HIGH-VELOCITY ION MICROPROBES AND THEIR SOURCE REQUIREMENTS

For many years, beams of high velocity ions have been widely used for relatively nondestructive investigation of surfaces or thin films. Man y 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. Rece ntly there has been increasing interest in the application of microbea ms of these high velocity ions and two streams of activity have emerge d-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 so urces commonly used in high energy ion accelerators. These energies co mmonly are of the order of 3 MeV for very light ions, but there are se veral developing fields in which much higher energies and heavier ions are of interest. This paper looks at the wide range of information ob tainable with these high velocity ion microprobes, the limitations pla ced on them by their ion optics, the great improvements which would fl ow in all cases from the development of better ion sources, the best c andidates for such sources, and some recent progress. (C) 1996 America n Institute of Physics.