A method and apparatus for plotting automatically the secondary electron emission yield curves from metals in an ultra-high vacuum environment are described. The yield curves from metals can be plotted in times of only a few seconds before the surfaces become contaminated. In addition, both the variation of the back-scattering coefficient with primary energy and the yield with angle of incidence of primaries may be plotted. Typical curves from Ni, Pt and Ta are presented to indicate the performance of the apparatus. Measurements using the apparatus are reported on the secondary electron emission characteristics of the three carbides TaC, TiC and ZrC as a function of primary energy and angle of incidence. In addition the yield curves are correlated with a theoretical universal yield curve.

The range of electrons as a function of primary energy below 2 keV, the escape depth of slow secondaries and the efficiency of back-scattered electrons in the production of slow secondaries have been determined in thin aluminium layers deposited on platinum, gold and silver substrates, using an automatic yield measuring device which enables the measurements to be made from contamination-free surfaces.

No abstract

No abstract

No abstract

No abstract

The secondary electron emission (SEE) yield delta of a clean and slowly oxidised Be surface has been investigated. The surface compositional changes were monitored simultaneously by Auger electron spectroscopy, and changes in the yield were measured as a function of oxygen coverage of the Be surface. The results indicate that as the maximum yield ( delta max) of 0.68 for a clean Be surface changes to 4.16 due to oxidation, the Ep max (the primary energy at which the yield is a maximum) shifts from 200 eV for the clean surface to 400 eV for the oxidised Be surface. Furthermore, the increase in yield appears to take place in two distinct stages. The faster and second stage is thought to originate from a band bending effect in the thin BeO layer.

It is shown that surfaces with low secondary electron yield (less than 1) can be prepared by evaporating metal films in a relatively high residual gas pressure.Yield measurements in the energy range 75-2000 eV have been made on surfaces prepared by evaporating gold, silver and copper at residual gas pressures of 0·5 torr in the gases H2, He, N2 and Ar. These surfaces are found after outgassing in uhv to have considerably lower yields and back-scattering coefficients than the pure metals. The rate of evaporation is shown to be an important parameter modifying the microscopic surface geometry. Scanning electron micrographs of some of the surfaces are presented showing the morphology. The results cannot be explained entirely in terms of geometrical factors.