Photoelectron emission from mica by light with energy lower than photothreshold

In order to determine the mechanism of photoelectron emission from the cleaved mica surface in more detail, the influence of the luminous intensity on the emission and the photothreshold was studied experimentally. The photoelectron emission from the mica surface is found to be considerably influenced by temperature and luminous intensity, and this phenomenon can mostly by attributed to the fact that the photothreshold for emission varies with intensity as well as temperature. The shift of the photothreshold with the temperature is comparatively large (0.63 eV between 20 degrees C and -100 degrees C), and therefore it is suggested that thermal excitation contributes to the process of photoelectron emission. The more intensive illumination causes the photothreshold to shift to the shallower levels in the surface states, with the result that the electrons trapped in the states are accumulatively excited and are finally emitted even under illumination with energy lower than the photothreshold.<>