Images of Thorium Atoms in Transmission Electron Microscopy

Hashimoto, H.; Kumao, A.; Hino, Kinnosuke; Yotsumoto, Haruo; Ono, Akishige

doi:10.1143/jjap.10.1115

Cited by 94 publications

(23 citation statements)

References 4 publications

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“…Advances in high-resolution transmission electron microscopy during the past several years have made possible the observation of individual heavy atoms on thin substrates of low atomic number (e.g., refs. [1][2][3][4][5]. Studies at atomic resolution of atoms adsorbed to light element substrates could be of value in acquiring an improved understanding of chemisorption, catalysis, and the earliest stages of thin film nucleation.…”

mentioning

confidence: 99%

Direct observations of atomic diffusion by scanning transmission electron microscopy

Isaacson

Kopf

Utlaut

et al. 1977

Proc. Natl. Acad. Sci. U.S.A.

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The feasibility of using a high-resolution scanning transmission electron microscope to study the diffusion of heavy atoms on thin film substrates of low atomic number has been investigated. We have shown that it is possible to visualize the diffusion of individual uranium atoms adsorbed to thin carbon film substrates and that the observed motion of the atoms does not appear to be induced by the incident electron beam. Advances in high-resolution transmission electron microscopy during the past several years have made possible the observation of individual heavy atoms on thin substrates of low atomic number (e.g., refs. 1-5). Studies at atomic resolution of atoms adsorbed to light element substrates could be of value in acquiring an improved understanding of chemisorption, catalysis, and the earliest stages of thin film nucleation. It is the purpose of this paper to demonstrate that a scanning transmission electron microscope (STEM) capable of atomic resolution may be a useful instrument for surface science studies and, in particular, that it is capable of reliably observing the diffusion of individual atoms on thin film substrates.In the STEM, an atomic resolution image can be formed by scanning an electron beam less than 5 A in diameter across a specimen in a raster fashion while collecting the transmitted elastically scattered electrons with an annular detector located beneath the specimen (6) (see Fig.

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mentioning

confidence: 99%

Direct observations of atomic diffusion by scanning transmission electron microscopy

Isaacson

Kopf

Utlaut

et al. 1977

Proc. Natl. Acad. Sci. U.S.A.

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“…Some of these claims were made by Crewe (1970Crewe ( a,b, 1974; Hashimoto (1971Hashimoto ( , 1974; Henkelman andOttensmeyer (1971, 1973); Formannek (1971); Baumeister and -4-and Hahn, (1973); and Parsons (1973Parsons ( , 1974. The justifications for atom images have mostly been based on the agreement between the experimental and theoretical contrast estimates and/or the agreement between the measured and the assumed distances of the heavy atoms in an organo-metallic compound.…”

Section: (D) Claims Of Single Atom Images and Shortcomings In The Evimentioning

confidence: 99%

Single atom imaging in high resolution electron microscopy

Chiu

1975

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A puzzling problem with III-nitride LEDs is why an external quantum efficiency of InGaN-based blue LEDs of over 80% can be achieved [4], whereas that of AlGaN-based deep UV LEDs is less than 10% [5].

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Atomic Resolution Imaging of Dislocations in AlGaN and the Efficiency of UV LEDs

et al. 2018

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Hatsujiro Hashimoto pioneered the imaging of single atoms in an electron microscope [1], developed an aberration-free electron microscopy technique [2], and was one of the first to image dislocations in an electron microscope [3]. This paper builds upon his brilliant achievements and reports the use of atomresolving aberration-corrected electron microscopy to study the dislocation structure of AlGaN, a key material for UV LEDs and lasers.A puzzling problem with III-nitride LEDs is why an external quantum efficiency of InGaN-based blue LEDs of over 80% can be achieved [4], whereas that of AlGaN-based deep UV LEDs is less than 10% [5]. A related puzzle is why the efficiency of InGaN-based blue LEDs is remarkably insensitive to a high density of dislocations [6] whereas the dislocation density appears to be an important factor limiting the efficiency of AlGaN-based LEDs [7]. The atomic structure of the dislocation core in GaN and InGaN has been widely studied [for example, refs 8, 9] because of the potential formation of states in the band-gap, which can act as non-radiative recombination centres. However, very little is known about the core structure of dislocations in AlGaN.AlGaN and InGaN epilayers were grown by metal-organic vapour phase epitaxy (MOVPE) in a Thomas Swan 6x2 inch close-coupled showerhead reactor. The epilayers were grown on a c-plane sapphire substrate. Further details are given in ref 10. Dislocations in the AlGaN epilayer were imaged using aberration-corrected high-angle dark field scanning transmission electron microscopy (HAADF-STEM) using FEI Titan G2 Chemi STEM and FEI Titan G3 PICO microscopes operating at 300kV and a detector semi-angle of 69 mrad. The sample was prepared using mechanical polishing and Ar + ion milling. The dislocations were viewed end-on, along the [0001] zone axis. Eshelby twist was observed for all dislocations with a screw component. The composition around the dislocations was studied using energy dispersive X-ray spectroscopy (EDX). For further details see ref 11. 100% of the edge dislocations have 5/7 atom ring cores. Some mixed dislocations were undissociated and some dissociated. The core structures in AlGaN are similar to those in InGaN.EDX mapping of the dislocations was performed inside the TEM, and geometric phase analysis of the HAADF-STEM images was performed for edge and mixed dislocations in both AlGaN and InGaN. This shows that the dislocation core is bounded on either side by a region of compressive strain and a region of tensile strain. EDX shows that there are compositional fluctuations around the dislocation, for AlGaN there is higher Ga content on the side of the dislocation under tensile strain, and higher Al content on the side under compressive strain. This is consistent with the Al-N bond being shorter than the Ga-N bond

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Images of Thorium Atoms in Transmission Electron Microscopy

Cited by 94 publications

References 4 publications

Direct observations of atomic diffusion by scanning transmission electron microscopy

Direct observations of atomic diffusion by scanning transmission electron microscopy

Single atom imaging in high resolution electron microscopy

Atomic Resolution Imaging of Dislocations in AlGaN and the Efficiency of UV LEDs

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