Transport of Adsorbed Species: Correlations with Concentration and Step Structure

  • Heribert Wagner
Part of the NATO Advanced Science Institutes Series book series (NSSB, volume 86)


The thermally activated motion of adsorbed atoms on solid surfaces may be described by single hops over activation barriers separating adjacent adsorption sites. Field ion microscopyl is ideally suited to study this process on the well defined crystal planes of field emitter tips. Activation energy and pre-exponential factor of the diffusion coefficient for this random walk process are readily determined. The presence of adsorbed atoms on neighbouring adsorption sites gives rise to mutual interactions which affect the random walk of the individual atom. Changes of the substrate structure e.g. different crystal planes or steps and kinks also modify the diffusive motion by inserting different activation barriers. To some extend these influences can also be investigated by field ion microscopy. Due to the small extension of the crystal planes present on field emitter tips and the insufficient resolution for high adsorbate coverage field ion microscopy can not be employed to investigate diffusion caused by a concentration gradient or, in more general terms, by a chemical potential gradient. Unlike the random walk diffusion this process leads to a true mass transport over distances much larger than the individual jump distance.


Work Function Auger Electron Spectroscopy Diffusion Profile Oxygen Coverage Step Density 
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Copyright information

© Plenum Press, New York 1983

Authors and Affiliations

  • Heribert Wagner
    • 1
  1. 1.Institut für Grenzflächenforschung und VakuumphysikKernforschungsanlage JülichJülichW.-Germany

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