Aluminum, oxidized electrolytically, and subsequently treated with caesium and oxygen possesses new and interesting properties when subjected to electron bombardment in the presence of an adjacent collector electrode whose potential is held positive with respect to the aluminum. True secondary electron emission from the treated surface results in the establishment of a positive charge on the surface and a polarization of the oxide film. This positive charge acting through the thin oxide film produces a high gradient, resulting in the emission of electrons through the surface. The emission increases with collector voltage and beam currents, obeying power laws, but exhibits saturation tendencies. The removal of the primary beam does not result in the immediate cessation of the field emission, but rather in a slow decay which is due to the fact that the surface charge takes an appreciable time to leak away. Similar time lags are noticed when the beam is first applied, particularly if the collector voltage has been reversed while the beam impinges on the surface. The surfaces are also light sensitive, in that light causes a decrease in the field emission and a speeding up of decay. Attempts were made to demonstrate this effect for other surfaces, but, with a few exceptions, the results were negative.

• Received 23 April 1936

DOI:https://doi.org/10.1103/PhysRev.50.48