Field emission from metallic emitter tips is generally described by the Fowl-er-Nordheim theory, which is based on a planar model of the tip with a classical imagecorrection. Within the free electron model and the WKB approximation, the planar tipmodel leads to the well-known Fowler-Nordheim cquation. The form of this equationpredicts that a plot of log J/ F~2 versus 1/F; where J is the current density and F, the