Secondary Emission of Beryllium

Abstract

The secondary electron emission of beryllium films prepared by evaporation in a high vacuum has been studied. As the beryllium is deposited the secondary emission ratio (defined as the ratio of the number of electrons leaving the surface, to the number of primary electrons impinging on it) rises from that of the support metal to a value in the neighborhood of 2.5. The position of the maximum with respect to energy of primary electrons remains near that of the support metal. As the thickness of the layer is increased the ratio falls to less than unity and the voltage of the primary electrons necessary to reach the maximum drops to about 200 volts. Heating the thick beryllium layer to a bright red for a few minutes raises the emission to about 1.6 with the maximum at a primary energy of about 630 volts. Oxidation of the surface increases the emission to about 4.1. Explanations of these effects are discussed and arguments are presented favoring the acceptance of the value of 1.6 as the maximum secondary emission ratio to be expected for pure bulk beryllium.