Field-enhanced photoemission from metals and coated materials

A model of photoemission from the surface of a metal coated with a submonolayer covering of an alkali or alkali earth coating and subjected to an applied field is developed and compared to experimental data of the quantum efficiency (QE) of cesium on tungsten and cesium on silver at various wavelengths. A method to determine the parameters needed in a Gyftopoulos-Levine model of work function for submonolayer coverage as well as an estimate of temperature rise as a function of laser intensity and pulse length for long pulses are given. The qualitative agreement is found to be good: significant differences in the quantitative comparison are found to be due to, first, the relaxation time in the QE model, evaluated from thermal conductivity data, which neglects the contribution of electron-electron scattering at higher energies, and, second, the quantum mechanical reflection for electrons with energies near the barrier maximum. The latter effect is investigated using a quantum distribution function approach to determine the potential barrier with and without a coating and, from it, the changes in the reflection probability.