### Abstract

The method proposed for phase determination is based on the use of overlapping diffraction discs (convergent beam interferometry) and does not assume weak scattering. The method appears to be most useful for the refinement of the inner ″bonding″ structure factors in crystals whose atoms are not spherical. Model calculations for silicon show the sensitivity of dynamical phases to the bonding structure factors at certain thicknesses. At 100 kV accelerating voltage a single overlapping convergent beam pattern allows many phase differences to be determined, however the reciprocity theorem does not refer these to a common incident beam direction, thus restricting the usefulness of the method. The accuracy of phase determination based on the phase grating approximation at 1 MeV using overlapping diffraction discs is shown to lead to errors of approximately 10% for thicknesses of 50 A of low atomic number specimens. Such a method would allow phase determination of all reflections in a zone (referred to a common incident beam direction) within the lattice resolution limit of the instrument and so suggests a technique for the structure determination of large unit cell biological specimens by high voltage convergent beam electron diffraction.

Original language | English (US) |
---|---|

Pages (from-to) | 61-68 |

Number of pages | 8 |

Journal | Scanning Electron Microscopy |

Volume | v |

Issue number | 1 |

State | Published - 1978 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Biophysics
- Control and Systems Engineering

### Cite this

**PRACTICAL PHASE DETERMINATION OF INNER DYNAMICAL REFLECTIONS IN STEM.** / Spence, John.

Research output: Contribution to journal › Article

*Scanning Electron Microscopy*, vol. v, no. 1, pp. 61-68.

}

TY - JOUR

T1 - PRACTICAL PHASE DETERMINATION OF INNER DYNAMICAL REFLECTIONS IN STEM.

AU - Spence, John

PY - 1978

Y1 - 1978

N2 - The method proposed for phase determination is based on the use of overlapping diffraction discs (convergent beam interferometry) and does not assume weak scattering. The method appears to be most useful for the refinement of the inner ″bonding″ structure factors in crystals whose atoms are not spherical. Model calculations for silicon show the sensitivity of dynamical phases to the bonding structure factors at certain thicknesses. At 100 kV accelerating voltage a single overlapping convergent beam pattern allows many phase differences to be determined, however the reciprocity theorem does not refer these to a common incident beam direction, thus restricting the usefulness of the method. The accuracy of phase determination based on the phase grating approximation at 1 MeV using overlapping diffraction discs is shown to lead to errors of approximately 10% for thicknesses of 50 A of low atomic number specimens. Such a method would allow phase determination of all reflections in a zone (referred to a common incident beam direction) within the lattice resolution limit of the instrument and so suggests a technique for the structure determination of large unit cell biological specimens by high voltage convergent beam electron diffraction.

AB - The method proposed for phase determination is based on the use of overlapping diffraction discs (convergent beam interferometry) and does not assume weak scattering. The method appears to be most useful for the refinement of the inner ″bonding″ structure factors in crystals whose atoms are not spherical. Model calculations for silicon show the sensitivity of dynamical phases to the bonding structure factors at certain thicknesses. At 100 kV accelerating voltage a single overlapping convergent beam pattern allows many phase differences to be determined, however the reciprocity theorem does not refer these to a common incident beam direction, thus restricting the usefulness of the method. The accuracy of phase determination based on the phase grating approximation at 1 MeV using overlapping diffraction discs is shown to lead to errors of approximately 10% for thicknesses of 50 A of low atomic number specimens. Such a method would allow phase determination of all reflections in a zone (referred to a common incident beam direction) within the lattice resolution limit of the instrument and so suggests a technique for the structure determination of large unit cell biological specimens by high voltage convergent beam electron diffraction.

UR - http://www.scopus.com/inward/record.url?scp=0018156406&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0018156406&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0018156406

VL - v

SP - 61

EP - 68

JO - Scanning Electron Microscopy

JF - Scanning Electron Microscopy

SN - 0586-5581

IS - 1

ER -