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Introduction to ProcessDiffraction

Introduction to ProcessDiffraction. János L. Lábár Erice, 9-20 June 2004. Basic types of SAED patterns. ProcessDiffraction. Single crystal patterns + crystallographic calculator Amorphous patterns Nano-crystalline patterns: Phase analysis Structure refinement Pattern decomposition.

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Introduction to ProcessDiffraction

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  1. Introduction to ProcessDiffraction János L. Lábár Erice, 9-20 June 2004

  2. Basic types of SAED patterns

  3. ProcessDiffraction • Single crystal patterns + crystallographic calculator • Amorphous patterns • Nano-crystalline patterns: • Phase analysis • Structure refinement • Pattern decomposition

  4. ProcessDiffraction: single crystal patterns • Helps accurate measurement of d-values and angles • Aids simultaneous indexing of a set of patterns taken from different known orientations • Helps planning tilting experiments

  5. ProcessDiffraction: amorphous patterns • Determination of a few nearest-neighbor distances • See the poster of Viki Kis

  6. ProcessDiffraction: nano-crystalline patterns • Primary processing: • Data format, additional information (L, , …) • Crop, gray-histogram • Centering, elliptical distortion • Black level correction • Integration / averaging • Cursor (correlation, d-values, peak-list) • Save / load working environment

  7. ProcessDiffraction: nano-crystalline patterns • Qualitative phase analysis • XRD database (availabble from ICDD) • ED, calculated for known structures • Define, save / load structure, data-checking • Kinematic (I~F*F)  Dynamic (I~F) • Units of x-axis (pixel, Q, 2), peak search • Average above average („spottyness” corr.) • Background, net, …

  8. ProcessDiffraction: nano-crystalline patterns • Quantitative phase analysis (with whole-profile fitting) • Background shape • Gaussian, log-Normal • Polynomial, Spline • Peak shape • Gaussian, Lorentzian • Pseudo-Voigt • Dowhill SIMPLEX + matrix inversion

  9. ProcessDiffraction: nano-crystalline patterns • Structure refinement • Atomic positions (checking of choice) • Debye-Waller factors • Camera length • Peak parameters • Additional (non-refinied) phase

  10. ProcessDiffraction: nano-crystalline patterns • Peak decomposition • Background • Effect of amorphous component • Peak-shapes • Constraints • SIMPLEX (all parameters)  Stability problems (amplitude, width)

  11. ProcessDiffraction: Conclusions • Useful features for common microscopists • Not to replace, but to supplement other programs • Available free from www.mfa.kfki.hu/~labar/ProcDif • New and improved features are planned

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