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The diffraction of electrons by thin films of organic compounds

Authors
  • Warren., J. B.
Publication Date
Jan 01, 1936
Source
Spiral - Imperial College Digital Repository
License
Unknown

Abstract

The examination by the method of electron diffraction of numerous thin films of organic materials is described. A general survey is made of the previous work in this field. The X-ray and electronic ray methods of structure analysis are compared with respect to both the theoretical treatment of the diffraction data and the experimental technique employed, the advantages and disadvantages of the latter method as applied to organic compounds being particularly stressed. The diffraction camera used and the practical methods employed for preparing suitable specimens are briefly described. The interpretation of the patterns obtained by the transmission of fast electrons through single crystal flakes is given together with an account of certain new diffraction phenomena observed in this work. The appearance of "extra" and "forbidden" diffractions, the presence of streaks passing through certain diffraction spots and the occurrence of large areas or bands of considerable intensity in the patterns obtained from these organic films are explained. The diffraction data and the interpretation thereof are given in detail for anthracene, hexamethylene tetramine, phthalimide, and for films of pure aliphatic long chain paraffins, alcohols, acids and esters. The results obtained from an examination of more complex highly polymerised substances, from substances of unknown crystal structure vaporised onto collodion films, and from dyed cellulosic films are briefly mentioned, concluding with an account of the crystal structure and surface orientation of Prussian Blue films as determined by the electron diffraction method. In the conclusion the complementary nature of electron diffraction to the X-ray method of analysis in this field and the particularly promising applications of the former method, such as to the investigation of the structure of thin monomolecular layers studied by Langmuir and Adam, are discussed. / Open access

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