Secondary-electron emission from complex surfaces

The secondary emission from metals on whose surfaces foreign substances (e.g. electropositive metals) have been deposited to various thicknesses up to a few atomic layers has been studied. It is shown experimentally that for sufficiently thin films of the contaminant the secondary emission for a given base metal depends only on the work function of the surface, and not at all on the nature of the contaminant. The form and magnitude of the variation of secondary emission with work function agree with those calculated from the energy-distribution of secondary electrons. From a study of thicker films information is obtained concerning the mean depth of liberation of secondary electrons. The significance of the results in connexion with more complex secondary-emitting materials is discussed.