On the Progress of Scanning Transmission Electron Microscopy (STEM) Imaging in a Scanning Electron Microscope

Sun, Cheng; Müller, Erich; Meffert, Matthias; Gerthsen, D.

doi:10.1017/s1431927618000181

Cited by 38 publications

(23 citation statements)

References 50 publications

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“…These accessories have become available only recently which explains the lack of defect investigations by STEM in a scanning electron microscope which will be denoted as low-keV STEM in the following. Preliminary investigations of dislocation Burgers vectors in InN by low-keV STEM were presented by us [12]. In addition, recently, Callahan et al [13] presented defect analyses by low-keV STEM in samples with a priori known orientation by comparing experimental images and simulations in various materials, but they were not able to systematically exploit the g·b = n criterion for instrumental reasons.…”

Section: Introductionmentioning

confidence: 99%

Analysis of crystal defects by scanning transmission electron microscopy (STEM) in a modern scanning electron microscope

Sun

Müller

Meffert

et al. 2019

Adv Struct Chem Imag

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Dislocations and stacking faults are important crystal defects, because they strongly influence material properties. As of now, transmission electron microscopy (TEM) is the most frequently used technique to study the properties of single dislocations and stacking faults. Specifically, the Burgers vector b of dislocations or displacement vector R of stacking faults can be determined on the basis of the g·b = n (g·R = n) criterion by setting up different two-beam diffraction conditions with an imaging vector g. Based on the reciprocity theorem, scanning transmission electron microscopy (STEM) can also be applied for defect characterization, but has been less frequently used up to now. In this work, we demonstrate g·b = n (g·R = n) analyses of dislocations and stacking faults in GaN by STEM imaging in a scanning electron microscope. The instrument is equipped with a STEM detector, double-tilt TEM specimen holder, and a charge-coupled-device camera for the acquisition of on-axis diffraction patterns. The latter two accessories are mandatory to control the specimen orientation, which has not been possible before in a scanning electron microscope. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Section: Introductionmentioning

confidence: 99%

Analysis of crystal defects by scanning transmission electron microscopy (STEM) in a modern scanning electron microscope

Sun

Müller

Meffert

et al. 2019

Adv Struct Chem Imag

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“…The scattering behaviour of electrons in the sample is simulated by the numerical solution of the electron transport equation by means of expansion in Legendre polynomials (Negreanu et al ., ) which is adequate for low‐keV STEM on a non‐atomic level for single, plural and multiple scattering conditions. The program CeTE1.4 (computation of electron transport equation) was developed by us (Sun et al ., ) and allows to calculate the angular distribution of the transmitted electrons for given values of material parameters ( Z , ρ, A ), t and E 0 . For chemical compounds, mean values of material parameters are used.…”

Section: Methodsmentioning

confidence: 99%

Electron beam broadening in electron‐transparent samples at low electron energies

Hugenschmidt

Müller

Gerthsen

2019

Journal of Microscopy

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Summary Scanning transmission electron microscopy (STEM) at low primary electron energies has received increasing attention in recent years because knock‐on damage can be avoided and high contrast for weakly scattering materials is obtained. However, the broadening of the electron beam in the sample is pronounced at low electron energies, which degrades resolution and limits the maximum specimen thickness. In this work, we have studied electron beam broadening in materials with atomic numbers Z between 10 and 32 (MgO, Si, SrTiO3, Ge) and thicknesses up to 900 nm. Beam broadening is directly measured using a multisegmented STEM detector installed in a scanning electron microscope at electron energies between 15 and 30 keV. For experimental reasons, the electron beam diameter is defined to contain only 68% of the total intensity instead of the commonly used 90% of the total beam intensity. The measured beam diameters can be well described with calculated ones based on a recently published model by Gauvin and Rudinsky. Using the concept of anomalous diffusion the Hurst exponent H is introduced that varies between 0.5 and 1 for different scattering regimes depending on t/Λel with the specimen thickness t and the elastic mean free path length Λel. The calculations also depend on the fraction of the beam intensity that defines the electron beam diameter. A Hurst exponent H of 1 is characteristic for the ballistic scattering regime with t/Λel → 0 and can be excluded for the experimental conditions of our study with 6 ≦ t/Λel ≦ 30. We deduced H = 0.75 from measured beam diameters which is larger than H = 0.5 that is expected under diffusion conditions. The deviation towards larger H values can be rationalised by our definition of electron diameter that contains only 68% of the total beam intensity and requires therefore larger sample thicknesses before the diffusion regime is reached. Our results clearly deviate from previous analytical approaches to describe beam broadening (Goldstein et al., Reed, Williams et al., Kohl and Reimer). Measured beam diameters are compared with simulated ones, which are obtained by solving the electron transport equation. This approach is advantageous compared to the commonly used Monte Carlo simulations because it is an exact solution of the electron transport equation and requires less computer time. Simulated beam diameter agree well with the experimental data and yield H = 0.80. Lay Description In scanning transmission electron microscopy (STEM), a focused electron beam is scanned over an electron‐transparent sample and an image is formed by detecting the intensity of the transmitted electrons by a STEM detector. STEM resolution is ultimately limited by the electron beam diameter and can be better than 0.1 nm for the best microscopes. However, the electron‐beam diameter increases with increasing specimen thickness because electrons are scattered by the interaction of the specimen material and electrons. Electron scattering leads to a change of the electron propagation direction and redu...

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“…The field of TSEM as applied to characterization of defects is nascent and offers exciting practical and fundamental benefits for materials research. Advancements in this vein are necessary, such as in navigating reciprocal space to specific diffraction conditions by making use of on-axis cameras providing diffraction patterns (88), as well as in advanced positioning systems analogous to those found in advanced X-ray synchrotron beamlines.…”

Section: Diffraction-contrast Scanning Transmission Electron Microscopymentioning

confidence: 99%

New techniques for imaging and identifying defects in electron microscopy

2019

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Defects in crystalline materials control the properties of engineered and natural materials, and their characterization focuses our strategies to optimize performance. Electron microscopy has served as the backbone of our understanding of defect structure and their interactions owing to beneficial spatial resolution and contrast mechanisms that enable direct imaging of defects. These defects reside in complex microstructures and chemical environments, demanding a combination of experimental approaches for full defect characterization. In this article, we describe recent progress and trends in methods for examining defects using scanning electron microscopy platforms, where several emerging approaches offer attractive benefits, for instance in correlative microscopy across length scales and in situ studies of defect dynamics.

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On the Progress of Scanning Transmission Electron Microscopy (STEM) Imaging in a Scanning Electron Microscope

Cited by 38 publications

References 50 publications

Analysis of crystal defects by scanning transmission electron microscopy (STEM) in a modern scanning electron microscope

Analysis of crystal defects by scanning transmission electron microscopy (STEM) in a modern scanning electron microscope

Electron beam broadening in electron‐transparent samples at low electron energies

New techniques for imaging and identifying defects in electron microscopy

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