The dissociation of the [a + c] dislocation in GaN

Hirsch, P. B.; Lozano, J.; Rhode, Sneha; Horton, Matthew K.; Moram, M. A.; Zhang, S.; Kappers, Menno J.; Humphreys, C. J.; Yasuhara, Akira; Okunishi, Eiji; Nellist, Peter D.

doi:10.1080/14786435.2013.797617

Cited by 36 publications

(52 citation statements)

References 38 publications

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“…2 In recent years, much instrumental and methodological effort has been put forward in developing of methods for direct imaging of light elements inside various technologically important materials using transmission electron microscopy (TEM). [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The realization and implementation of spherical aberration (Cs) correction for a round magnetic lens in TEM 19,20 have pushed the instrumental resolution limit of the TEMs down to the sub-Å ngstrom scale. 21,22 In addition, significant improvement of image contrast and signal to noise ratio has been achieved with Cs-corrected TEMs.…”

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confidence: 99%

Direct imaging of light elements by annular dark-field aberration-corrected scanning transmission electron microscopy

Lotnyk

Poppitz

Gerlach

et al. 2014

Applied Physics Letters

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In this report, we show that an annular dark-field detector in an aberration-corrected scanning transmission electron microscope allows the direct observation of light element columns in crystalline lattices. At specific imaging conditions, an enhancement of the intensities of light element columns in the presence of heavy element columns is observed. Experimental results are presented for imaging the nitrogen and carbon atomic columns at the GaN-SiC interface and within the GaN and SiC compounds. The crystal polarity of GaN at the interface is identified. The obtained findings are discussed and are well supported by image simulations.

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mentioning

confidence: 99%

Direct imaging of light elements by annular dark-field aberration-corrected scanning transmission electron microscopy

Lotnyk

Poppitz

Gerlach

et al. 2014

Applied Physics Letters

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“…These two values correspond to the constants mentioned in [19] and [17], respectively. Previous transmission electron microscopy investigations, for example, [2,3,5,15], show that a large fraction of TDs cross the free surface with directions parallel or not far from the c axis. They can be of edge-type, screw-type, or mixedtype.…”

Section: Application To Ganmentioning

confidence: 99%

“…The growth of GaN can be stabilized by epitaxial growth on bulky GaN substrates or a foreign substrate, for example, (111)Si, SiC, or sapphire [2,4,5,15]. An investigation on GaN thin films is of particular interest because of its TDs that have anisotropic electrical properties regarding cathodoluminescence and photoluminescence.…”

Section: Application To Ganmentioning

confidence: 99%

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Threading Dislocations Piercing the Free Surface of an Anisotropic Hexagonal Crystal: Review of Theoretical Approaches

Neily

Dhouibi

Bonnet

2018

Advances in Condensed Matter Physics

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Inclined threading dislocations (TDs) piercing the oriented free surface of a crystal are currently observed after growth of oriented thin films on substrates. Up to date the unique way to treat their anisotropic elastic properties nearby the free surface region is to use the integral formalism, which assumes no dislocation core size and needs numerical double integrations. In a first stage of the work, a new and alternative approach to the integral formalism is developed using double Fourier series and the concept of a finite core size, which is often observed in high-resolution transmission electron microscopy. In a second stage, the integral formalism and the Fourier series approaches are applied to the important case of a TD piercing the basal free surface of a hexagonal crystal. For this particular geometry, easy-to-use expressions are derived and compared to a third approach previously known for a plate-like crystal. Finally, the numerical interest and the convergence of these approaches are tested using the basal free surface of the GaN compound, in particular for TDs with Burgers vectors c and (a + c).

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“…It has been used to observe the depth-dependence of the strain field due to the Eshelby twist associated with dislocations containing a screw component in thin STEM samples. The measurement of the magnitude of the displacement confirmed the screw Burgers vector for dislocations in GaN [1] and allowed the identification of a new dissociation reaction of mixed [c+a] dislocations [2]. The optical sectioning approach has also been applied to the direct observation of the c-component of the dissociation reaction of mixed [c+a] dislocations in GaN by imaging a dislocation lying transverse to the electron beam [3].…”

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Evaluation of Aberration-corrected Optical Sectioning for Exploring the Core Structure of ½[111] Screw Dislocations in BCC Metals

et al. 2017

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The introduction of spherical-aberration correctors in the Scanning Transmission Electron Microscope (STEM) has allowed an improvement in spatial resolution to the sub-angströn scale accompanied by a reduction of the depth of focus (due to the increase in probe convergence angles),which in a modern instrument is just a few nanometers, thus often less than the sample thickness. This can be exploited to extract information along the beam direction by focusing the electron probe at specific depths within the sample. Optical sectioning has been proved to be a powerful tool for the study of the core structure of screw dislocations. It has been used to observe the depth-dependence of the strain field due to the Eshelby twist associated with dislocations containing a screw component in thin STEM samples. The measurement of the magnitude of the displacement confirmed the screw Burgers vector for dislocations in GaN In this communication we will evaluate the optical sectioning technique to explore the core structure of ½[111] screw dislocations in body-centred cubic (BCC) metals. The study of this structure is of high interest because the low-temperature plastic deformation of BCC metals is controlled by the glide of ½[111] screw dislocations. Their low mobility is caused by the non-planar nature of their cores [4] which are extended into several planes in the zone of the Burgers vector. The non-planar spreading of the core is characterized by displacements of the atoms around the core in the directions parallel and perpendicular to the dislocation line, also called screw and edge components respectively. In the last 47 years [5] these studies have been made by molecular statics using a number of different interatomic potentials. However, attempts at experimental observations by TEM have been hindered by the Eshelby twist effect [6,7]. The aim of this work is to investigate whether the edge and screw displacements associated with ½[111] screw dislocations in BCC metals can be detected by optical sectioning in highangle annular dark field (HAADF) imaging in STEM conditions. Here we show, by using atomistic and image simulations, how this technique can be used to image the core structure of these screw dislocations at atomic resolution along a direction transverse to the screw axis. Figure 1 shows that the helicoidal displacements around the core of a ½[111] screw dislocation in Mo can be imaged with the dislocation lying transverse to the electron beam by optically sectioning the plane containing the dislocation. In order to reveal the effect of the spreading of the core, we have considered the atomic positions obtained from two different models. In the first, we treat the dislocation as a singularity in an anisotropic elastic continuum for which the displacement field around the dislocation is well-known [8]. The second model utilizes the Bond Order Potential for Mo [9] to determine the relaxed core of a non-singular dislocation. This is shown to be spread on three {110} planes in the zone of the [111] axis. The edge an...

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The dissociation of the [a + c] dislocation in GaN

Cited by 36 publications

References 38 publications

Direct imaging of light elements by annular dark-field aberration-corrected scanning transmission electron microscopy

Direct imaging of light elements by annular dark-field aberration-corrected scanning transmission electron microscopy

Threading Dislocations Piercing the Free Surface of an Anisotropic Hexagonal Crystal: Review of Theoretical Approaches

Evaluation of Aberration-corrected Optical Sectioning for Exploring the Core Structure of ½[111] Screw Dislocations in BCC Metals

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