Field calibration using the energy distribution of field ionization

The accuracy of data obtained by field-ion microscopy is often limited by a ± 15% uncertainty of converting measured voltages into field strengths. Plotting the difference of relative energy deficits of free-space ionized H2, D2, or Kr for sets of two applied voltages against the logarithm of the voltage ratios yields a field factor k. The surface field F0=Vkrt is obtained with the 3% accuracy by which the tip radius rt can be known. The method is applicable to all metals accessible to field-ion-microscopy.