3.3.1 Overview

Figures 3.5 to 3.8 depict a summary of the measured secondary electron yields for different surfaces versus primary energy. The yields increased considerably with energy but no simple pattern was found.

Figure: Secondary electron yield for tungsten single crystal and a tantalum foil. The angle of incidence was 82 (circles) and 60 (squares). The data for tungsten at 60 was taken from [14]. The tantalum foil surpasses clearly the tungsten singe crystal. This is probably caused by an altered surface structure of the tantalum foil due to the rolling process used to make the foil.

Figure 3.6: Energy dependence of ion induced secondary electron yield for CVD diamond for three angles of incidence. The high value for 82 and 190eV energy per atom is probably due to the simplifications made in Equation 3.10 for the calculations. The yields were remarkably high and exceeded unity from particle energies above 400eV per atom. The lines are shown to guide the eye.

Figure 3.7: Energy dependence of secondary electron yield for the WMgFTiO multilayer sample for two angles of incidence. No measurements were performed for incidence angles of 82 because of the uncertainties introduced by the ionization efficiency becoming important at this angle. The value of one was not reached even at 750eV per atom primary energy. The surfaces with tungsten top layer performed better than a tungsten single crystal. This was probably because the single crystal was heated to much higher temperatures than 80 C to remove adsorbates from the surface.

Figure: Secondary electron yield for AlO and MgO coated surfaces. The values plotted represent what are believed to be initial values as these surfaces were subject to a time dependent secondary electron yield as described in Chapter 3.3.3.