The technology underlying the ability to focus MeV ion beams to spot sizes ranging from 100 nm to 1 μm using nuclear microprobes has continually evolved over the last 30 years to a high state of sophistication. However, it is only in the last few years that powerful analytical techniques have been developed that fully exploit its capabilities for materials analysis. This has opened up new and exciting applications for the characterization of crystallograph-ic and electronic properties of materials and increased our basic understanding of ion-solid interactions.

The operation of a nuclear microprobe is analogous to that of a scanning electron microscope, in which a focused beam of charged particles is swept over the sample surface to produce spatially resolved images using an analytical signal produced by the ion-solid interactions. Nuclear microprobes were originally developed to image variations in sample composition by measuring x-rays emitted from the sample, backscattered ions, or nuclear-reaction products, as are widely used with unfocused beams. Accounts of these analytical techniques using focused ion beams for applications in biomedicine, geology, and archaeology, and the micro-probe hardware required to accomplish them, are given in References 2–4.

Their high magnetic rigidity means that MeV ions require much stronger magnetic fields to focus them than those required for keV electrons in a scanning electron microscope.