The Caesium-Oxygen-Silver Photoelectric Cell

Abstract

Technique is described permitting the formation of caesium-oxygen-silver photoelectric cells under controlled conditions. It is shown that the essential conditions are a quantitative control of the degree of oxidation of the silver cathode base and the amount of caesium generated together with a regulation of the amount of chemical interaction by a control of the time and temperature of the heat treatment. Variations in sensitivity to integral light at 2,710∘ K. color temperature are shown as a function of the initial amounts of oxygen and caesium and the time of heat treatment. Small amounts of oxygen were permitted to react with the standard cathode surface. The sensitivity of the cathode fell but recovered due to the diffusion of free caesium to the surface from the underlying material. The effects are shown in relation to the integral sensitivity and the spectral response from 6,000 Â. to 10,000 Â. The effects of depositing minute amounts of free caesium upon the standard cathode surface are also shown in relation to the spectral response. The active surface of the cathode appears to be a film of free caesium of atomic dimensions adsorbed upon a matrix of caesium oxide and silver containing free caesium and a small amount of silver oxide. The spectral characteristics of the photoelectric response appear to depend largely upon the thickness of the surface film of free caesium. This film thickness is determined by the caesium concentration in the underlying matrix and is maintained by a diffusion equilibrium.