Annular dark-field image simulation of the YBa2Cu3O7−δ/BaF2 interface

Lee, J.L; Silcox, J.

doi:10.1016/s0304-3991(00)00020-6

Cited by 7 publications

(4 citation statements)

References 19 publications

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“…Strain induced ADF contrast has been observed in various systems although no quantitative measurement has been reported 23, 24. Taking advantage of the unique sensitivity to displacement in MAADF imaging, we, for the first time, were able to directly measure local displacement through structure refinement, based on a series of HAADF and MAADF image pairs.…”

Section: The Effect Of Displacement On Image Intensitymentioning

confidence: 99%

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Origin of Phonon Glass–Electron Crystal Behavior in Thermoelectric Layered Cobaltate

Meng

Jooß

et al. 2013

Adv Funct Materials

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Measurement of local disorder and lattice vibrations is of great importance for understanding the mechanisms whereby thermoelectric materials efficiently convert heat to electricity. Attaining high thermoelectric power requires minimizing thermal conductivity while keeping electric conductivity high. This situation is achievable by enhancing phonon scattering through specific structural disorder (phonon glass) that also retains sufficient electron mobility (electron crystal). It is demonstrated that the quantitative acquisition of multiple annular‐dark‐field images via scanning transmission electron microscopy at different scattering‐angles simultaneously allows not only the separation but also the accurate determination of static and thermal atomic displacements in crystals. Applying the unique method to the layered thermoelectric material (Ca2CoO3)0.62CoO2 discloses the presence of large incommensurate displacive modulation and enhanced local vibration of atoms, largely confined within its Ca2CoO3 sublayers. Relating the refined disorder to ab initio calculations of scattering rates is a tremendeous challenge. Based on an approximate calculation of scattering rates, it is suggested that this well‐defined deterministic disorder engenders static displacement‐induced scattering and vibrational‐induced resonance scattering of phonons as the origin of the phonon glass. Concurrently, the crystalline CoO2 sublayers provide pathways for highly conducting electrons and large thermal voltages.

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Section: The Effect Of Displacement On Image Intensitymentioning

confidence: 99%

“…Circles are experimental data for (Ca 2 CoO 3 ) 0.62 CoO 2 along the b direction (green, right vertical axis) and MgO (blue, left vertical axis) taken from ref. 13, 24, respectively. Solid lines are fitting curves based on specific heat, DOS, group velocity, and MFP.…”

Section: The Effect Of Displacement On Phonon Scatteringmentioning

confidence: 99%

Origin of Phonon Glass–Electron Crystal Behavior in Thermoelectric Layered Cobaltate

Meng

Jooß

et al. 2013

Adv Funct Materials

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confidence: 99%

Low angle ADF STEM defect imaging

Phillips

Graef

Kovařík³

et al. 2012

Microsc Microanal

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Scanning transmission electron microscopy (STEM) has experienced an increased popularity in recent decades, both in the high resolution [1][2][3] and defect analysis [4][5] fields. In terms of defect analysis, it has been shown that STEM allows one to collect images from relatively thick samples, while in a zone axis orientation. With these increased imaging capabilities afforded by employing STEM for diffraction contrast analysis, it was quickly realized that many defects in question were simply too small to image without resorting to high resolution techniques. Thus, the present contribution focuses on the application of low angle annular dark field STEM to defect imaging, across a wide range of length scales, including atomic resolution.Defect features in thin foils of a deformed Ni-based superalloy were examined with a probe-corrected FEI Titan 3 STEM operated at 300 kV; in all cases, the crystal was aligned such that the incident beam was parallel to a principal zone axis, generally (011). The camera length (CL) was systematically varied in order to change the acceptance angles of the annular dark eld (ADF) detector. This variation of CL allowed for the immediate transition between high angle and low angle (HA/LA) annular dark field images. That is, a transition from traditional Z-contrast HAADF to defect contrast visible in LAADF. For the computational component, two different methods are presented here, simply because of the dramatic difference in length scales explored. Simulations on the atomic scale were performed with the multislice code of Kirkland [6], while low magni cation simulations were performed with the STEM scattering matrix code developed in [4].Indeed defects are readily visible with the crystal aligned along a low-index zone and the microscope in a LAADF configuration (see Fig. 1). By decreasing the CL (increasing the scattering angle), Z-contrast returns. Furthermore, it is possible to retain atomic resolution while also imaging defect contrast, as presented in the right-hand image of Fig. 1. At the scattering angles examined here, no contrast reversals were evident and the images remained directly interpretable. Both scattering matrix simulations of specimens with random defects introduced, and multislice simulations of a single-layer stacking fault showed similar trends in terms of defect or Z-contrast at high or low CL, respectively.As previously proposed by Cowley [7], de-channeling of the electron probe in the wake of imperfect lattice channels is observed here. This is believed to be a primary cause of the defect contrast while in a low angle scattering condition. The topic of de-channeling will be discussed further, as will the application of LAADF STEM imaging to various types of defects in multiple materials, which will be presented in conjunction with computational results. 676

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“…However, when using a more modest scattering angle as in low angle annular dark-eld (LAADF), while still in a zone-axis con guration, enhanced contrast from crystalline defects results. Early work on the origin of this contrast has suggested that atoms, displaced near defects and potentially offset from perfect lattice channels, cause the electron beam to be de-channeled while penetrating the specimen [4][5][6].…”

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confidence: 99%

Atomic Resolution Defect Analysis Using Low Angle ADF-STEM

2011

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High-resolution scanning transmission electron microscopy (STEM) has recently been one of the most important techniques in advancing the analysis of crystalline materials. Traditionally, high-resolution STEM is performed in the Z-contrast mode, wherein the annular dark-eld (ADF) detector is situated such that only high-angle scattering is accepted. It has been shown that under these conditions, the resulting intensity can be approximated using an incoherent imaging model [1]. Because the low-angle Bragg scattering is not collected by the ADF, the resulting contrast is generally directly interpretable, and does not suffer some of the drawbacks of phase-contrast high-resolution TEM, such as strong dependencies on defocus and thickness [2].Much of the initial work on Z-contrast STEM was rather ambiguous in de ning the "high angle" necessary for incoherent imaging to apply, yet other calculations yielded an inner detector angle so large that the resulting signal would be very weak [1][2][3]. However, when using a more modest scattering angle as in low angle annular dark-eld (LAADF), while still in a zone-axis con guration, enhanced contrast from crystalline defects results. Early work on the origin of this contrast has suggested that atoms, displaced near defects and potentially offset from perfect lattice channels, cause the electron beam to be de-channeled while penetrating the specimen [4-6].The present contribution highlights LAADF imaging of defects, while maintaining atomic resolution. Speci cally, various defects present in a Ni-based superalloy were examined using an FEI Titan 3 80 300 probe-corrected monochromated S/TEM operated at 300 kV. The camera length (CL), i.e., ADF detector acceptance angle, was systematically varied to show either Z-contrast or defect contrast. Fig. 1 illustrates the defect contrast obtained in zone-axis oriented LAADF. The left image was taken from the same area as the right, only with the ADF acceptance angle adjusted to 14 91 mrad (CL = 285 mm); paired dislocations exhibit bright contrast throughout the left image, highlighted with red lines. The right image was acquired with the ADF acceptance angle ranging from 69 422 mrad (CL = 58 mm), and is considered to be Z-contrast in nature. As shown in Fig. 2, atomic resolution LAADF images remain interpretable, despite the contribution of low-angle scattering to the image. The stacking fault present runs parallel to one set of {111} planes, with interplanar spacing 0.206 nm. When the CL is adjusted for Z-contrast (right image), note the lack of enhanced intensity over the fault, indicating that the bright contrast observed in LAADF is not a result of heavy-element segregation to the fault or any variance in chemical species. Since such heavy-element segregation can occur at planar defects, it is particularly important to accurately understand the LAADF contrast, in order to distinguish it from Z-contrast.Additionally, high-resolution images were acquired in defect-free regions of the crystal. Within the given range of ADF detector acc...

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Annular dark-field image simulation of the YBa2Cu3O7−δ/BaF2 interface

Cited by 7 publications

References 19 publications

Origin of Phonon Glass–Electron Crystal Behavior in Thermoelectric Layered Cobaltate

Origin of Phonon Glass–Electron Crystal Behavior in Thermoelectric Layered Cobaltate

Low angle ADF STEM defect imaging

Atomic Resolution Defect Analysis Using Low Angle ADF-STEM

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