Interference Effects in the Reflection of Low-Energy Electrons from Thin Films of Au on Ir

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Abstract
Retarding field measurements were taken on thin films (10–−‐100 Å) of Au evaporated on an Ir (111) surface. In the range of 0–5 eV the current‐vs‐voltage plots exhibited a decaying periodic variation in amplitude. The amplitude and period of the variations both decreased with film thickness. This interference phenomenon is interpreted as being due to electron reflection occurring at both the film‐vacuum and the film‐substrate interfaces. Measurements of the period as a function of film thickness agree well with a simple free‐electron picture for the phase shift experienced by electrons traversing the film, giving an effective inner potential of 16 eV for Au. From the temperature dependence of the energy at which maxima and minima occur the thermal expansion coefficient for the films is determined. Also, estimates of the mean‐free path for electrons in the film are obtained from the decay of the variation amplitude with thickness. Values obtained for both these quantities are consistent with previously published values.