The liberation of electrons from metal surfaces by positive ions. Part II.—Theoretical

Abstract

In this paper we propose to consider the process of electron capture by positive ions at a metal surface, and the emission of electrons which occurs as a secondary phenomenon. The discussion which we venture to give is admittedly crude, and it is to be hoped that an adequate theoretical treatment of the problem will not be long delayed. As a preliminary we shall discuss some aspects of present knowledge regarding electrical conditions near metal surfaces. Recent experiments of Compton and van Voorhis suggest that positive ions capture an electron from a metal before making thermal contact with the surface, so we require to know the nature of the electric field at some distance from the mechanical boundary. We shall proceed to some calculations on the probability of neutralisation, basing our work on the supposition that neutralisation is due to auto-electronic emission under the influence of the electrostatic field of the approaching positive ion. We shall then discuss the phenomenon from the viewpoint of the transition of an electron through a potential barrier between two states of equal energy, and attempt to apply the results obtained to an explanation of the mechanism of secondary electron emission.