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Yoshimi Horio - One of the best experts on this subject based on the ideXlab platform.
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Reflection High-Energy Electron Diffraction
Compendium of Surface and Interface Analysis, 2018Co-Authors: Yoshimi HorioAbstract:Reflection High-Energy Electron Diffraction (RHEED) (Ichimiya and Cohen in Reflection high-energy Electron Diffraction, Cambridge University Press, Cambridge, 2004 [1]) is one of the powerful methods for surface structural analysis.
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Low-Energy Electron Diffraction
Compendium of Surface and Interface Analysis, 2018Co-Authors: Yoshimi HorioAbstract:Low-energy Electron Diffraction (LEED) [1] is one of the Diffraction techniques utilizing low-energy Electrons and a powerful method for surface structural analysis.
Jian-min Zuo - One of the best experts on this subject based on the ideXlab platform.
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Kinematical Theory of Electron Diffraction
Advanced Transmission Electron Microscopy, 2016Co-Authors: Jian-min Zuo, John C. H. SpenceAbstract:In this chapter, we develop the theory of transmission Electron Diffraction based on the assumption of single scattering or the so-called kinematical approximation.
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Solving difficult structures with Electron Diffraction
IUCrJ, 2015Co-Authors: Jian-min Zuo, J L RouviéreAbstract:Electrons diffract in the same way as X-rays and neutrons, except that the Electron wavelength is very small (of the order of a few picometers for 80–300 keV Electrons), and the Electron scattering cross-section is much larger, about a million times that of X-rays. Inside a transmission Electron microscope (TEM), the Electron beam can be focused down to ~1 A in diameter with the current reaching hundreds of picoamps (1 pA ≃ 6.3x106 e s−1), so the scattering power of an Electron beam is larger than that of a synchrotron. Since Electron Diffraction was discovered by Davisson and Germer, and Thomson and Reid, in 1927, transmission Electron Diffraction and the related Electron imaging have developed into powerful tools for the analysis of defects, microstructure, surfaces and interfaces in a broad range of materials. So why haven’t more unknown crystal structures been solved with high-energy Electrons? The short answer lies in Electron dynamic Diffraction: the same strong interaction between Electrons and matter that gives rise to large Electron scattering cross sections also leads to strong multiple scattering. The theory of Electron multiple scattering was developed as early as 1928 by Hans Bethe in his remarkable PhD thesis. Electron dynamic Diffraction can allow the phase of structure factors to be determined to an accuracy of 0.2° by refining the Electron Diffraction intensity recorded in a convergent beam Electron Diffraction (CBED) pattern using the calculated dynamic intensities (Jiang et al., 2010 ▶). However, the refinement method requires a known structure. A general method for solving unknown crystal structures using dynamic Diffraction intensities has yet to be developed, despite many outstanding efforts in the past (Spence et al., 1999 ▶; Allen et al., 2000 ▶; Koch, 2005 ▶). In the topical review by Midgley and Eggeman (Midgley & Eggeman, 2015 ▶), the authors describe the remarkable progress made in an alternative approach to Electron structure solution, precession Electron Diffraction (PED), a technique discovered 20 years ago by Vincent & Midgley (1994 ▶). In PED, the incident Electron beam rotates around a crystal direction, keeping a constant angle – the ‘precession angle’ – with this crystal direction. To compensate for the motion of diffracted beams as the incident beam rotates, the outgoing beams are deflected back (Fig. 1 ▶ in Midgley & Eggeman, 2015 ▶), similar to the double rocking technique for the recording of large-angle CBED patterns (Eades, 1980 ▶). By recording Electron Diffraction patterns with the incident Electron beam in precession, PED is able to provide the integrated Electron Diffraction intensity across the Bragg condition for many reflections. The use of such intensities for structure solution in numerous test structures has shown surprising robustness against crystal thickness variations and small crystal misorientations, which could have a dramatic effect on Electron Diffraction intensities recorded using conventional techniques (see Fig. 1 ▶). Using PED intensities, crystal structures can be solved by a combination of phasing and structure refinement, where the R factor can be reduced to less than 10% by further including dynamic effects (Palatinus et al., 2013 ▶; Jacob et al., 2013 ▶). Figure 1 CBED patterns recorded using 200 kV Electrons from Si along [001] (left) without and (right) with precession (precession angle 0.6°), respectively. Over the past decade, the development of aberration correctors for high-resolution Electron microscopes has brought worldwide excitement and tremendous progress in real-space-based structure determinations using atomic resolution imaging and chemical analysis. Applications of these techniques tend to focus on the so-called radiation-hard materials, such as metals and ceramics. Since Electron Diffraction provides the strongest analytical signal inside a TEM, it can therefore be applied to small and complex (difficult) crystals. With the welcoming developments in PED, and its integration with the data acquisition tools of automated Diffraction tomography (ADT, Kolb et al., 2007 ▶), scanning and automated Diffraction pattern indexing and analysis (see review in Midgley & Eggeman, 2014 ▶), Electron Diffraction is rapidly developing into a truly quantitative crystallographic tool for the determination of atomic structure as well as complex microstructures. It is thus heartening to see a broad range of structures, including organic frameworks, complex zeolites, germano–silicate frameworks and organic crystals solved by PED (see Midgley & Eggeman, 2015 ▶). What is the future for Electron Diffraction? The quality of Electron Diffraction data, as well as speed of acquisition, is increasing rapidly with the development of fast cameras, sophisticated beam and sample manipulation methods, and data analysis (Koch, 2011 ▶; Kim & Zuo, 2013 ▶; Kim et al., 2013 ▶). Thus, in a not too distant future, we can expect more identifications of new structures and their solutions, especially in mixed phase materials or at interfaces and grain boundaries. Another intriguing possibility is to combine precession with high-order aberration corrections for precession scanning transmission Electron microscopy (PSTEM). By reducing dynamical effects in the Electron probe scattering using precession, significant gains can be achieved in quantitative three-dimensional Electron imaging as well as chemical analysis.
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Encyclopedia of Inorganic Chemistry - High‐Energy Electron Diffraction
Encyclopedia of Inorganic and Bioinorganic Chemistry, 2008Co-Authors: Jian-min ZuoAbstract:High-energy Electrons have very short wavelengths associated with particle waves and Electron Diffraction is used to probe the atomic structure of both inorganic and organic materials. Electrons have a large scattering cross section and can be focused into small probes by magnetic lenses. This makes Electron Diffraction very useful for studying “small” crystals, surfaces, or material's microstructure. The principles and the modern aspects of Electron Diffraction are described here with the intention to provide an introduction that both the novice and the expert will find useful as a guide for Electron Diffraction. The chapter starts with an introduction to different Electron Diffraction techniques. This is followed by the background theories which are useful for the interpretation of Diffraction patterns. Experimental procedures are described at the end of the technical background. The applications section has a large collection of examples from relatively straightforward tasks to more advanced ones that are under development for their promises. Experimental details are provided when it is appropriate to give some idea of what it takes to do Electron Diffraction. Keywords: Electron Diffraction; Diffraction techniques; Diffraction theory; structure determination; nanostructure characterization; high resolution Electron microscopy
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Quantitative Convergent Beam Electron Diffraction
Materials Transactions, 2007Co-Authors: Jian-min ZuoAbstract:This chapter introduces quantitative convergent-beam Electron Diffraction from quantitative Electron Diffraction intensity recording to quantitative structural retrieval by Electron Diffraction intensity refinement and pattern matching. It is shown that structure information, such as unit cell parameters and Electron structure factors, can be obtained from experimental Diffraction intensities by optimizing the fit between the experimental and theoretical intensities through the adjustment of structural parameters in a theoretical model. While the principle of refinement is similar to the Rietveld method in X-ray powder Diffraction, its implementation in Electron Diffraction is powerful since it includes the full dynamic effect. The accuracy of this technique will be demonstrated through the accurate determination of lattice parameters for strain mapping and charge density for the study of crystal bonding.
J L Rouviére - One of the best experts on this subject based on the ideXlab platform.
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Solving difficult structures with Electron Diffraction.
IUCrJ, 2015Co-Authors: J M Zuo, J L RouviéreAbstract:Precession Electron Diffraction has solved a long-standing challenge in Electron Diffraction. Further progress promises a general technique for structure determination of difficult crystals.
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Solving difficult structures with Electron Diffraction
IUCrJ, 2015Co-Authors: Jian-min Zuo, J L RouviéreAbstract:Electrons diffract in the same way as X-rays and neutrons, except that the Electron wavelength is very small (of the order of a few picometers for 80–300 keV Electrons), and the Electron scattering cross-section is much larger, about a million times that of X-rays. Inside a transmission Electron microscope (TEM), the Electron beam can be focused down to ~1 A in diameter with the current reaching hundreds of picoamps (1 pA ≃ 6.3x106 e s−1), so the scattering power of an Electron beam is larger than that of a synchrotron. Since Electron Diffraction was discovered by Davisson and Germer, and Thomson and Reid, in 1927, transmission Electron Diffraction and the related Electron imaging have developed into powerful tools for the analysis of defects, microstructure, surfaces and interfaces in a broad range of materials. So why haven’t more unknown crystal structures been solved with high-energy Electrons? The short answer lies in Electron dynamic Diffraction: the same strong interaction between Electrons and matter that gives rise to large Electron scattering cross sections also leads to strong multiple scattering. The theory of Electron multiple scattering was developed as early as 1928 by Hans Bethe in his remarkable PhD thesis. Electron dynamic Diffraction can allow the phase of structure factors to be determined to an accuracy of 0.2° by refining the Electron Diffraction intensity recorded in a convergent beam Electron Diffraction (CBED) pattern using the calculated dynamic intensities (Jiang et al., 2010 ▶). However, the refinement method requires a known structure. A general method for solving unknown crystal structures using dynamic Diffraction intensities has yet to be developed, despite many outstanding efforts in the past (Spence et al., 1999 ▶; Allen et al., 2000 ▶; Koch, 2005 ▶). In the topical review by Midgley and Eggeman (Midgley & Eggeman, 2015 ▶), the authors describe the remarkable progress made in an alternative approach to Electron structure solution, precession Electron Diffraction (PED), a technique discovered 20 years ago by Vincent & Midgley (1994 ▶). In PED, the incident Electron beam rotates around a crystal direction, keeping a constant angle – the ‘precession angle’ – with this crystal direction. To compensate for the motion of diffracted beams as the incident beam rotates, the outgoing beams are deflected back (Fig. 1 ▶ in Midgley & Eggeman, 2015 ▶), similar to the double rocking technique for the recording of large-angle CBED patterns (Eades, 1980 ▶). By recording Electron Diffraction patterns with the incident Electron beam in precession, PED is able to provide the integrated Electron Diffraction intensity across the Bragg condition for many reflections. The use of such intensities for structure solution in numerous test structures has shown surprising robustness against crystal thickness variations and small crystal misorientations, which could have a dramatic effect on Electron Diffraction intensities recorded using conventional techniques (see Fig. 1 ▶). Using PED intensities, crystal structures can be solved by a combination of phasing and structure refinement, where the R factor can be reduced to less than 10% by further including dynamic effects (Palatinus et al., 2013 ▶; Jacob et al., 2013 ▶). Figure 1 CBED patterns recorded using 200 kV Electrons from Si along [001] (left) without and (right) with precession (precession angle 0.6°), respectively. Over the past decade, the development of aberration correctors for high-resolution Electron microscopes has brought worldwide excitement and tremendous progress in real-space-based structure determinations using atomic resolution imaging and chemical analysis. Applications of these techniques tend to focus on the so-called radiation-hard materials, such as metals and ceramics. Since Electron Diffraction provides the strongest analytical signal inside a TEM, it can therefore be applied to small and complex (difficult) crystals. With the welcoming developments in PED, and its integration with the data acquisition tools of automated Diffraction tomography (ADT, Kolb et al., 2007 ▶), scanning and automated Diffraction pattern indexing and analysis (see review in Midgley & Eggeman, 2014 ▶), Electron Diffraction is rapidly developing into a truly quantitative crystallographic tool for the determination of atomic structure as well as complex microstructures. It is thus heartening to see a broad range of structures, including organic frameworks, complex zeolites, germano–silicate frameworks and organic crystals solved by PED (see Midgley & Eggeman, 2015 ▶). What is the future for Electron Diffraction? The quality of Electron Diffraction data, as well as speed of acquisition, is increasing rapidly with the development of fast cameras, sophisticated beam and sample manipulation methods, and data analysis (Koch, 2011 ▶; Kim & Zuo, 2013 ▶; Kim et al., 2013 ▶). Thus, in a not too distant future, we can expect more identifications of new structures and their solutions, especially in mixed phase materials or at interfaces and grain boundaries. Another intriguing possibility is to combine precession with high-order aberration corrections for precession scanning transmission Electron microscopy (PSTEM). By reducing dynamical effects in the Electron probe scattering using precession, significant gains can be achieved in quantitative three-dimensional Electron imaging as well as chemical analysis.
Paul A. Midgley - One of the best experts on this subject based on the ideXlab platform.
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Precession Electron Diffraction
Acta Crystallographica Section A, 2014Co-Authors: Paul A. MidgleyAbstract:The strong Coulombic interaction between a high energy Electron and a thin crystal film gives rise to Electron Diffraction patterns encoded with information that is remarkably sensitive to the crystal potential. That exquisite sensitivity can be advantageous, for example in the determination of local symmetry and bonding, but can also be problematic in that in general the dynamical scattering inherent in Electron Diffraction prohibits the use of conventional crystallographic methods to recover structure factor phase information and solve unknown structures. One way to reduce this problem is to use precession Electron Diffraction (PED), introduced 20 years ago [1] as the Electron analogue of Buerger's X-ray technique, in which the Electron beam is first rocked in a hollow cone above the sample and then de-rocked below, the net effect of which is equivalent to precessing the sample about a stationary Electron beam. PED is now used almost routinely as a starting point to solve crystal structures that cannot be solved for a variety of reasons using x-ray or neutron methods. In this keynote lecture we explore why the PED technique has been successful for structure determination, focussing on the PED geometry, the variation of intensities with precession angle and specimen thickness, and how this `mimics' kinematic behaviour, and the use of unconventional structure solution and refinement approaches [2]. New acquisition geometries will be discussed that rely on tilt series of PED patterns to yield a more complete 3D data set. The lecture will focus on how PED has been used also as a method for nanoscale orientation mapping [3], providing more information than conventional Electron Diffraction and a robust method with which to determine local crystallographic orientation. By scanning the beam, accurate orientation images can be derived from series of PED patterns and, by combining with tomographic methods, sub-volume orientation information is also available.
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Precession Electron Diffraction
Advances in Imaging and Electron Physics, 2012Co-Authors: Alexander S. Eggeman, Paul A. MidgleyAbstract:Abstract Precession Electron Diffraction is considered a key technique available to Electron microscopists to elucidate the structure of a wide variety of crystals. Although originally envisaged as a method to produce integrated intensities that could be used for structure solution and refinement, precession Electron Diffraction has proved much more versatile, enabling symmetry determination, texture analysis, and even measurements of bonding charge densities. In this report, we explain the mechanisms by which precession can improve the quality of Electron Diffraction data and how these benefits can be applied to different solution algorithms, including novel charge-flipping and maximum entropy methods, and to acquire other crystallographic information about a material. Such improvements have allowed the wide use of precession Electron Diffraction to solve a range of inorganic and organic crystal structures. Indeed, many X-ray crystallographers are now exploring the advantages of precession Electron Diffraction for solving crystal structures that are not amenable to conventional X-ray methods.
J M Zuo - One of the best experts on this subject based on the ideXlab platform.
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Solving difficult structures with Electron Diffraction.
IUCrJ, 2015Co-Authors: J M Zuo, J L RouviéreAbstract:Precession Electron Diffraction has solved a long-standing challenge in Electron Diffraction. Further progress promises a general technique for structure determination of difficult crystals.
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Automation in Electron Diffraction analysis
Proceedings annual meeting Electron Microscopy Society of America, 1995Co-Authors: J M ZuoAbstract:Automated lattice parameter measurement and orientation analysis are often needed in the characterization of microstructures using Electron Diffraction, and is made possible with increasingly popular use of slow scan CCD camera and imaging plates. Both of these two detectors are largely linear and digital. Typical Electron Diffraction analysis has three steps: 1) Diffraction pattern measurement, 2) Diffraction pattern indexing and 3) solution. Full automation in all these three steps is desired, however, may be hard to achieve especially for complex crystal structures. The importance of automation in each of these steps depends on the type of analysis and the number of analysis needed. Full automation is necessary in the type of applications where the same analysis is repeated many times, such as in texture analysis. In table 1, various applications of Electron Diffraction and automation needed are listed.There are two types of approach to the automatic indexing. The commonly used method is to matching a calculated list of g's with the measured ones.
