Abstract
AbstractThe validity of the Fowler‐Nordheim equation is discussed for field emission from protrusions on extended metal surfaces. With the model of a semi‐spheroid on a plane the permeability of the potential barrier is calculated. It is found that the field enhancement factor calculated from the slope of the Fowler‐Nordheim plots is then less than its value on the tip of the protrusion. Furthermore, this slope depends on the field, and it is nearly constant only if the height of the protrusion is above a certain limit.For a multitude of emitters the resulting slope of the Fowler‐Nordheim plots is calculated. It is found that this slope is determined practically by the site with the highest field enhancement factor.Finally the influence of gas adsorption is discussed. Patch fields caused by inhomogeneous adsorption, and variation of the adsorption state by secondary processes may have a strong influence on the emission. In this case it is impossible to obtain the values of the field enhancement factor and of the emitting surface from the Fowler‐Nordheim plots in a simple way.
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