Models for electron emission from metals with adsorbed monolayers

The need for employing chemical rather than particle models to describe the electronic properties of a metal-gas interface has been investigated theoretically. Using the Thomas-Fermi-Dirac theory, both the microscopic charge distribution and the total electronic energy of the interface have been evaluated in such a way that one can distinguish between the coulombic and quantum mechanical contributions. It has been shown that the quantum mechanical corrections are a significant part of the total energy and may not be neglected. The differences between various macroscopic models are discussed, and it is concluded that a particle model, using only the concepts of electrostatics and statistical mechanics, does not represent adequately the electronic properties of alkali-refractory metal or alkaline earth-refractory metal interfaces. Detailed results for both cesium and barium adsorption on (100) and (110) faces of tungsten are presented.