Atom Probe Field Ion Microscope (APFIM)

An atom probe field ion microscope (APFIM) is a combination of a field ion microscope (FIM) and a time-of-flight mass spectrometer of a single ion sensitivity. When high electric field is applied on a surface of a sharp needle tip, imaging gas atoms are ionized at the protruding sites on the surface. These ions hit screen, forming brightly imaging spots. Hence, the FIM is a projection type microscope of an atomic resolution with an approximate magnification of a few million times. By appling higher electric filed, surface atoms of the specimen are also ionized. By this field evaporation process, one can sample atoms of the specimens from the surface. Measuring the time-of-flight of individual atoms which go through a small aperture in the center of the screen makes it possible to determine the mass to charge ratios of individual atoms. Atoms are collected only within the aperture. The effective size of the aperture is typically from 0.5 to 5 nm. Hence, atom probe has a spatial resolution of this demension in the lateral direction. Atoms always evaporate from the surface, so the spacial resolution in the depth direction is a mono-atomic layer. A unique feature of the atom probe compared with the other analytical instrument is its extremely high spatical resolution and the equal detection efficiency for light elements.

A Typical FIM Image