Experimental barrier heights and the image potential in scanning tunneling microscopy

The effect of the classical image potential on the tunnel-barrier heights deduced from scanning tunneling microscopy is considered. An earlier prediction that the image potential should lead to an observable difference in barrier heights as deduced from two different measurements is shown to be incorrect. Using an approximation to the full multiple image potential we find that the barrier height deduced from the variation of current with tunnel-barrier width is extremely close to the unreduced work function, and we discuss what characteristic of the image potential leads to this result. © 1988.