RESOLUTION OF THE FIELD-ION MICROSCOPE

Equations for resolution in the field ion microscope are reviewed and modifications are suggested. Calculations are made of each contributing term, based on a proposed model for the electric field variation. Comparison with experimental results is made. The revised equations strongly indicate that thermal accommodation of He imaging gas prior to ionisation is almost complete. Instead of the gas temperature being 6. 5 to 7. 3 times the tip temperature as estimated by Chen and Seidman, a factor of only 1. 3 to 1. 5 now seems plausible.