FIELD CALIBRATION USING THE ENERGY DISTRIBUTION OF A FREE-SPACE FIELD IONIZATION.

Utilizing free-space field ionization, a new method of field calibration for field ion emitters has been developed. Plotting the differences of relative energy deficits of free-space ionized H//2, D//2, or Kr for sets of various applied voltages V against the logarithm of the voltage ratios yields a field factor k from which the surface field F//0 equals V/kr//t//i//p is obtained with 3% accuracy. Refinement of this method also enabled us to determine the local radii of the specimen tip. In addition to new and more reliable data of evaporation fields of various materials, such as W, Mo, Rh, Ir, Pt, and Ni, it has revealed several significant facts on the geometrical shape of the emitter. These results are relevant to field-ion microscopy.