Electron energy loss due to surface modes in a thin ionic crystal film

A local theory for the energy loss of a relativistic electron beam, incident normally on A thin ionic crystal film, is developed and applied to the energy region of the surface modes of vibration. It is found that the loss function including retardation is essentially the same as that without retardation. Important effects associated with experimental resolution in energy and momentum are included in the analysis. With the inclusion of the characteristics of the apparatus, the theoretical line shapes and positions are in good agreement with the experimental results on LiF obtained by Boersch, Geiger, and Stickel. A study of the effects of substrate thickness and conductivity is reported. A good conductor, like aluminum, has a strong effect on the loss function, whereas a poor conductor, like carbon, has little effect.