimental and calculated image intensities.…”

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Progress in Applications of Quantitative STEM

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Zhang²,

Stemmer³

2014

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High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) is highly sensitive to the type and number of atoms in the atomic columns of a sample. Image contrast in HAADF-STEM agrees quantitatively with image simulations [1]. An important complementary method in STEM is position averaged convergent beam electron diffraction (PACBED), which is highly sensitive to information that cannot easily be obtained from HAADF-STEM images, such as small displacements of atom or tilts of oxygen octahedra in perovskite materials [2,3]. In this presentation, we will discuss our recent [4,5] work in applications of quantitative HAADF-STEM and PACBED to pertinent problems in materials science.Our first example concerns the determination of the three-dimensional location of individual Gd dopant atoms in SrTiO3 [4]. The method is based on using quantitative comparisons of experimental and calculated image intensities. Quantitative measures of the error and a criterion for the dopant visibility were established using an undoped SrTiO3 sample. The overall dopant concentration measured from atom column intensities agrees quantitatively with Hall carrier density measurements. The method is applied to analyze the 3D arrangement of dopants within small clusters containing 4-5 Gd atoms (Fig. 1).Our second example discusses the correlation between oxygen octahedral tilts, A-site cation displacements, and ferromagnetism in thin, confined GdTiO3 layers. We show that PACBED in combination with HAADF-STEM imaging can be used to obtain independent information on tilts and displacements (Fig. 2) [5]. With decreasing GdTiO3 film thickness, structural distortions are reduced, concomitant with a reduction in the Curie temperature. Ferromagnetism persists to smaller deviations from the cubic perovskite structure than is the case for the bulk rare earth titanates, which allows for insights into strong electron correlation physics.[1] J.

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Three-Dimensional Imaging of Individual Dopant Atoms inSrTiO3

Cited by 88 publications

References 38 publications

Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

Response of the Lattice across the Filling-Controlled Mott Metal-Insulator Transition of a Rare Earth Titanate

Imaging Point Defects in Complex Oxides Using Quantitative STEM

Progress in Applications of Quantitative STEM

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