For many years, beams of high velocity ions have been widely used for relatively nondestructive investigation of surfaces or thin films. Many properties may be investigated, associated with the large number of interactions, most of the information obtained being complementary to that from high velocity electron beams or low velocity ion beams. Recently there has been increasing interest in the application of microbeams of these high velocity ions and two streams of activity have emerged-one using traditional techniques and requiring beams of hundreds of picoamps to give spatial resolutions of the order of 1 mu m, the other using many new techniques and requiring currents from femtoamps down to single ions to give resolutions of an order of magnitude better. In both cases, the resolution is limited by the low brightness of ion sources commonly used in high energy ion accelerators. These energies commonly are of the order of 3 MeV for very light ions, but there are several developing fields in which much higher energies and heavier ions are of interest. This paper looks at the wide range of information obtainable with these high velocity ion microprobes, the limitations placed on them by their ion optics, the great improvements which would flow in all cases from the development of better ion sources, the best candidates for such sources, and some recent progress. (C) 1996 American Institute of Physics. References: 20
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