The Decomposition of Thin Films on Bombardment with Slow Electrons

Abstract

The thresholds are determined for the incidence of electron absorption, decomposition and secondary emission for several types of thin film bombarded with slow electrons. With crystalline barium oxide, electron absorption and decomposition both set in at a bombarding energy near 4 eV, and are intensified at 7 eV. Secondary emission is initiated at 5 eV and increases at 7 eV and 10 eV. The optical absorption threshold is at 3.8 eV, and is attributed to exciton formation; it seems likely that the electron absorption and the decomposition are also due to exciton formation. With oxidized films of barium, crystalline barium oxide is not formed; the absorption and decomposition thresholds are at 7 eV, and the main secondary emission threshold at 10 eV. Decomposition of barium chloride sets in at 5 eV, and of barium sulphate at 7 eV. With films of the alkali halides, the decomposition is intensified at an energy corresponding with the first optical absorption band, having been initiated at a lower energy. A tentative explanation of this is proposed.