The Legnaro ion microprobe in low current experiments

The focused ion microprobe of the Laboratori Nazionali di Legnaro has been recently employed in experiments requiring very low beam current. This article will discuss the performance of our apparatus in this application, the drawbacks which showed up and the appropriate solutions. We present IBIC observations of grain boundaries in polycrystalline silicon solar cells and IBIC and IBIL measurements on CVD diamond samples. The modifications introduced in the experimental setup are outlined. We emphasise the problems typical of these measurements and propose the interposition of thin gold foils in the beam line, as a way to handle very different current intensities. We study the effects of these foils on beam quality and their effectiveness in reducing the current. A new designed system for easy interchange of foils and related collimators is described, which will be inserted upstream in the beam line.