Energy Distribution of Secondary Electrons: II. Normalization and Extrapolation of Experimental Data

experimental data on the energy spectra of secondary electrons can be determined effectively by plotting the ratio of the measured cross section to the Rutherford cross section as a function of the inverse of the energy transfer. The plot is known as the Platzman plot. As was shown earlier (1), the Platzman plot enables us to check secondary-electron spectra for their consistency on the shape for slow secondaries and on the shape and magnitude for fast secondaries. Furthermore, the area in the Platzman plot is proportional to the total ionization cross section (1), and hence the plot is also convenient for the normalization of experimental data when reliable ionization cross sections are available. In this paper, we extend the method so that the energy distribution is tested further for its consistency in the incident-energy dependence, especially for high incident energies where the Born approximation is expected to be valid. The incident-energy dependence is best examined by another graphical presentation known as the Fano plot (2), a plot of the product of the cross section and the incident energy as a function of the logarithm of the incident energy. By combining the Fano and Platzman plots, we obtain secondary-electron spectra that exhibit consistent behavior on both the primary- and secondaryelectron energies.