The energy distribution of electrons scattered inelastically from solid targets has been studied for primary energies from 50 to 400 volts, using a method of magnetic deflection. Target surfaces of Cu, Ag and Au were deposited by evaporation in vacuum immediately before the measurements were made. For certain values of the energy loss suffered by the scattered electron the curves exhibit maxima, which are characteristic of the material of the target and independent of the primary voltage in the range studied. All three metals have two maxima below 10 volts, the most pronounced one being that for Ag at 3.9 volts. These maxima appear to correspond roughly to the regions of high optical absorption for the same substance. An estimate of the depth of penetration of the scattered electron was obtained from energy distribution measurements on films of Ca, CaO, Ba and BaO of known thickness, deposited on Ag. The results indicate, that the inelastic scattering is determined by the first few atomic layers near the surface. The fresh deposits of Ca and Ba show a very high rate of oxidation, even when the total pressure is <${10}^{-7\mathrm{}}$ mm; the distribution curves for the oxide are entirely different from those for the parent metal and exhibit a rather complicated structure. Measurements of the energy distribution of scattered electrons should in some cases prove a sensitive tool for the study of surfaces. A deposit of 5×${10}^{14}$ atoms/${\mathrm{cm}}^2$ of Ca on CaO— less than a monatomic layer in the Ca-crystal—is easily detected by this method.

• Received 9 May 1936

DOI:https://doi.org/10.1103/PhysRev.50.138