Electron Emission of Metals in Electric Fields II. Field Dependence of the Surface Photo-Effect

The photoelectric current emitted under the influence of an applied electric field is found to contain a term analogous to the Schottky term for thermionic emission and also a term periodic in the field intensity similar to that recently found and explained for thermionic emission. If frequencies near the threshold are used, then for fields of 3×${10}^5$ volts ${\mathrm{cm}}^{-1\mathrm{}}$ the periodic term has a magnitude of about four percent of the nonperiodic part of the current. If the photoelectric threshold frequency for zero field is used to eject the electrons, the resultant plot of the nonperiodic part of the photo-current against the field is a straight line for high field intensities. This line gives the most convenient reference system for observing the periodic term; in addition, the use of the zero field threshold gives the fractional magnitude of the periodic term a relatively large value.