Thermionic and Adsorption Characteristics of Caesium on Tungsten and Oxidized Tungsten

Electron emission—Curves showing the logarithm of the electron current per ${\mathrm{cm}}^2$ from tungsten and oxidized tungsten over a wide range of filament temperatures are given for several vapor pressures of caesium. At high temperatures the tungsten is covered only to a slight extent with adsorbed caesium. As the filament temperature is lowered more caesium is adsorbed. This lowers the electron work function and increases the emission many thousandfold. The process continues until a temperature is reached at which the tungsten is just covered with a monatomic layer when the work function has a minimum value. At still lower temperatures the surface is more than completely covered, the work function increases again, and the emission decreases rapidly.