ion microscopy field ion microscopy field-ion microscopy field ionisation microscopy FIM field-ionisation microscopy field ionization microscopy Microscopy where atoms of an inert gas in the vicinty of the specimen (which is in the form of a very sharp tip <10 m diameter) are ionised by the application of a strong electric field to the tip and an image is produced by the projection of the ions onto a fluorescent screen. The image consists of a pattern of spots of light which correspond to individual atoms on the specimen surface. field-ionization microscopy CHMO:0000098