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Dynamical diffraction calculations for RHEED and REM (1986)

Peng, L. m. ; Cowley, J. M.

[S.l.] : International Union of Crystallography (IUCr)

Acta crystallographica 42 (1986), S. 545-552

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ISSN: 1600-5724

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: The multislice formulation of the many-beam dynamical diffraction theory has been applied to the Bragg case of electron diffraction for the extended surface of a perfect crystal and also for a crystal surface with a surface step. The wavefunctions within and outside the crystal have been calculated and used to derive the standing-wave pattern in the top atomic layers of the crystal, the intensities of the reflection high-energy electron diffraction (RHEED) pattern and the contrast of the reflection electron microscopy (REM) image. Calculations made for the diffraction of 19, 40 and 80 keV electrons from (111) surfaces of Pt and Au demonstrate the channeling of electrons under the conditions of surface resonance, the perturbation of the standing-wave field in the crystal by a one-atom-high surface step and the REM contrast for a through-focus series of images of a surface step. The method is applicable to models including surface relaxations and reconstructions and any kind of local defect of the surface or of the bulk crystal.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0108767386098756

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Electron diffraction phenomena observed with a high resolution STEM instrument (1986)

Cowley, J. M.

New York, NY : Wiley-Blackwell

Journal of Electron Microscopy Technique 3 (1986), S. 25-44

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ISSN: 0741-0581

Keywords: Electron diffraction ; Scanning transmission electron microscopy ; Microdiffraction ; In-line holography ; Small particles ; Crystal structure ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Natural Sciences in General

Notes: Because of the high brightness of the cold field emission source used in a dedicated scanning transmission electron microscopy (STEM) instrument, it is possible to focus electrons to a cross-over of width 3Å or less and, with a suitable detection system, to obtain diffraction patterns from specimen regions of this size or greater. Coherent interference effects are visible in shadow images (in-line holograms) and in convergent beam diffraction patterns. Special techniques have been developed for gathering information from the diffraction patterns for application to the study of the structures of crystal defects, crystal surfaces and small particles. Possibilities have been explored for holographic reconstruction from shadow images.

Additional Material: 14 Ill.