Phase dependence of Kikuchi patterns. I. Theory

Bird, David M.; Wright, A. G.

doi:10.1107/s0108767388009304

Cited by 19 publications

(14 citation statements)

References 13 publications

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“…The difference between thej =j' and j #j' terms is very closely related to the dependent/independent Bloch wave result in inelastic scattering theory (e.g. Bird & Wright, 1989, and references therein). The j =j' terms (independent waves) tend to dominate in thicker crystals because these terms increase linearly with thickness, while the j #j' terms oscillate.…”

Section: ~E (J)mentioning

confidence: 82%

Absorption in high-energy electron diffraction from non-centrosymmetric crystals

Bird¹

1990

Acta Crystallogr A Found Crystallogr

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Section: ~E (J)mentioning

confidence: 82%

Absorption in high-energy electron diffraction from non-centrosymmetric crystals

Bird¹

1990

Acta Crystallogr A Found Crystallogr

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“…If absorption is included exactly (not using perturbation theory), then small differences appear between the g and -g rocking curves in two-beam theory. These are responsible for asymmetries in Kikuchi lines (Allen & Rossouw, 1989;Bird, 1990;Bird & Wright, 1989) and on inner-shell energy-loss spectra (Tafto, 1987), both of which may also be used to determine the polarity of acentric crystals. (Energy 'absorbed' by inelastic processes from the elastic 'channel' makes a positive contribution to peaks in the energy-loss spectrum.…”

Section: F/ Lmentioning

confidence: 99%

On the accurate measurement of structure-factor amplitudes and phases by electron diffraction

Spence¹

1993

Acta Cryst Sect A

139

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A review is given of research into the measurement of crystal structure-factor amplitudes and phases by transmission electron diffraction. Accuracies for amplitudes are commonly a fraction of a percent (after conversion to X-ray structure factors) while phases may now be measured in favorable cases using three-beam electron diffraction to an accuracy of much better than 1 °. Following a brief review of theory, the main techniques are outlined. These include quantitative convergent-beam electron diffraction, the critical-voltage method, the intersecting K_ikuchi-and HOLZ-Iine methods and methods based on weak high-order reflections in wide-angle patterns. Enantiomorphs and polarity are discussed. Summaries are given of measurements of the mean inner potential and of structure factors generally. A brief review of the implications of this work for studies of crystal bonding and ordering in alloys is given, and its use to test ab initio computations of charge density. The mean inner potential is found to be the quantity most sensitive to the bonding distribution of valence electrons and sensitively constrains accurate X-ray structure-factor measurements. Electron diffraction techniques are to be preferred for studies of individual microcrystals or artificially formed structures and for the very accurate measurement of structure-factor phases in acentric crystals with small unit cells.

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“…4 which shows that for the (202 1 ) plane the N atoms are offset from the Ga atoms. Modelling of the electron diffraction intensities from the non-centrosymmetric (202 1 ) plane will allow us to determine which face of the (202 1 ) plane each Kikuchi line corresponds [9]. Once this is determined, it will be possible to ascertain the polarity of the GaN epilayer under investigation.…”

Section: Resultsmentioning

confidence: 99%

Electron Backscattered Diffraction Patterns from Cooled Gallium Nitride Thin Films

Sweeney

Trager‐Cowan

Hastie

et al. 2001

phys. stat. sol. (b)

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The acquisition of electron backscattered diffraction (EBSD) (or Kikuchi diffraction) patterns in the scanning electron microscope is proving to be a useful technique with which to probe the structural properties of nitride thin films. In this paper we show that if a sample is cooled the patterns improve dramatically, an increase in intensity of the Kikuchi lines and a decrease in the intensity of the diffuse background is observed. Kikuchi lines from higher order planes become visible and the HOLZ rings become better defined. Such cooled patterns yield more information on the sample, particularly on non-centrosymmetric planes, from which the polarity of the nitride thin film under investigation may be deduced.Introduction The acquisition of electron backscattered diffraction (EBSD) (or Kikuchi diffraction) patterns in the scanning electron microscope is a very powerful method for the microstructural characterisation of crystalline materials. EBSD is at present predominantly used in metallurgy for the measurement of texture, i.e., the mapping of the orientation of individual grains in polycrystalline samples [1], and to identify different crystalline phases. However, Wilkinson [2] and Troost et al. [3] applied EBSD to the measurement of strain in SiGe epilayers while Baba-Kishi [4] has used EBSD to investigate crystallographic polarity of non-centrosymmetric structures. These results strongly suggest that EBSD may be a useful technique to apply to the characterisation of nitride thin films.In previous work [5] we have used EBSD to reveal the relative orientation of a nitride thin film with respect to its substrate; determine the tilt of a GaN thin film; detect improved surface quality in As-doped GaN films grown under high As 4 flux; and observe more detail in EBSD patterns from cooled GaN thin films. In this paper we show that EBSD patterns obtained from cooled GaN thin films can provide information on non-centrosymmetric planes, from which the polarity of the nitride thin film under investigation may be deduced.

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Phase dependence of Kikuchi patterns. I. Theory

Cited by 19 publications

References 13 publications

Absorption in high-energy electron diffraction from non-centrosymmetric crystals

Absorption in high-energy electron diffraction from non-centrosymmetric crystals

On the accurate measurement of structure-factor amplitudes and phases by electron diffraction

Electron Backscattered Diffraction Patterns from Cooled Gallium Nitride Thin Films

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