Isotopic variations in field evaporation charge-state of boron ions

The mass to charge ratio of boron ions field evaporated from FeB and CoB metallic glasses has been observed. For FeB the proportion of 10 B 2+ in the B 2+ peak is only 18.6% while the proportion of 10 B + in the B + peak is 21.6%. For CoB the proportions are 17.8% and 21.8% respectively. This effect is predicted by the post-ionisation model of field evaporation, though there is a discrepancy between experiment and theory. A model of field evaporation of boron ions by ionic tunnelling may resolve this discrepancy.