Secondary Emission from Composite Surfaces

A method was utilized of determining the secondary emission threshold energy for various composite surfaces. It was found that each compound had its own threshold energy value below which primaries would not yield true secondaries and above which primary electrons would cause the emission of secondary electrons. The experimental results were checked by means of two very different experimental structures.Comparisons were made of the electron energy necessary to remove an electron and these represent almost the same values as the energy necessary to remove an electron from the filled band to the vacuum when compared with optical experiments and with calculations.It was concluded that true secondaries originate from the filled band of the compound rather than from electron traps, as several authors previously supposed. In addition, it was found that the addition of silver to caesium oxide did cause an increase in secondary emission yield, not due to traps, but because of the formation of a new filled band level, less deep than that of caesium oxide without the silver additive. It was inferred that the action of the silver was to form a new compound, more active as a secondary emitter than caesium oxide.