Thermionic constants of metals and semiconductors III. Monovalent metals

Abstract

In this part are described measurements on the thermionic constants of the monovalent metals copper, silver and gold, made by the effusion method. Owing to the low meltingpoints of these metals, and the consequent low vapour pressure of the electron gas in thermal equilibrium with them, the effusion holes used had to be much larger than in the measurements with the other metals. The maximum size of the effusion hole that can be used with an electron gas chamber of given dimensions without disturbing appreciably the equilibrium condition in the chamber, and the effect of the large size of the effusion hole on the saturation current, are discussed in some detail. For all the three metals, the A coefficient in Richardson’s equation for thermionic emission is found to be only slightly short of the theoretical value of 120 amp cm -2 deg -2 . This experimental finding is of significance, since the lowering of the thermodynamic potential of the degenerate electron assemblage in these metals, consequent on the thermal expansion of the metal, is considerable.