Low-Dose, Low-Temperature Convergent-Beam Electron Diffraction and Multiwavelength Analysis of Hydrocarbon Films by Electron Diffraction

Jinsong Wu, John Spence

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

Aromatic hydrocarbon (perylene, coronene) and tetracontane films are shown to produce useful convergent-beam electron diffraction (CBED) patterns under low-dose and low-temperature conditions. These were obtained using a Zeiss LEO-921 electron microscope with an omega energy filter at liquid helium and nitrogen temperatures. The usefulness of patterns showing CBED disks of constant intensity ("blank disks," indicating kinematic scattering) for structure analysis is investigated, with the aim of avoiding film-bending artifacts. Using CBED patterns from thicker areas, sample thickness was experimentally determined using either two-beam or three-beam patterns. Koehler mode illumination (a new form of SAD pattern offering smaller areas) was also used, and the possibility of obtaining structure factor moduli using the kinematic and two-beam approximations was investigated by comparing measured diffraction intensities with experimental ones for these known structures. The commonly used approximation |F| ∼ Ig (intended to account for bending) was found to be a worse approximation than the two-beam approximation with well-defined excitation error for these microdiffraction experiments. A new multiwavelength method of retrieving structure factor moduli and thickness from microdiffraction patterns using two-beam theory is demonstrated for tetracontane.

Original languageEnglish (US)
Pages (from-to)428-441
Number of pages14
JournalMicroscopy and Microanalysis
Volume9
Issue number5
DOIs
StatePublished - Oct 2003

Fingerprint

Electron diffraction
electron diffraction
hydrocarbons
Hydrocarbons
dosage
Diffraction patterns
Kinematics
Aromatic hydrocarbons
Temperature
Helium
Electron microscopes
Diffraction
Lighting
approximation
Scattering
Nitrogen
kinematics
diffraction patterns
Liquids
blanks

Keywords

  • Aromatic hydrocarbons
  • CBED
  • Electron microdiffraction
  • Organic molecular crystal
  • Radiation damage
  • Structure factors

ASJC Scopus subject areas

  • Instrumentation

Cite this

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abstract = "Aromatic hydrocarbon (perylene, coronene) and tetracontane films are shown to produce useful convergent-beam electron diffraction (CBED) patterns under low-dose and low-temperature conditions. These were obtained using a Zeiss LEO-921 electron microscope with an omega energy filter at liquid helium and nitrogen temperatures. The usefulness of patterns showing CBED disks of constant intensity ({"}blank disks,{"} indicating kinematic scattering) for structure analysis is investigated, with the aim of avoiding film-bending artifacts. Using CBED patterns from thicker areas, sample thickness was experimentally determined using either two-beam or three-beam patterns. Koehler mode illumination (a new form of SAD pattern offering smaller areas) was also used, and the possibility of obtaining structure factor moduli using the kinematic and two-beam approximations was investigated by comparing measured diffraction intensities with experimental ones for these known structures. The commonly used approximation |F| ∼ Ig (intended to account for bending) was found to be a worse approximation than the two-beam approximation with well-defined excitation error for these microdiffraction experiments. A new multiwavelength method of retrieving structure factor moduli and thickness from microdiffraction patterns using two-beam theory is demonstrated for tetracontane.",
keywords = "Aromatic hydrocarbons, CBED, Electron microdiffraction, Organic molecular crystal, Radiation damage, Structure factors",
author = "Jinsong Wu and John Spence",
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AB - Aromatic hydrocarbon (perylene, coronene) and tetracontane films are shown to produce useful convergent-beam electron diffraction (CBED) patterns under low-dose and low-temperature conditions. These were obtained using a Zeiss LEO-921 electron microscope with an omega energy filter at liquid helium and nitrogen temperatures. The usefulness of patterns showing CBED disks of constant intensity ("blank disks," indicating kinematic scattering) for structure analysis is investigated, with the aim of avoiding film-bending artifacts. Using CBED patterns from thicker areas, sample thickness was experimentally determined using either two-beam or three-beam patterns. Koehler mode illumination (a new form of SAD pattern offering smaller areas) was also used, and the possibility of obtaining structure factor moduli using the kinematic and two-beam approximations was investigated by comparing measured diffraction intensities with experimental ones for these known structures. The commonly used approximation |F| ∼ Ig (intended to account for bending) was found to be a worse approximation than the two-beam approximation with well-defined excitation error for these microdiffraction experiments. A new multiwavelength method of retrieving structure factor moduli and thickness from microdiffraction patterns using two-beam theory is demonstrated for tetracontane.

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