The Caesium-Oxygen-Silver Photoelectric Cell

A R L Y studies of the photoelectric effect were made on pure metals, eliminating, in so far as possible, the effects of absorbed gases. B u t since the alkali metals alone respond appreciably to visible light, and these only to light at the blue end of the spectrum, the development of photoelectric cells of greater response to ordinary light sources has led to the study of thin films of the alkali metals and of various composite surfaces. The enhanced photoelectric activity of the thin films of the alkali metals was first brought out by Ives 1 who also noted that the m a x i m u m response and the greatest extension of sensitivity toward the red end of the spectrum were obtained when the film thickness was of the order of one molecular diameter. Later w o r k 2 has shown that the m a x i m u m excursion of the photoelectric threshold of an alkali metal film on a metallic base 1 2 E H . E. Ives, Astrophys. J., 60, 4 (1924). Ives a n d O l p i n , Phys. Rev., 34, 117 (1929). 334 C/ESIUM-OX YGEN-SIL VER